Transparent Photocatalytic Antimicrobial Coatings

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Title:
Transparent Photocatalytic Antimicrobial Coatings
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1 online resource (172 p.)
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english
Creator:
Bai, Wei
Publisher:
University of Florida
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Gainesville, Fla.
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Thesis/Dissertation Information

Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Environmental Engineering Sciences
Committee Chair:
Koopman, Ben L
Committee Co-Chair:
Moudgil, Brij M
Committee Members:
Wu, Chang-Yu
Bonzongo, Jean-Claud
Svoronos, Spyros

Subjects

Subjects / Keywords:
antimicrobial -- coatings -- fullerenol -- fullerol -- photocatalysis -- tio2
Environmental Engineering Sciences -- Dissertations, Academic -- UF
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Environmental Engineering Sciences thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
A study was carried out to develop and evaluate thin, transparent, photocatalytic coatingsfor inactivating microbes on outdoor and indoor surfaces under UVA or visiblelight. The photocatalysts investigated were P25, anatase with crystallite sizesof 7 and 15 nm, rutile with crystallite sizes of 22 and 99 nm and a commercialphotocatalyst. The photocatalysts were characterized by XPS, XRD, BET surface area, SEM, dynamic light scattering, adsorption and zeta potential. Coatingstructure was characterized by SEM and coating performance was characterized bydye degradation and microbe inactivation. The TiO2 particles with small crystallite size exhibited much higher activity than commercialphotocatalyst. Photocatalysis with the smaller sizes of rutile and anatase was found to utilize different portions of the visible light spectrum. Polyhydroxyfullerene (PHF) was tested as an enhancer of photocatalysis. Nanocomposites ofPHF and anatase self-assemble by adsorption of PHF onto anatase. PHF was foundto enhance the UVA-photocatalytic performance by a factor of 2 to 3. This was achieved with a PHF/anatase weight ratio of 0.01, at which the anatase surface wasfound to be nearly saturated with PHF. Photocatalytic performance of anatase coating under visible light was also enhanced by PHF. The degree of enhancement was up to 2-fold relative to anatase alone with a PHF/anatase ratio of 0.1. Sodium dodecyl sulfate (SDS), Tween 20 and NaOH were evaluated as dispersant for aqueousTiO2 suspension. Addition of any these chemicals at the appropriate concentrations stabilized TiO2 suspensions. However, SDS and Tween20 impaired the photocatalytic activity of TiO2. The coatingperformance of TiO2 was found to be related to the pH of the TiO2 suspension used to make the coating. At either high (13) or low (7.5) pH, TiO2 particles aggregated in suspension, reducing the surface coverage of thecoating and decreasing photocatalytic activity. At TiO2 suspensionpH in the range of 9 to 12, the TiO2 aggregate size was minimizedand coating performance was maximized. The performance of three photocatalystsystems using commercial photocatalyst, a rutile/anatase mixture and the PHF/anatase nanocomposite as the top coats were evaluated in beta facilities in southern Florida. The commercial photocatalyst and the rutile/anatase were marginally effective in reducing microbe counts. Preliminary data indicate that the PHF/anatase nanocomposite is highly effective in reducing microbe counts at a beta facility.
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In the series University of Florida Digital Collections.
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Includes vita.
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Includes bibliographical references.
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Description based on online resource; title from PDF title page.
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This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Wei Bai.
Thesis:
Thesis (Ph.D.)--University of Florida, 2012.
Local:
Adviser: Koopman, Ben L.
Local:
Co-adviser: Moudgil, Brij M.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2013-08-31

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lcc - LD1780 2012
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UFE0044644:00001


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1 TRANSPARENT PHOTOCATALYTIC ANTIMICROBIAL COATINGS By WEI BAI A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2012

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2 2012 Wei Bai

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3 To my family

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4 ACKNOWLEDGMENTS I would like to express my greatest gratitude to my advisor, Dr. Ben Koopman, for his support, guidance, encouragement over the past five years I am also very gr ateful to my co chair, Dr. Brij Moudgil, for bringing me into the fascinating discipline of interfacial phenomena and providing me with many opportunities to present my research in conferences. Most achievements during my Ph.D. study would not be possible without their excellent guidance and support s I like to extend my appreciation to my Ph.D. committee members, Dr. Chang Yu Wu, Dr. Jean Claude Bonzongo and Dr. Spyros Svoronos for their generous help and support during my graduate study at the University of Florida and to Dr. Myoseon Jang for attending my Ph.D. defense as a substitute for Dr. Wu I am grateful to Dr. Vijay Krishna, who always provide d me with valuable feedback and insightful suggestions for my research. I am thankful to Dr. Jie Wang and D r. Angelina Georgieva, for their hard work on synthesizing polyhydroxy fullerenes for my research. I am thankful to the MAIC facult y members Dr. Luisa Amelia Dempere, Dr. Valentin Craciun and Dr. Eric Lambers, for training me on electron microscopy and X ray analysis. I am thankful to Dr. Gill Brubaker and Mr. Gary Scheiffel e for training me on the particle sizing and surface characterization instruments in PERC. I would like to that are not yet mentioned : Dr. Jie Gao, Dr. Hideya Nakamura, Ailin Qin, Matt Shore, Jonathan Solomon, Kyle Fischer, Wilton Mui Gayathri Mohan and Abhinav Thakur. I would like to acknowledge financial support from the Center for Nano Bio Sensor s ( University of Florida) NSF I/UCRC for Particulate and Surfactant Systems, NSF AIR ( A ward number: 1127830) and U niversity of Florida A lumni F ellowship. I

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5 would also like to acknowledge my industrial collaborator, Mr. Joseph Navarro (CEO of NanoHygienix L LC), for his support on my research. A special thank s of mine goes to my wife, Fan Li, who is always by my side and encourage s m e whenever I fe el exhausted. Without her, my life would be less colorful. I wish to thank my parents and parents in law for thei r unconditional love and unwavering support They sacrifice d their personal time to help take care of my children, enabling my wife and I to focus on our Ph.D. studies. I arrived in Gainesville alone five years ago. Right now I have a growing family with t wo adorable kids Roger and Chloe I cherish every moment in this lovely neighborhood and value all the friendship s I have made throughout th e journey

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 9 LIST OF FIGURES ................................ ................................ ................................ ........ 11 ABSTRACT ................................ ................................ ................................ ................... 16 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ ........ 18 1.1 Problem Statement ................................ ................................ ........................... 18 1.2 Conventional Disinfection Technology ................................ .............................. 19 1.3 Antimicrobial Surfaces ................................ ................................ ...................... 20 1.3.1 Microbioside releasing Coatings ................................ ............................. 20 1. 3.2 Polycationic Coatings ................................ ................................ .............. 20 1.3.3 Light activated Coatings ................................ ................................ .......... 21 1.4 Methods to Enhance TiO 2 Photocatalysis ................................ ......................... 22 1.4.1 Extend Visible Light Adsorption ................................ ............................... 22 1.4.2 Enhance Surface Reactivity ................................ ................................ .... 24 1.5 Go al and Objectives of the Study ................................ ................................ ..... 25 1.6 Overview of the Dissertation ................................ ................................ ............. 26 2 ENHANCEMENT OF NANO TITANIUM DIOXIDE PHOTOCATALYSIS IN T RANSPARENT COATINGS BY POLYHYDROXY FULLERENE ......................... 29 2.1 Experimental ................................ ................................ ................................ ..... 30 2.1.1 Chemicals and Reagents ................................ ................................ ........ 30 2.1.2 Culturing and Enumeration of Aspergillus niger Spores .......................... 31 2.1.3 Coating Preparation and Testing ................................ ............................. 31 2.1.4 Aqueous Aggregate Size, Zeta Potential and BET Surface Area ............ 35 2.1.5 Adsorption ................................ ................................ ............................... 35 2.1.6 Data Analysis ................................ ................................ .......................... 36 2.2 Results ................................ ................................ ................................ .............. 37 2.2.1 Characterization ................................ ................................ ...................... 37 2.2.2 Dye Degradation ................................ ................................ ..................... 37 2.2.3 Spore Inactivation ................................ ................................ .................... 38 2.2.4 Kinetics of Dye Degradation and Spore Inactivation ............................... 39 2.3 Discussion ................................ ................................ ................................ ........ 40 2.4 Summary ................................ ................................ ................................ .......... 42 3 VISIBLE LIGHT ACTIVE, TRANSPARENT, ANTIMICROBIAL SURFACES ............. 56

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7 3.1 Experimental ................................ ................................ ................................ ..... 57 3.1.1 Chemicals and Reagents ................................ ................................ ........ 57 3.1.2 Microbe Culture and Enumeration ................................ ........................... 57 3.1.3 Coating Preparation and Testing ................................ ............................. 59 3.1.4 Characterization of TiO 2 Particles and Coatings ................................ ...... 62 3.1.5 Adsorption ................................ ................................ ............................... 64 3.1.6 Data Analysis ................................ ................................ .......................... 65 3.2 Results ................................ ................................ ................................ .............. 65 3.2.1 Characterization ................................ ................................ ...................... 65 3.2.2 Photocatalytic Performance of TiO 2 with Different Crystallite Sizes ........ 67 3.2.3 Light Utilization by Rutile22 and Anatase7 ................................ .............. 68 3.2.4 Photocatalytic Performance of PHF/anatase7 ................................ ......... 69 3. 2.5 Photocatalytic Inactivation of Staphylococcus aureus ............................. 71 3.3 Discussion ................................ ................................ ................................ ........ 71 3.3.1 Visible Light Photocatalysis ................................ ................................ ..... 71 3.3.2 Unified Model for the Effect of PHF on TiO 2 Photocatalysis .................... 75 3.4 Summary ................................ ................................ ................................ .......... 75 4 THE EFFECT OF DISPERSANT ON THE PERFORMANCE OF TITANIUM DIOXIDE COATING ................................ ................................ .............................. 105 4.1 Experimental ................................ ................................ ................................ ... 107 4.1.1 Chemicals and Re agents ................................ ................................ ...... 107 4.1.2 Characterization of TiO 2 Particles ................................ .......................... 107 4.1.3 Dispersion ................................ ................................ ............................. 109 4.1.4 Coating Preparation ................................ ................................ ............... 110 4.1.5 Dye Degradation ................................ ................................ ................... 111 4.1.6 Statistical Analysis ................................ ................................ ................. 112 4.2 Results ................................ ................................ ................................ ............ 113 4.2.1 Characterization ................................ ................................ .................... 113 4.2.2 Effects of Dispersant Systems on P25 Suspen sion Characteristics and Coating Performance ................................ ................................ ........... 113 4.2.3 Performance Comparison of Coatings prepared from P25 versus a 1:1 Mixture of Rutile and Anatase ................................ ................................ ..... 115 4.2.4 Optimization of the NaOH Dispersant System for 1:1 Rutile/anatase Mixture ................................ ................................ ................................ ........ 116 4.3 Discussion ................................ ................................ ................................ ...... 117 4.3.1 The Effect of Dispersant ................................ ................................ ........ 117 4.3.2 The Effect of pH on Coating Performance ................................ ............. 118 4.4 Summary ................................ ................................ ................................ ........ 119 5 PROTOTYPE TESTING OF TITANIUM DIOXIDE coatED ANTIMICROBIAL SURFACES ................................ ................................ ................................ .......... 141 5.1 Experimental ................................ ................................ ................................ ... 142 5.1.1 Beta Facilities ................................ ................................ ........................ 142 5.1.2 Chemicals and Reagents ................................ ................................ ...... 144

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8 5.1.3 Coating Preparation ................................ ................................ ............... 144 5.1.4 Microbial Sampling Procedures ................................ ............................. 145 5.2 Results ................................ ................................ ................................ ............ 146 5.2.2 Venice Regional Medical Center ................................ ........................... 146 5.2.3 Luke Haven Skilled Nursing Facility ................................ ...................... 147 5.3 Discussion ................................ ................................ ................................ ...... 148 5.4 Summary ................................ ................................ ................................ ........ 149 6 CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER RESEARCH ......... 158 LIST OF REFERENCES ................................ ................................ ............................. 162 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 172

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9 LIST OF TABLES Table page 2 1 Comparison of first order fits and second order fits t o photocatalytic dye degradation and spore inactivation data* ................................ ........................... 43 2 2 Effect of enhancers on UVA photocatalytic degradation of organic dyes by TiO 2 coatings ................................ ................................ ................................ ...... 44 3 1 Properties of photocatalysts employed in present research, as provided by manufacturers ................................ ................................ ................................ ..... 77 3 2 Elemental composition of TiO 2 ................................ ................................ ............ 77 3 3 Binding energy (eV) of TiO 2 ................................ ................................ ................ 77 3 4 BET specific surface area and calculated specific surface area based on mean crystallite size ................................ ................................ ........................... 78 3 5 X ray diffraction parameters used for calculation of mean crystallite size of P25, anatase and rutile ................................ ................................ ....................... 78 3 6 Comparis on of crystallite size in nanometers based on XRD and SEM .............. 78 3 7 Band gap of TiO 2 ................................ ................................ ................................ 78 3 8 Comparison of first order fits and second order fits to photocatalytic dye degradation data* ................................ ................................ ............................... 78 3 9 Optical properties of filter FGL400* ................................ ................................ ..... 79 3 10 Optical properties of filter FGL495* ................................ ................................ ..... 79 3 11 Relative activity of photocatalysts under filtered light ................................ .......... 79 3 12 Comparison of enhancem ent ratio* of PHF/anatase to anatase alone under UVA and visible light ................................ ................................ ........................... 79 4 1 Properties of photocatalysts employed in present research, as given by manufacturers ................................ ................................ ................................ ... 120 4 2 X ray diffraction parameters used for calculation of mean crystallite size of P25, anatase and rutile ................................ ................................ ..................... 120 4 3 BET specific surface area a nd calculated specific surface area based on mean crystallite size ................................ ................................ ......................... 120 5 1 Identification of trends in microbe counts at Saint Stephen's Episcopal School 150

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10 5 2 Identification of trends in microbe counts at Venice Regional Medical Center .. 150

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11 LIST OF FIGURES Figure page 1 1 The role of surfaces and antimicrobial coatings in the transmission of hospital acquired infections. Redrawn from Page et al 15 ................................ ... 28 2 1 Procedure for testing performance of phot ocatalytic coatings ............................. 45 2 2 Langmuir isotherm for adsorption of PHF onto TiO 2 at pH 6 and 25C .............. 46 2 3 Aqueous aggregate size and zeta potential of TiO 2 and PHF/TiO 2 .................... 47 2 4 Coating appearance and structure ................................ ................................ ..... 48 2 5 Optimization of PHF/TiO 2 m ass ratio (0.02, 0.01, 0.005, 0) in photocatalytic nanocomposite. Error bars represent 1.0 SD. (Error bars for the dark control are too small to be seen.) Model lines represent second order fits ......... 49 2 6 False color image of Aspergillus niger spores on PHF/TiO 2 nanocomposite coating (Spores are red spheres; coating is green background; whitish coloring indicates charging of the coating during microscopy.) .......................... 50 2 7 Recovery of A. niger from test surfaces. Error bars represent 1.0 SD ............. 51 2 8 Inactivation of A. niger spores by test surfaces. Error bars represent 1.0 SD. Model lines represent first order fits ................................ ............................ 52 2 9 Temporal changes of spore morphology on photocatalytic coatings exposed to UVA ................................ ................................ ................................ ................ 53 2 10 Photocatalytic enhancement by the nanocomposite at different PHF/TiO 2 ratios (0.005, 0.01 and 0.02) relative to TiO 2 alone ................................ ............ 54 2 11 Surface coverage of PHF on TiO 2 as a function of the PHF/TiO 2 formulation ratio ................................ ................................ ................................ .................... 55 3 1 XPS spectrum of TiO 2 powders ................................ ................................ .......... 80 3 2 X ray diffraction pattern of TiO 2 ................................ ................................ .......... 82 3 3 Scanning electron micrographs of TiO 2 powders ................................ ................ 83 3 4 Absorbance spectrum of TiO 2 coating made from 1 wt% suspen sion. A white Teflon plate was used as reference ................................ ................................ .... 88 3 5 Screening of alternative photocatalysts for visible light photocatalysis (Visible light irradiance = 2 W/m 2 UVA irradiance = 0.01 W /m 2 ). Photos were taken

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12 with a Nikon D90 with AF S DX NIKKOR 35mm f/1.8G lens using a SB 400 flash at 90 to horizontal ................................ ................................ ..................... 89 3 6 Dye degradation on coating made from TiO 2 with different phas e and crystallite size under visible light (2 W/m 2 ). Model fits based on second order reaction kinetics ................................ ................................ ................................ .. 90 3 7 Comparison of the second order dye degradation rate coefficient on TiO 2 coati ngs under visible light (2 W/m 2 confidence interval ................................ ................................ .............................. 91 3 8 Fluorescent lamp spectra for General Electric model T8 Ultramax F28T8 SPX41 ................................ ................................ ................................ ................ 92 3 9 Dye degradation on two layer coatings under visible light (1.5 W/m 2 ) with neutral or cut off optical filters. A thin polystyrene Petri dish cover with 90% transmission above 300 nm was used as a neutral filter ................................ .... 93 3 10 Appearances of two layer coating ................................ ................................ ....... 94 3 11 Langmuir isotherm for adsorption of PHF onto anatase7 at pH 6 and 25C. The PHF to anatase r atios were 0.001, 0.005, 0.01, 0.05 and 0.1. .................... 95 3 12 Time dependent dye degradation on two layer coating with rutile22 as bottom coat and PHF/anatase7 as top coat. PHF/anatase7 ratios were 0 0.005, 0.01, 0.05 and 0.1. Error bars represent 1.0 SD. Second order model fits are shown. ................................ ................................ ................................ .......... 96 3 13 Comparison of second order dye degradation rate coefficients on two layer coatings with rutile22 as bottom coat and PHF/TiO 2 (anatase7) nanocomposite at different weight ratios as top coat ................................ .......... 97 3 14 Time dependent S. aureus inactivation on two layer coating system with rutile22 as bottom coat. Top coats were anatase7 (dark), anatase7, PHF/anatase7 weight ratios of 0.01 or 0.1 and SiO 2 ................................ .......... 98 3 15 Coating appearance rutile22 and rutile99 at different surface loadings ............... 99 3 16 Time dependent dye degradation on rutile22 at the reference surface loading of 128 g/cm 2 rutile99 at the reference loading, rutile99 at 10 reference loading and rutile99 at 50 refe rence loading ................................ ................... 102 3 17 Effect of photocatalyst surface loading on second order reaction rate coefficient. The correlation shown is for rutile99 ................................ ............... 103 3 18 The relationship of enhancement ratio and surface coverage of PHF on anatase under both UVA and visible light ................................ ......................... 104

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13 4 1 X ray diffraction pattern of TiO 2 ................................ ................................ ........ 121 4 2 Scanning electron micrograph of TiO 2 coating ................................ .................. 122 4 3 P25 suspended in DI water after 24 hours ................................ ........................ 123 4 4 P25 suspended in NaOH solutions at various concentrations (10 2 10 5 M) after 24 hours ................................ ................................ ................................ ... 124 4 5 P25 suspended in Tween 20 solutions at va rious concentrations (volume fraction) ................................ ................................ ................................ ............ 125 4 6 P25 suspended in SDS solutions at various dosed concentrations (10 5 10 1 M) after 24 hours ................................ ................................ .............................. 126 4 7 Mean diameter and zeta potential of P25 suspension with and without dispersant ................................ ................................ ................................ ......... 127 4 8 Scanning electron micrographs of P25 coating prepared using DI water conta ining no dispersant ................................ ................................ ................... 128 4 9 Scanning electron micrographs of P25 coating prepared using 0.001 M of NaOH ................................ ................................ ................................ ............... 129 4 10 Scanning electron micrographs of P25 coating prepared using Tween 20 as dispersant. ................................ ................................ ................................ ........ 130 4 11 Scanning electron micrographs of P25 coating prepared using SDS as dispersant. ................................ ................................ ................................ ........ 131 4 12 Dye degradation performance of P25 coating made from the suspensions with different dispersants. The coatings were exposed to visible light at 2 W/m 2 ................................ ................................ ................................ ................. 132 4 13 Dye degradation kinetics of P25 and anatase coating after exposed to visible light at 2 W/m 2 ................................ ................................ ................................ .. 133 4 14 Temporal stability of TiO 2 suspension at different pH ................................ ....... 134 4 15 Aqueous aggregate size of anatase/rutile at various pH conditions .................. 135 4 16 Zeta potential of rutile and anatase at pH 9 ................................ ...................... 136 4 17 Relationship of dye degradation of rutile/anatase coating made from the suspensions adjusted at different pH after exposure to visible light irradiance of 2 W/m 2 ................................ ................................ ................................ ......... 137

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14 4 18 Relationship of dye degradation of rutile/anatase coating and the aqueous mean diameter of the suspension used to make the coating after exposure to visible light irradiance of 2 W/m 2 ................................ ................................ ...... 138 4 19 Scanning electron micrographs of rutile/anatase coating ................................ .. 139 4 20 Scanning electron micrographs of rutile/anatase coating ................................ .. 140 5 ................... 151 5 2 Microbial sampling locations of an ICU station at Venice Re gional Medical Center: wall, bed rail, counter top and (door) knob ................................ ........... 152 5 3 Time dependent change in microbe counts on surfaces coated with photocatalyst system 1 in the dressing room of Sa School ................................ ................................ ................................ .............. 153 5 4 Time dependent change in microbe counts on surfaces coated with 154 5 5 Time dependent change in CFU on uncoated surfaces in Classroom 3 of ................................ ................................ .... 155 5 6 Time dependen t changes in microbe counts on surfaces in the ICU stations of Venice Regional Medical Center. Surfaces in station 2 were not coated; surfaces in station 4 were previously coated with photocatalyst system 1; surfaces in station 3 were coated with photocata lyst system 2 ......................... 156 5 7 Time dependent changes in microbe counts on surfaces coated with photocatalyst system 3 in the Luke Haven Skilled Nursing Facility of Village on the Isle Retirement F acility. Sampling locations where a significant decrease (P < 0.05) in microbe counts between the treatment date and the latest sampling date are marked by an asterisk ................................ ................ 157

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15 LIST OF ABBREVIATIONS CFU COLONY FORMING UNIT PHF P OLYHYDROXY FULLERENE T I O 2 TITANIUM DIOXIDE UVA ULTRAVIOLET A

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16 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy T RANSPARENT PHOTOCATALYTIC ANTIMICROBIAL COATINGS By Wei Bai August 2012 Chair: Ben Koopman Cochair: Brij Moudgil Major: Environmental Engineering Sciences A study was carried out to develop and evaluate thin, transparent, photocatalytic coating s for ina ctivating microbes on outdoor and indoor surfaces under UVA and visible light. The p hotocatalysts investigated were P25, anatase with crystallite sizes of 7 and 15 nm, rutile with crystallite sizes of 22 and 99 nm and a commercial photocatalyst The photoc atalysts were characterized by XPS, XRD, BET surface area, SEM, dynamic light scattering, adsorption and zeta potential. C oating structure was characterized by SEM and coating performance was characterized by dye degradation and microbe inactivation. The T iO 2 particles with small crystallite size exhibited much higher activity than commercial photocatalyst. Photocatalysis with the smaller sizes of r utile and anatase was found to utilize different portions of the visible light spectrum Polyhydroxy fullerene (PHF) was tested as an enhancer of photocatalysis Nanocomposites of PHF and anatase self assemble by adsorption of PHF onto anatase PHF was found to enhance the UVA photocatalytic performance by a factor of 2 to 3. This was achieved with a PHF/ anatase w eight ratio of 0.01, at which the anatase surface was found to be nearly saturated with PHF. P hotocatalytic performance of anatase coating under visible light was also enhanced by PHF. The degree of

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17 enhancement was up to 3 fold relative to anatase alone wi th a PHF/ anatase ratio of 0.1. S odium dodecyl sulfate (SDS), Tween 20 and NaOH were evaluated as dispersant for aqueous TiO 2 suspension. Addition of any of these chemicals at the appropriate concentrations stabilized TiO 2 suspensions However, SDS and Twee n 20 impaired the photocatalytic activity of TiO 2 The coating performance of TiO 2 was found to be related to the pH of the TiO 2 suspension used to make the coating. At either high (13) or low (7.5) pH, TiO 2 particles aggregated in suspension reducing the surface coverage of the coating and decreasing photocatalytic activity At TiO 2 suspension pH in the range of 9 to 12, the TiO 2 aggregate size was minimized and coating performance was maximized. The performances of three photocatalyst systems using comme rcial photocatalyst, a rutile/anatase mixture and the PHF/anatase nanocomposite as the top coats were evaluated in beta facilities in southern Florida. T he commercial photocatalyst and the rutile/anatase were marginally effective in reducing microbe counts Preliminary data indicate that the PHF/ anatase nanocomposite is highly effective in reducing microbe counts at a beta facility

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18 CHAPTER 1 INTRODUCTION 1.1 Problem Statement Surfaces of windows, walls, furniture, carpets etc. in buildings are repositor ies of viruses, bacteria and fungi that cause infections, allergies and respiratory problems. 1 5 Viral infections such a s influenza lead to $12 billion/year medical costs and productivity loss in the US alone 6 Pandemics with emerging pathogens such as H1N1 virus could cost $3 trillion globally 7 The Noroviru s (Norwalk) virus, notable for infecting cruise ship passengers with incapacitating gastrointestinal illness, can live on surfaces for up to four weeks. Hospital acquired (nosocomial) infections cause or contribute to 99,000 deaths in the U.S. each year 8 These infections can involve antibiotic resistant bacteria, such as methicillin resistant Staphylococcus aureus (MRSA) Asthma affects nine million U.S. children under the age of 18, and causes an estimated $20 billio n per year in medical expenses and productivity loss in the U.S. 9 Control of environmental asthma triggers such as allergens and air pollutants could substantially reduce asthma in children 10 12 Common alcohol or hypochlorite disinfectants are ineffective against bacteria, viruses and fungal spores 12 Prevention of surface transmitted infe ctions within the indoor environment can be accomplished by reduction of microbial survival using disinfecting chemicals, heat, radiation or antimicrobial surfaces. Desirable features of an antimicrobial agent are: easy to apply and long lasting does not i nvolve harmful chemicals destroys pathogenic microbes retains the appearance and texture of the underlying surface activating agents such as light, if necessary, are present in the normal indoor environment low cost

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19 1.2 Conventional Disinfection Technolog y C onventional technolog ies for microbe inactivation are heat, radiation and chemical based inactivat ing agents. 13 These techniques and their limitations are briefly outlined below. Heat: Heat is not a feasible met hod for disinfecting surfaces as the high temperature application is expensive and could damage the surfaces. Furthermore, thermal techniques cannot be applied for inactivation of all microorganisms present on surfaces 14 Radiation: Germicidal ultraviolet (UV C ) and g amma ray s are the two major types of radiation utilized for inactivation. The major disadvantage associated with this technique is cost. High intensity radiation is required to ensure complete inactivation of microorganisms 14 Inactivation with g amma rays requires special facilities, whereas UV C radiation requires, at a minimum, eye and skin protection Chemical agents: A lcohols, aldehydes and surfactants are commonly em ployed for cleaning surfaces. However, they are effective against only against certain bacteria. Strong chemical agents, such as chlorine bleach, are not recommended for treating surfaces as they can easily oxidize and damage them. A major disadvantage of chemical agents is that they generate toxic byproducts, including mutagens and carcinogens 14 As can be seen from the above discussion, conventional disinfectants suffer disadvantages which prevent them from being eff ective at stopping surface mediated transmission of disease. Need for frequent re application and the potential for damage to surfaces are two of their most notable limitations. Antimicrobial surfaces break the cycle of infection in healthcare and other fa cilities that are prone to surface mediated infectious diseases (Fig. 1 1). Two sets of approaches can be delineated from research on control of microbial populations on walls, ceilings, and other surfaces 15 The first approach is to prevent microbial adhesion to the surfaces. The prominent methodologies for coating large areas are super hydrophilic (e.g., TiO 2 based self cleaning coatings from Saint Gobain and Pilkington) or

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20 superhydrophobic coatings. Antiadhesiv e products intended only for small area applications, such as poly (ethylene glycol) coatings, diamond like carbon coatings and Although, super hydrophilic and super hydrophobic coatings may be effective in pr eventing adhesion of microbes on surfaces, they do not destroy the microbes. The second approach antimicrobial surfaces are discussed next. 1.3 Antimicrobial Surfaces The second approach is destruction of microbes with passive or active coatings, which are discussed below. 1.3.1 Microbioside releasing Coatings Antimicrobial agents, such as antibiotics or inorganic antimicrobials, are incorporated in a polymer matrix for slow release by diffusion. Commercial microbioside releasing coatings are Microban, whi ch contain Triclosan as broad + ions for destroying microbes. These coatings can induce microbial resistance and, thus, are not desirable in healthcare settings. The coatings have a finite lifetime that is related to the rate of release of the antimicrobial agents. Furthermore, silver ions and dioxins produced by Triclosan under UV light are toxic to humans. 1.3.2 Polycationic Coatings Cationic polymers destroy microbes by electrostatic int eractions with the negatively charged parts of microbes containing surface coatings have been shown to be effective against some bacteria and viruses, but not against bacterial spores.

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21 1.3.3 Light activated Coatings L ight activated release of potent reactive oxygen species, such as hydroxyl radicals is another way of destroying microbes Light activated coatings act against all microbes, and because they attack the microbial surface, there is no potential fo r inducing resistance. Furthermore, these coatings tend to be longer lasting. The two categories of light activated coatings are discussed below: Photosensitizers: Organic dye molecules with absorption in visible light, such as Rose Bengal and Toluidine bl ue, have antimicrobial properties. The photosensitizer is usually incorporated in a polymer matrix for producing antimicrobial coatings. The polymer matrix is susceptible to degradation by the reactive oxygen species produced by the photosensitizer. Photoc atalysts: Materials such as titanium dioxide (TiO 2 ) and zinc oxide can convert light energy to chemical energy. The chemical energy produced is usually in form of free radicals (hydroxyl and superoxide radicals). Photocatalytic technology is an attractive approach for destroying environmental pollutants and pathogenic microbes because of the following characteristics : 13 The TiO 2 coating is easy to apply and is long lasting Preparation of coatings from TiO 2 powders re quire no harmful chemicals (disinfectants) and does not release toxic byproducts Microbes are not only killed, but are completely mineralized Coatings can be made thin enough so that the appearance and texture of the underlying surface are retained TiO 2 fo rmulations are low in cost The chief disadvantage of TiO 2 is low quantum efficiency, which typically necessitate thick, white coatings to achieve antimicrobial action over feasible time

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22 scales. Recently, technologies for enhancing TiO 2 photocatalysis have shown promise for increasing microbial inactivation rates under visible light. 1.4 Methods to Enhance TiO 2 Photocatalysis The quantum yield [ 1 ] of TiO 2 is low, normally less than 1% 16 In addition to quantum yield, t wo major phenomena affect the efficiency of TiO 2 photocatalysis, including light adso rption and the fate of charge carrier s (electrons, holes) at the photocatalyst surface Accordingly, two major strategies to enhance TiO 2 photocatalysis are to extend the range of wavelengths over which TiO 2 can a b sorb light and to enhance the surface reactivity of the photocatalyst. 1.4.1 Extend Visible Light Adsorption Pure anatase absorbs electromagnetic radiation with wavelength less than 380 nm (UVA, UVB), which const itute s only 3% of the solar spectrum 17 Extending the a b sorption spectrum of anatase to the visible region significantly improves the overall capture of incident photons It also makes it possible to apply TiO 2 pho tocatalysis for indoor applications. Dop ing with non metal and transition metal Numerous studies have indicated that dop ing with non metal elements, such as boron, carbon, nitrogen, sulfur or phosphorous, significantly enhance s the capability of visible light adsorption of TiO 2 18 21 Nitrogen is the most frequently used dopant because its atomic size is close to that of oxygen, it has a low ionization energy and it is highly stable As a consequence, n itrogen can readily substitute for oxygen within the TiO 2 crystal lattice. Through [ 1 ] Quantum yield is defined as the number of events occurring per photon absorbed per photon absorbed. 112 In TiO 2 photocatalysis, quantum yield can be specified as the number of charges transferred to adsorbed species per photon absorbed.

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23 nitrogen doping, the band gap energy of TiO 2 can be reduced from 3.2 eV to 2.7 2.9 eV. 18 Transiti on metals, such as Cr, Co, V and Fe, 22 25 are also able to extend the optical response of TiO 2 to the visible region. Doping with a transition m etal in the crystal lattice of TiO 2 gives rise to a decrease in the band gap energy of TiO 2 Dopant free method Although dopants can improve the solar spectrum usage, they can also act as charge carrier recombination centers, adversely affect ing the effic iency of TiO 2 photocatalysis 26 B and gap engineering techniques have recently been applied to create dopant free, pure TiO 2 phase s that are visible light active 27 30 Chen et al. 27 introduced disorder in the surface layers of nanophase TiO 2 through hydrogenation, obtaining black TiO 2 nanoparticles with band gap of 1.0 eV Tao et al 28 synthesized a new dopant free, low band gap phase of TiO 2 on the surface of rutile TiO 2 by oxidation of bulk titanium interstitials. The band gap of the resulting phase was 2.1 eV. Zuo et al. 29 synthesized partially reduced TiO 2 with Ti 3+ present in the bulk material The TiO 2 containing Ti 3+ exhibited high visible light activity. The literature cited above show s the crucial role of defects and surface disorder in enginee ring the band gap of TiO 2 Dye photo sensitization Dye photosensitization has been reported to be an effective way enhanci ng visible light photocatalysis 31 34 Various dyes, such as coumarin 35 Ru(bpy) 3 2+ 36 Eosin Y 37 merocyanine 38 etc have been e mployed to increase the efficiency of solar cell s photocatalytic pollutant degradation and hydrogen production under visible light. The dye photosensitization process starts with electron excitation from the highest occupied mo lecular orbital of the dye t o the lowe st

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24 unoccupied molecular orbital upon absorption of visible light. The photoex c ited dye subsequently transfer s an electron into the conduction band of TiO 2 Th is conduction band electron of TiO 2 subsequently migrates to the surface and react s with electron acceptors, generating a free radical ( O 2 OOH or OH ) 39 41 1.4.2 Enhance Surface Reactivity Effect of particle size The amount of TiO 2 surface availabl e for reaction directly relates to the particle size of TiO 2 which affects specific surface area, the band gap and charge carrier recombination. A s the particle size decreases, the specific surface area increases, giving more reactive surface area for org anic pollutant degradation and microbe inactivation. 42 As the particle size of TiO 2 is decreased to its critical size, typically 10 nm or less 43, 44 the TiO 2 particle behaves as photogenerated charge carrier upon illumination cannot fit into such a small particle. In other word s the band of TiO 2 spilt s into discrete electronic states with in the conduction band and valence band. 45 As a result, the band gap increases and the band gap edges shift to yield large redox potentials. 16 Kormann et al 46 synthesized a 2 4 nm anatase and rutile nanoparticles. The blue shift of band gap for anatase and rutile with respect to their bulk phases were 0.15 and 0.1 eV, respectively. T he quantum size effect of TiO 2 does increase the redox potential of TiO 2 but it requires incident light with higher energy to activate the photocatalyst. Influences of particle size on the charge carrier recombination were also reported. 47, 48 Recombination of electrons and holes can take place within the interior or at the surface of the photocatalyst. In larger particles of TiO 2 recombination of the charge carrier s within the interior of the particle is dominant. As particle size decreases,

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25 the diffusion dist ance is also decreased, so that eventually surface recombination becomes dominant. 48 Thus, methods to inhibit surface recombination would be effective only for smaller particles. Methods to synthesize small particle s of TiO 2 with narrow size distribution were reported. Satoh et al. 49 used a dendrimer template to synthesize TiO 2 nanoparticles with a di a meter of 1 2 nm with a standard deviation of 0.3 0.6 nm. The highly branched macromo lecules have well defined structures that enable them to bind metal ions to generate precursors that can be converted into nanoparticles. Yan et al. 50 reported a microemulsion mediated hydrothermal method to synthes ize TiO 2 nanocrystalline (size range from 9 to 18 nm) under low temperature condition. Dop ing with noble metal s Deposition of noble metal s such as Pt, Au or Ag within the crystal lattice enhance s the photocatalytic activity of TiO 2 51 53 The n oble metals serv e as electron scavengers, decreasing the rate of recombination of electron and holes, thus increas ing the interfacial transfer rate of the charge carrier s Semiconductor coupling Research on the coupling of semiconductor photocatalysts into nanocomposite alloys such as CdS/TiO 2 54 ZnO/TiO 2 55 and Bi 2 S 3 /TiO 2 56 were reported. These coupled semiconductors decreased the recombination rate of charge carrier s enhancing the overall photocatalytic efficiency. 1.5 Goal and Objective s of t h e Study Most of the methods described above such as doping or nanocomposite formation, require a sol gel process, which is energy intensive, requires toxic chemicals and is expensive. These drawbacks have hindered large scale applications of TiO 2 photocataly sis Thus, engineering a highly active TiO 2 photocatalyst formulation th at utilizes a facile synthesis procedure is highly desirable.

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26 Fullerene, a new class of carbon allotrope 57 exhibit s strong electron affinity which is beneficial for charge carrier separation in the TiO 2 photocatal ytic process However, the interaction of fullerene and TiO 2 is weak due to poor aqueous solubility of fullerene. Chemically modified f ullerene with multiple hydroxyl groups ( polyhydroxy fullerene fullerol or fullerenol ) significantly increases the aqueou s solubility of fullerene, while retaining its electron affinity Krishna et al. 58 demonstrated that polyhydroxy fullerene (PHF) enhance s TiO 2 photocatalysis in aqueous system s N anocomposites of PHF and TiO 2 form thro ugh physical mixing Other advantages of using PHF as an enhancer of photocatalysis include the small amount required [ 2 ] and its biocompatibility [ 3 ] The goal of this study was to develop stable formulation s of polyhydroxy fullerene/TiO 2 nanocomposite s for application as transparent, antimicrobial coating s for use under UVA or visible light The specific objectives of this research were : Optimize the PHF/TiO 2 nanocomposite composition to maximize the microbe inactivat ion rate under UVA or visible light ; Se lect and optimize a system for dispersing TiO 2 particles in aqueous suspension Evaluate the performance of prototype TiO 2 formulation s in beta facilities 1.6 Overview of the Dissertation The dissertation is organized into a total of six chapters In C hapte r 2, a study to develop a single layer coating of the PHF/TiO 2 with anatase phase of TiO 2 nanocomposite is described. The nanocomposite was optimized for application under low irradiance UVA light Dye degradation was used as initial indicator for perfor mance for optimization. The optimized nanocomposite coating was tested for inactivation of [ 2 ] The concentration of PHF required for enhanced photocatalysis is10 times lowe r than other enhancers, such as metals or dyes [ 3 ] The concentration of PHF used in this study is a magnitude lower than the LC 50 for mammalian cells.

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27 Aspergillus niger spores In C hapter 3, a study to develop a two layer TiO 2 coating for indoor applications is described. The two coat system mimics current commerci al practice in application of photocatalytic coatings. A nanocomposite of PHF and anatase was found to be superior to rutile or anatase alone. The coating system was optimized using dye degradation as performance measure, and then tested for its ability to inactivate Staphylococcus aureus a surrogate for MRSA In C hapter 4 a study to select and optimize a dispersion system is described T hree dispersant system s were tested : NaOH for pH adjustment, Tween 20 and sodium dodecyl sulfate. T wo model photocataly st s were employed : P25 and a 1:1 mixture of rutile and an a tase S ettling rate and visual opacity were used as indicators of the degree of dispersion while dye degradation was used as the indicator of performance In C hapter 5, a study to evaluate prototyp e photocatalyst formulations in three different Florida beta facilities was carried out Performance of photocatalytic coatings was monitored for up to 8 month s after coating application Finally, i n C hapter 6, the overall conclusion s from this work and su ggestions for future work are given.

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28 Figure 1 1 The role of surfaces and antimicrobial coatings in the transmission of hospital acquired infections Redrawn from Page et al 15

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29 CHAPTER 2 ENHANCEMENT OF NANO TI TANIUM DIOXIDE PHOTO CATALYSIS IN TRANSPARENT COATINGS BY POLYHYDROXY FULLE RENE Microbe transmission via surfaces is a common mode for the spreading of infectious diseases 15 A simple way to combat disease transmi ssion via surfaces is to apply antimicrobial coatings. The ideal antimicrobial coating has the following properties: 1) effective in killing pathogenic microorganisms; 2) requires no toxic or hazardous chemicals for synthesis; 3) does not alter the appe arance or texture of underlying materials ( i.e. transparent) 4) activated by agents that are readily available, such as light 5) inexpensive Ultraviolet A (UVA) active, photocatalytic coatings based on titanium dioxide (TiO 2 ) have the potential to satis fy all of these criteria. Furthermore, they also destroy organic pollutants such as volatile organic compounds and are self cleaning. To achieve thin, transparent coatings that are also antimicrobial, it is important to maximize the efficiency of the photo catalyst in converting light energy to chemical energy. A number of approaches have been devised to improve the efficiency of TiO 2 photocatalysis under UVA illumination. Doping or forming nanocomposites with noble metals (Pt, Au and Ag) 51 53 metal ions 59 metal oxide 60 carbon nanotubes 61, 62 graphene oxide 63 fullerene 64, 65 and polyhydroxy fullerene 58, 66 enhances photocatalytic effic iency. However, doping or nanocomposite formation typically requires a sol gel process, which is energy intensive, requires toxic chemicals and is expensive. In contrast, nanocomposites of polyhydroxy fullerene (PHF) and TiO 2 form spontaneously through sel f assembly when the two components are mixed. Krishna et al 58, 66

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30 demonstrated that PHF/TiO 2 nanocomposite in aqueous suspension photocatalytically degraded organic dye 2.6 times faster and inactiv ated Escherichia coli 1.9 times faster than TiO 2 alone. They showed that PHF physically adsorbs on TiO 2 and postulated that the adsorbed PHF serves as an electron scavenger, which facilitates electron hole pair separation, and leads to greater production of hydroxyl radicals. Electron paramagnetic resonance spectroscopy confirmed that photocatalytic production of hydroxyl radicals was increased in the presence of PHF. Polyhydroxyfullerene is water soluble, biocompatible and biodegradable and has been shown to possess antioxidant properties, inhibit allergic response and inhibit tumor growth 67 71 The concentrations of PH F utilized in the PHF/TiO 2 nanocomposite are four orders of magnitude lower than the LC10 reported for human dermal fibroblasts 72 Until now, the capability of PHF to enhance the photocatalytic activity of TiO 2 in a coating has not been evaluated. The objective of this study was therefore to test the effectiveness of thin, transparent coatings made of PHF/TiO 2 nanocomposite. The optimal ratio of PHF to TiO 2 for use in formulating the nanocomposite was determined using dye degradation as the performance measure. The optimized nanocomposite was then tested for inactivation of Aspergillus niger a fungal species commonly occurring in both indoor and outdoor environments and frequently cited as a contributor to respi ratory diseases, such as asthma 73 A. niger spores are highly resistant to photocatalysis, in comparison to viruses and bacteria 74 2. 1 Experimental 2. 1 .1 Chemicals and Reagent s Chemicals were obtained from Fisher Scientific, except as noted. Titanium dioxide (anatase, 5 nm) was obtained from Alfa Aesar (Ward Hill, MA). Polyhydroxy fullerene

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31 (PHF) was obtained from BuckyUSA (Houston, TX) or synthesized in our laboratory accordi n g to the protocol of Gao et al 75 Procion red MX 5B dye was obtained from Sigma Aldrich Inc. (St. Louis, MO). Phosphate buffered saline (PBS) solution was prepared by dissolving 12.36 g Na 2 HPO 4 1.80 g NaH 2 PO 4 and 85.0 0 g NaCl in 1000 mL of deionized water and then diluting 10x immediately before use. PBS/SDS solution was prepared by adding 0.576 g sodium dodecyl sulfate (SDS) to 1000 mL of PBS and then autoclaving at 120C and 16 bar for 15 minutes. 2. 1 .2 Culturing an d E numeration of A spergillus niger S pores Asperigillus niger (ATCC 16888) were grown on potato dextrose agar for 7 days at 37C and then fungal spores were scraped from the agar plate with an inoculation loop and suspended in sterile deionized water. A s eries of 10 fold dilutions (10 1 to 10 5 ) was prepared from the suspension by adding 0.333 mL of sample to 3.0 mL sterile PBS/SDS in a dilution tube, followed by vortexing for 10 seconds. To enumerate the spores in a dilution, a volume of 0.1 mL was sprea d over sterile dichloran rose bengal chloramphenicol agar in 10015mm Petri dishes. The plates were inverted and then incubated at 37C for 24 hours. Where possible, results were taken from plates that contained between 30 and 300 colonies. 2. 1 .3 Coating P reparation and Testing The steps of each experiment are described below (Fig. 2 1). Step 1 Ten mg of TiO 2 was added to a volume of 9 mL of deionized water in a 20 mL scintillation vial. The TiO 2 suspension was sonicated (Misonix Sonicator 3000, Farmingdal e, NY) at the highest power level (providing 180 200 W) for 30 minutes total (10 min on/2 min off 3). A volume of 1 mL of PHF solution, containing 200, 100, 50 or

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32 0 mg/L PHF, was then added and the suspension was mixed with magnetic stirrer for 10 minute s. Step 2 Grout was chosen as a test substrate because it is prone to fungal colonization. Grout surface was prepared by mixing grout powder (Mapei KeracolorTM U, Deerfield Beach, FL) with deionized water at a 2:1 mass ratio using a spatula for 5 minutes allowed to stand unmixed for 10 minutes, and then mixed for another 2 minutes. The grout water mixture (0.15 g wet weight) was spread over a glass slide (2.5 cm 1.8 cm) and dried overnight at room temperature. Thickness of TiO 2 coatings on grout surfac es was calculated from = (2 1) where d = calculated thickness of TiO 2 coating, c = aqueous concentration of TiO 2 V = volume of TiO 2 suspension applied to surface, = density of TiO 2 A = area of surface and f d = maximum volume fraction of randomly close packed spheres = 0.634 76 Ceramic tiles were used to test photocatalytic inactivation of A. niger spores, because commercial grout formulation contains antimicrobial age nts. Tiles (2.5 cm 2.5 cm) were obtained from American Olean Inc. (Dallas,TX). The tile surfaces were almond colored with a matte finish. PHF/TiO 2 nanocomposite suspension was pipetted onto the grout or tile surface to give a surface loading of 64 g/cm 2 The coated surfaces were dried overnight at room temperature. Additional tiles were coated with Stber silica (SiO 2 ; Geltech) to serve as an inert control surface. SiO 2 suspension was prepared by adding 10 mg of SiO 2 to a volume of 10 mL deionized water, giving a concentration of 0.1 wt%. The suspension was sonicated as described previously. A volume of 0.4 mL of

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33 SiO 2 suspension was pipetted onto the tile surface to give a surface loading of 64 g/cm 2 Step 3 Organic dye or A. niger spores were applied to the test surfaces. A volume of 0.1 mL of Procion red MX 5B solution (100 mg/L) was pipetted onto coated or bare grout and allowed to spread. The dye was air dried for 1 hour before testing. A volume of 0.2 mL of A. niger suspension (2 310 5 spores/mL) was pipetted onto each coated tile surface and allowed to spread, giving a surface loading of 6400 9600 spores/cm 2 The tiles with spores were dried in the dark in a biosafety cabinet for 24 hours. Step 4 The photocatalytic experiments were carried out in a chamber with 16 solar UVA lamps (320 to 400 nm with peak intensity at 350 nm). The UVA lamps (RPR 3500A) were purchased from Southern New England Ultra Violet Company (Branford, CT). Air was circulated in the chamber to maintain uniform temperature of 30 3 2 C. Grout or tile surfaces were placed on a platform in a plastic bin (42 cm 28 cm 15 cm) filled to a depth of 4 cm with deionized water. The bin was covered by a plastic film in order to maintain relative humidity of 80 85%. No condensate formed on the film during the experiments. A Thermo Hydro probe was utilized to monitor the temperature and relative humidity. The distance between samples and UVA lamps was 49.5 cm, giving an intensity of 15 17 W/m 2 under the film, which is typical of the UVA irrad iance under indirect sunlight. The UVA intensity was measured by a PMA2110 detector (Solar Light Co., Glenside, PA). Step 5 Performance of the photocatalytic coatings was measured by dye degradation or spore inactivation. Dye degradation was based on UV/V IS reflectance after 0, 6, 12 and 24 hours of exposure to UVA. Reflectance was measured with a

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34 Perkin Elmer Lambda 800 with PELA 1000 Reflectance Spectroscopy Accessory at a wavelength of 538 nm, at which absorbance of MX 5B Procion Red dye is highest. Dye degradation was calculated according to: % dye degradation = (2 2) where A 0 is the calculated absorbance of dye coated on photocatalytic or bare grout surface before exposure to UVA and A t is the absorbance of dye coated on photocata lytic or grout surface after exposure to UVA at a given time. Absorbance was calculated as the negative log 10 of reflectance expressed as fraction. Because the color of bare grout varied somewhat, it was necessary to subtract this background color. Therefo re, A 0 and A t were calculated from A 0 =A 0' A b (2 3) A t =A t' A b (2 4) where A 0 and A t are the measured absorbance of dye on grout at time zero and time t, respectively, and A b is the measured absorbance of the bare or photocatalytically coated grout surface without dye at a given time. Photocatalytic inactivation of A. niger spores was based on viable spore counts after exposure of spores on test surfaces to UVA. Spores were recovered by immersing a tile in 20 mL PBS/SDS within a polyprop ylene centrifuge tube and vortexing for 15 seconds. The tube was then sonicated at highest power for 3 minutes. During sonication, the tube was immersed in a flowing water bath at 28 C. After sonication, the tube was vortexed for 15 seconds and the tile w as removed from the centrifuge tube using a sterile forceps. The tube was then vortexed again for 15 seconds. The viable

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35 spores in a volume of 0.1 mL suspension from the centrifuge tube were enumerated as described previously. Inactivation was calculated f rom (2 5) where CFU t is the number of colonies after time t and CFU 0 is the number of colonies at time zero. Step 6 Morphological changes to A. niger on photocatalytic coating exposed to UVA were observed using scanning electron micros copy (JOEL 6335F FEG SEM) at 10 kV accelerating voltage and 15 mm working distance. Because of the potentially detrimental effects of vacuum and the electron beam on spores, each tile was observed once under SEM. Hence, three different tiles with spores we re prepared and then observed, one at each exposure time. 2. 1 .4 Aqueous Aggregate Size, Zeta Potential and BET Surface Area Aggregate size of the nanocomposite and of TiO 2 in aqueous suspension was measured by dynamic light scattering (Nanotrac ULTRA, Micr otrac, Inc. York, PA). Zeta potential was measured by doppler shift analysis (ZetaPlus, Brookhaven Instruments Corporation, Holtsville NY). Specific surface area of TiO 2 powder was measured under nitrogen using a NOVA 1200 with multipoint BET (Quantachrome Instruments, Boynton Beach, FL). TiO 2 was degassed and dried under vacuum at 110C for 12 hours prior to measurement. 2. 1 .5 Adsorption PHF was combined with TiO 2 as described previously in the section on coating preparation and testing. A 2 mL volume of t he mixture was transferred to a centrifuge tube, followed by 30 minute centrifugation at 20,800g. The supernatant was carefully

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36 removed by pipette and the procedure was repeated two more times. The concentration of free PHF in the final supernatant was me asured by UV/Vis spectroscopy at 330 nm 77, 78 The extent of adsorption was found to follow the Langmuir relationship: (2 6) where is the mass PHF adsorbed per mass TiO 2 c is the concentration of free PHF in equilibrium with TiO 2 max is the maximum mass PHF adsorbed per mass TiO 2 and K is max and K were estimated by least squares non linear regression. The fraction of surface coverage of TiO 2 by PHF was calculated from (2 7) where N A is Avogadro's constant, A P is the projected area of a PHF molecule (1.33 nm 2 58 m P is the molecular weight of PHF (1094 g/mol from the empirical formula C 60 (O H) 22 ) and A S is the specific surface area of TiO 2 (109.2 m 2 /g as measured in the present study). 2. 1 .6 Data Analysis First order fits between the extent of dye degradation or spore inactivation and UVA exposure time were based on the equation (2 8) and second order fits were based on the equation (2 9)

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37 where c t and c 0 represent absorbance or colony forming units at times t and t 0 respectively, k and k' are the reaction rate coefficients for the first and seco nd order fits, respectively, and b and b' are arbitrary constants. The parameter values (k, b, k', b') for the fits were determined by least squares linear regression. One way ANOVA and post sided tests through NCSS statistical analysis and graphics software (NCSS, Kaysville, UT). The significance of differences between R 2 values of least square fits to experimental data was determined using the Fisher r to z transformation 79 2. 2 Results 2. 2 .1 Characterization The isotherm for adsorption of PHF on TiO 2 is given in Fig. 2 2. The theoretical maximum adsorption of PHF on TiO 2 was found to be 7.2 mg/g. This level was reached at a formulation ratio (g PHF added/g TiO 2 ) of 0.02. A decrease of the formulation ratio to 0.01 had almost no effect on the amount of PHF adsorbed, whereas dropping the formulation ratio still further to 0.005 decreased the amount of PHF adsorbed to 4.7 mg/g. The mean aggregate size of TiO 2 base d on number distribution was 104 nm. This dropped to 94 nm for the nanocomposite at a formulation ratio of 0.005, and further dropped to the range of 83 86 nm at formulation ratios of 0.01 and 0.02. (Fig. 2 3). Zeta potential of TiO 2 was 41 mV at pH 6, co mpared to 48 to 49 mV for the nanocomposite (Fig. 2 3). 2. 2 .2 Dye D egradation TiO 2 coatings with calculated thickness ranging from 2.5 to 12.5 m changed the color of grout surfaces from almond to white, whereas a coating with a calculated

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38 thickness of 0 .25 m had no effect on surface appearance of the grout (Fig. 2 4 A D ). A scanning electron micrograph of the 0.25 m thick coating shows its uniform, particulate make up. (Fig. 2 4 E ). Accordingly, a TiO 2 coating thickness of 0.25 m was chosen for subseque nt experiments. Another consideration in coating design is the effect of PHF on appearance. PHF is dark brown in color, giving PHF/TiO 2 suspensions a brown tint at higher PHF/TiO 2 ratios. To ensure that coatings remained colorless under all experimental co nditions, a maximum PHF/TiO 2 weight ratio of 0.02 was established for performance testing. Time dependent degradation of Procion red dye on coated and bare grout is shown in Figure 2 5. Under UVA exposure with photocatalyst, degradation ranged from 66% to 74% in 24 hours. Without photocatalyst, degradation was 43%, which can be attributed to UVA photolysis. Almost no (4%) dye degradation was observed in the dark. PHF/TiO 2 degradatio n at all sampling times, whereas a PHF/TiO 2 ratio of 0.005 significantly enhanced degradation only in the first 6 hours. The extent of dye degradation with the nanocomposite at 6 hours was almost doubled in comparison to TiO 2 alone. Based on these results, a PHF/TiO 2 ratio of 0.01 was selected for the spore inactivation study. 2. 2 .3 Spore Inactivation A surface loading of 6400 9600 spores/cm 2 on the photocatalytic surface was chosen to give a sparse distribution of spores (Fig. 2 6), which limited spore agg lomeration and thus allowed more precise enumeration of individual spores. The efficiency of spore recovery from test surfaces was evaluated by applying spores, allowing the surfaces to dry overnight in the dark, and then applying the recovery procedure. C omplete recovery (within experimental error) was achieved from coatings

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39 of the nanocompos i te or TiO 2 whereas little more than half of applied spores were recovered from bare tile (Fig 2 7). This result is likely due to separation of particulate coatings f rom the tiles during the recovery procedure, carrying the spores with them. A particulate material without photocatalytic properties, SiO 2 was therefore used as a non photocatalytic coating. As Figure 2 7 shows, complete recovery of spores was achieved fr om the SiO 2 coating. The time dependent inactivation of A. niger spores on photocatalytic and non photocatalytic surfaces under UVA exposure is shown in Fig. 2 8. A 12 hour inactivation of 60% was achieved with TiO 2 alone. This was increased to 78% with th e nanocomposite at a PHF/TiO 2 ratio of 0.01. Decreases in the numbers of viable spores with time on the photocatalytic surfaces paralleled decomposition of spores as imaged by scanning electron microscopy (Fig. 2 9). The difference in performance levels be tween TiO 2 alone and the PHF/TiO 2 As Figure 2 8 shows, there was negligible inactivation of spores on the photocatalytic surfaces in the dark. Moderate (41% in 12 hours) inactivation was observed on SiO 2 coated surfaces. 2. 2 .4 Kinetics of Dy e Degradation and Spore Inactivation Time dependent data for dye degradation and spore inactivation were modeled by first order and second order least square fits, as summarized in Table 2 1. Since the first order and second order equations at each contain two parameters, it was possible to test the significance of the differences between R 2 values obtained with the two different equations. In modeling photocatalytic dye degradation, second order fits were significantly bett er than first photocatalytic spore inactivation by the PHF/TiO 2 nanocomposite, the first order fit was

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40 significantly better than the second on TiO 2 were equally well described by first order and second order fits. The enhancement of dye degradation and spore inactivation achieved by the nanocomposite are compared in Fig. 2 10. In the dye degradation tests, the PHF/TiO 2 ratios of 0.01 and 0.02 give equival ent results, which are significantly better than obtained with the 0.005 ratio. In the spore inactivation experiments, the degree of variability between replicates was greater, which is not unusual when testing biological materials. As a result, there was no statistical difference in the enhancement of photocatalysis achieved with nanocomposites with PHF/TiO 2 ratios of 0.005, 0.01 or 0.02. 2. 3 Discussion The findings of this research show that PHF enhances the performance of TiO 2 photocatalyst in thin, tran sparent coatings. As shown in Table 2 2, the 1.9 times enhancement of dye degradation achieved with the PHF/TiO 2 nanocomposite compares favorably with the enhancement ratios of 1.1 to 2.2 reported for other enhancers (Ag, Au, Cu, Fe, La, N, Sn, Sr). Given its comparable performance, the competitive advantage of PHF as an enhancer of photocatalysis lies in the fact that it is biocompatible, biodegradable, and the nanocomposite of PHF and TiO 2 requires no synthesis steps. The findings also raise three points for discussion: how the optimum PHF/TiO 2 ratio differs in a coating vs. the aqueous environment; how the kinetics of photocatalysis appear to change depending on the target component (dye vs. microbes); and how the observed enhancement of photocatalytic pe rformance changes from the beginning to the end of the exposure period.

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41 In the present study, the optimal ratio of PHF to TiO 2 was found to be 0.01, which is 10 times higher than reported by Krishna et al. 66 for aqu eous suspensions of the PHF/TiO 2 nanocomposite. The adsorption isotherm developed in this study indicates that the maximum amount of PHF that can adsorb to TiO 2 is 7.2 mg/g. This corresponds to a maximum surface coverage of TiO 2 by PHF of 4.9%, which is ne arly reached at a formulation ratio of 0.01 g PHF/g TiO 2 (Fig. 2 11). Increasing the ratio to 0.02 increases the surface coverage very slightly. Consequently, the photocatalytic activity of the nanocomposite is not significantly increased beyond a formulat ion ratio of 0.01. On the other hand, dropping the ratio to 0.005 significantly decreases the surface coverage to 3.2%, which results in lower photocatalytic activity. Unlike the aqueous system studied by Krishna et al., an excess of PHF in the coating doe s not impair activity, because the excess simply drains from the coating and does not shade the nanocomposite. Assuming that hydroxyl radical is produced at a constant rate in a photocatalytic reaction, the reaction can be theoretically considered as pseud o first order, which is supported by various studies 16, 80 However, our experimental data for photocatalytic dye degradation are better described by second order reaction kinetics. This can be attr ibuted to the production of colorless intermediates that accumulate during the experiment and consume hydroxyl radicals, decreasing the availability of hydroxyl radicals to unreacted dye. Hu et al. 81 using ion mass spectra, identified more than 12 intermediate products in the photocatalytic degradation of Procion red dye, all of which are capable of reacting with hydroxyl radicals. The degree to which dye degradation and spore inactivation are enhanced by the PHF/Ti O 2 nanocomposite is time dependent. At 6 hours, the PHF/TiO 2 nanocomposite

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42 surface degraded nearly 2 times as much dye as TiO 2 alone, compared to 1.1 at 24 hours. In the case of microbial inactivation, the nanocomposite surface inactivated 3 times as many spores as TiO 2 alone at 3 hours, compared to an enhancement of 1.3 at 12 hours. This relationship is expected as the remaining dye or viable spores on the surfaces approaches zero at longer exposure times. 2. 4 Summary The present study has shown that PH F enhances the UVA photocatalytic performance of a thin, transparent TiO 2 coating by a factor of 2 to 3. This is achieved with a PHF/TiO 2 ratio of 0.01, at which the TiO 2 surface is nearly saturated with PHF. The enhanced performance of the PHF/TiO 2 nanoco mposite was demonstrated by organic dye degradation and fungal spore inactivation. The self assembled PHF/TiO 2 nanocomposite is very promising for use as thin, transparent, antimicrobial coatings.

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43 Table 2 1. Comparison of first order fits and second orde r fits to photocatalytic dye degradation and spore inactivation data* Contaminant Treatment First Order Reaction Kinetics Second Order Reaction Kinetics 1st 2nd order Equation R 2 Equation R 2 P Dye PHF/TiO 2 =0.02 y= 0.053x 0.210 0.90 y=0.123x+1.1 53 0.99 0.0001 PHF/TiO 2 =0.01 y= 0.053x 0.181 0.92 y=0.123x+1.107 0.99 0.0006 PHF/TiO 2 =0.005 y= 0.042x 0.142 0.92 y=0.081x+1.099 0.99 0.0006 PHF/TiO 2 =0 y= 0.045x 0.058 0.98 y=0.083x+1.005 1.00 <0.0001 Microbes PHF/TiO 2 =0.01 y= 0.127x+0.048 0.99 y=0.3 00x+0.639 0.95 0.0009 PHF/TiO 2 =0 y= 0.079x 0.007 0.97 y=0.129x+0.836 0.95 0.29 1st order: y is ln c/c 0 ; 2nd order: y is c 0 /c

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44 Table 2 2. Effect of enhancers on UVA photocatalytic degradation of organic dyes by TiO 2 coatings Study Type of TiO 2 Enhancer Mass ratio of enhancer to TiO 2 Model pollutant UVA intensity (W/m2) Time exposed to UVA (h) Increase in rate This study* Anatase PHF 0.01 Procion red MX 5B 15 17 6 1.9 Arabatzis et al. 51 Anatase and rutile (sol gel) Ag 0.013 Methyl orange 0.717 1 1.8 Arabatzis et al 52 Anatase and rutile (sol gel) Au 0.051 Methyl orange 0.717 1 2.2 Arpac et al. 82 Anatase (sol gel) Sn 0. 15 Malachite Green N/A ** 4 1.1 Hermann et al. 83 Anatase (sol gel) Ag Malic acid N/A 0.5 1.3 Somekawa et al. 84 Degussa P25 N Methylene blue N/A N/A 1.2 Wu et al. 85 Anatase (sol gel) Fe and Au Fe: 0.005 Au: 0.02 2,4 dichlorophenol 12.3 5 2.0 Kumaresan et a l. 86 Anatase (sol gel) Sr 0.001 2,4 dinitrophenol N/A 5 1.8 Okte and Yilmaz 87 Anatase (sol gel) La 0.0028 Methyl orange N/A 3 1.3 Carvalho et al. 88 Amorphous Cu 0.007 Methylene blue N/A 2 1.8 *The TiO 2 film was exposed to air in this study, and t o water in all other studies **Not available in the reference

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45 Figure 2 1. Procedure for testing performance of photocatalytic coatings

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46 Figure 2 2. Langmuir isotherm for adsorption of PHF onto TiO 2 at pH 6 and 25C

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47 Figure 2 3. Aqueous aggregate size and zeta potential of TiO 2 and PHF/TiO 2

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48 A B C D E Figure 2 4. Coating appearance and structure. A ) Effect of calculated TiO 2 thickness on appearance on grout surface. B) Effect of 0.25 m thick TiO 2 coating on appearance on grout surface. C) Effect of 2.5 m thick TiO 2 coating on appearance on grout surface. D) Effect of 12.5 m thick TiO 2 on appearance on grout surface. E ) S canning electron micrograph of TiO 2 at the thickness of 0.25 m

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49 Figure 2 5. Optimization of PHF/TiO 2 mass ratio (0.02, 0.01, 0.005, 0) in photocatalytic nanocomposite. Error bars represent 1.0 SD. (Error bars for the dark control are too small to be seen.) Model lines represent second order fits

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50 Figure 2 6. False color imag e of Aspergillus niger spores on PHF/TiO 2 nanocomp os ite coating (Spores are red spheres; coating is green background; whitish coloring indicates charging of the coating during microscopy.)

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51 Figure 2 7. Recovery of A. niger from test surfaces. Error bars r epresent 1.0 SD

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52 Figure 2 8. Inactivation of A. niger spores by test surfaces. Error bars represent 1.0 SD. Model lines represent first order fits

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53 Figure 2 9. Temporal changes of spore morphology on photocatalytic coatings exposed to UVA 0 h 3 h 6 h

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54 A B Figure 2 10. Photocatalytic enhancement by the nanocomposite at different PHF/TiO 2 ratios (0.005, 0.01 and 0.02) relative to TiO 2 alone. A ) D ye degradation B ) spore inactivation

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55 Figure 2 11. Surface coverage of PHF on TiO 2 as a function of the PH F/TiO 2 formulation ratio

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56 CHAPTER 3 VISIBLE LIGHT ACTIVE TRANSPARENT, ANTIM ICROBIAL SURFACES Chapter 2 demonstrated that PHF significantly enhances TiO 2 photocatalysis in transparent coating under UVA irradiance. The novel PHF/TiO 2 nanocomposite coating is very promising as it can be used for antimicrobial coating applications, reducing surface acquired infections. However, surface acquired infections occur more frequently in indoor environment, such as hospitals, assisted living facilities and other public buildings, where UVA (315 400 nm) is not available. Visible light (fluorescent lamp with wavelength above 400 nm) is readily available in indoor environments. The photocatalytic activity of PHF/TiO 2 under visible light is not yet identified. Hence, the ob jective of this study is to evaluate and optimize the visible light activity of PHF/TiO 2 nanocomposite and test its efficacy against model microbes (fungal and bacteria). The first task was to select a coating system that is active under visible light. TiO 2 nanoparticles with different crystallite sizes and phases from four manufacturers were selected. They were characterized by XPS, XRD, BET surface area measurement, light adsorption and photocatalytic performance. The second task was to combine the s elected visible light active TiO 2 with PHF. The PHF/TiO 2 nanocomp os ite coating was optimized by varying the weight ratio of PHF to TiO 2 The photocatalytic performance was determined by organic dye degradation. The optimized PHF/TiO 2 nanocomposite was used to inactivate Staphylococcus aureus a surrogate for MRSA and spores of Aspergillus niger a common household allergen.

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57 3. 1 Experimental 3. 1 .1 Chemicals and Reagents Five model photocatalysts were used: the mixed phase P25, rutile (rutile22 [ 4 ] and rutile9 9) and anatase (anatase7 and anatase15). The properties of these photocatalysts as given by the manufacturers are collected in Table 3 1. Commercial TiO 2 formulations (NuTiO TM Primer and NuTiO TM TiO 2 ) were obtained from Bioshield, Inc. (Fort Lauderdale, FL ). A solution of Procion red MX 5B dye (Sigma Aldrich Inc., St. Louis, Missouri) was prepared at a concentration of 2000 mg/L by dissolving 0.02 g dye powder in 10 mL deionized water. Polyhydroxy fullerene (PHF) was synthesized in our laboratory according to the protocol of Gao et al. 75 Phosphate buffered saline (PBS) solution was prepared by dissolving 12.36 g Na 2 HPO 4 1.80 g NaH 2 PO 4 and 85.00 g NaCl in 1000 mL of deionized water and then diluting 10 immediately before u se. PBS/SDS solution was prepared by adding 0.576 g sodium dodecyl sulfate (SDS) to 1000 mL of PBS and then autoclaving at 120C and 16 bar for 15 minutes. 3. 1 .2 Microbe Culture and Enumeration The culture media for Staphylococcus aureus (ATCC 25923) was tryptic soy agar and tryptic soy broth (Becton, Dickinson and Company, Sparks, MD), which were used for culturing and enumerating the bacteria. Agar plates were prepared by adding a mass of 40 g Tryptic soy agar powder to 1 L of deionized water and mixing thoroughly with heating to the boiling point. The solution was then autoclaved at 120 C and 16 bar for 15 minutes. Plates were made by pouring the autoclaved agar into 10015 mm sterile plastic Petri dishes (Fisher Scientific) and air dried in a laminar f low hood (LABCONCO [ 4 ] The phase of TiO 2 followed by its crystallite size was used to identify each TiO 2 powder in this stud y

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58 purifier class 2 safe cabinet) for 24 hours. The dried agar plates were used immediately or stored in inverted position in a refrigerator at 4C. Broth was prepared by adding a mass of 32 g tryptic soy broth powder to 1 L of deionized wa ter and mixing thoroughly with heating to the boiling point. The solution was then autoclaved at 120 C and 16 bar for 15 minutes. Autoclaved tryptic soy broth was used immediately or stored in a refrigerator at 4C. The S. aureus was maintained by streak ing the bacteria on tryptic soy agar in a Petri dish. The inoculated plate was inverted and incubated at 37C for 24 hours. An inoculation loop was used to transfer a loop ful l of S. aureus from the plate to a 250 mL Erlenmeyer flask containing 100 mL of t ryptic soy broth. The flask with S. aureus was incubated at 37C for 24 hours. A volume of 1 mL of 24 hour S. aureus suspension was added to ten centrifuge tubes, respectively. Each tube contained 1 mL of 50% glycerol as cryoprote c tant. The mixture of S. a ureus and glycerol was stored at 84C. S. aureus was cultured by adding a 2 ml aliquot of S. aureus that was previously frozen at 84C in 25% glycerol to a 250 mL Erlenmeyer flask containing 100 mL of sterile tryptic soy broth. The culture was incubated in a shaker incubator at 150 rpm and 37C for 24 hours. The suspension was washed three times with sterile deionized water and the final pellet was resuspended in 15 mL of deionized water. The number of colony forming units in a suspension of S. aureus wa s determined by serial dilution and viable plate counts. A series of 10 fold dilutions (10 1 to 10 7 ) was prepared from the S. aureus suspension by adding 0.333 mL of sample to 3.0 mL sterile deionized water in a dilution tube, followed by vortexing for 10 seconds. A volume of 0.1 mL of diluted sample was spread over the surface of tryptic soy agar using a Teflon rod

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59 in each of three 10015mm Petri dishes. The inoculated plates were inverted and then incubated at 37C for 24 hours. Where possible, results w ere taken from plates that contained between 30 and 300 colonies. 3. 1 .3 Coating Preparation and Testing The steps of coating preparations are described below Step 1 Ten mg of TiO 2 or SiO 2 was added to 10 mL of deionized water in a 20 mL scintillation vial The suspension was sonicated (Misonix Sonicator 3000, Farmingdale, NY) at the highest power level (providing 180 200 W) for 30 minutes total (10 min on/2 min off 3). PHF/TiO 2 nanocomposite was prepared by adding ten mg of anatase7 to 9 mL of deionized water in a 20 mL scintillation vial. The anatase7 suspension was sonicated (Misonix Sonicator 3000, Farmingdale, NY) at the highest power level (providing 180 200 W) for 30 minutes total (10 min on/2 min off 3). A volume of 1 mL of PHF solution, containi ng 1000, 500, 100, 50 or 0 mg/L PHF, was then added to the anatase7 suspension, mixed with magnetic stirrer for 10 minutes in dark. The Bioshield NuTiOTM TiO 2 and Bioshield Primer formulations were applied directly from the manufacturer's containers. Step 2 Ceramic tiles were used to test photocatalytic degradation of organic dye and inactivation of microbes. Tiles (2.5 cm 2.5 cm) were obtained from American Olean Inc. (Dallas,TX). The tile surfaces were almond colored with a matte finish. A volume of 0 .4 mL of TiO 2 or SiO2 (as inert control) suspension or Bioshield Primer was pipetted on the tile surface as a bottom coat. The coated surfaces were dried overnight at room temperature. A second coat of TiO 2 PHF/TiO 2 nanocomposite, SiO 2 or Bioshield NuTiO was applied following the same procedure as described above. This gave final surface TiO 2 loadings of 128 g/cm 2 (TiO 2 on TiO 2 ), 64 g/cm 2 (SiO 2 on TiO 2 )

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60 or 0 g/cm 2 (SiO 2 on SiO 2 ). The TiO 2 surface loadings of coatings with either Bioshield Primer or Bios hield NuTiO were not determined. Step 3 Organic dye or S. aureus suspension was applied to the test surfaces. (a) Testing with organic dye. A volume of 0.01 mL of Procion red MX 5B solution (2000 mg/L) was pipetted onto coated tile and allowed to spread The dye was dried at 50C for 20 minutes before testing. (b) Testing with S. aureus A volume of 0.1 mL of S. aureus suspension (2 310 5 CFU/mL) was pipetted onto each coated tile surface and allowed to spread, giving a surface loading of 6400 9600 C FU/cm 2 The tiles with S. aureus were dried in the dark in a biosafety cabinet for 3 hours. Step 4 The photocatalytic experiments were carried out under fluorescent lamps (General Electric model T8 Ultramax F28T8 SPX41) at an irradiance of 1.8~2.0 W/m 2 UVA irradiance was measured by a PMA2110 meter with a PMA 2110 UVA Detector or PMA 2140 Global Detector (Solar Light Co., Glenside, PA). Dye degradation was based on absorbance, as calculated from reflectance measured at 538 nm after 0, 3, 6, 12 and, somet imes, 24 hours of exposure to fluorescent light. Reflectance of coated or uncoated tile surfaces was measured with a Perkin Elmer Lambda 800 with PELA 1000 Reflectance Spectroscopy Accessory. Absorbance was calculated as the negative log 10 of reflectance e xpressed as fraction. Coated tiles without dye were used as the internal reference in the measurement. Dye degradation was calculated according to: % dye degradation = (3 1)

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61 where A 0 is the calculated absorbance of dye coated on phot ocatalytic or bare grout surface before exposure to fluorescent light and A t is the absorbance of dye coated on photocatalytic or grout surface after exposure to fluorescent light at a given time. Because the color of bare grout varied somewhat, it was nec essary to subtract this background color. Therefore, A 0 and A t were calculated from A 0 =A 0' A b (3 2) At=A t' A b (3 3) where A 0' and A t' are the measured absorbance of dye on grout at time zero and time t, respectively, and A b is the meas ured absorbance of the bare or photocatalytically coated grout surface without dye at a given time. Photocatalytic inactivation of microbes was based on viable counts after exposure of spores on test surfaces to fluorescent light. Bacteria were recovered b y immersing a tile in 20 mL PBS/SDS within a polypropylene centrifuge tube and vortexing for 15 seconds. The tube was then sonicated at highest power for 1 minute. During sonication, the tube was immersed in a flowing water bath at 28 C. After sonication, the tube was vortexed for 15 seconds. The viable bacteria in a volume of 0.1 mL suspension from the centrifuge tube were enumerated as described previously. Inactivation was calculated from (3 4) where CFU t is the number of colonies a fter time t and CFU 0 is the number of colonies at time zero.

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62 3. 1 4 Characterization of TiO 2 Particles and Coatings X ray photoelectron spectroscopy X ray photoelectron spectroscopy (XPS) was used to measure the purity of the TiO 2 powders used in this stud y. XPS analysis was performed with an XPS/ESCA Perkin Elmer PHI 5100ESCA system using a wafer as a substrate, followed by spectrum analysis with AugerScan software (Thermo Fisher Scientific, Waltham, MA). When a material is irradiated with a beam of alumin um or magnesium X rays, XPS simultaneously measures the kinetic energy (KE) and electrons escaping from the top 1 to 10 nm of the material. The electron binding energy (BE) can be determined based on the equation: (3 5 ) where E binding is the energy of the electron emitted from one electron configuration within the atom; E photon is the energy of the X ray photons being used; E kinetic is the kinetic function of the spectrometer. BET surface area Specific surface area of TiO 2 was measured under nitrogen using a NOVA 1200 with multipoint BET (Quantachrome Instruments, Boynton Beach, FL). TiO 2 powder was degassed and dried under vacuum at 110C prior to measuremen t. X ray diffraction Powder X ray diffraction was measured on a APD 3720 diffractometer (Philips, Andover, MA) with Cu K radiation (40 kV, 25 mA) and diffracted step. Crystal structure was identified according to the database of International Centre for Diffraction Data.

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63 The crystallite si ze of TiO 2 was determined from the Scherrer equation: 89 (3 6 ) where L is the average crystallite size, K is the shape factor (0.9), is the x ray wavelength of Cu K radiation (1.54 ), B is the overall line broadening in radians at the full width at half maximum (FWHM) intensity, b is the line broadening in radians at the angle at which highest intensit y was observed. The crystallite size measured from XRD was used to compute an estimate of the specific surface area of TiO 2 for comparison with the measurement from BET surface area, according to the following equation: (3 7 ) where 2 form and d is the crystallite size of TiO 2 as determined by XRD. Scanning e lectron m icroscopy Scanning electron microscopy (JOEL 6335F FEG SEM) was used to observe the ultrastructure of TiO 2 coating at the conditions of 10 kV ac celerating voltage and 10 mm working distance. UV/VIS r eflectance s pectroscopy A Perkin Elmer Lambda 800 UV/VIS spectrophotometer with PELA 1000 reflectance accessory was used to measure light adsorption by TiO 2 over a range of 300 to 700 nm. The band ga p energy was determined from: E = hc/ (3 8 ) where is the wavelength at which a strong cut off in adsorption was observed, h is the Plank constant (4.1410 15 eV s) and c is the speed of light in vacuum (3.0010 8 m/s). A

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64 volume of 0.4 mL of 1 wt% [ 5 ] TiO 2 suspension was pipetted onto a tile surface, followed by drying overnight in a biosafety cabinet. A white Teflon plate was used as the internal reference. 3. 1 .5 Adsorption PHF was combined with anatase7 as described previously in the section on coating preparation and testing. A 2 mL volume of the mixture was transferred to a centrifuge tube, followed by 30 minute centrifugation at 20,800g. The supernatant was carefully removed by pipette and the procedure was repeated two more times. The concentration of free PHF in the final su pernatant was measured by UV/Vis spectroscopy at 330 nm. 77, 78 The extent of adsorption was found to follow the Langmuir relationship: (3 9) where is the mass PHF adsorbed p er mass TiO 2 c is the concentration of free PHF in equilibrium with TiO 2 max is the maximum mass PHF adsorbed per mass TiO 2 and K is the Langmuir equilibrium constant. The Langmuir parameters max and K were estimated by least squares non linear regres sion. The fraction of surface coverage of TiO 2 by PHF was calculated from (3 10) where N A is Avogadro's constant, A P is the projected area of a PHF molecule (1.33 nm 2 58 m P is the molecular weight of PHF (1094 g/mol from the empirical formula C 60 (OH) 22 ) [ 5 ] The concentration of TiO 2 suspension was ten times higher in order to increase signal to noise ratio of TiO 2 and eliminate signals coming from the bare tile surface.

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65 and A S is the specific surface area of anatase with a crystallite size of 7 nm ( 231 m 2 /g as measured in the present study). 3. 1 .6 Data Analysis First order fits between the extent of dye degradatio n or microbe inactivation and UVA exposure time were based on the equation (3 11) and second order fits were based on the equation (3 12) where c t and c 0 represent absorbance or colony forming units at times t and t 0 respectively, k and k' are the reaction rate coefficients for the first and second order fits, respectively, and b and b' are arbitrary constants. The parameter values (k, b, k', b') for the fits were determined by least squares linear regression. One way ANOVA and post sided tests through NCSS statistical analysis and graphics software (NCSS, Kaysville, UT). The significance of differences between R 2 values of least square fits to experimental data was determined using the Fisher r to z transformation. 79 3. 2 Results 3. 2 .1 Characterization XPS gives a measure of the elemental composition of a powder to a depth of 1 to 10 nm. The XPS spectrum of the TiO 2 particles used in this study is displayed in Figure 3 1. Each of the powders contained titanium, oxygen and carbon (Table 3 2). The carbon is present as surface impurity due to exposure of the powder to the laboratory

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66 atmosphere. P25 contained a small amou nt of silicon and rutile22 contained a small amount of aluminum in addition to Ti, O and C. Binding energies are given in Table 3 3. The binding energies exhibited a shift of 3.7 7 eV above the binding energies published in the NIST X ray Photoelectron Spe ctroscopy Database 90 Because the shifts between the measured and database binding energies for electrons are consistent both in magnitude and direction, the measurements were considered to be consistent with the database. The BET specific areas of rutile22, rutile99, anatase7, anatase15 and P25 were 35, 1, 231, 110 and 44 m 2 /g, respectively (Table 3 4). These values deviated slightly from the specific surface area calculated on the basi s of the crystallite sizes calculated from XRD and spherical particles. X ray diffraction gives information about the crystallographic structure of powders. X ray diffraction patterns of the TiO 2 powders used in this study are shown in Figure 3 2 Diffract ion patterns of characteristic of both anatase and rutile were found by XRD analysis of P25. This indicates that P25 has a mixed phase structure. 91 The diffraction patterns of rutile22 and rutile99 were in good agreeme nt with the pattern for rutile from the database of International Centre for Diffraction Data (ICDD). 92 The diffraction pattern of anatase7 was in good agreement with the diffraction pattern for anatase from the ICDD database, whereas anatase15 contained a small peak at Miller index 110, which is indicative of a slight rutile impurity. The mean crystallite size calculated on the basis of XRD was 22 nm for rutile22, 99 nm for rutile99, 7 nm for anatase7, 15 nm for anatase15 and 25 nm for P25 (Table 3 5 ). The x ray diffraction parameters used for these calculations are also given in Table 3 5.

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67 Scanning electron micrographs of TiO 2 powders employed in this research are given in Figure 3 3. The asp ect ratio of anatase crystallites was noticeably higher than that of rutile or P25. The anatase coating also appears less dense than the rutile or P25 coatings. The smaller dimension of the crystallites was 23 28 nm for rutile22 (Fig. 3 3 A ), 97 280 nm for rutile99 (Fig. 3 3 B ), 16 25 nm for anatase7 (Fig. 3 3 C ), 21 59 nm for anatase15 (Fig. 3 3 D ) and 30 47 nm for P25 (Fig. 3 3 E ). Table 3 6 gives a comparison of crystallite size based on XRD and SEM. The light a b sorption spectra of TiO 2 coatings used in this study are shown in Figure 3 4. The band gaps were determined to be 3.0 eV for rutile22, 3.0 eV for rutile99, 3.2 eV for anatase7, 3.2 eV for anatase15 and 3.1 eV for P25 (Table 3 7). These values are consistent with band gaps for these materials that are reported in the literature 93, 94 3. 2 .2 Photocatalytic Performance of TiO 2 with Different Crystallite Sizes Top coats of a commercial photocatalyst (NuTiO TiO 2 ), P25 and anatase15 on bottom coats o f NuTiO Primer, rutile99 and SiO 2 was screened for their ability to degrade organic dye under visible light, as shown in Figure 3 5. Dye degradation on bare tile over the 4 days of exposure to visible light was minimal. NuTiO TiO 2 appeared to have almost n o photocatalytic activity. P25 and anatase15 exhibited modest photocatalytic activity with bottom coat of NuTiO Primer, and almost complete photocatalytic dye degrad ation on bottom coats of rutile 99 and SiO 2 The visible light photocatalytic performance of coatings made from rutile22 or anatase7, as well as coatings made from rutile99, anatase15 and P25, is shown in Figure 3 6. The largest particles, rutile99, were inactive. TiO 2 coatings made from powders with crystallite size smaller than P25 outperform ed P25. Rutile22 exhibited the highest photocatalytic activity.

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68 Table 3 8 summarizes model fits to the time dependent dye degradation data with first order and second order reaction kinetics. There is no significant difference between the correlation coef ficients of the first order and the second order fits. In the case of UVA experiments, as reported in Chapter 2, second order fits were significantly better for dye degradation. In order to maintain consistency with the Chapter 2 results, the second order reaction rate coefficients are used to compare dye degradation performance of alternative coatings. The second order dye degradation rate coefficients are compared in Figure 3 7 in relation to crystallite size. The reaction rate coefficient for rutile99 i s near zero, significantly lower than the coefficients of other coatings. All coatings except rutile99 have significantly higher reaction rate coefficients than P25. The dye degradation rate coefficient for rutile22 was significantly greater than that for the other coatings. Anatase7 and anatase15 were equivalent in performance. The coatings of anatase7 and rutile22 were more uniform and transparent than coatings of other powders. Due to their ability to produce coatings with excellent visible light activit y and transparency, rutile22 and anatase7 were selected for further development. 3. 2 .3 Light Utilization by Rutile22 and Anatase7 The light source used in this study was fluorescent lamp, which contained a wide spectrum of electromagnetic radiation rangin g from far end of UVA to near infrared. The emission spectrum of the fluorescent light used in this study (Fig. 3 8) indicated that only a small peak in intensity was present below 400 nm, comprising less than 3% of the total intensity. Two peaks are prese nt between 400 and 500 nm, together accounting for 17% of total intensity. Light from 500 to 700 nm constitutes 80% of total intensity.

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69 Optical filters were used to identify the effect of different portions of the spectrum of fluorescent light on photocat alytic activity of rutile22 and anatase7. The 400 nm cut off filter ha s zero transmission below 380 nm, with a transition to 90% transmission between 380 and 400 nm. The 495 nm cut off filter ha s zero transmission below 470 nm, with a transition to 90% tra nsmission between 470 and 495 nm (Table 3 9 and 3 10 ). The effects of the optical filters on dye degradation are shown in Figure 3 9. Application of the 400 nm cut off filter reduced dye degradation by rutile22 by 22% relative to the dye degradation obtain ed under neutrally filtered light (Table 3 1 1 ), indicating that about one fourth of the activity of this photocatalyst is due to UVA. Application of the 495 nm cut off filter further decreased dye degradation by 62% relative to the neutral filter, indicati ng that about one half of the activity of rutile22 is due to light between 400 and 495 nm. Thus, most of the activity of rutile22 appears to derive from sub 495 nm light. In the case of anatase7, application of the 400 nm cut off filter reduced dye degrada tion by 22% relative to the neutral filter, indicating that about one fourth of the activity of this photocatalyst, as with rutile22, is due to UVA. Application of the 495 nm cut off filter further decreased dye degradation by only 4% relative to the neutr al filter, indicating that almost none of the activity of anatase7 is due to light between 400 and 495 nm. Thus, most of the activity of anatase7 appears to derive from sub 400 nm and supra 495 nm light. 3. 2 4 Photocatalytic Performance of PHF/anatase7 Si nce anatase7 and rutile22 utilize different spectrum of fluorescent light, the combination of these TiO 2 particles as part of a coating system can be expected to exhibit superior photocatalytic activity. Scanning electron micrographs of anatase7 and rutile 22 (Fig. 3 10) shows that a two layer rutile22 coating is more uniform and denser

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70 than a two layer anatase7 coating. In Figure 3 10 B some bare area seemed to appear in addition to aggregates on the antase7 coating. However, this area was covered with ultr afine, sparsely distributed anatase7 particles (16 25 nm) as shown previously in Figure 3 3. As a result, the coating design with rutile22 as a dense and uniform bottom coat and with the ultrafine anatase7 or PHF/anatase7 nanocomposite as top coat was expe cted to maximize the photocatalytic performance of the coating. The isotherm for adsorption of PHF on anatase7 is given in Figure 3 11. The theoretical maximum adsorption of PHF on anatase was 39.7 mg/g whereas the highest level reached experimentally wa s 31 mg/g at the PHF/anatase7 ratio of 0.1. The effectiveness of PHF/anatase7 nanocomposite with ratios of 0, 0.005, 0.01, 0.05 and 0.1 as top coat with rutile22 as bottom coat was tested. Figure 3 1 2 describes the time dependent degradation of procion re d MX 5B dye on this coating system under fluorescent light. A dark control with anatase7 as top coat and rutile22 as bottom coat suggested that no dye degradation took place in dark. Previously (Fig. 3 5), it was shown that dye photolysis under visible lig ht is negligible. TiO 2 photocatalysis was definitely enhanced even with small amount of PHF. After 3 hour exposure to fluorescent light, up to 2.3 times enhancement was observed for PHF/anatase7 at the ratio of 0.1, and the extent of dye degradation for o ther ratios of PHF/anatase7 (0.005, 0.01 and 0.05) were also significantly different from that of anatase7 coating. After 6 hours, the speed up was1.4 times for PHF/anatase7 ratios of both 0.05 and 0.1. The second order dye degradation rate coefficient was found to be significantly correlated (P = 0.001) with the PHF/anatase7 ratio, as shown in Figure 3 1 3

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71 3. 2 5 Photocatalytic Inactivation of Staphylococcus aureus The time dependent inactivation of S. aureus on photocatalytic and non photocatalytic surfac es under fluorescent light is shown in Figure 3 1 4 There was 42% inactivation over 24 hours without light, which can be attributed to desiccation of S. aureus on a surface. Under visible light, on the SiO 2 /rutile22 coating, there was 80% inactivation of S aureus Under visible light, on the photocatalytic coating s, there was 91% to 97% inactivation. The effect of PHF was most pronounced in the first 6 hours of the experiment. At this time, the concentrations of viable S. aureus remaining on the coatings o f PHF/anatase7 nanocomposite were significantly lower than the remaining concentration on anatase7 ( 0.01 and 0.1 gave inactivation rates of 1.5 and 2.0 times the rate obtained with anatase7, respectively. 3. 3 Discussion 3. 3 .1 Visible Light Photocatalysis The anatase and rutile phases of TiO 2 are gen erally regarded as inactive under visible light. However, anatase and rutile with smaller crystallite size were found to be active in this study. Possible reasons for the observed visible light photocatalytic activity of rutile and anatase are the presence of dopants in the crystal lattice, sufficiently small crystallite size or stray UVA. The XPS data suggested that rutile99, anatase7 and anatase15 powders exhibited high purity, whereas rutile22 contained 4.9 atomic % of aluminum and P25 contained 3.5 atom ic % of silicon. The presence of impurity can exist as dopants or surface contaminants. Kim et al. 95 suggested that in aluminum (6 12 atomic% ) doped TiO 2 film, peak at binding energy (Al bonding with Ti) at 530 eV was present I t was reported that

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72 TiO 2 doped with aluminum usually exhibits an increase in band gap energy. 96 Neither of these phenomena was observed in our measurements based on XPS and UV/Vis measurement This s uggests that aluminum is present as surface contamination only and does not act as a dopant. The small amount of silicon present in P25 is also due to surface contamination. Yan et al. 97 indicated that TiO 2 doped with Si exhibited an increase of band gap energy. This was not observed in our study. The characterization studies (XPS, XRD and UV/Vis) indicated that rutile22, rutile99, anatase7 and anatase15 are dopant free, highly crystalline single phase photocatalyst, w hereas P25 is dopant free, highly crystalline mixed phase photocatalyst. The observed visible light photocatalytic activity is not due to dopants in the crystal lattice of TiO 2 The photocatalytic activity of rutile22, rutile99, anatase7, anatase15 and P25 differed widely R utile with crystallite size of 22 nm is the most active photocatalyst in this study whereas rutile with crystallite size of 99 nm is the least active one Rutile can adsorb a small portion of visible light, but was generally reported to be less active than anatase due to a relatively smaller band gap (3.0 eV), which cause rapid recombination of electron hole pair s Harada et al. 98 argued that as the size of rutile is less than 40 nm, the photoca talytic activity increases dramatically. This is due to combined effect of larger reactive surface area and shorter diffuse distance between the point of ejection of electrons to conduction band and the particle surface Thus, t he observed photocatalytic a ctivity of rutile22 may be due to small crystallite size. In order to test this hypothesis, the photocatalytic performance of rutile at different size was normalized at the same surface area basis by adjusting the con centration of rutile suspension. BET s urface area measurement indicated that the ratio of specific

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73 surface area of rutile22 to rutile99 rutile is about 50. Therefore the suspension concentration of rutile99 used in preparing the coating was increased to 5 wt % as compared to concentration of r utile22 at 0.1% The corresponding calculated coating thicknesses [ 6 ] were 0.4 8 m for rutile22 and 23 m for rutile99. The micrograph in Figure 3 1 5 suggests that the crystallite is crucial in controlling surface coverage of photocatalyst. Under the same weight basis, as the crystallite size of TiO 2 increases, surface will be less covered by photocatalyst. Figure 3 1 5 A indicates that the coating of rutile22 is uniform with high surface coverage of photocatalyst. Figure s 3 1 5 B and 3 15 C show the appearance of a rutile99 coating is not completely covered with photocatalyst (less than 40%). Figure s 3 1 5 D and 3 1 5 E indicate that the coating of rutile99 at higher dose gave complete surface coverage and much bigger rutile99 aggregate s As shown in Figure 3 1 6 d y e degradation on less covered rutile99 surface (Rutile99 in the figure legend) resulted in the poor est performance. As the surface loading and, concomitantly, surface coverage increase, dye degradation performance also increase. Interestingly, rutile22 coa ting with smaller crystallite size and high surface coverage performed equally as well as rutile99 with larger crystallite size at 50 time higher dose. Figure 3 1 7 relates the dye degradation rate coefficient to the surface loading This correlation is sig nificant (P<0.0001). The dye degradation rate coefficient of rutile99 with 50 times higher surface loading is comparable to the rate coefficients of rutile22 and anatase7. Apparently, coatings with high surface coverage, even with a very thin layer, can co ntribute to highly active photocatalytic surfaces. Thus, the observed visible light photocatalytic activity in this study is not due to smaller [ 6 ] The method to calculate thickness was described in Equation 2 1 in Chapter 2 v

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74 crystallite size. Photocatalyst with smaller crystallite size is beneficial to construct thin coatings with high photocatalytic activity. Some literature suggested that TiO 2 photocatalysis can take place even under ultralow UVA intensity (360 W/m 2 100 mW/m 2 ) 99 101 The dye de gradation experiment with optical filters suggested that rutile22 and anatase7 did utilize stray UVA, which contributed a quarter of the total photocatalytic activity. The rest of the total activity came from visible light. A natase, without any dopant, is generally reported in the literature to be inactive under visible light. In contrast, results of the present study indicated that anatase with crystallite sizes of 7 nm is able to utilize significant amount of visible light beyond 495 nm, whereas hardly u ses visible light between 400 and 495 nm Rutile with crystallite size of 22 nm is able to utilize visible light between 400 and 495 nm, whereas only use slight amount of visible light beyond 495 nm. This result contradicted many existed literature, which suggests that p hoton energy is a prerequisite for photocatalysis. Only and migrate to surface, reacting with other species. Nevertheless, the dye degradation experiment indicated that pu re anatase and rutile phase of TiO 2 can utilize visible light for photocatalytic degradation of organic dye. O ne study conducted by Ariga et al. 30 synthesized a rutile (001) surface, of which the band gap is 2.3 eV (530 nm cut off wavelength) in spite of its bulk band gap is 3.0 eV. Th e study by Ariga et al. was the first to investigate the photocatalytic reaction on a single crystal surface of TiO 2 instead of the bulk reaction, using scanning tunneling microscopy. The rutile22 used in the present study also exhibited photocatalytic activity under visible light (400 495 nm) even though

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75 its bulk band gap is 3.02 eV (410 nm cut off wavelength). Thus, it is possible that the surface band gap of rutile22 is much lower th an its bulk band gap, allowing utilization of low photon energy in the visible range. Anatase7 is expected to have a much lower surface band gap, which allow it to use even lower photon energy (wavelength > 495 nm). Further study is required to identify th e visible light photocatalytic activity of rutile22 and antase7 3. 3 .2 Unified Model for t he Effect of PHF on TiO 2 Photocatalysis The enhancement effect of PHF on TiO 2 photocatalysis under both UVA and visible light is given in Table 3 1 2 The adsorption of PHF was estimated from isotherms for PHF adsorption on anatase with a crystallite size of 15 nm as used in the experiment with UVA (Fig. 2 2), and anatase with a crystallite size of 7 nm, as used with visible light (Fig. 3 11). Interestingly, anatase7 (39.7 mg/g) exhibited much higher adsorption of PHF than anatase15 (7.2 mg/g) under the same pH. This can be attributed to much larger specific surface area of anatase7. Another possible reason is that the electrostatic attraction between anatase7 and PHF is much stronger than that between anatase15 and PHF. F urther experiment s to identify the IEP of anatase7 and anatase15 may help explain this differential adsorption effect. As shown in Figure 3 1 8 the enhancement of TiO 2 photocatalysis by addition of PH F is highly correlated with the surface coverage of PHF on anatase. Notably, data obtained with two different sizes of anatase follow the same relationship. 3. 4 Summary Photocatalytic performance of anatase and rutile coatings is influenced by the surface coverage. Most of the photocatalytic activity of rutile with a crystallite size of 22 nm is obtained with light below 500 nm.

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76 Anatase with a crystallite size of 7 nm can use light below 400 nm and above 500 nm, but cannot use light between 400 and 500 nm Anatase visible light photocatalysis is effective for inactivating Staphylococcus aureus The enhancement of anatase photocatalysis by addition of PHF is controlled by the surface coverage of PHF.

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77 Table 3 1. Properties of photocatalysts employed in p resent research, as provided by manufacturers Photocatalyst Component Manufacturer Product Name Primary Particle Size (nm) Mass Density (g/cm 3 ) Rutile22 R utile MKnano (Missisauga, Ontario, Canada) MKN TiO2 R050P 50 4.23 Rutile99 R utile Sigma Aldrich ( St. Louis, MO) N/A 4.17 Anatase7 A natase MKnano MKN TiO2 C7 7 3.9 Anatase15 A natase Alfa Aesar (Ward Hill, MA) 5 3.9 P25 M ixed phase particles Evonik Industries AG (Essen, Germany) P25 N/A 4.26 Table 3 2. Elemental composition of TiO 2 Rutile22 Rutile99 Anatase7 Anatase15 P25 Ti % 12.6 16.5 17.1 16.2 17.9 O % 57.3 55.4 55.0 50.5 35.8 C % 25.2 28.1 27.9 33.3 42.8 Al % 4.9 0.0 0.0 0.0 0.0 Si % 0.0 0.0 0.0 0.0 3.5 Table 3 3. Binding energy (eV) of Ti O 2 Element/ orbital Rutile22 Rutile99 Anatase7 Anatase15 P25 NIST Database Ti 2s 569 568 568 569 568 561 Ti 2p1/2 469 468 468 468 468 464.3 464.6 Ti 2p3/2 463 462 462 462 462 458.3 459.2 O 1s 534 533 533 533 533 529.7 530.2 C 1s 290 289 288 289 289 28 4.5 285.0 Al 2s 124 N/ D* N/ D N/ D N/ D 116.2 121.0 Al 2p 79 N/ D N/ D N/ D N/ D 72.0 76.7 Si 2s N/ D N/ D N/ D N/ D 158 149.3 154.6 Si 2p N/ D N/ D N/ D N/ D 107 98.0 104.0 not detected by XPS

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78 Table 3 4. BET specific surface area and calculated specific surface area based on mean crystallite size Rutile22 Rutile99 Anatase7 Anatase15 P25 BET specific surface are (m 2 /g) 35 0.7 231 110 44 Calculated specific surface area (m 2 /g) 66 15 200 95 56 Table 3 5. X ray diffraction parameters used for calculation of mea n crystallite size of P25, anatase and rutile Rutile22 Rutile99 Anatase7 Anatase15 P25 K: shape factor 0.9 0.9 0.9 0.9 0.9 ray wavelength () 1.54 1.54 1.54 1.54 1.54 B: line broadening in FWHM intensity () 0.45 0.153 1.210 0.618 0.391 b: line broadening in FWHM intensity caused by instrument () 0.07 0.07 0.07 0.07 0.07 27.598 27.662 25.401 2 5.409 25.402 L: mean crystallite size (nm) 22 99 7 15 25 Table 3 6. Comparison of crystallite size in nanometers based on XRD and SEM Technique Rutile22 Rutile99 Anatase7 Anatase15 P25 XRD 22 99 7 15 25 SEM 23 28 97 280 16 25 21 59 30 47 Table 3 7. Band gap of TiO 2 Rutile22 Rutile99 Anatase7 Anatase15 P25 Cut off wavelength (nm) 410 418 385 386 407 Band gap energy (eV) 3.02 2.97 3.22 3.21 3.05 Table 3 8. Comparison of first order fits and second order fits to photocatalytic dye degradation data Treatment First Order Reaction Kinetics Second Order Reaction Kinetics 1st 2nd order Equation R 2 Equation R 2 P Rutile22 y= 0.1311x 0.0968 0.98 y=0.352x+0.8244 0.99 0.46 Rutile99 y= 0.0015x 0.0249 0.21 y= 0.0026x+1.0354 0.50 0.41 Anatase7 y= 0.0813x 0.0184 0.99 y=0.1485x+0.919 0.95 0.08 Anatase15 y= 0.0765x 0.0893 0.95 y=0.1342x+1.0328 0.98 0.32 P25 y= 0.0457+0.0265 0.99 y=0.0611x+0.949 0.98 0.46 1st order: y is ln c/c 0 ; 2nd order: y is c 0 /c

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79 Table 3 9 Optical properties of filter FGL40 0* Range of Wavelength (nm) 200 380 380 400 400 1800 %Transmission 0 <10 90 Thorlabs (Newton, NJ) Table 3 10 Optical properties of filter FGL495* Range of Wavelength (nm) 200 470 470 495 495 1800 %Transmission 0 <50 90 Thorlabs (Newton, NJ) Table 3 1 1 Relative activity of photocatalysts under filtered light Rutile22 Anatase7 %Dye degradation* Relative activity** %Dye degradation* Relative activity** Neutral filter 51 100 46 100 400 nm cut off filter 40 78 36 78 495 nm cut off fil ter 8 16 34 74 after 12 hours ** as percent of the activity with neutral filter Table 3 1 2 Comparison of enhancement ratio of PHF/anatase to anatase alone under UVA and visible light UVA Visible light PHF / anatase ratio ** 0.005 0.01 0.02 0.005 0.0 1 0.05 0.1 Estimated anatase) ** 4.7 7.0 7.1 5.0 9.6 22 31 Surface coverage of PHF to anatase (%) 3.1 4.7 4.7 1.6 3.0 6.8 9.8 Enhancement ratio 1.1 1.8 1.9 1.7 1.9 2.5 3.1 The enhancement ratio (E) was calculated from: (3 1 3) where k n is the second order rate coefficient with the PHF/anatase nanocomposite k a is the second order rate coefficient with anatase and k c is the second order rate coefficient with non photocatalytic surface. ** Anatase with a crystallite size o f 15 nm was used in the experiments under UVA, whereas anatase with a crystallite size of 7 nm was used in the experiments under visible light ** is estimated from the isotherm s in Figures 2 2 and 3 11 for a suspension pH of 6.

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80 Figure 3 1. XPS spectrum of TiO 2 powders

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81 Figure 3 1. continued

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82 Figure 3 2. X ray dif fraction pattern of TiO 2

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83 A Figure 3 3. Scanning electron micrographs of TiO 2 powders A) Rutile22. B) Rutile99. C) Anatase7. D) Anatase22. E) P25

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84 B Figure 3 3. Continued

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85 C Figure 3 3. Continued

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86 D Figure 3 3. Continued

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87 E Figure 3 3. Continued

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88 F igure 3 4. A b sorbance spectrum of TiO 2 coating made from 1 wt% suspension. A white Teflon plate was used as reference

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89 Figure 3 5. Screening of alternative photocatalysts for visible light photocatalysis (Visible light irradiance = 2 W/m 2 UVA irradiance = 0.01 W/m 2 ). Photos were taken with a Nikon D90 with AF S DX NIKKOR 35mm f/1.8G lens using a SB 400 flash at 90 to horizontal

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90 Figure 3 6. Dye degradation on coating made from TiO 2 with different phase and crystallite size under visible light (2 W/m 2 ). Model fits based on second order reaction kinetics

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91 Figure 3 7. Comparison of the second order dye degradation rate coefficient on TiO 2 coatings under visible light (2 W/m 2 ) (

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92 Figure 3 8. Fluorescent lamp spectra for General Electric model T8 Ultramax F28T8 SPX41

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93 A B Figure 3 9. Dye degradation on two layer coatings und er visible light (1.5 W/m 2 ) with neutral or cut off optical filters. A thin polystyrene Petri dish cover with 90% transmission above 300 nm was used as a neutral filter. A ) R utile22 coating. B ) A natase7 coating

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94 A B Figure 3 10 Appearances of two layer coating. A ) R utile 22 coating. B ) A natase 7 coating

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95 Figure 3 11. Langmuir isotherm for adsorption of PHF onto anatase7 at pH 6 and 25C The PHF to anatase ratios were 0.001, 0.005, 0.01, 0.05 and 0.1.

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96 Figure 3 1 2 Time dependent dye degradation on two layer coating with rutile22 as bottom coat and PHF/anatase7 as top coat. PHF/anatase7 ratios were 0, 0.005, 0.01, 0.05 and 0.1. Error bars represent 1.0 SD. Second order model fits are shown.

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9 7 Figure 3 1 3 Comparison of second order dye degradation rate coefficients on two layer coatings with rutile22 as bottom coat and PHF/TiO 2 (anatase7) nanocomposit e at different weight ratios as top coat

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98 Figure 3 1 4 Time dependent S. aureus inactivation on two layer coating system with rutile22 as bottom coat. Top coats were anatase7 (dark), anatase7, PHF/anatase7 weight ratios of 0.01 or 0.1 and SiO 2

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99 A Figure 3 1 5 Coating appearance rutile22 and rutile99 at different surface loadings. A ) 128 g/cm 2 of rutile22 B ) 128 g/cm 2 of rutile99. C ) 128 g/cm 2 of rutile99 at higher magnification D ) 1280 g/cm 2 of rutile99. E ) 6400 g/cm 2 of rutile99

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100 B C Figure 3 1 5 continued.

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101 D E Figure 3 1 5 continued.

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102 Figure 3 1 6 Time dependent dye degradation on rutile22 at the reference surface loading of 128 g/cm 2 rutile99 at the reference loading, rutile99 at 10 reference loading and ru tile99 at 50 reference loading

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103 Figure 3 1 7 Effect of photocatalyst surface loading on second order reaction rate coefficient. The correlation shown is for rutile99

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104 Figure. 3 1 8 The relationship of enhancement ratio and surface coverage of PHF on ana tase under both UVA and visible light

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105 CHAPTER 4 THE EFFECT OF DISPER SANT ON THE PERFORMA NCE OF TITANIUM DIOXIDE COATING A convenient method of applying TiO 2 coatings on walls, benches, tables and other indoor surfaces of buildings is to spray an aqueous su spension of TiO 2 onto the surfaces using a high volume, low pressure (HVLP) electric sprayer. The concentration of the TiO 2 suspension in the sprayer's feed reservoir should remain constant throughout the application period to obtain a consistent coating c overage. Also, the formation of large aggregates of TiO 2 that could clog the spray equipment should be prevented. TiO 2 nanoparticles, suspended in aqueous system, are subject to random drifting caused by Brownian motion of water molecules. Random drifting of TiO 2 nanoparticles increases the probability of particle aggregation in aqueous system, which is caused by Van der Vaal attractive force. Once TiO 2 nanoparticles are aggregated, they tend to not fragment easily, eventually resulting in sedimentation. A ccording to the DLVO theory, 102 104 the surface electrical charge of TiO 2 nanoparticles is an important factor controlling its aqueous stability. Manipulation of electros tatic repulsion in TiO 2 suspension by pH can change the surface potential of TiO 2 nanoparticles, giving stable suspension. The isoelectric point (IEP) of TiO 2 ranges from 3.9 to 8.2, depending on the crystal structure, crystallographic orientation or synth esis procedure. 91, 105, 106 The electrical charge of TiO 2 surface varies as a function of pH: (4 1)

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106 As the pH of TiO 2 suspension decreases below IEP, the surface of TiO 2 is protonated, giving a net positive charge. Conversely, a net negative charge is developed on TiO 2 surface with elevated pH beyond IEP. Further increase or decrease pH away from IEP significantly increases the electrical charge o f TiO 2 surface, leading to a stable suspension. Addition of surfactants can stabilize TiO 2 suspensions through electrostatic forces or steric hindrance. Surfactants form a monolayer on particle surfaces when the free surfactant concentration is low. At hi gher free surfactant concentration, surfactant structures, such as micelles, are formed and these structures can adsorb to the particle surfaces. The minimum concentration of free surfactant at which micelles form is called the critical micelle concentrati on (CMC). The purpose of the research described in the present chapter was to design a chemical dispersant system to prevent or limit aggregation of TiO 2 and thus make it compatible with spray application equipment. Chemical dispersion of the TiO 2 would also make it easier to keep the suspension well mixed during the application period. The approaches tested were to increase electrostatic repulsion or steric hindrance between TiO 2 particles. Adjustment of pH by adding sodium hydroxide and adsorption of an ionic surfactant (sodium dodecyl sulfate) were tested for increasing electrostatic repulsion, whereas addition of nonionic surfactant (Tween 20) was tested for creating steric hindrance. P25 was used as the model photocatalyst in the experiments for disper sant selection. Once a dispersant was chosen, further experiments designed to refine the dispersant

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107 system were carried out on a simple mixture of anatase with a crystallite size of 7nm and rutile with a crystallite size of 22 nm. These two photocatalysts were discovered to be more active than P25 under visible light, as reported in chapter 3. The long term stability of the nanocomposite suspension was tested with the criteria that the suspension remains stable for a minimum of a week and is compatible with HVLP sprayers. Performance evaluation was carried out to determine the effect of alternative dispersant systems on photocatalytic activity. 4. 1 Experimental 4. 1 .1 Chemicals and Reagents The two model photocatalysts used were the mixed phase (anatase and r utile) P25, manufactured by Evonik Industries AG (Essen, Germany), and a simple 1:1 mixture of rutile and anatase powders obtained from MKnano (Missisauga, Ontario, Canada). Properties of these photocatalysts are given in Table 4 1. A solution of Procion r ed MX 5B dye (Sigma Aldrich Inc., St. Louis, Missouri) was prepared at a concentration of 2000 mg/L by dissolving 0.02 g dye powder in 10 mL deionized water. Non ionic surfactant Tween 20 (Sigma Aldrich Inc.), anionic surfactant sodium dodecyl sulfate (Fis her Scientific, Waltham, Massachusetts) or sodium hydroxide (Acros Organics, New Jersey) was used to increase the stability of TiO 2 suspension. 4. 1 .2 Characterization of TiO 2 Particles BET surface area Specific surface area of TiO 2 was measured under nitr ogen using a NOVA 1200 with multipoint BET (Quantachrome Instruments, Boynton Beach, FL). TiO 2 powder was degassed and dried under vacuum at 110C prior to measurement.

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108 X ray diffraction Powder X ray diffraction was measured on a APD 3720 diffractometer ( Philips, Andover, MA) with Cu K radiation (40 kV, 25 mA) and diffracted beam monochromator, using a step scan mode with the step of 0.075 of International Centre for Diffra ction Data. The crystallite size of TiO 2 was determined from the Scherrer equation: 89 (4 2) where L is the average crystallite size, K is the shape factor (0.9), is the x ray wavelength of C u K radiation (1.54 ), B is the overall line broadening in radians at the full width at half maximum (FWHM) intensity, b is the line broadening in radians at the FWHM intensity caused by the instrument itself gle at which highest intensity was observed. The crystallite size measured from XRD was used to compute an estimate of the specific surface area of TiO 2 for comparison with the measurement from BET surface area, according to the following equation: (4 3) 2 form and d is the crystallite size of TiO 2 as determined by XRD. Scanning e lectron m icroscopy Scanning electron microscopy (JOEL 6335F FEG SEM) was used to observe the ultrastructure of TiO 2 coating at the conditions of 10 kV or 15 kV accelerating voltage and 10 mm working distance. In addition to the secondary electron imaging mode, the backscattering electron imaging mode was used to get elemental contrast if necessary.

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109 4. 1 .3 Dispersion A series of dispersant concentrati ons with a constant weight percentage (0.1 wt%) of P25 was prepared as follows. P25 dispersed with NaOH was prepared by adding 1.0 mL of 25 M NaOH to 24.0 mL of deionized water, giving a concentration of 1 M, which was then serially diluted (10 each dilu tion) to 10 6 M in deionized water. A mass of 10 mg of P25 was added to 10 mL of each dilution, followed by sonication (Misonix Sonicator 3000, Farmingdale, NY) at the highest power level (providing 180 200 W) for 30 minutes total (10 min on/2 min off 3) Each suspension of P25 with a specific NaOH concentration was used within 1 hour. P25 dispersed with sodium dodecyl sulfate (SDS) was prepared by adding 0.29 g of SDS to 10 mL of deionized water, giving a concentration of 0.1 M, which was then serially diluted to 10 6 M. A mass of 10 mg of P25 was added to 10 mL of each dilution, followed by sonication (Misonix Sonicator 3000, Farmingdale, NY) at the highest power level (providing 180 200 W) for 30 minutes total (10 min on/2 min off 3). There was moder ate foaming as the TiO 2 was added to the SDS solutions, but no forming was observed during sonication. Each suspension of P25 with a specific Tween 20 concentration was used within 1 hour. P25 dispersed with Tween 20 was prepared by adding 1.0 mL of Tween 20 to 9 mL of deionized water, giving a volume fraction of 0.1, which was then serially diluted to 10 6 v/v. A mass of 10 mg of P25 was added to 10 mL of each dilution, followed by sonication (Misonix Sonicator 3000, Farmingdale, NY) at the highest power l evel (providing 180 200 W) for 30 minutes total (10 min on/2 min

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110 off 3). There was moderate foaming as TiO 2 was added to the solution of Tween, but no foaming during sonication. Each suspension of P25 with a specific Tween 20 concentration was used withi n 1 hour. The settling of P25 was monitored visually for 24 hours after sonication. The aqueous aggregate size, size distribution and zeta potential of P25 suspension was measured within one hour of sonication. Particle size and size distribution were mea sured by Nanotrac ULTRA (Microtrac Inc., York, PA). Zeta potential was measured by Brookhaven ZetaPlus (Brookhaven Instruments Corporation, Holtsville, NY). Further studies into the effect of suspension pH on settling of TiO 2 particles and photocatalytic performance of coatings prepared with the suspension were carried out on a 1:1 mixture of anatase and rutile. Rutile/anatase dispersed with NaOH was prepared by adding 1.0 mL of 25 M NaOH to 24.0 mL of deionized water, giving a concentration of 1 M, which was then serially diluted (10 each dilution) to 10 6 M in deionized water. A mass of 5 mg of rutile and 5 mg of anatase were added to 10 mL of each dilution, followed by sonication (Misonix Sonicator 3000, Farmingdale, NY) at the highest power level (prov iding 180 200 W) for 30 minutes total (10 min on/2 min off 3). Each suspension of rutile/anatase with a specific NaOH concentration was used to particle size analysis and coating preparation within 1 hour. The settling of the rutile/anatase suspension wa s observed over a period of one week. 4. 1 .4 Coating Preparation Ceramic tiles were used as substrates for photocatalytic performance evaluation. Tiles (2.5 cm 2.5 cm) were obtained from American Olean Inc.

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111 (Dallas,TX). The tile surfaces were almond colo red with a matte finish. The coating was applied in two steps to be consistent with commercial TiO 2 coating practice. In the dispersant selection experiments, P25 coating was prepared by pipetting a volume of 400 L of P25 suspension containing NaOH, Tween 20 or SDS onto the tile surface, followed by drying overnight in a biosafety cabinet. A second coat of P25 was then applied using the same procedure, giving a surface loading of 128 g/cm 2 In the dispersant refinement experiments, rutile/anatase coating was prepared by pipetting a volume of 400 L of rutile/anatase suspension containing NaOH onto the tile surface, followed by drying overnight in a biosafety cabinet. A second coat of rutile/anatase was then applied using the same procedure, giving a surfac e loading of 128 g/cm 2 4. 1 .5 Dye Degradation The photocatalytic performance of TiO 2 coatings was determined based on organic dye degradation. A volume of 0.01 mL of Procion red MX 5B solution (2000 mg/L) was pipetted onto coated tile and allowed to dry in an oven (55C) for 20 minutes. Samples were exposed to fluorescent light (model, distance to the samples, detector) at an irradiance of 1.8~2.0 W/m 2 Dye degradation was based on absorbance, as calculated from reflectance measured at 538 nm after 0, 12 and 24 hours of exposure to fluorescent light. Reflectance of coated or uncoated tile surfaces was measured with a Perkin Elmer Lambda 800 with PELA 1000 Reflectance Spectroscopy Accessory. Absorbance was calculated as the negative log10 of reflectance exp ressed as fraction. Coated tiles without dye were used as the internal reference in the measurement. Dye degradation was calculated according to:

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112 % dye degradation = (4 4) where A 0 is the calculated absorbance of dye coated on photoca talytic or bare grout surface before exposure to fluorescent light and A t is the absorbance of dye coated on photocatalytic or grout surface after exposure to fluorescent light at a given time. Because the color of bare grout varied somewhat, it was necess ary to subtract this background color. Therefore, A 0 and A t were calculated from A 0 =A 0' A b (4 5) At=A t' A b (4 6) where A 0' and A t' are the measured absorbance of dye on grout at time zero and time t, respectively, and Ab is the measured absorbance of the bare or photocatalytically coated grout surface without dye at a given time. 4. 1 .6 Statistical Analysis First order fits between the extent of dye degradation and visible light exposure time were based on the equation (4 7) and second order fits were based on the equation (4 8) where c t and c 0 represent absorbance at times t and t 0 respectively, k and k' are the reaction rate coefficients for the first and second order fits, respectively, and b and b' are arbitrary constants. The parameter values (k, b, k', b') for the fits were determined by least squares linear regression.

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113 One way ANOVA and post hoc testing were carried out using the sided tests through NCSS statistical analysis and graphics software (NCSS, Kaysville, UT). 4. 2 Results 4. 2 .1 Characterization X ray diffraction patterns of the TiO 2 powders used in this study are shown in Figure 4 1. The diffraction pattern of P25 exhibited a combination of anatase and rutile patter ns, which is due to its mixed phase structure. 91 The diffraction patterns of anatase and rutile from MKnano were in good agreement with the patterns shown in the database of International Centre for Diffraction Data (h ttp://www.icdd.com). The mean crystallite size calculated on the basis of XRD was 25.4 nm for P25, 7.1 nm for anatase and 21.5 nm for rutile (Table 4 2). Scanning electron microscopy showed that the smaller dimension of primary particles of P25 was in the range of 28 59 nm (Fig. 4 2 A ). In the rutile/anatase coating (Fig. 4 2 B ), the smaller dimension of primary particles ranged from 15 to 38 nm. The BET specific areas of P25, anatase and rutile were 44, 231 and 35 m 2 /g, respectively (Table 4 3). These value s deviated slightly from the specific surface area calculated on the basis of the crystallite sizes calculated from XRD, with assumed spherical particles. 4. 2 .2 Effects of Dispersant Systems on P25 Suspension Characteristics and Coating Performance P25 sus pended in deionized water containing no dispersant (pH = 6 7) completely settled within 24 hours (Fig. 4 3). P25 prepared in 10 2 or 10 3 M

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114 NaOH (pH 10.4 or 9.2, respectively) remained in suspension for 24 hours, whereas P25 prepared in 10 4 or 10 5 M NaOH (pH 8.0 or 6.9, respectively) settled within 24 hours (Fig. 4 4). In the concentration range of 10 2 to 10 6 v/v Tween 20, there was no settling of TiO 2 at the lowest dilution, and complete settling at dilutions of 10 3 to 10 6 v/v (Fig. 4 5 A ). A series of dilutions centered on 10 2 v/v confirmed this concentration was optimal for stabilizing P25 (Fig. 4 5 B ). There was complete settling of P25 within 24 hours at SDS concentration of 10 3 10 4 and 10 5 M SDS. No settling occurred in 10 2 M SDS, whereas t he 10 1 M concentration exhibited some settling (Figure 4 6). The aqueous aggregate size and zeta potential of P25 suspensions with no dispersant and at the optimum NaOH, Tween 20 and SDS concentrations are shown in Figure 4 7. The aggregate size (mean di ameter based on number distribution) was 179 nm with no dispersant. T he size was not significantly to the range of 86 to 89 nm with NaOH or SDS. Zeta potential of P25 with no dispersant was 0 mV. Addition of Tween 20 significantly increased zeta po tential to 8 mV, whereas addition of SDS or sodium hydroxide significantly decreased the zeta potential to the range of 38 to 42 mV. Coatings of P25 with the three alternative dispersant systems were examined under SEM. Figures 4 8 and 4 9 indicate that the pH of the P25 suspension used to prepare the coatings did not change the appearance of the coatings with respect to surface coverage and granularity. The P25 coating

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115 prepared with Tween 20 as dispersant is shown in Figure 4 10. At 200, this coating w as similar in appearance to that of coating prepared with the pH stabilized suspension. At 5,000, this coating appeared to be very uniform with no granularity. Figure 4 11a indicates that addition of SDS to the P25 suspension resulted in a coating exhibit ing a ridge and valley pattern. At higher magnification, segregation of the coating components is apparent, with P25 (bright areas in backscattering mode) overlaying SDS (dark areas in backscattering mode) (Fig. 4 11 C and 4 11 D ). Dye degradation under visi ble light by P25 coatings made with optimum dispersant concentrations (0.001 M NaOH, 0.01 M SDS and 0.01 v/v Tween 20) is shown in Fig. 4 12. Coatings made from P25 dispersed by either Tween 20 or de from P25 containing either no dispersant or NaOH. Coating made from P25 dispersed by NaOH performed equivalently to coating made from P25 with no dispersant. 4. 2 .3 Performance Comparison of Coatings prepared from P25 versus a 1:1 Mixture of Rutile and A natase The results presented in chapter 3 indicated that rutile with crystallite size of 22 nm or anatase with crystallite size of 7 nm are more photocatalytically active under the light spectrum of fluorescent bulbs than P25. It was also found that the ru tile and anatase used different portions of the visible light spectrum. Thus, it is expected that a mixture of rutile and anatase would exhibit superior performance to either anatase or rutile alone. This was confirmed by a comparison of a 1:1 rutile/anata se mixture to P25. As shown in Figure 4 13, the rutile/anatase mixture was five times more active than P25. Therefore, in the present study,

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116 optimization of NaOH concentration for dispersion and photocatalytic performance of a 1:1 rutile/anatase mixture wa s carried out. 4. 2 .4 Optimization of the NaOH Dispersant System for 1:1 Rutile/anatase Mixture The NaOH dispersant system was further optimized using a 1:1 mixture of rutile and anatase as a model photocatalyst. The rutile/anatase photocatalyst was suspen ded in NaOH solutions ranging from 100 to 10 7 M NaOH, which gave a pH range from 6.8 to 13.4 (Fig. 4 14). The rutile/anatase particles were unstable at pH of 12.7 or higher and at pH of 6.9 or lower, settling within 12 hours. The stable range of pH was d etermined to between 7.5 and 11.8. The aqueous aggregate size of rutile/anatase particles at the stable pH values is shown in Fig. 4 15. At pH of 10.6 or 11.8, the aggregate size was in the range of 69 to 78 nm, which was significantly smaller than the ag gregate size of 176 nm at pH 7.5. The zeta potential of rutile and anatase are 46.9 and 45.1 mV, respectively (Fig. 4 16). Figure 4 17 relates dye degradation by a coating of rutile/anatase particles to the pH of the suspension from which the coating was prepared. The maximum rate of dye degradation was achieved by coating prepared from suspensions with pH in the range of 10.6 to 11.8. Performance dropped sharply with coating prepared from a suspension with pH of 12.7. Decrease in performance of coatings prepared from suspensions with pH lower than the optimum was more modest. A secondary minimum in dye degradation was obtained with coating prepared from a suspension with pH 7.5.

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117 4. 3 Discussion 4. 3 .1 The Effect of Dispersant Surfactant s mediated stabilizat ion of TiO 2 suspension is through electrostatic repulsion or steric hindrance. The zeta potential of P25 in deionized water containing no dispersant (pH 6 7) was 0.5 mV. This is consistent with a reported IEP of 6.5 for P25. 91 The suspension was unstable, settling within 24 hours. Adding NaOH made the zeta potential more electronegative, consistent with equation 4 1. At 10 3 M NaOH (pH 9.2), the zeta potential was sufficiently electronegative ( 38 mV) to stabilize the suspension for 24 hours. Interestingly, the zeta potential at which SDS stabilized the P25 ( 42 mV) was very close to the zeta potential at which NaOH stabilized P25 ( 38 mV). This suggests that the mechanism of stabilization by both SDS and NaOH is decrea se of zeta potential away from IEP, leading to increased electrostatic repulsion between TiO 2 particles. Tween 20 had only a slight effect on the P25 zeta potential; not sufficient to stabilize the TiO 2 suspension through electrostatic forces. The optim um dosed concentration of Tween 20 for dispersion was 100 times higher than its CMC (0.0001 v/v, ref), suggesting that stabilization of TiO 2 was mediated by micelles creating steric hindrance to aggregation. The presence of surfactants impaired t he performanc e of P25 coating. Surfactants, physically adsorbed to the P25 particle surface, serve as radical sinks, diminishing the availability of hydroxyl radicals for dye degradation. 107, 108 The EDS analysis also indicated there is a high weight percentage of carbon (55.6 0.2% for Tween 20, 54.9 0.3% for SDS) on the P25 coating prepared using SDS or Tween 20 as dispersant, while carbon is absent from the P25

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118 coating (prepared without dispersant or using NaOH as dispersant). Thus, the observed degradation of photocatalysis upon addition of surfactant is most likely due to reaction of photocatalytically generated free radicals with the surfactant molecules. Additionally, the continuity of the P25 coating was disturbed with the presence of SDS, giving a lower surface coverage of P25. This may also contribute to low er photocatalytic performance. 4. 3 .2 The Effect of pH on Coating Performance The performa nce of photocatalyst coatings was fou nd to depend on the pH of the suspension s from which they are prepared Possible explanations for this effect are pH dependent adsorption of dye on photocatalyst or pH dependent aggregation of photocatalyst. Many studies suggest that photocatalytic degrada tion depend s on the pH dependent charge of dye molecule s which affect s adsorption of dye on photocatalst 109, 110 In this case, the effect of adsorption, however, may not be relevant because d ye was allowed to dry on the coating As suggested from the aqueous stability study, excessive or insufficient of NaOH caused instability an d larger aggregate size. At constant surface loading, surface coverage of photocatalyst decreases as photocatalyst par ticle size increases (Figure 4 18) This seemingly obvious observation has not been reported in the literature. This observation was also confirmed from the scanning electron micrographs. Figure 4 19 and 4 20 indicated that larger aggregated size of photoc atalyst gave rise to a lower surface coverage, while smaller aggregated size contribute to a uniform coating with high surface coverage photocatalyst.

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119 4. 4 Summary Sodium dodecyl sulfate and Tween 20 are effective in stabilizing aqueous suspension of TiO 2 However, they inhibit photocatalytic activity. NaOH effectively stabilizes aqueous TiO 2 suspensions and does not inhibit photocatalysis at concentrations of 10 2 M or less. Aggregate size influences surface coverage and consequently performance of TiO 2 coatings. Maintaining TiO 2 aqueous formulations within a pH range that stabilizes the formulations thus improves photocatalytic activity of coatings prepared from the formulations.

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120 Table 4 1. Properties of photocatalysts employed in present research, as given by manufacturers Photocatalyst Component Manufacturer Product Name Primary Particle Size (nm) Mass Density (g/cm 3 ) P25 M ixed phase particles Evonik Industries AG P25 N/A 4.26 1:1 rutile/anatase mixture R utile particles MKnano MKN TiO2 R050P 50 4.23 A natase particles MKnano MKN TiO2 C7 7 3.9 Table 4 2. X ray diffraction parameters used for calculation of mean crystallite size of P25, anatase and rutile P25 Anatase Rutile K: shape factor 0.9 0.9 0.9 ray wavelength () 1.54 1.54 1.54 B: line broadening in FWHM intensity () 0.391 1.210 0.45 b: line broadening in FWHM intensity caused by instrument () 0.07 0.07 0.07 25.402 25.401 27.598 L: mean crystallite size (nm) 25 .4 7.1 21.5 Table 4 3. BET specific surface area and calculated specific surface area based on mean crystallite size P25 Anatase Rutile BET specific surface are (m 2 /g) 44 231 35 Calculated specific surface area (m 2 /g) 56 200 66

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121 Figure 4 1. X ray diffraction pattern of TiO 2

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122 A B Figure 4 2. Scanning electron micrograph of TiO 2 coating. A ) P25 coating. B ) Rutile/anatase coating

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123 Figure 4 3. P25 suspended in DI water after 24 hours

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124 Figure 4 4. P25 s uspended in NaOH solutions at various concentrations (10 2 10 5 M) after 24 hours

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125 A B Figure 4 5. P25 suspended in Tween 20 solutions at various concentrations (volume fraction) A ) 10 6 10 2 v/v B ) 10 3 10 1 v/v after 24 hours

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126 Figure 4 6. P25 suspended in SDS solutions at various dosed concentrations (10 5 10 1 M) after 24 hours

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127 Figure 4 7. Mean diameter and zeta potential of P25 suspension with and without dispersant

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128 A B Figure 4 8. Scanning electron micrographs of P25 coating prepared using DI water containing no dispersant. A ) 200 time magnification. B ) 5000 time magnification

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129 A B Figure 4 9. Scanning electron micrographs of P25 coating prepared using 0.001 M of NaOH A ) 200 time magnification. B ) 5000 time magnification

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130 A B C Figure 4 10. Scanning electron micrographs of P25 coating prepar ed using Tween 20 as dispersant. A) 200 time magnification (second ary electron imaging mode) B) 5000 time magnification (second ary electron imagi ng mode). C ) 5000 time magnification ( backscattering electron mode )

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131 A B C D Figure 4 11. Scanning electron micrographs of P25 coating p repared using SDS as dispersant. A) 200 time magnification (second ary electron imaging mode) B) 200 time ma gnification ( backscattering electron mode ). C ) 5000 time magnification (second ary electron imaging mode). D ) 5000 time magnification ( backscattering electron mode )

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132 Figure 4 12. Dye degradation performance of P25 coating made from the suspensions with di fferent dispersants. The coatings were exposed to visible light at 2 W/m 2

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133 Figure 4 13. Dye degradation kinetics of P25 and anatase coating after exposed to visible light at 2 W/m 2

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134 Figure 4 14. Temporal stability of TiO 2 suspension at different pH

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135 F igure 4 15. Aqueous aggregate size of anatase/rutile at various pH conditions

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136 Figure 4 16. Zeta potential of rutile and anatase at pH 9

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137 Figure 4 17. Relationship of dye degradation of rutile/anatase coating made from the suspensions adjusted at diffe rent pH after exposure to visible light irradiance of 2 W/m 2

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138 Figure 4 18. Relationship of dye degradation of rutile/anatase coating and the aqueous mean diameter of the suspension used to make the coating after exposure to visible light irradiance of 2 W/m 2

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139 A B Figure 4 19. Scanning electron micrographs of rutile/ana tase coating. A ) deionized water (pH 6 7) B ) 0.01 M of NaOH (pH 11.7)

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140 A B Figure 4 20. Scanning electron microg raphs of rutile/anatase coating. A ) deionized water (pH 6 7) B ) 0. 01 M of NaOH (pH 11.7). The feature in the images did not necessary represent the entire coating. However, larger aggregate with lower surface coverage of photocatalyst was more frequently observed for A

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141 CHAPTER 5 PROTOTYPE TESTING OF TITANIUM DIOXIDE CO AT ED ANTIMICROBIAL SURFACES T he effectiveness of PHF/TiO 2 nanocomposite in inactivating microbes on surface under both UVA and visible light irradiance was discussed in Chapters 2 and 3. Nanohygienix, a start up company using TiO 2 based coating s to control indoor infections, express ed strong interest in applying PHF/TiO 2 nanocomposite as a photocatalyst for use in indoor facility with heavy human traffic Commercial sources of photocatalyst formulations that are claimed to have activity in the visible rang e include Showa Denko, Marusyo Sangyo and Sumitomo Chemicals from Japan, and Advanced Surface Treatments, BioShield, Inc. and EcoActive Surfaces, Inc. from the US. The Particle Engineering Research Center ha s tested visible light active photocatalyst s from Japanese companies in our lab and found them to be incapable of microbial inactivation ( u npublished data). Advanced Surface Treatments adverti s es their coatings for odor removal and organic degradation, but not for destruction of microbes. EcoActive Surfa ces, Inc. has a visible light active product, respectively. It can be concluded that v isible light photocatalysts that are capable of rapidly destroying harmful microbes (90% reduction of bacteria within few hours) are not commercially available. The objective of the research reported in this chapter was to evaluate the effectiveness of coating indoor surfaces at three beta facilities with rutile/anatase and PHF/anatase formul ations for photocatalytic inactivation of microbes. The beta facilities Center (VRMC) (Venice, FL) and Village on the Isle Retirement Facility (Venice, FL).

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142 Surfaces at the beta facilities that were coated with a commercial product (Bioshield Primer and NuTiO) were monitored for comparison 5. 1 Experimental 5. 1 .1 Beta Facilities Three beta facilities in Florida were chosen for testing prototype photocatalytic manufactured by th e University of Florida, as described below. School is a private school (from PK3 to grade 12) located in Bradenton, Florida with 650 students enrollment. Three rooms (a dressing r oom in a gym and second grade classrooms #2 and #3) were selected for microbial sampling. Samples were taken from three different locations on the wall adjacent to the entrance; at one location on three different lockers; and at two locations on one bench and one location on a second bench in the dressing room (Fig. 5 1a and b). The dressing room had a fluorescent light that was left on continuously and no window. The visible irradiance measured at the sampled surfaces ranged from 0.04 to 0.07 W/m 2 In clas srooms #2 and #3, three locations were tested on the wall adjacent to the window, the table and the counter top (Fig. 5 1c). Classrooms #2 and #3, which were across the hallway from each other, had windows and fluorescent lights that were turned off at nig ht and on weekends. The visible irradiance at the sampled surfaces during the day ranged from 0.3 to 3.4 W/m 2 while the UVA irradiance ranged from 0.01 to 0.33 W/m 2 Venice Regional Medical Center (Venice, FL) The Venice Regional Medical Center (VRMC) i s a 312 bed regional healthcare system located in Venice, FL. Intensive care unit (ICU) stations 2, 3 and 4 were selected to collect microbial samples. Each ICU station contained a bed, counter top and closet (Fig. 5 2). Light was provided

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143 by fluorescent l amps and windows. The visible irradiance measured at the sampled surfaces (wall, counter top, bed rail and knob) ranged from 0.5 to 2.02 W/m 2 (0.11 to 1.08 W/m 2 when the blind was closed). The UVA irradiance at the sampled surfaces ranged from 0 to 0.11 W/ m 2 (0 W/m 2 when the blind was closed). Samples were taken in three different locations on each of the selected surfaces. Village on the Isle r etirement f acility (Venice, FL) Village on the Isle is the licensed continuing care retirement community located in Venice, Florida. The facility provides independent living (Matthew Hall and Trinity Hall), assisted living (Mark Manor) and skilled nursing (Luke Haven). Microbial sampling was conducted at the Luke Haven Skilled Nursing Facility. Two patient rooms and a staff break room were selected for sampling. Each patient room contained two beds, a bathroom, chairs and cabinets. Light was provided by fluorescent lamps and windows. The visible irradiance measured at the sampled surfaces (wall, bathroom rail, soap di spenser, bed rail and thermostat) ranged from 0.16 to 1.87 W/m 2 The UVA irradiance at the sampled surfaces ranged from 0 to 0.01 W/m 2 The staff break room contained a table, counter top, chairs, lockers and two bathrooms. Light was provided by fluorescen t lamps. The visible irradiance measured at the sampled surfaces (counter top, door knob and lockers) ranged from 0.32 to 0.6 W/m 2 The UVA irradiance at the sampled surfaces ranged from 0 to 0.01 W/m 2 Samples were taken in three different locations on ea ch of the selected surfaces. Visible and UVA irradiance was measured using a light detector (PMA2110, Solar Light Co., Glenside, PA) with UVA and visible light probes.

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144 5. 1 .2 Chemicals and Reagents Titanium dioxide (anatase, 7 nm; rutile, 20 nm ) was obtaine d from MKnano (Williamsville, NY). Polyhydroxy fullerene (PHF) was synthesized in our laboratory according to the protocol of Gao et al. [22]. A 50% sodium hydroxide (NaOH) solution was obtained from Acros Organics (NJ, USA) and diluted to desired concentr ations in deionized water. Commercial TiO 2 formulations (NuTiO Primer and NuTiO TiO 2 ) were obtained from Bioshield, Inc. (Fort Lauderdale, FL). Tryptic soy agar (Becton, Dickinson and Company, Sparks, MD) was used to culture microbes. A mass of 40 g Trypti c soy agar powder was suspended in 1 L of deionized water and mixed thoroughly with heating to the boiling point. The solution was then autoclaved at 120 C and 16 bar for 15 minutes. Plates were made by pouring the autoclaved agar into 10015 mm sterile p lastic Petri dishes (Fisher Scientific) and air dried in a laminar flow hood (LABCONCO purifier class 2 safe cabinet) for 24 hours. The dried agar plates were used immediately or stored in inverted position in a refrigerator at 4C. 5. 1 .3 Coating Preparati on Three different TiO 2 based, photocatalyst systems were used at the beta facilities. Photocatalyst system 1 consisted of Bioshield NuTiOTM TiO 2 formulation for use as top coat and Bioshield Primer formulation for use as bottom coat. Photocatalyst system 2 consisted of rutile/anatase formulation for use as top coat and Bioshield Primer formulation for use as bottom coat. Photocatalyst system 3 consisted of PHF/TiO 2 nanocomposite formulation for use as top coat and Bioshield Primer formulation for use as bo ttom coat.

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145 The Bioshield NuTiOTM TiO2 and Bioshield Primer formulations were applied directly from the manufacturer's containers. The rutile/anatase formulation was prepared by adding 100 mg of rutile and 100 mg of anatase to 200 mL of diluted NaOH soluti on (pH = 9 9.5). The rutile/anatase suspension was sonicated (Misonix Sonicator 3000, Farmingdale, NY) at the highest power level (providing 180 200 W) for 30 minutes total (10 min on/2 min off 3). This procedure was repeated to accumulate a total volume of 5 L. The PHF/TiO 2 nanocomposite formulation was prepared by adding 200 mg of anatase to 180 mL of diluted NaOH solution (pH = 9 9.5). The anatase suspension was sonicated (Misonix Sonicator 3000, Farmingdale, NY) at the highest power level (providing 1 80 200 W) for 30 minutes total (10 min on/2 min off 3). A volume of 20 mL of PHF solution, containing 1000 mg/L of PHF, was then added and the suspension was mixed with magnetic stirrer for 10 minutes. This procedure was repeated to accumulate a total vo lume of 5 L. All surfaces (walls, ceilings, furniture, attached fixtures, etc.) were steamed prior to coating to remove contaminants and ensure adhesion of the coating. After 15 minutes of drying, Bioshield NuTiOTM primer was applied using an electric spra yer (Model 2600, American Air & Water, Inc. Hilton Head Island, SC). After 15 minutes of drying time, the top coat formulation was applied to all surfaces. 5. 1 .4 Microbial Sampling Procedures After coatings were applied on surface, sterile cotton swabs w ere used to collect microbes from selected surfaces. A swab was immersed in sterile DI water, followed by wiping on selected surfaces (1010 cm) back and forward 5 times. Microbes adhered to the wetted cotton were streaked on Tryptic soy agar plates. The p lates were inverted

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146 and then placed in a 37C incubator for 48 hours. Colony forming units (CFUs) were counted. 5. 2 Results 5. 2 Figure 5 3 shows the variation of microbe counts on a wall, lockers and benches coated with photocatalyst system 1 in the dressing room at Saint Stephens's Episcopal School. The microbial population on benches was much higher than those on the walls or lockers. A consistent decreasing trend (from 537 to 64 CFU/swab; almost a 90% reduction) in mic robial counts was observed on the benches over a period of 8 months (Table 5 1). The walls and lockers were much less contaminated at the beginning. There were no consistent changes in counts on walls or lockers over an 8 month period. Figure 5 4 shows the variation of microbe counts on a counter top, wall and table coated with photocatalyst system 1 in classroom #2. There wa s n o consistent trend in microbe counts for any of the surfaces (Table 5 1) Figure 5 5 shows the variation of microbe popul ations on u ncoated counter top, wall and table in classroom #3. There was n o consistent change on any of the surfaces (Table 5 1) A h igh spike in microbe counts for the table was observed at month 4 It appears that marginal effect of photocatalyst system 1 in terms of reducing microbe populations 5. 2 .2 Venice Regional Medical Center Figure 5 6 shows the variation of microbe populations on a wall, counter and bed rail in three different ICU stations at the Venice Regional Medical Center. A closet door knob was also s ampled in two of the ICU stations.

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147 The surfaces in station 2 were uncoated. In station 4, the surfaces were coated with photocatalyst system 1. In station 3, the surfaces were coated with photocatalyst system 2. As shown in Figure 5 6, the microbe counts o f the selected surfaces in the VRMC were low at the initial sampling, ranging from 1 to 16 CFU/swab. Microbe counts on the bed rail in the ICU station coated with photocatalyst system 2 exhibited a decreasing trend, whereas counts on the wall and counter e xhibited no consistent trend. (Table 5 2). At the ICU station coated with photocatalyst system 1, microbe counts were generally higher and more variable. No consistent trends in microbe counts were exhibited on any of the surfaces. Microbe counts in the u ncoated ICU station exhibited very high numbers and variability between locations. There was an increasing trend in microbe counts on counter top and no consistent trends on the other surfaces (Table 5 2). 5. 2 .3 Luke Haven Skilled Nursing Facility Figure 5 7 shows the variation of microbe counts on a wall, bathroom rail, soap dispenser, bed rail and thermostat among two patient rooms and door knob, lockers and cou nter top in a staff break room at the Luke Haven Skilled Nursing Facility. As can be seen from the microbe counts before treatment and after treatment, the effectiveness of steam cleaning was variable. Two months after coated with photocatalyst system 3, significant decreases in microbe counts were found six of the eight surfaces we sampled. Four o f the eight surfaces showed more than 90% decrease in microbe counts. There was no significant change in microbe counts on two surface s (wall in patient room and bathroom rail ). In the case of wall s the initial count of microbes is very low, which made it difficult to quantify the effect. M inim al microbe reduction on the bathroom rail s may be due to intermittent lighting in the bathroom.

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148 5. 3 Discussion The variation of microbe count on all selected surfaces of the beta testing facilities was generally larg e, which may be due to the spatial random distribution of microbes in the built environment. The spatial distribution of microbe is affected by building attributes, such as the source of ventilation air, airflow rates, relative humidity and temperature. 111 Photocatalyst system 1 failed to kill microbes effectively, but seemed to have an effect on preventing microbe reproduction. A consistent decrease in microbe counts on the benches coated with photocatalyst syst Episcopal School was observed. This may be due to constant lighting condition, making the coating more efficient. The microbial counts at all the ICU stations were low because the units were subject to frequent cleaning with chemical disinfectants. Low microbial counts made it harder to quantify microbial reduction. However, photocatalyst system 2 still manifested an inactivation effect on one of the coated surfaces. Steam cleaning was inconsistent in killing all the microbes on surfaces at the Luke Haven Skilled Nursing Facility. Extended steaming may be required for more effective inactivation of microbes on surfaces prior to coating. Photocatalyst system 3 has only been monitored at one time (2 months) after co ating. The preliminary indication is that this photocatalyst system is superior to the other photocatalyst systems. This suggests that polyhydroxy fullerene has an extended beneficial effect on photocatalysis. However, additional testing in the Luke Haven facility is required to confirm this conclusion.

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149 5. 4 Summary Without photocatalyst coating, microbe counts in indoor facilities subject to heavy human traffic are typically variable and, in some cases, trend upwards with time. A commercial photocatalyst an d a rutile/anatase based photocatalyst were marginally effective in reducing microbe counts in the facilities. A PHF/anatase nanocomposite based system is still in testing phase, but has exhibited promising capability for reducing microbe counts at a beta facility. Steam cleaning procedure currently used by NanoHygienix is inconsistent at reducing initial microbe counts prior to coating

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150 Table 5 1 Identification of trends in microbe counts at Saint Stephen's Episcopal School Dressing room (coated with PS 1) Classroom #2 (coated with PS 1) Classroom #3 (uncoated) wall lockers benches counter top wall table counter top wall table r 0.098 0.522 0.745 0.207 0.228 0.187 0.508 0.248 0.002 P 0.763 0.081 0.005 0.519 0.476 0.561 0.1107 0.437 0.995 Tre nd* No change No change Decrease No change No change No change No change No change No change r: Pearson correlation coefficient Table 5 2 Identification of trends in microbe counts at Venice Regional Medical Center Station 3 (coated with PS 2) Station 4 (coated with PS 1) Station 2 (uncoated) wall counter bed rail wall counter knob bed rail wall counter kn ob bed rail r 0.120 0.315 0.736 0.000 0.603 0.438 0.035 0.294 0.662 0.082 0.712 P 0.742 0.375 0.024 1.000 0.065 0.205 0.923 0.409 0.037 0.821 0.113 Trend* No change No change Decrease No change No change No change No change No change Increase No change No change r: Pearson correlation coefficient *Based on

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151 A B C Figure 5 1 A) Wall in the dressing room. B) B enches a nd lockers in the dressing room. C) W all, counter top and table in one of the classrooms Wall Benches Lockers Wall Table Counter top

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152 Figure 5 2 Microbial sampling locations of an ICU station at Venice Regional Medical Center: wall, bed rail, counter top and (door) knob

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153 Figure 5 3 Time dependent change in microbe counts on surfaces coated with photocatalyst system 1 in the dressing room of

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154 Figure 5 4 Time dependent change in microbe counts on surfaces coated with photocatalyst system 1 in classroom #2 of

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155 Figure 5 5 Time dependent change in CFU on uncoated surfaces in C

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156 Figure 5 6 Time dependent changes in microbe counts on surfaces in the ICU stations of Venice Regional Medical Center. Surfaces in station 2 were not coated; surfaces in station 4 were previously coated with photocatalyst system 1; surfaces in station 3 were coated with photocatalyst system 2

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157 Figure 5 7 Time dependent changes in microbe counts on surfaces coated with photocatalyst system 3 in the Lu ke Haven Skilled Nursing Facility of Village on the Isle Retirement Facility Sampling locations where a significant decrease (P < 0.05) in microbe counts between the treatment date and the latest sampling date are marked by an asterisk

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158 CHAPTER 6 CONCLUSIO NS AND RECOMMENDATIONS FOR FURTHER RESEARCH In the present study, thin, transparent coatings of anatase and rutile were found to be capable of inactivating microorganisms under UVA or visible light. Polyhydroxy fullere ne was found to adsorb to anatase and enhance the rate at which photocatalytic inactivation takes place by a factor of two to three. Photocatalysis on both anatase and PHF/anatase coatings under UVA is capable of inactivating highly resistant spores of a common household fungus, Asperigillus niger Under visible light, photocatalysis on both anatase and PHF/anatase coatings is capable of inactivating a bacterium commonly used as a surrogate of MRSA, Staphylococcus aureus The degree to which both UVA and visible light photocatalysis is enhance d by PHF is controlled by the percentage of the anatase surface that is covered by this molecule. The ability of nano TiO 2 coatings to catalyze dye degradation and microbe inactivation under visible light is unexpected, considering the measured band gaps o f these materials. Utilization of visible spectrum by rutile and anatase has been confirmed with optical filter studies. While both rutile and anatase are capable of utilizing sub 400 nm light, only rutile can use light in the 400 nm to 500 range, and most of its activity is from light in this range. Anatase cannot use light in the 400 500 nm range, indicating that most of its photocatalytic activity is from light in the supra 500 nm portion of the spectrum. The confirmed purity of the TiO 2 powders used rul e out aluminum or silicon as inadvertent dopants. Recent literature that raises the possibility that surface band Stabilization of aqueous TiO 2 suspensions prior to application to co at surfaces is important from the point of view of compatibility with spray application equipment and,

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159 furthermore, has a strong influence on coating performance. Despite their effectiveness in stabilizing aqueous TiO 2 suspensions, surfactants are not prac tical as dispersants because they act as free radical sinks in the coating and thus impair coating performance. Sodium hydroxide at is also effective as a dispersant and at concentrations of 1E 2 M or less, does not impair coating performance. Aggregate s ize influences surface coverage and consequently performance of TiO 2 coatings. Maintaining TiO 2 aqueous formulations within a pH range that stabilizes the formulations thus improves photocatalytic activity of coatings prepared from the formulations. The we ll dispersed, photocatalytic active rutile/anatase and PHF/anatase nanocomposite formulations developed in the present study were applied and evaluated in the beta testing facilities, as compared to the commercial photocatalyst formulation (NuTiO TiO 2 ) and uncoated surfaces. Without photocatalyst coating, microbe counts in indoor facilities subject to heavy human traffic are typically variable and, in some cases, trend upwards with time. The commercial photocatalyst and a rutile/anatase based photocatalyst were marginally effective in reducing microbe counts in the testing facilities. The PHF/anatase nanocomposite based system is still in testing phase, but has exhibited promising capability for reducing microbe counts at a beta facility. Based on the findi ngs of the present research, the first proposed task for future research is to investigate the mechanism on different ial visible light spectrum utilization by rutile 22 and anatase 7 Rutile 22 was found to utilize visible light mainly between 400 and 495 nm in this study. This result is consistent with the findings of Ariga et al. 30 in which he proposed that the surface band gap (2.3 eV) of rutile differ ed from its bulk

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160 band gap (3.0 eV). Anatase 7 was found to be active under visible light irradiance beyond 495 nm, but not active between 400 and 495 nm. This surprising finding has not been reported in the literature yet. E xperiment s with additional optical filters at the cut off wavelength of 5 90 nm (provides zero transmission below 570 nm) and at the cut off wavelength of 665 nm (provides zero transmission below 640 nm) are required to identify the specific visible light spectrum of the fluorescent lamp that anatase7 can use. Further studies are needed to identif y whether surface aberrations in the crystal la ttice of TiO 2 contributed to visible light activity PHF/TiO 2 nanocomposite is subject to mechanical abrasion in indoor facilit ies with heavy human traffic Thus, the second proposed task is to evaluate the adhesion property of PHF/TiO 2 nanocomposite to co mmon surfaces. Commercial wipe can be used to test the remov al of PHF/TiO 2 deposi ted on some common surfaces such as ceramics, glasses or metal surfaces. S EM EDS can provide qualitative and quantitative analysis of the remaining of PHF/TiO 2 coating after w iping. Alternatively developing a chemical binder for PHF/TiO 2 nanocomposite can extend the lifetime usage of the coating applied in indoor facilities Binder selected or developed for the PHF/TiO 2 nanocomposite should have the following characteristics: high adherence minimum effect on PHF/TiO 2 performance, non toxic and low cost. The third proposed task is to conduct prototype testing of PHF/TiO 2 nanocomposite coating with more controlled parameters. Light sensors can be employed to record the total exp osure time. Temperature and relative humidity should be monitored. The infection rate in the testing facilities should be recorded as well. All

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161 these parameters should be taken into account to identify the effectiveness of PHF/TiO 2 nanocomposite coating.

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172 BIOGRAPHICAL SKETCH Wei Bai was born in Guangzhou, China. He received a bachelor degree in environmental engineering from Jinan University in 2007. H e received his master degrees in e nvironmental e ngineering s ciences and materials science and engineering at the University of Florida in 2010 He wa s a Ph.D. student under the supervis i on of D r. Ben Koopman and Dr. Brij Moudgil. He receive d his Ph.D. degree in environmental engineering sciences in the s ummer of 2012