Citation
Titanium Dioxide-Polyhydroxy Fullerene Nanocomposite for Photocatalytic, Antimicrobial Surfaces

Material Information

Title:
Titanium Dioxide-Polyhydroxy Fullerene Nanocomposite for Photocatalytic, Antimicrobial Surfaces
Creator:
Bai, Wei
Place of Publication:
[Gainesville, Fla.]
Publisher:
University of Florida
Publication Date:
Language:
english
Physical Description:
1 online resource (86 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.E.)
Degree Grantor:
University of Florida
Degree Disciplines:
Environmental Engineering Sciences
Committee Chair:
Koopman, Ben L.
Committee Members:
Moudgil, Brij M.
Wu, Chang-Yu
Graduation Date:
8/7/2010

Subjects

Subjects / Keywords:
Aspergillus niger ( jstor )
Carbon ( jstor )
Catalysis ( jstor )
Dyes ( jstor )
Electrons ( jstor )
Fullerenes ( jstor )
Fungi ( jstor )
Grouts ( jstor )
Nanocomposites ( jstor )
Tiles ( jstor )
Environmental Engineering Sciences -- Dissertations, Academic -- UF
enhancement, microbial, polyhydroxy, surfaces, tio2
Genre:
Electronic Thesis or Dissertation
bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
Environmental Engineering Sciences thesis, M.E.

Notes

Abstract:
The deposition and growth of microbes in the built environment have adverse public health and economic impacts. Illuminated surfaces of TiO2 have potential for photocatalytic destruction of the most resistant microbes. However, TiO2 alone is effective only with opaque and heavy coatings that obscure the appearance underlying the material. A translucent, antimicrobial photocatalytic coating was developed using polyhydroxy fullerene (PHF) as an enhancer for TiO2 photocatalysis on surfaces. TiO2-PHF nanocomposite was coated on grout and tiles surface. Photocatalytic activity was optimized by varying the ratio of PHF to TiO2, as indicated by decolorization of a red organic dye (Procion MX-5B). TiO2-PHF nanocomposite manifested 2 times enhancement in terms of dye degradation at the optimal ratio of PHF to TiO2 between 0.01 and 0.02. The optimized TiO2-PHF nanocomposite coatings were then used for inactivation of Aspergillus niger. TiO2-PHF nanocomposite coatings exhibit almost 3 times enhancement of within 3-hour exposure to UVA. ( en )
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
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.
Thesis:
Thesis (M.E.)--University of Florida, 2010.
Local:
Adviser: Koopman, Ben L.
Statement of Responsibility:
by Wei Bai.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Embargo Date:
10/8/2010
Resource Identifier:
004979728 ( ALEPH )
705932737 ( OCLC )
Classification:
LD1780 2010 ( lcc )

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288


290


292


Binding Energy (eV)



Figure 4-4. Experimental C1s XPS spectrum (red) of Polyhydroxy Fullerenes with fitted curves representing three different oxidation states of
carbon.


Experimental
- Peak Fitting
--C60
--C-OH
-- Henniketal
Baseline


282


284









was from Song's (2001) study, which used a WO3 to enhance TiO2 photocatalysis. PHF and gold

(Arabatzis et al. 2003a) is the second best enhancer, which showed 2 times enhancement. In

addition, based on the mass ratio of enhancer to TiO2, the amount of PHF used in photocatalysis

is about 5 to 15 times less than other enhancers used on TiO2 films.

4.3 Photocatalytic Inactivation of Fungi on Tile Surface

4.3.1 Recovery of Aspergillus niger from Different Surfaces Coated on Tiles

Complete and consistent recovery of microbes from surface is crucial for the evaluation of

photocatalytic performance on surface because attachment of microbes on surface will give

misleading result. Three different surfaces: TiO2-PHF, TiO2 and bare tile surface (no

photocatalysts) were used as substrate to evaluate the recovery of Aspergillus niger compared to

the control group. Figure 4-10 indicated that the recovery of Aspergillus niger on TiO2-PHF and

TiO2 surface are 91.4% and 90.6%, respectively, and statistical test validated that there was no

difference between these groups and the control group. However, the recovery rates on bare tile

surfaces were not ideal that only 50% of Aspergillus niger were recovered, significantly different

from control group. The recovery of Aspergillus niger from bare tile surface is very low,

probably due to the adhesive force between Aspergillus niger and tile surface or the

agglomeration of Aspergillus niger during sonication. The size measurement of Aspergillus niger

(Fig. 4-11) showed that the mean number size is about 4.5 [im with a narrow size distribution,

which is in the range of the size of Aspergillus niger spore (2-5 im). Accordingly, it eliminated

the possibility of Aspergillus niger agglomeration, and it is likely due to the strong adhesive

force between the tile surface and Aspergillus niger. The difference of recovery can be

explained in a way: particle based coating such as TiO2-PHF and TiO2 were very easily removed

from tile during proper sonication, and Aspergillus niger was resuspended at the same time.









3.4.5 Measurement of Destruction of the Dye (Procion Red MX-5B) on Grout

Photocatalytic destruction of Procion red MX-5B was quantified in terms of rate of

decolorization, as measured by UV/VIS reflectance spectroscopy. Dye degradation was

calculated based on percentage reflectance at the adsorption peaks as measured by UV/VIS

reflectance spectroscopy. Percentage reflectance was converted to adsorbance (A) according

to the equation:

1
A = log (3-3)
log Percentage reflectance (3

Dye degradation was calculated according to:

% Dye degradation = (A -A(background )-(At-A(background )) 100 (3-4)
A -A (background )

where Ao is the absorbance of dye coated on photocatalytic or grout surface before exposed

to UVA, Ao(background) is the absorbance of photocatalytic or grout surface before exposed to

UVA, At is the absorbance of dye coated on photocatalytic or grout surface after exposure to

UVA at a given time, and At(background) is the absorbance of photocatalytic or grout surface

after exposure to UVA at a given time.

3.4.6 Exposure of Surfaces to UVA

The photocatalytic experiment was carried out in a UVA chamber with 16 solar UV

lamps (RPR 3500A lamp, Southern New England Ultra Violet Company, Branford,

Connecticut) with peak intensity is at 350 nm. Air was circulated in the UV chamber by a fan

to limit the heat generation. Samples were placed on a platform in a plastic bin (42 x 28 x 15

cm) filled one forth capacity of deionized water. The bin was covered by a plastic film in

order to maintain relative humidity around 80-85%. The distance between samples and UV

lamps was 49.5 cm, giving an intensity of 15-17 W/m2 (as measured by a UVA detector

(PMA2110, Solar Light Co., Glenside, PA) (Fig. 3-1 showed the complete configuration of

UVA chamber). Temperature was maintained at 30-32 C under UVA radiation. A Thermo-

Hydro probe (Fisher Scientific) was utilized to monitor the temperature and relative humidity

33










300


250



200



150



100



50



0


Positive control


TI02-PHF


TiO2


Bare tile


Figure 4-10. Recovery of Aspergillus niger from different surface

Based on one-way ANOVA and Dunnett's two-sided test (a=0.05), there is no significant difference between control group and
treatment TiO2+PHF or treatment TiO2, while control is significantly different from treatment PHF and treatment no photocatlysts













70.0% *


60.0%


50.0%
=*

" 40.0%


^ 30.0%


20.0%


10.0%


0.0%


1000 mg/L TiO2


10000 mg/L TiO2

SW/ PHF W/O PHF


50000 mg/L TiO2


Figure 4-9. Photocatalytic degradation of Procion red MX-5B on TiO2-PHF(#I) nanocomposite (PHF/TiO2=0.01)

As measured by UV/VIS spectroscopy (with PELA-1000 Reflectance Spectroscopy Accessory). Based on One-way ANOVA and
Tukey-Kramer test (a=0.05), the mean of 0.1 wt% TiO2+PHF is significantly different from the other 5 means.

65









LIST OF FIGURES


Figure page

1-1 The molecular structure of Procion Red MX-5B ..................................................... 14

2-1 Major steps in photoelectrochemical mechanism, redrawn from Hoffmann (1995).........24

3-1 U V A cham ber configuration .. .................. ....................................... ...................................... 4 1

4-1 Cluster size distributions for PH F ............................. ... ...................................... 57

4-2 Possible aqueous cluster structure ofpolyhydroxy fullerenes (Vileno et al 2006)............58

4-3 M measured X P S spectrum ......................................................................... ......................... 59

4-4 Experimental Cls XPS spectrum (red) ofPolyhydroxy Fullerenes with fitted curves
representing three different oxidation states of carbon..................... ..... .............. 60

4-5 1H NM R spectrum of PHF ............................ ............................................ 61

4-6 Different concentration of TiO2 coated on grout surface ................................................62

4-7 Full spectrum scan of Procion red MX-5B on grout ............... ..................................63

4-8 Photocatalytic degradation of Procion red MX-5B on TiO2-PHF (#II) with different
ratio of PHF to TiO2 (from 0 to 0.02) ............... .................................. ..................... 64

4-9 Photocatalytic degradation of Procion red MX-5B on TiO2-PHF(#I) nanocomposite
(P H F /T iO 2= 0 .0 1) ....................................................................... ...................6 5

4-10 Recovery of Aspergillus niger from different surface .............................. ............... 66

4-11 Particle size of Aspergillus niger, as measured by lazer diffraction (Coulter
LS13320) ............ ..... ........................................... 67

4-12 Recovery of Aspergillus niger from TiO2 and silica based surfaces ..............................68

4-13 Aqueous dye degradation in silica, TiO2 rutile and anatase suspension....................... 69

4-14 Photocatalytic inactivation of Aspergillus niger on TiO2 and TiO2-PHF (#II) coated
tile s ............................................................................... ...... ............... 7 0

4-15 Photocatalytic inactivation of Aspergillus niger on tile coated with TiO2, TiO2+PHF
(B atch # 111) an d S i 2 ....................................................... ................................................ 7 1

4-16 Photocatalytic inactivation of Aspergillus niger on TiO2, TiO2-PHF (Batch III), SiO2
coated tiles (12-hour U V A exposure) .................................................................................... 72


















SReA, CO/C.HIHO
HO TC



Primary processes Characteristic time

(1) Formation of charge carriers by photon excitation
n270 +hv h .k +e;, 10-1 s

(2) Recombination of charge carriers, generating heat
{>TP OH'*+ +e-, > TiF-OH slow (1Cr7 5)
{> rTiOH) + k T2nw'OH fast (10 s)

(3) Reaction of valence-band hole with electron donor
{> Ti'OH'} +Red > Ti-OH+Red'+ slow (107 s)

(4) Reaction of conduction-band electron with electron acceptor
e, + Ox = TiZ OH + Ox- very slow (10 ns)

(5) Mineralization of final reactants

(6) Formation of Ti(lll) by trapping of a conduction-band electron through a dangling
surficial bond
>Jl- +e=>> 'Im deep trap (11i8 ns) (irreversible)

(7) Trapping of a valence-band hole at a surficial titanol group
> Ti"'OH +kh, {> li"r'OH*' fast (1 Cr s)
> nT'OH +ec [{> IlOH} shallow trap (10-10 s) (dynamic equilibrium)

where >TiOH represents the primary hydrated surface functionality of TiO2, e& is a
conduction-band electron, etr is a trapped conduction-band electron, h,," is a valence-
band hole, Red is an electron donor (ie reductant), Ox is an electron acceptor (ie ,
oxidant), {>Ti"OH'}* is the surface-trapped VB hole (i.e., surface-bound hydroxyl radical,
and {>Ti"'OH} is the surface-trapped GB electron


Figure 2-1. Major steps in photoelectrochemical mechanism, redrawn from Hoffmann (1995)









Table 3-1. Reagent volumes for TiO2/PHF mixtures I


Volume of TiO2
PHF/TiO2 suspension
(111 mg/L)/mL
0 0
0.1 9
0.02 9
0.01 9
0.005 9
0.001 9


Volume of Ti02
suspension
(1000mg/L)/mL
10
0
0
0
0
0


Volume of PHF
solution
(1000mg/L)/mL
0
1
0
0
0
0


Volume of PHF
solution
(200mg/L)/mL
0
0
1
0
0
0


Volume of PHF
solution
(100mg/L) /mL
0
0
0
1
0
0


Volume of PHF
solution
(50mg/L)/mL
0
0
0
0
1
0


Volume of
PHF solution
(10mg/L)/mL
0
0
0
0
0
1









Crittenden, J.C.; Zhang, Y.; Hand, D.W.; Perram, D.L.Marchand, E.G. Solar Detoxification of
Fuel-Contaminated Groundwater using Fixed-Bed Photocatalysis. Water Environment
Research. 1996, 68, 270-278.

Ding, Z.; Hu, X.; Yue, P.L.; Lu, G.Q.Greenfielda, P.F. Synthesis ofAnatase TiO2 Supported on
Porous Solids by Chemical Vapor Deposition. Catalysis Today. 2001, 68, 173-182.

Djordjevic, A.; Canadanovic-Brunet, J.M.; Vojinovic-Miloradov, M.Bogdanovic, G. Antioxidant
Properties and Hypothetic Radical Mechanism of Fullerenol C-60(OH)(24). Oxidation
Communications. 2004, 27, 806-812.

Emslie, A.G.; Bonner, F.T.Peck, L.G. Flow of a Viscous Liquid on a Rotating Disk. Journal of
AppliedPhysics. 1958, 29, 858-862.

Energy Efficiency and Renewable Energy 2003, The Business case for sustainable Design in
Federal Facilities, U.S. Department of Energy.

Flannigan, B., Samson, R.A. and Miller, J.D. 2001, Microorganisms in Home and Indoor Work
Environments : Diversity, Health Impacts, Investigation and Control, New York, NY :
Taylor & Francis.

Fretwell, R. and Douglas, P. An Active, Robust and Transparent Nanocrystalline Anatase TiO2
Thin Film Preparation, Characterisation and the Kinetics of Photodegradation of Model
Pollutants. Journal of Photochemistry and Photobiology A: Chemistry. 2001, 143, 229-240.

Fujishima, A.; Rao, T.N.Tryk, D.A. Titanium Dioxide Photocatalysis. Journal of Photochemistry
andPhotobiology C: Photochemistry Reviews. 2000, 1, 1-21.

Fujishima, A. and Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode.
Nature. 1972, 238, 37-38.

Hench, L. and West, J. The Sol-Gel Process. ChemicalReviews. 1990, 90, 33-72.

Herrmann, J.M.; Tahiri, H.; Ait-Ichou, Y.; Lassaletta, G.; Gonzalez-Elipe, A.R.Fernandez, A.
Characterization and Photocatalytic Activity in Aqueous Medium of TiO2 and Ag-TiO2
Coatings on Quartz. Applied Catalysis B: Environmental. 1997, 13, 219-228.

Hoffmann, M.R.; Martin, S.T.; Choi, W.Bahnemann, W. Environmental Applications of
Semiconductor Photocatalysis. ChemicalReview. 1995,.

Hu, C.; Yub, J.C.; Hao, Z.Wong, P.K. Photocatalytic Degradation of Triazine-Containing Azo
Dyes in Aqueous TiO2 Suspensions. Applied Catalysis B: Environmental. 2003, 42, 47-55.

Husebo, L.; Sitharaman, B.; Furukawa, K.; Kato, T.Wilson, L. Fullerenols Revisited as Stable
Radical Anions. Journal of the American Chemical Society. 2004, 126, 12055-12064.

Hwang, Y.S. and Li, Q. Characterizing Photochemical Transformation of Aqueous nC(60) Under
Environmentally Relevant Conditions Environmental Science & Technology. 2010,.









air are a major cause of food spoilage. Each year, crops worth $9.1 billion are lost in the U.S.

because of crop diseases, and fungi are the major contributors of these diseases (Agrios 2005).

Humans are also affected by fungi, especially for those who are immunologically

compromised. The Center for Disease Control and Prevention (CDC) states that about 1.7

million patients in the U.S. suffer from hospital-acquired infections, and 99,000 people die from

disease transmission in hospitals annually. Fungi are the third largest group of microorganisms

causing hospital-acquired infections. Infectious species include those from the genera Candida

and Aspergillus. The annual medical cost of hospital-acquired infections ranges from $28.4 to

$33.8 billion (Scott 2009). Excessive amounts of fungal spores in the air lead to respiratory

allergies. The CDC states that about 9 million U.S. children under the age of 18 have been

diagnosed with asthma (LungUSA 2005).

The deleterious effects of fungi are not restricted to living organisms. Fungi easily grow

and accumulate on damp surfaces such as air conditioning ducts and walls. Aspergillus niger are

frequently found in the built environments and often contaminate foods and damp household

surfaces by forming black molds (spores) (Flannigan et al. 2001).Excessive amounts of molds

cause sick building syndrome. This syndrome, associated with poor indoor air quality, costs 150

billion workdays and about $15 billion in lost productivity each year in the United States

(Energy Efficiency and Renewable Energy 2003).









CHAPTER 4
RESULTS AND DISCUSSION

4.1 Characterization of Polyhydroxy Fullerenes

4.1.1 Size and Size Distribution

Polyhydroxyl fullerenes are water-soluble, but it is reported that as the concentration of

PHF solution increases, size increases due to the formation of PHF cluster. Since TiO2-PHF

nanocomposite was assembled in aqueous system in this study, the size and amount of PHF

molecules or clusters in aqueous system are crucial, affecting the coverage of PHF on TiO2

surface. For example, equal amount of PHF but differing in size can lead to different coverage of

PHF on TiO2 surface. With the increasing size of PHF, the actual amount of PHF required for

optimal enhancement of TiO2 performance may increase as well. PHF concentrations in the

TiO2-PHF suspensions used in preparing coatings range from 1 to 1000 mg/L, hence this range

of concentrations was selected for particle size characterization. The PHF characterized was

batch #1I synthesized in our laboratory according to the protocol as described in chapter 3.1.2.

Dynamic light scattering was used to determine the mean size and size distribution. Based

on Table 4-1 and Figure 4-1, the mean particle sizes of PHF (based on volume, number and

surface area) in different concentrations are roughly between 3.25 and 3.51 nm. The size

distribution is narrow, with a range of 3 to 4 nm. The measured size, which is about three times

larger than the reported 1.0 nm size of polyhydroxy fullerene molecules, can possibly be ascribed

to cluster formation. Vileno (2006) observed polyhydroxy fullerenes cluster in aqueous solution

and proposed a possible cluster structure, as shown in Figure 4-2. Clusters of PHF molecules are

held together by hydrogen bonding. Negatively charged groups are located on the outsides of the

clusters, preventing further aggregation due to electrostatic repulsion between clusters. Cluster









Sputtering is a process in which high-energy ions are used to bombard elemental sources

of semiconductor material, causing ejection of atoms which are then deposited in thin layers on a

substrate. Liu et al. (2008) utilized sputtering to form a film of TiO2 doped with nitrogen.

Sputtering power and substrate temperature were the two most important parameters affecting

the structure and composition of the films.

2.4 Enhancement of TiO2 Photocatalysis

The low quantum yield2 for TiO2 serves as an obstacle for its widespread application to

control pollutants and pathogens. Consequently, methods to enhance TiO2 photocatalysis have

been investigated extensively. These methods can be divided into two categories. One approach

is to increase the adsorption of organic compounds and microorganisms on the TiO2 surfaces

with absorbents such as silica, alumina, zeolites, and activated carbon (Matos et al. 2001).

However, this approach depends on the adsorption characteristics of pollutant molecules. An

alternate approach is to hinder electron-hole pair recombination, thus directing more of the

electrons and holes toward formation of reactive species such as hydroxyl free radicals.

Hindering electron-hole pair recombination is attractive because it can help accelerate the

degradation of any pollutant.

Noble metals such as platinum, gold and silver (Sun et al. 2003, Arabatzis et al. 2003a,

Vamathevan et al. 2002) and the noble metal ions Ag+ and Au+ have been of great interest during

the past few years (Szab6-Bardos et al. 2003, Arabatzis et al. 2003b, Li and Li 2001) as dopants

for hindering electron-hole recombination in TiO2 photocatalysis. A noble metal in TiO2 attracts

photoexcited electrons, decreasing electron-hole recombination and increasing the number of


2
2Quantum yield is defined as the number of events occurring per photon absorbed (Linsebigler et al. 1995). In TiO2
photocatalysis, quantum yield can be specified as the number of charges transferred to adsorbed species per photon
absorbed.









To sum up, the fitted peak with a binding energy of 285.4 eV was assigned as nonoxygenated

carbon, the peak at 287.3 eV was assigned as monooxygenated carbon (C-OH), and the peak at

289 eV was assigned as dioxygenated carbon (hemiketal group: RO-C-OH).

According to area integration of carbon peaks, the percentages of different carbon can be

calculated as follows (Table 4-3): nonoxygenated carbon 61.37%, monooxygenated carbon

33.68%, and hemiketal carbon 4.95%. The functional groups within a PHF molecule is listed in

Table 4-4. Quantification of functional groups is based on the assumption that the PHF cage

structure is still intact with 60 carbon atoms, which is supported by a mass spectroscopy (Krishna

2007). Therefore, the numbers of hydroxyl groups and hemiketal groups within PHF are 20 and

3, respectively. Na+ can be calculated based on the percentage ofNal s in the XPS spectrum;

hence the number of Na+ per molecule is 2.

Finally, the empirical formula ofpolyhydroxy fullerenes can be deduced as

Na2C6003(OH)23 with a molecular weight of 1149.4. The parameter R, proposed by Xing et al.

(2004), is the ratio of impure groups to hydroxyl groups of PHF as determined by XPS. Xing et

al. (2004) showed that the value of R is related to the stability of PHF. PHF having an R of less

than 0.2 with fewer than 36 hydroxyl groups tends to be stabile. The R of PHF batch #061708 in

this study was 0.15 with 20 hydroxyl groups, which indicates a stable formulation.

4.1.2.2 Nuclear Magnetic Resonance Spectroscopy

Due to a large amount of OH group bonded to polyhydroxy fullerenes, H NMR can

possibly characterize different functional groups containing 1H in terms of chemical shift. It can

also give the ratio of different functional groups based on peak area integration. The hydroxyl

groups exhibit a wide range of chemical shift in H NMR spectrum, strongly depending on the

adjacent functional groups and chemical bonding. The existence of multiple double bonds

(conjugated carbon bonds) in PHF tends to move the chemical shift of hydroxyl group

44








NaO ONa
N -N..
IN
CI N NH OH
N N
Cl
Figure 1 -1. The molecular structure of Procion Red MX-5B









TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S ............................................................................................... ............... 4

L IST O F TA B L E S .......................................................................................... 7

L IST O F FIG U R E S ................................................................. 8

A B S T R A C T ............................................................................................... ...... 10

CHAPTER

1 IN TR O D U C TIO N ...................................................... 11

2 LITERATURE REVIEW ......................................... 15

2.1 TiO 2 Photocatalysis .................................. ....... 15
2.2 Mechanism of TiO2 Photocatalysis.......................... ........ 16
2.3 Methods for Preparing TiO2 Coatings ................................. ......................... 16
2.4 Enhancement of TiO2 Photocatalysis ....................... ........................... 19
2.5 Application of TiO2 Thin Films for Environmental Control ................ ........... ....20
2.6 Polyhydroxy Fullerenes (PHF) .......... ............................. 21
2.7 Fungi .......... ...................................... ..... 22

3 M A TER IA L S A N D M E TH O D S .......................................................................... ............... 25

3.1 Chemicals, Reagents and Biological Culture Media .................................................... 25
3.1.1 Phosphate-Buffered Saline .................................................................. ..... 25
3.1.2 Polyhydroxy Fullerenes (PH F) .................. ............. .. ................................. 25
3.1.3 Titanium Dioxide (TiO2) Suspension ........................ ......................................26
3.1.4 Procion Red M X-5B .. .... ............................................................................... 26
3.1.5 Culture M edia for Aspergillus niger ................... .... .................. ... ............ 26
3.2 Coatings .............................. ................ 27
3.2.1 Grout Preparation .................................... .............................................. 27
3.2.2 Photocatalytic Coating on Grout.................................................. ............... 27
3.2.3 Dye Coating on Grout................................................... ............................ 28
3.2.4 Photocatalytic Coatings on Tiles ........................................... ........................ 28
3.3 M icrobes ............................ ........................... ......................... 28
3.3.1 Culturing and Enumeration of Aspergillus niger............. .... ...........28
3.3.2 Recovery of Aspergillus niger from Tiles............................................ ............... 29
3.4 C characterization ................................. ..................... 30
3.4 .1 Size M easurem ent................................................. .......................... ....... .......... 30
3.4.2 X-ray Photoelectron Spectroscopy ........................................................... 30
3.4.3 Nuclear M magnetic Resonance............................................. ............................. 31
3.4.4 Light Absorption by Surface Dye ......... ..................... ...... ......... .. 32
3.4.5 Measurement of Destruction of the Dye (Procion Red MX-5B) on Grout...........33









TiO2-PHF nanocomposite was initially optimized and coated on some representative

surface, such as grout used in bathroom tiles, upon which fungi tends to readily deposit and

grow. Two methods of application of TiO2-PHF nanocomposite to grout were explored: a.

mixing grout with TiO2-PHF nanocomposite, and b. coating of TiO2-PHF nanocomposite on

grout surface. Procion red MX-5B (C19HioCl2N6Na206S2) was selected as the target organic

pollutant for this study. The red dye has a strong adsorption band ranging from 510 nm to 540

nm (Hu et al. 2003). The molecular structure (Fig. 1-1) of red dye reveals that there are three

aromatic rings present in the structure, which is very resistant to degradation compared to other

simple organic dyes. Additionally, the presence ofNa+ and SO32- within the molecule makes it

very easy for the molecule to adsorb on either negatively or positively charged surfaces. Previous

study (Krishna 2007) showed that the optimum ratio of PHF to TiO2 in aqueous TiO2-PHF

photocatalysis is between 0.001-0.003. Accordingly, it is reasonable to speculate that it should

have an optimum ratio on surface as well. Procion red MX-5B was also used as an indicator for

photocatalytic activity.

2) Apply TiO2-PHF nanocomposite on surface for the prevention and elimination of a

model fungi Aspergillus niger, the black mold fungi. Aspergillus niger is used as a model

microbe because of its widespread occurrence and contribution to health problems such as

asthma and sick building syndrome (Chauhan et al. 2006, Schwab and Straus 2004). Grout-tile

system in bathroom was utilized as substrate for the growth of Aspergillus niger.










0.8


0.7


0.6


0.5


< 0.4


0.3


0.2


0.1




200 300 400 500 600 700 800

Wavelength (nm)



Figure 4-7. Full spectrum scan of Procion red MX-5B on grout









SiO2 is not photocatalytically active. Thus, the killing ofAspergillus niger is due to UVA effect

alone.

PHF batch II was first used in this experiment. Figure 4-14 indicated that PHF was unable

to enhance the photocatalytic inactivation efficiency. There is no significant difference between

TiO2 (0.0536 h-1) and TiO2-PHF (0.0448 h-1) surface in terms of the overall inactivation rate of

Aspergillus niger, as confirmed by student's t-test (a=0.05).

PHF batch #111 was then used to make TiO2-PHF nanocomposite to evaluate whether it can

enhance the photocatalytic performance or not. Figure 4-15 listed the percentage of inactivation

of Aspergillus niger at different time slots. Figure 4-16 and 4-17 described the inactivation

kinetics ofAspergillus niger within 12 and 24 hours. In Figure 4-15, the commercial PHF

showed significant enhancement of%inactivation in 3 hours, which showed almost 3 times

enhancement compared to that of TiO2 alone. The enhancement was also observed in 6 and 12

hours, but the degree of enhancement gradually decreased. After 24-hour exposure to UVA, the

inactivation rate of TiO2-PHF was very similar to that of TiO2 alone. In Figure 4-16, the

inactivation rate of TiO2-PHF (0.0553 h-1) is about 1.6 times faster than that of TiO2 (0.0344 h1)

alone in 12 hours. However, the inactivation rate of TiO2, as shown in Figure 4-17, caught up

with the rate of TiO2-PHF in 24 hours exposure to UVA. All the results were analyzed with One-

Way ANOVA and Tukey-Kramer test and student's t-test.

4.3.3 Evaluation of the Reusability of TiO2-PHF Nanocomposite Coating

The reusability of TiO2-PHF nanocomposite coating and TiO2 coating are tested. As shown

in Figure 4-18, although the mean value of % inactivaion of TiO2-PHF coating is higher than that

of TiO2 coating after 3, 6 and 12 hours exposure to UVA, there is no significant difference

between them, as confirmed by student's t-test (a=0.05). Figure 4-19 and 4-20 indicated that the

overall inactivation rate coefficients of both coatings decrease by a factor of 2 to 2.5 compared to

52



















S-------------- --I-------- ---- -- :-----------
------ -------.---- -. -- .-------- ---- ; -... ....-...... 3.



-------------- ---------- --------- -----------


C I
~I-- ---~-i~- --- -- -- --1 ------I------- ---- -----


--------------- I.---- -
I:l---------- ------- --------- -- ------- ---------- ---5
0 L --- 1 .- J ---- -- .1
o_____0


10 100
Size{nanometers)


10 100
Size(narnoeters)


I i
(0a
* 41.1L-


1,000 10,000


d







I I
5 I


1.000 10,000


30-
10
0 1


0




1 i0


-41'


.30 !

-J


-11


... ..........
--- -- -- -- -- -r ----





S. -.- T-.- --.
- -.- .-. .T -- ---.. -. ...-. .- -. .. .- -
.~ .


-1 1 10 100 1,000 10CiOO
Size(nanometer s)


-, ---------- -- i ----- i ------------ 1 cc


20



10
-Fr



0
30-


0-1


1 10 100
Sizeinanometers)


1,000


10,000


Figure 4-1. Cluster size distributions for PHF


Concentration at (a) 1 mg/L, (b) 10 mg/L, (c) 100 mg/L and (d) 1000 mg/L


.......... ..... ... .......... .......... .. .....
------- --r-----~-- ----- --- -- ------ -
-------- -- r------ ---- ---- ------ -- -------- -----------




- -........ ...i.. I-


........... .....i .....i ..................... ....... .....


1


.......... ..... .... .......... ........-...........


- -- -- ---- -- -------
- -- -- -- -- .-- -- --- --- -- -




S.........
*- ---------------- -----------------------------------


.. --


. .. LP


!-U


i


,,I l'


I









However, high efficiency photocatalysis usually requires thick TiO2 coating, which is not

cost-effective and also obscures the appearance of surface upon which TiO2 particles are

deposited on. Hence the goal of proposed research is to develop and test translucent,

antimicrobial and photocatalytic coatings. In order to achieve this research goal, a novel

photocatalytic enhancer, polyhydroxy fullerenes (PHF), is utilized to form TiO2-PHF

nanocomposite, which possibly decrease TiO2 requirement while maintaining high photocatalytic

efficiency. PHF serves as electron scavenger (Krishna et al. 2006, Krishna et al. 2008),

accelerating the photocatalytic rate by producing more hydroxyl radicals, which were reported as

the primary oxidative species for microbial inactivation (Salih 2002, Cho et al. 2005). In

addition, there are several advantages regarding TiO2-PHF nanocomposite: first of all, the

nanocomposite can be easily synthesized through self-assembly, avoiding any chemical reaction;

secondly, the concentration of PHF applied in this nanocomposite is about 10-100 times lower

than other photocatalytic enhancer, such as metals or dye; Last but not least, PHF is non-toxic

and currently used for therapeutic and cosmetics.

Previous research (Krishna et al. 2006) demonstrated the enhancement of TiO2

photocatalysis in aqueous media using polyhydroxy fullerenes (PHF), with the increment of dye

degradation and E.coli inactivation rates by factors of 2.6 and 1.9, respectively, over the rates

achieved with TiO2 alone. The hypothesis of this research is that PHF can also act as an enhancer

for TiO2 photocatalytic coatings on surfaces exposed to the atmosphere. The specific objectives

within this research include:

1) Optimize the ratio of PHF to TiO2 to procure maximum photocatalytic efficiency on

surface;









ACKNOWLEDGMENTS

I would like to express my sincere gratitude to Dr. Ben Koopman, who is always ready,

available and patient to guild me with academic problems and discussion during my graduate

study at the University of Florida. I would also like to extend my appreciation to my advisory

committee members Dr. Brij Moudgil and Dr. Chang-Yu Wu, for their encouragement and

academic supports.

I am grateful to Dr. Vijay Krishna, who always provides me with insightful suggestions

and valuable feedbacks to my research. I am thankful to Dr. Jie Wang and Dr. Angelina

Georgieva, for their hard working on synthesizing polyhydroxy fullerenes for my research. I am

also thankful to Dr. Jie Gao, Dr. Hideya Nakamura, Paul Indeglia and Wilton Mui, for their

contributions to discussion on my research during our group meetings.

My gratitude to my wife, Fan Li, is beyond words. She always has faith in me and

encourages me to pursue my dream. If without her, my life would be much less colorful. Lastly, I

would like to express my special gratitude to my parents in China, for their tremendous love and

unwavering support all the time.










present on tile surface is too low to be detected by spectroscopic method. Thus, new

methodology is needed to develop to evaluate the stability of TiO2-PHF nanocomposite on tile

surface.










90%




70%




a 50%




30%




10%



3 6 12 24
-10%
Time (hour)

OTiO2 TiO2+PHF


Figure 4-18. Reusability test: photocatalytic inactivation ofAspergillus niger on tile coated with TiO2, TiO2+PHF (Batch #111)

Data are analyzed with student's t-test









































Figure 4-2. Possible aqueous cluster structure of polyhydroxy fullerenes (Vileno et al. 2006)











0 3 6 9 12 15
0.1


0.05





-0.05


-0.1


S-0.15


-0.2


-0.25


-0.3


-0.35
Time (hour)

*TiO2 TiO2+PHF


Figure 4-19. Reusability test: photocatalytic inactivation ofAspergillus niger on TiO2, TiO2-PHF (Batch #111) coated tiles (12-hour
UVA exposure)

Data are analyzed with student's t-test









(30.6%), and its degradation rate is even lower than just 1 wt%/ TiO2 alone (45.4%). For 50000

mg/L TiO2-PHF nanocomposite, there is no significant difference between TiO2 alone (47.0%)

and TiO2 with PHF (50.9%) in terms of dye degradation. However, there is no significant

difference of dye degradation between 50000 mg/L TiO2-PHF coating and pure TiO2 coating.

This observation can be attributed to the agglomeration of TiO2 and PHF particles on surface

coating. Agglomeration readily occurs in high solid loading of TiO2 suspension if without

appropriate di spersant.

4.2.5 Discussion

As the ratio of PHF to TiO2 decreases to 0.005, dye degradation decreases, which is due to

the fact that the amount of PHF is too low to act as an effective enhancer, resulting in less dye

degradation. On the other hand, when using higher amount of PHF, PHF itself can potentially

block UVA radiation (shading effect) from TiO2 surface, diminishing the photocatalytic

efficiency, and this phenomenon was also observed from Arabatzis's (2003b) study, in which

silver particle was employed as a photocatalytic enhancer for TiO2 thin film. Additionally,

shading effects induced by enhancers were also reported in aqueous TiO2 photocatalysis

(Sclafani et al. 1991, Crittenden et al. 1996, Qi et al. 2004). The optimum ratio of PHF to TiO2 of

TiO2-PHF photocatalysis appears at 0.01-0.02, at which the electron scavenger ability of PHF

outcompetes its shading effect at the greatest level.

The optimal ratio of PHF to TiO2 in TiO2-PHF coating is about 3 to 10 times higher than

that obtained in aqueous photocatalytic study (Krishna et al. 2008). This difference is possibly

due to several reasons. First of all, in the preparation of TiO2-PHF coating, agglomeration may

occur in the drying process on grout or tile. With the increasing size of PHF, the actual amount

of PHF required for optimal TiO2 performance may increase as well because of the change of

coverage of PHF on TiO2 surface. Hence, more amount of PHF is required to obtain the optimal

48









experiment may either block UVA from reaching the TiO2 surface or prevent subsequent

inoculated Aspergillus niger from contacting TiO2 directly, causing the decrease of

photocatalytic activity. Additionally, TiO2-PHF nanocomposite did not show enhancement in the

reusability test, probably resulting from the fact that most PHF already degraded from the

previous experiment under UVA. Thus the enhancement effect was not observed in the

reusability test.






















trtt-'~ "'-twrr. r .u "--r


h r


. I I I I i f iF I *i... p .** I 1 I p I .' .
L 12 LD 0 6 a ppM
1. 496
1.00 4.9i6


Figure 4-5. 1H NMR spectrum of PHF









Commercial PHF (BuckyUSA) was denoted as batch #111 in this study. A mass of 0.015 g

PHF particles was weighed and dissolved in 15 mL deionized water in a 20 mL scintillation

vial, giving a final concentration of 1000 mg/L. Serial dilutions were carried out to PHF

concentrations ranging from 200 to 1 mg/L.

3.1.3 Titanium Dioxide (TiO2) Suspension

Different concentrations of TiO2 suspension were obtained by adding appropriate

weights of TiO2 anatase5 (Alfa Aesar, Ward Hill, MA) to deionized water to in a 20 mL

scintillation vial, followed by 30-minute sonication at the sequence of 10-minute on, 2-

minute off, 10-minute on, 2-minute off and 10-minute on (Misonix Sonicator 3000,

Farmingdale, NY) at the highest power level 10.0, at which the power fluctuates between 180

and 200 W. The scintillation vial was placed in a water bath that connecting to this sonicator,

and continuous water flow was applied to diminish heat generated by sonication and maintain

the water temperature at 27.8 C.

3.1.4 Procion Red MX-5B

An aqueous stock solution of Procion red MX-5B dye (Sigma-Aldrich Inc., St. Louis,

MO) was prepared at a concentration of 1000 mg/L by dissolving 0.01 g dye powder in 10

mL deionized water. Dilution of dye was carried out from this stock solution.

3.1.5 Culture Media for Aspergillus niger

Potato dextrose agar was used to culture Aspergillus niger. A mass of 39 g Potato

Dextrose Agar was suspended in 1 L of deionized water and mixed thoroughly with heating.

The solution was then autoclaved at 120 oC and 16 bar for 15 minutes. Plates were made by

pouring the autoclaved agar into 100x15 mm sterile plastic Petri dishes (Fisher Scientific)

and air dried in the laminar flow hood (LABCONCO purifier class 2 safe cabinet) for 24

hours. The dried agar plates were used immediately or stored in a refrigerator at 4 OC.


5 Particle size: 5 nmas reported from the manufacturer









CHAPTER 1
INTRODUCTION

The deposition and growth of microbes on surfaces such as walls, windows and tables

pose substantial threat to human health. The Center of Disease Control and Prevention (CDC)

states that 9 million U.S. children under the age of 18 have been diagnosed with asthma, which is

commonly caused by bacterial and fungal spore exposures (LungUSA 2005). Viral respiratory

infections, the most widespread infectious disease in the United States, cause about $25 billion in

direct and indirect losses every year (Bertino 2002). Nosocomial infections (e.g., Staphylococcus

aureus) are also of intense concern. The CDC estimates that nearly two million patients each year

will contract an infection while in a United States hospital, and about 90,000 of them will die

from the infection (Weinstein 1998). Surface transmission of pathogenic microbes is a common

mode for disease transmission. Hence, efficient and effective techniques for surface disinfection

are needed.

Disinfection techniques include heat treatment, radiation, and chemical agents. Heat

treatment is the most widely used technique for disinfection, but many surfaces cannot withstand

the high temperatures required. Radiation such as germicidal ultraviolet or gamma rays can

effectively kill microbes on surfaces, but are precluded in many instances because of safety

concerns. Chlorine is effective in inactivating microbes, but can generate toxic by-products

including mutagens and carcinogens (Block 2001), which restricts its application. Strong

chemical agents can also damage surfaces. Some bioparticulates, including bacterial and fungal

spores, can survive under extreme environments, exhibiting strong resistance to the traditional

disinfection techniques. TiO2 photocatalysis can overcome these disadvantages. Photocatalysts

with higher efficiency are desired for inactivation of hazardous bioparticulates.









Kim, J.; Seo, G.; Cho, D.; Choi, B.; Kim, J.; Park, H.; Kim, M.; Song, S.; Kim, G.Kato, S.
Development of Air Purification Device through Application of Thin-Film Photocatalyst.
Catalysis Today. 2006, 111, 271-274.

Kong, L.; Tedrow, O.; Chan, Y.F.Zepp, R.G. Light-Initiated Transformations of Fullerenol in
Aqueous Media Environmental Science & Technology. 2009, 43, 9155-9160.

Kontturi, E.; Johansson, L.; Kontturi, K.; Ahonen, P.; Thune, P.Laine, J. Cellulose Nanocrystal
Submonolayers by Spin Coating. Langmuir. 2007, 23, 9674-9680.

Krishna, V.B. 2007, Enhancement of Titanium Dioxide Photocatalysis n ith Polyhydroxy
Fullerenes, University of Florida.

Krishna, V.; Noguchi, N.; Koopman, B.Moudgil, B. Enhancement of Titanium Dioxide
Photocatalysis by Water-Soluble Fullerenes. Journal of Colloid and Interface Science. 2006,
304, 166-171.

Krishna, V.; Yanes, D.; Imaram, W.; Angerhofer, A.; Koopman, B.Moudgil, B. Mechanism of
Enhanced Photocatalysis with Polyhydroxy Fullerenes. Applied Catalysis B: Environmental.
2008, 79, 376-381.

Kuhn, K.P.; Chaberny, I.F.; Massholder, K.; Stickler, M.; Benz, V.W.; Sonntag, H.Erdinger, L.
Disinfection of Surfaces by Photocatalytic Oxidation with Titanium Dioxide and UVA Light.
Chemosphere. 2003, 53, 71-77.

Lambert, J.B. 1987, Introduction to Organic Spectroscopy, New York: Macmillan.

Lee, S.; Pumprueg, S.; Moudgil, B.Sigmund, W. Inactivation of Bacterial Endospores by
Photocatalytic Nanocomposites. Colloids and Surfaces B: Biointerfaces. 2005, 40, 93-98.

Li, J.; Takeuchi, A.; Ozawa, M.; Li, X.; Saigo, K.Kitazawa, K. C60 Fullerol Formation Catalysed
by Quaternary Ammonium Hydroxides. Journal of the Chemical Society, Chemical
Communications. 1993,, 1784-1785.

Li, X.Z. and Li, F.B. Study of Au/Au3+-TiO2 Photocatalysts Toward Visible Photooxidation for
Water and Wastewater Treatment. Environmental Science & Technology. 2001, 35, 2381-
2387.

Linsebigler, A.; Lu, G.Yates, J. Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and
Selected Results. ChemicalReviews. 1995, 95, 735-758.

Liu, B.; Wen, L.Zhao, X. The Structure and Photocatalytic Studies of N-Doped TiO2 Films
Prepared by Radio Frequency Reactive Magnetron Sputtering. Solar Energy Materials and
Solar Cells. 2008, 92, 1-10.

LungUSA 2005, Trends in Asthma Morbidity and Mortality, Americal Lung Association:
Epidemiology and statistics unit.









CHAPTER 3
MATERIALS AND METHODS

3.1 Chemicals, Reagents and Biological Culture Media

Chemicals were obtained from Fisher Scientific, except as noted.

3.1.1 Phosphate-Buffered Saline

Phosphate-buffered saline (PBS) stock solution was prepared by dissolving 12.36 g

Na2HPO4, 1.80 g NaH2PO4 and 85.00 g NaCl in 1000 mL of deionized water. The PBS

working solution (0.01 M phosphate, pH 7.6) was diluted from PBS stock solution by adding

100 mL of stock solution to 900 mL deionized water. PBS/SDS solution was prepared by

adding 0.576 g sodium dodecyl sulfate (SDS) to 1000 mL of PBS working solution, with

thorough mixing. All buffer saline was autoclaved at 120 OC and 16 bar for 15 minutes before

used.

3.1.2 Polyhydroxy Fullerenes (PHF)

PHF was obtained from BuckyUSA (Houston, TX) and was also synthesized in our

laboratory. The protocol used for synthesis was that proposed by Li (1993) with a few

modifications. PHF was synthesized by the reaction of C60 with aqueous NaOH at the

presence of tetrabutylammonium hydroxide (TBAH):

1) Chemical reaction: starting from C60 dissolving in toluene, C60 reacts with NaOH at the

presence of TBAH as catalyst.

2) Purification: Several purification steps take place, including evaporation of organic

solvent, filtration, desalting chromatography.

3) Dry: followed by the purification processes, freeze dry is applied to dry the final products

Synthesized PHF particles (#I3 and #II4), which was synthesized in March and June

2008, were stored in a 20 mL scintillation vial covered with aluminum foil in a freezer.


3 Batch 2
4 Batch 061708









However, for bare tile surface, Aspergillus niger directly attach to the tile surface, which made it

very hard to remove during sonication.

An approach was developed to improve the recovery of Aspergillus niger from bare tile

surface. A coating that is not photocatalytically active and not adhesive to Aspergillus niger is

desired for this experiment. TiO2 rutile particle and amorphous silica particle were selected as a

coating for improving the recovery of Aspergillus niger from these two surfaces. The reason for

choosing TiO2 rutile particles is that it was reported as inactive or less active as photocatalysts,

and it shares similar chemistry with TiO2 anatase. Amorphous silica was also not

photocatalytically active. Figure 4-12 shows that the recovery of Aspergillus niger from particle

based coating (TiO2 rutile, Geltech silica and Stober silica) is very high, from 94%-108%, which

is not different from the control group, while the recovery from bare tile (no photocatalysts) is

only 50%.

After knowing that both TiO2 rutile and silica get high recovery, photocatalytic experiment

was carried out to find out whether these particles were photocatalytically active or not. Aqueous

dye degradation in different particle suspension was carried out. Figure 4-13 indicated that silica

aqueous suspension does not degrade red dye at all, while TiO2 rutile particle suspension showed

strong degradation of dye (there is no significantly different between TiO2 anatase and TiO2

rutile in terms of reaction coefficient). Thus, silica base coating can serve as a control for

Aspergillus niger photocatalytic inactivation experiment because it show perfect recovery of

Aspergillus niger and photocatalytically inactive.

4.3.2 Photocatalytic Inactivation of Aspergillus niger

The photocatalytic inactivation of TiO2-PHF (at optimal ratio of PHF to TiO2) coated tile

on Aspergillus niger was evaluated. Generally, SiO2 surface manifest significant slower

inactivation of Aspergillus niger at a factor of 1.8 to 2.9 compared to other two surfaces because

51















T T


- T


-'-I


Time (hour)


ENophotocatalysts *0.02 0.01


0.005 0


Figure 4-8. Photocatalytic degradation of Procion red MX-5B on TiO2-PHF (#II) with different ratio of PHF to TiO2 (from 0 to 0.02)

As measured by UV/VIS spectroscopy (with PELA-1000 Reflectance Spectroscopy Accessory). One-Way ANOVA and Tukey-
Kramer test at 6, 12 and 24 hours were conducted at a=0.05 to validate the experimental result, respectively.


90%

80%

70%


6 60%
o

| 50%

40%

0 30%


20%

10%


0% +-


' I









TITANIUM DIOXIDE-POLYHYDROXY FULLERENE NANOCOMPOSITE FOR
PHOTOCATALYTIC, ANTIMICROBIAL SURFACES






















By

WEI BAI















A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING


UNIVERSITY OF FLORIDA

2010
























a


C

Figure 3-1. UVA chamber configuration

a) UVA chamber with 16 solar UV lamps with a distance of 49.5 cm to the surface
of sample; b) a fan was utilized to circulate air in the UV chamber to limit the heat
generation; c) Sample was placed in plastic bin with constant humidity by covering
the bin by a plastic film











Table 4-5. Comparison of photocatalytic activity between different enhancer


Literature


Type of TiO2


Mass
ratio of
Enhancer
enhancer
to TiO2


Model pollutant


Films
exposed
to
aqueous
or air


UVA
intensity
(W/m2)


Time
exposure
to UVA
(hour)


Enhancements


This study


PHF (#II)


PHF
(#061708)


Anatase


Arabatzis et al. (2003b)


Arabatzis et al. (2003a)

Arpac et al. (2007)

Hermann et al. (1997)

Somekawa etal.(2008)


Song et al. (2001)


Anatase and rutile (sol-gel)

Anatase and rutile (sol-gel)

Anatase (sol-gel)

Anatase (sol-gel)

Degussa P259


Sol-gel


Au

Sn

Ag

N

MoO3

WO3


0.01


0.013

0.051

0.15




0.05

0.07


Procion red MX-
5B


Methyl orange

Methyl orange

Malachite Green

Malic acid

Methylene blue

2-propanol (gas
phase)


12

6
15-17
12

24


Aqueous 0.717


Aqueous

Aqueous

Aqueous

Aqueous


0.717


1

4

0.5



0.75


9 Degussa P25 is a commercial Ti02 product, containing 75% of anatase and 25% of rutile


2x

2x

1.1x
lx

1.8x

2x

1.lx

1.3x

1.2x

0.33x

3x









downfield. In this NMR experiment, the spectrum shows two distinct proton peaks with

chemical shifts centered at roughly 6 9.9 and 14.9 ppm 1. The large D20 solvent peak was

centered at 4.8 ppm (Fig. 4-5). The peak at 9.9 ppm refers to hydroxyl groups bonding to a sp3

carbon, while the peak at 14.9 ppm can be attributed to some carbonyl structures such as ketal or

hemiketal. This confirms the result from XPS with the existence of hydroxyl groups and

hemiketal groups. The ratio of hemiketal groups to hydroxyl groups based on these results is

0.20.

As noted above, the ratio of hemiketal group to hydroxyl group based on NMR spectrum

(0.20) differs from the ratio of 0.15 deduced from XPS. The ratio measured by NMR manifests

fewer hydroxyl groups in aqueous solution. This deviation is mainly caused by hydrogen

bonding in the solution. Hydroxyl groups in one molecule tend to interact with hydroxyl groups

of surrounding molecules through hydrogen bonding, forming small clusters and resulting in

partial chemical shift. The particle size measurements discussed previously support the existence

of clusters through hydrogen bonding.

The second explanation is that XPS measurement double counted monooxygenated carbon.

Since XPS might not differentiate C-O-C from C-OH, R-O in the hemiketal group (RO-C-OH)

may be falsely considered as C-OH, causing more hydroxyl groups being counted. To correct

this artifact, the correct hydroxyl group of PHF should minus the amount of hemiketal group of

PHF, giving approximately 17 hydroxyl groups. The R becomes 0.18, much more closed to the

NMR measurement.



1 ppm is a common unit used in 1H NMR and "C NMR spectrum. Generally, tetramethylsilane (TMS) is employed
as a reference with the peak setting at zero Hz at the right-hand edge because its proton and carbon are more
shielded than almost all organic protons and carbon. Given a experimental peak centered at a resonance frequency
(Hz) from TMS (zero Hz), the resonance frequency (Hz) is divided by the magnetic field Bo (MHz), giving a
dimensionless unit (ppm) independent of the magnetic field (Silverstein et al. 2005).

45









phased pollutants such as VOCs (Yamazaki-Nishida et al. 1995). TiO2 coated on walls, windows

and ceramic tiles can purify the polluted air in the room. Flat plate reactors are commonly used.

In these reactors, air is purified by passing through the gap between flat plates that are coated

with TiO2 (Bimie et al. 2006).

TiO2 thin films also have promise for surface disinfection, especially in hospitals and

microbial laboratories. In Kuihn (2003), TiO2 thin film was used in surface disinfection for

typical microorganisms, including Escherichia coli, Pseudomonas aeruginosa, Staphylococcus

aureus, Enterococcusfaecium and Candida albicans. After one hour exposure to UV, log

reductions in excess of 5 were achieved for E. coli and P. aeruginosa, 3.9 for S. aureus, 3.1 for E.

faecium, and 1.2 for C. albicans on TiO2 surface, exhibiting significant enhancement of

inactivation compared to uncoated TiO2 surface. Zan (2007) coated TiO2 nanoparticles on

ceramic plates for photocatalytic inactivation of Hepatitis B surface antigen (HBsAG). About

94% of HBsAG was inactivated after 4-hour exposure to UV lamps with a light intensity of

0.05mW/cm2. Four hours of exposure of the TiO2-coated plate to room daylight destroyed

87.5% of the HBsAg.

Kim et al. (2006) investigated the ability of a photocatalytic filter coated with TiO2 to

remove gas-phase contaminants and airborne microbes. Trimethylamine, ammonia,

acetaldehyde, hydrogen sulfide, methylmercaptan and formaldehyde were removed by 75% to

100% and microbes were removed by more than 99.9%.

2.6 Polyhydroxy Fullerenes (PHF)

Fullerenes (e.g., C60) and their derivatives have attracted research interest due to their

unique physical and chemical properties. Polyhydroxy fullerenes (PHF), a class of water-soluble

fullerenes, have been studied and applied in a variety of fields. PHF can be utilized in clinical

application to serve as drug carriers, bypassing the blood ocular barriers (Roberts et al. 2008). It

21









was also reported that PHF can reduce oxidative stress on cells by scavenging reactive oxygen

species (Djordjevic et al. 2004). PHF have been considered as a starting material for synthesis of

fullerene-containing polymers, as probes for investigating the surface properties of biomaterials,

as coating for solid-phase microextraction, and as cytotoxic agents (Vileno et al. 2006). Besides

a great number of medical and clinical applications, it was recently found that PHF can serve as

an excellent electron scavenger to improve TiO2 photocatalysis in aqueous media (Krishna et al.

2008).

2.7 Fungi

Fungi are eukaryotic organisms that are widely distributed around the world, with 80,000

to 120,000 species formally documented. Fungi are heterotrophic, using organic compounds as

carbon source and energy source, and grow in soils, dead matter and as symbionts of plants,

animals or other fungi. They tend to grow more easily when the environment is damp and dark.

The morphology of fungi includes microscopic and macroscopic forms. Fungi share similarities

with plants in that they have a cell wall, which is mainly comprised ofglucans and biopolymer

chitins. Most fungi produce long filaments, called hyphae. The gathering of intertwined and

interconnected hyphae forms mycelium. Fungi mycelium can be observed macroscopically,

appearing as molds on various surfaces such as walls, bathroom tiles and food (Webster and

Weber 2007).

Fungi and human have a long relationship with. Fungi are used in the food industry and

medicine. Fungal species have been used as direct sources of food (mushrooms) and in the

fermentation of products such as wine and beer. Some fungal species can be utilized to produce

antibiotics and a variety of enzymes used in medicine. However, certain fungal species pose

substantial threats to human health and economic loss. For example, fungal spores floating in the









Dichloran rose bengal chloramphenicol (DRBC) agar was utilized to enumerate fungal

colonies. Because of the low pH (5.6+0.2), this medium can prevent the fungi from

spreading. The presence of rose bengal in the medium suppresses the growth of bacteria and

restricts the size and height of colonies of the more rapidly growing molds. A mass of 31.6 g

of DRBC agar powder was suspended in 1 L of deionized water and mixed thoroughly with

heating. The solution was then autoclaved at 1200C and 16 bar for 15 minutes. Plates were

made by pouring the autoclaved agar into 100x15 mm sterile plastic Petri dishes (Fisher

Scientific) and air dried in the laminar flow hood for 24 hours. The dried agar plates were

used immediately or stored in a refrigerator at 40C.

3.2 Coatings

3.2.1 Grout Preparation

A mass ratio of 2:1 of grout powder (Mapei KeracolorTM U, Deerfield Beach, FL) to

deionized water was mixed by spatula for 5 minutes, allowed to stand unmixed for 10

minutes, and then mixed for another 2 minutes. A layer of the grout-water mixture

(approximately 0.15 g wet weight) was coated on top of each glass slide (2.5 x 1.8 cm) and

dried overnight at room temperature.

3.2.2 Photocatalytic Coating on Grout

Selected volumes of 100 mg/L PHF solution and 1111 mg/L TiO2 suspension (after

sonication, described in section 3.1.3) were mixed to obtain a total volume of 10 mL with

ratios of 0.1, 0.02, 0.01, 0.005 and 0.001 PHF/TiO2 in a 20 mL scintillation vial (Detailed

description are listed in Table 3-1). A control without PHF was also prepared. The suspension

was mixed under magnetic stir and transfer a volume of 0.3 mL suspension onto the grout

surface, gently spread using a pipette, and allowed to dry in a 500C oven (Fisher Scientific

Isotemp 500 series) for 2 hours. The preparation of A volume of 300 [L suspension was









BIOGRAPHICAL SKETCH

Wei Bai was born in Guangzhou, China. He received a bachelor degree in environmental

engineering from Jinan University in 2007. Right after graduation, he was admitted to

Department of Environmental Engineering Sciences at the University of Florida for graduate

study. He has been conducting doctoral research since 2009 under the supervisory of Dr. Ben

Koopman.









3.4.6 Exposure of Surfaces to UVA............................ ...................... 33
3.4.7 Measurement of the Size and Size Distribution of Aspergillus niger ..................34
3.5 Experim mental Procedures ..................... ...... ...... ........................ ................. 34
3.5.1 Selection of TiO2 Concentration for Surface Coating on Grout.........................34
3.5.2 Optimization ofPHF/TiO2 Nanocomposite on Grout Surface ...........................35
3.5.3 Effect of TiO2 Concentration at Optimum PHF/TiO2 Ratio............................. 35
3.5.4 Recovery of Aspergillus niger from Different Surfaces Coated upon Tiles........35
3.5.5 Dye Degradation in Aqueous Particle Suspension................... ................36
3.5.6 Photocatalytic Inactivation ofAspergillus niger............................... ............... 37
3.5.7 Evaluation of the Reusability of TiO2-PHF Nanocomposite Coating................. 38
3.6 Statistical A analysis ............................................... 38

4 RESU LTS AN D D ISCU SSION ................................................... ................................. 42

4.1 Characterization of Polyhydroxy Fullerenes................................. ................................... 42
4.1.1 Size and Size D distribution ............... .............................................................. 42
4.1.2 C hem ical C haracterization ............... ......................... .......................................... 43
4.1.2.1 X-ray photoelectron spectroscopy.......................... ........... .... 43
4.1.2.2 Nuclear Magnetic Resonance Spectroscopy...........................................44
4.2 Photocatalytic Dye Degradation on Grout Surface..................... ................... 46
4.2.1 Selection of TiO2 Concentration for Surface Coating on Grout...........................46
4.2.2 Full Spectrum Scanning of Procion Red MX-5B on Grout Surface ....................46
4.2.3 Optimization of PHF/TiO2 Nanocomposite on Grout Surface .............................46
4.2.4 Effect of TiO2 Concentration at Optimum PHF/TiO2 Ratio ..............................47
4 .2 .5 D iscu ssio n ................................... ......... ................................................. 4 8
4.3 Photocatalytic Inactivation of Fungi on Tile Surface.............................................. 50
4.3.1 Recovery of Aspergillus niger from Different Surfaces Coated on Tiles............50
4.3.2 Photocatalytic Inactivation of Aspergillus niger......................... ............... 51
4.3.3 Evaluation of the Reusability of TiO2-PHF Nanocomposite Coating.................. 52
4.3.4 Discussion .... ......... ............................... 53

5 CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH ................................ 77

L IS T O F R E F E R E N C E S ................................................................................................................... 80

B IO G R A PH IC A L SK E T C H ........................................................ ............................................... 86









2.2 Mechanism of TiO2 Photocatalysis

TiO2 contains a low-energy valence band full of electrons and a high energy conduction

band, separated by a band gap of 3.2 eV. TiO2 can be photoexcited by light with a wave length of

less than 380 nm-in the range of ultraviolet (UV). Under UV irradiation, valence band electrons

are photoexcited and migrate to the conduction band, leaving holes in the valence band.

Conduction band electrons and valence band holes migrate to the surface of TiO2, where they

can undergo redox reactions with other chemical species, or recombine, liberating heat.

Conduction band electrons can be trapped at the TiO2 surface by the primary hydrated surface

functionality of TiO2, whereas valence band holes can be trapped by surficial titanol groups

(Hoffmann et al. 1995). Some general processes and characteristic times of TiO2 photocatalysis

are given in Figure 2-1.

2.3 Methods for Preparing TiO2 Coatings

Spin coating is effective in producing flat, smooth and uniform surface films from

solutions containing a single component, single component with doped component1 or multiple

components. A solution is placed onto a solid substrate that is rapidly spinning. The solution

flows outward by centrifugal force, evenly and completely covering the substrate with a thin,

uniform liquid layer. A volatile solvent is frequently incorporated in the applied solution and

evaporates as the solution spreads, accelerating formation of a thin and uniform solid film

(Emslie et al. 1958, Meyerhofer 1978).

An advantage of spin coating is the creation of uniform films of well-controlled thickness

on a substrate. Three major factors control the thickness of the solid films: spinning velocity,




1 Doping is the inclusion of a small amount of impurity into a material in order to change its properties. Typical
dopants for TiO2 are transition metals and nonmetals such as iron, silver, carbon or silicon (Sakthivel et al. 2004).

16









formation is also supported by the results for XPS and NMR, as reported in the following

section.

4.1.2 Chemical Characterization

4.1.2.1 X-ray photoelectron spectroscopy

XPS was used to measure the elemental composition of polyhydroxy fullerenes and

characterize different chemical (oxidation) states of carbon, leading to deduction of its empirical

formula and molecular weight. Based on the XPS spectrum (Fig. 4-3), PHF batch #11 comprised

carbon, oxygen, nitrogen, silicon and sodium. Hydrogen is not detectable by XPS. Nitrogen,

silicon and sodium are impurities. Nitrogen is probably from air, silicon is detected from the

wafer substrate, and sodium is a residue from the PHF synthesis process. The percentages of

different elements as provided by the XPS spectrum are listed in Table 4-2.

High resolution was applied on the binding energy range between 283 and 291 eV, which

is the typical binding energy range for carbon. In Figure 4-4, the broad range of binding energy

of Cs carbon in the XPS spectrum indicates that highly oxidized carbon exists. In addition, a

range of 8eV binding energy rules out the possibility that only one oxidation state of carbon is

present in the sample. Assuming that the peak separation between each carbon oxidation state is

around 1.8 eV, curve fitting analysis allowed the assignment of three different oxidation states of

carbon (Husebo et al. 2004). Since the binding energy increases when carbon is oxidized, the

peak with the lowest binding energy was considered as nonoxygenated carbon. Accordingly, the

second lowest peak represents monooxygenated carbon, and the peak with highest binding

energy can be referred to as dioxygenated carbon such as carbonyl, ketal or hemiketal, which are

the most highly oxygenated forms. Chiang et al. (1993), using infrared spectroscopy, found only

hemiketal groups bound to carbon in polyhydroxy fullerenes. Thus, it is reasonable to reach a

conclusion that the hemiketal group contributes to higher binding energy carbon in the sample.

43









The positive control consisted of adding a volume of 0.2 or 0.3 mL Aspergillus niger

suspension (depending on the initial concentration usually adjusted between 200,000 and

300,000 cfu/mL) to a 50 mL polypropylene centrifuge tube containing 19.7 or 19.8 mL

PBS/SDS, followed by vortexing for 30 seconds. The procedure for plate counting was the

same as described in last paragraph.

3.4 Characterization

3.4.1 Size Measurement

Cluster size and size distribution of PHF in aqueous media was measured by Nanotrac

ULTRA (Microtrac Inc.York, PA). The fundamental principle of this instrument is dynamic

light scattering. Dynamic light scattering (DLS) is based on the principle of detecting and

correlating the intensity fluctuations of the light scattered from small particles in solution.

These intensity fluctuations are caused by the Brownian motion of the particles and are

related to particle mobility, which is a function of the size of the particles, the viscosity of the

fluid, and the temperature.

3.4.2 X-ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy (XPS) is a spectroscopic technique that can be

utilized to characterize elemental composition, empirical formula, chemical state or electron

state of element. When a material is irradiated with a beam of aluminum 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:

Ebinding = Ephoton Ekinetic 0 (3-1)

where Ebinding is the energy of the electron emitted from one electron configuration

within the atom; Ephoton is the energy of the X-ray photons being used; Ekinetic is the kinetic









plotting the log survival ratio versus time to give a linear regression, and the value of slope is

the inactivation rate coefficient.

3.5.7 Evaluation of the Reusability of TiO2-PHF Nanocomposite Coating

The reusability of TiO2-PHF nanocomposite coatings is tested based on Aspergillus

niger inactivation experiment. The methods for coating preparation and microbial inoculation

are the same as the procedures described in section 3.5.6. After exposing tiles coated with

TiO2-PHF nanocomposite for 36 hours (All of Aspergillus niger from the previous

inoculation were inactivated), Aspergillus niger suspension (with the same concentration)

was inoculated on the coatings again, and allow it to dry for 24 hours under laminar flow

hood. After that, the UVA exposure experiment was carried out again following the same

procedure as described in section 3.6.7. Data processing utilized the same fashion as

described in section 3.6.7 as well.

3.6 Statistical Analysis

Data obtained from photocatalytic dye degradation and Aspergillus niger inactivation

were analyzed by Student's t-test or One-way ANOVA (Sokal and Rohlf 1994) with Tukey-

Kramer or Dunnett's two-sided tests (Montgomery 2008) through NCSS statistical analysis

and graphics software (NCSS, Kaysville, Utah). If the comparison of treatments was no more

than two groups, student's t-test was used to analyze the data. Vice versa, ANOVA with post

tests were used instead.









4.2 Photocatalytic Dye Degradation on Grout Surface

4.2.1 Selection of TiO2 Concentration for Surface Coating on Grout

Figure 4-6 indicates that TiO2 coatings formed from suspensions of 10000 and 50000 mg/L

significantly altered the appearance of the grout surface, whereas the coating formed from a

suspension of 0.1 wt% did not change the appearance of the grout surface. Accordingly, a

suspension concentration of 0.1 wt% TiO2 was chosen for subsequent studies.

4.2.2 Full Spectrum Scanning of Procion Red MX-5B on Grout Surface

A full spectrum scan (200nm-800nm) of the absorbance of Procion red MX-5B coated on

grout was carried out to identify the adsorption peak of this dye. As shown in Fig. 4-7, there are

two adsorption peaks in the visible light spectrum centering at 512 and 538 nm, with the peak at

512 nm the higher of the two. A stronger adsorption band is present in the ultraviolet region.

However, PHF, as well as organic compounds with conjugated double bonds, also adsorb

strongly in this region. Accordingly, the absorption peak at 512 nm was selected for

measurement of Procion red MX-5B.

4.2.3 Optimization of PHF/TiO2 Nanocomposite on Grout Surface

Optimization of the PHF/TiO2 ratio of the photocatalytic nanocomposite was next carried

out. Krishna (2007) showed that the optimum PHF/TiO2 ratio for photocatalysis in aqueous

media was between 0.001-0.003. The amount of PHF (usually brown in color) present on the

surface could affect the surface's appearance. Visual observation of nanocomposites coated on

grout surfaces indicated that while the ratio of PHF to TiO2 is less than 0.05, the coating remains

translucent. A slightly lower ratio of 0.02 was chosen as a maximum for performance testing by

dye degradation. The lowest ratio tested is 0.005, as preliminary experiments indicated that a

drop-off dye degradation at lower ratios. The rate of dye degradation was quantified by UV/VIS

reflectance spectroscopy.










9 12 15 18


0.2


0


-0.2


-0.4


Time (hour)


STiO2 TiO2+PHF


Si02


Figure 4-17. Photocatalytic inactivation ofAspergillus niger on TiO2, TiO2-PHF (Batch #III), SiO2 coated tiles (24-hour UVA
exposure)

Data are analyzed with student's t-test


3 6


21 24 27












0 3 6 9 12 15 18 21 24 27
0.1





-0.1


-0.2





-0.4


-0.5


-0.6


-0.7
Time (hour)



*TiO2 TiO2+PHF



Figure 4-20. Reusability test: photocatalytic inactivation ofAspergillus niger on TiO2, TiO2-PHF (Batch #111) coated tiles (12-hour
UVA exposure)

Data are analyzed with student's t-test









Yamazaki, S.; Matsunaga, S.Hori, K. Photocatalytic Degradation of Trichloroethylene in Water
using TiO2 Pellets. Water Research. 2001, 35, 1022-1028.

Yamazaki-Nishida, S.; Cervera-March, S.; Nagano, K.; Anderson, M.Hori, K. An Experimental
and Theoretical Study of the Reaction Mechanism of the Photoassisted Catalytic Degradation
of Trichloroethylene in the Gas Phase. The Journal of Physical Chemistry. 1995, 99, 15814-
15821.

Yu, J.C.; Yu, J.Zhao, J. Enhanced Photocatalytic Activity of Mesoporous and Ordinary TiO2
Thin Films by Sulfuric Acid Treatment. Applied Catalysis B: Environmental. 2002, 36, 31-
43.

Zan, L.; Fa, W.; Peng, T.Gong, Z. Photocatalysis Effect of Nanometer TiO2 and TiO2-Coated
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Biology. 2007, 86, 165-169.
















0 wt%


0.1 w~ t%


Figure 4-6. Different concentration of TiO2 coated on grout surface


1 wt%


5 wt%















Mm: 427 Max: 78913


Nals
19%









O KLL



O s15
Sr | 27.0 %
----------------- --I-------------- ----------------- -------------------------------------- --------------- ------------------------- C -------- ----------------- -----------------





















0408%




Si 2p3
S,2s 22% INa2s 0O
----------- -- -------- ----------------------------------------------


11UU


Bii Energ e
Binding Energy (eV}


Figure 4-3. Measured XPS spectrum











0 3 6 9 12 15
0.1




T

-0.1


-0.2


S-0.3


S-0.4


-0.5


-0.6


-0.7


-0.8
Time (hour)


*TiO2 TiO2+PHF ASiO2



Figure 4-16. Photocatalytic inactivation ofAspergillus niger on TiO2, TiO2-PHF (Batch III), SiO2 coated tiles (12-hour UVAexposure)

Data are analyzed with student's t-test











0 6 12 18 24 30 36 42
0.5 .



0



-0.5



U -1



-1.5



-2



-2.5
Time (hour)



A Ti2 TiO2+PHF



Figure 4-14. Photocatalytic inactivation ofAspergillus niger on TiO2 and TiO2-PHF (#II) coated tiles

Data are analyzed with student's t-test










120%



100%



80%
0


60%



40%



20%



0% -


Stober silica


Geltech silica


Figure 4-12. Recovery of Aspergillus niger from TiO2 and silica based surfaces

One-way ANOVA and Dunnett's two sided test (a=0.05) were conducted: The recovery of Aspergillus niger from Stober silica,
Geltech silica and TiO2 rutile is not significantly different from control, while the recovery from bare tile was significantly different
from control.


Bare tile


TiO2 rutile









water, giving the final concentration of 1000 mg/L. In addition, a control without any coating

was set up for comparison. The procedure for preparing the coating on tiles was described in

section 3.2.4. After that, Inoculation and recovery ofAspergillus niger followed the

procedure described in section 3.3.2.

3.5.5 Dye Degradation in Aqueous Particle Suspension

This experiment is to test whether TiO2 rutile and silica are photocatalytically active or

not, from which it can be determined if these particles can be used as a control (not

photocatalytically active surface) for inactivation of Aspergillus niger on coated tile surfaces.

A positive control in this experiment is aqueous dye degradation without any particle, while

the negative control is aqueous dye degradation in TiO2 anatase suspension. The procedure

followed Krishina (2006): TiO2 rutile, TiO2 anatase, Geltech silica were prepared in

deionized water at the concentration of 1000 mg/L (Section 3.1.3); The concentration of 200

mg/L Procion red MX-5B was prepared (Section 3.1.4). The reagents described above were

mixed with deionized water to give a final concentration of particle suspension at 30 mg/L

and dye at 3 mg/L (Table 3-4). The mixture was poured into a 35x100 mm Petri dish and

mixed for 10 min under dark using a magnetic stirrer. Two 0.8 mL samples were collected

and pipetted into a 2 mL centrifuge tube. The UV lamps were then turned on (the distance

between sample and UV lamb was fixed at 20 cm. Samples were collected using the same

fashion every 15 min for one hour. The collected sample were sit under dark for a day to let

the particle residue settle, followed by a 20-miunte centrifuge at 20,000 rcf The volume of 1

mL supernatant was pipetted and transferred to a new 2 mL centrifuge tube, and the

centrifuge process was repeated. After that, a volume of 0.2 mL of supernatant was pipetted

and transferred to a well within a 96 coaster clear plate. A microplate reader was utilized to

measure the absorbance at the wavelength of 536 nm.









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Sun, B.; Vorontsov, A. Smirniotis, P. Role of Platinum Deposited on TiO2 in Phenol
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Szab6-Bardos, E.; Czili, H.Horvath, A. Photocatalytic Oxidation of Oxalic Acid Enhanced by
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Vinodgopal, K.; Hotchandani, S.Kamat, P. Electrochemically Assisted Photocatalysis: Titania
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University Press.

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However, in spin coating using nanoparticles, agglomeration of particles tends to occur,

negatively affecting the quality of thin films obtained. A search of the literature revealed only

one paper reporting the preparation of nanostructured TiO2 films by directly using TiO2 particles

in the spin coating process. Song et al. (2001) used commercial TiO2 particles whose surface was

modified by MoO3 and WO3 to form a transparent film. With the formation ofMoO3/TiO2 or

W03/TiO2 particles, TiO2 could be stably dispersed before use in coating a surface, greatly

reducing the chance of agglomeration. The quality of the films was reported to be as good as

those obtained by the sol-gel process.

Dip-coating, chemical vapor deposition and sputter coating have also been used to create

uniform TiO2 thin films. The dip-coating process consists of immersion, followed by drying and

sintering. A fine TiO2 suspension is prepared, followed by immersing the substrate and then

lifting it out of the suspension. The layer thickness can be controlled by the speed at which the

substrate is lifted from the suspension and by the solids content of the suspension (Arfsten et al.

1997). The coated substrate is dried and then sintered at 673K for 1 to 2 hours to ensure that the

TiO2 film is strongly attached to the substrate and is stable over a wide range of pH (Vinodgopal

etal. 1993).

Chemical vapor deposition (CVD) is another way to produce a semiconductor thin film.

A substrate is exposed to one or more vaporized compounds. A chemical reaction is initiated at

or near the substrate surface to produce the desired material that will condense on the substrate.

Use of CVD to coat TiO2 on particle surfaces is seldom reported, however. Ding (2001) applied

CVD to coat anatase TiO2 onto three different substrates. This research examined the effect of

precursor concentration, temperature and coating time on coating quality.









A series of 10-fold dilutions (10-1, 10-2, 10-3, 10-4, 10-5) was carried out in order to

identify the original concentration of spores in the stock suspension. A volume of 0.333 mL

suspension was added to a volume of 3.0 mL sterile PBS/SDS, followed by vortexing for 10

seconds. This process was repeated up to five times to obtain dilutions giving between 30 and

300 colonies on a plate. A volume of 0.1 mL of each selected dilution was placed on dry

DRBC agar at plastic Petri dish (100x15mm), and a sterile Teflon rod was used to evenly

spread the Aspergillus niger suspension. The plates were inverted and then placed in a 37C

incubator for 24 hours. Visible colonies were then counted.

3.3.2 Recovery of Aspergillus niger from Tiles

Sterile white tiles were used as substrates for photocatalytic inactivation of Aspergillus

niger. A volume of 0.2 or 0.3 mL Aspergillus niger suspension (depending on the

concentration, usually adjusted between 200,000 and 300,000 spores/mL) was pipetted onto a

coated tile and allowed to spread. After inoculation in this fashion, the tiles were allowed to

dry in darkness under a laminar flow hood for 24 hours.

Aspergillus niger was removed from the surface of tiles prior to enumeration. Tiles

were immersed in a 50 mL polypropylene centrifuge tube containing 20 mL PBS/SDS and

vortexed for 15 seconds. The centrifuge tubes were then sonicated at a power setting of 10.0,

which gave a measured power between 180-200 W (Misonix Sonicator 3000, Farmingdale,

NY) for 3 minutes. During sonication, the centrifuge tubes were immersed in a flowing water

bath at a temperature 27.8 C. After sonication, tubes were vortexed for 15 seconds and tiles

were removed from the suspension using a sterile force. Tubes were vortexed again for 15

seconds. A volume of 0.1 mL suspension from the centrifuge tube was placed on dry DRBC

agar in a plastic Petri dish (100x 15mm) in triplicate, and a sterile Teflon rod was used to

spread the suspension over the agar. The plates were inverted and then placed in a 37C

incubator for 24 hours. Visible colonies were then counted.









Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering

TITANIUM DIOXIDE-POLYHYDROXY FULLERENE NANOCOMPOSITE FOR
PHOTOCATALYTIC, ANTIMICROBIAL SURFACES

By

Wei Bai

August 2010

Chair: Ben Koopman
Major: Environmental Engineering Sciences

The deposition and growth of microbes in the built environment have adverse public

health and economic impacts. Illuminated surfaces of TiO2 have potential for photocatalytic

destruction of the most resistant microbes. However, TiO2 alone is effective only with opaque

and heavy coatings that obscure the appearance underlying the material.

A translucent, antimicrobial photocatalytic coating was developed using polyhydroxy

fullerene (PHF) as an enhancer for TiO2 photocatalysis on surfaces. TiO2-PHF nanocomposite

was coated on grout and tiles surface. Photocatalytic activity was optimized by varying the ratio

of PHF to TiO2, as indicated by decolorization of a red organic dye (Procion MX-5B). TiO2-PHF

nanocomposite manifested 2 times enhancement in terms of dye degradation at the optimal ratio

of PHF to TiO2 between 0.01 and 0.02. The optimized TiO2-PHF nanocomposite coatings were

then used for inactivation ofAspergillus niger. TiO2-PHF nanocomposite coatings exhibit almost

3 times enhancement of within 3-hour exposure to UVA.









instability of the PHF cage structure because it can be converted to ketone group, the presence of

which creates an open structure of fullerene cage. This uncertainty should be addressed in the

synthesis procedures. The ratio of hemiketal group to hydroxyl group should be controlled by

varying the factors, such as NaOH concentration, mixing time and the concentration of

surfactants. In addition, the purification process of PHF after synthesis should also be optimized.

Secondly, the aging of PHF can impair the enhancement effect induced by PHF. As

mentioned in the result section, batch #II PHF can enhance photocatalytic dye degradation, but

failing to improve microbial inactivation after 8 months. The XPS spectrum indicated that the

number of hydroxyl and hemiketal groups has changed after 8-month storage.

Thirdly, the performance of TiO2-PHF nanocomposite decreases as longer exposure to

UVA. As mentioned in the result section, Batch #III PHF can significantly enhance TiO2

photocatalysis within 12 hours. However, when coming to 24 hours, there is no significant

difference between TiO2-PHF nanocomposite coatings and TiO2 coatings in terms of

%inactivation at 24 hours. This phenomenon may come from the fact that UVA may degrade

PHF gradually. PHF degradation under UVA or sunlight exposure is also observed in parallel

studies (Kong et al. 2009, Hwang and Li 2010). Because of this, the TiO2-PHF coating did not

enhance photocatalytic efficiency as well in the reusability test. To overcome this limitation,

modification of the coating methods or making the PHF much more UVA resistance should be

considered.

For real life application, the stability TiO2-PHF nanocomposite on tile-grout system is of

great importance. The preliminary result indicated that TiO2 coating can stick to the tile surface

very well. PHF is water soluble, so hypothetically it can be easily washed off. However, it is

very difficult to quantify the amount of PHF being washed off because the total amount of PHF









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Bimie, M.; Riffat, S.Gillott, M. Photocatalytic Reactors: Design for Effective Air Purification.
International Journal ofLow Carbon Technologies. 2006, 1, 47-58.

Block, S.S. 2001, Disinfection, Sterilization and Preservation, 5th edn, Philadelphia, PA:
Lippincott Williams & Wilkins.

Chauhan, N.; Latge, J.Calderone, R. Singalling and Oxidant Adaptation in Candida Albicans and
Aspergillus Fumigatus. Nature Reviews Microbiology. 2006, 4, 435-444.

Chiang, L.Y.; Upasani, R.B.; Swirczewski, J.W.Soled, S. Evidence of Hemiketals Incorporated
in the Structure of Fullerols Derived from Aqueous Acid Chemistry. Journal of the American
ChemicalSociety. 1993, 115, 5453-5457.

Cho, M.; Chung, H.; Choi, W.Yoon, J. Different Inactivation Behaviors of MS-2 Phage Nad
Escherichia Coli in TiO2 Photocatalytic Disinfection. Applied and Environmental
Microbiology. 2005, 71, 270-275.













0.1





0





-0.1
o




-0.2





-0.3





-0.4


* TiO2 anatase


Figure 4-13. Aqueous dye degradation in silica, TiO2 rutile and anatase suspension

Data are analyzed with student's t-test


Time (minutes)

* Control U Geltech Si02 ATi2 rutile









initial solution concentration and viscosity. Generally, the influence of these factors on film

thickness can be expressed as (Kontturi et al. 2007)

h oc co Y2 q co (2-1)

where hoo represents the thickness of the film; co is referred to as spinning velocity; f is

viscosity and cO denotes the initial solution concentration.

The sol-gel process has been utilized with spin coating. Sol-gel is a process to fabricate

metal oxide from colloidal particles (sol), which are produced by the chemical reaction of metal

alkoxides and metal chlorides in solution. When sol converts to a liquid phase (gel), metal oxide

is formed, connecting the metal center with M-O-M or M-OH-M bridges with the formation of

metal oxide or metal hydroxide. The remaining liquid is removed by drying (Hench and West

1990).

Makishima (2004) prepared a TiO2-CeO2 film on glass slides by the spin-coating process

using sol-gel solution. A fine texture and pattern film at the nano scale were obtained. Que

(2006) tested the anatase TiO2 sol-gel spin coating process under different ethanol molar content

and temperatures. He concluded that a heat treatment temperature of 500 C and a solution with

50M ethanol content are necessary to achieve good quality crystalline anatase TiO2 thin films.

Sayikan (2007) made thin films of TiO2 doped with Sn4+ by sol-gel spin coating using

hydrothermal process at lower temperatures, in which the crystallite size of TiO2 is less than 10

nm. Comparison of TiO2 doped with Sn4+ with undoped TiO2 indicated that introduction of

Sn4+ decreased particle size and yielded a more spherical particle shape.

Disadvantages of the sol-gel spin coating process for TiO2 thin films are high cost, high

temperature requirements, and technical difficulty of preparing films over large areas (Song et al.

2001). Substituting a nano TiO2 suspension for sol-gel could substantially decrease costs.









4-17 Photocatalytic inactivation of Aspergillus niger on TiO2, TiO2-PHF (Batch #III),
SiO 2 coated tiles (24-hour U V A exposure) .......................................... ......................... 73

4-18 Reusability test: photocatalytic inactivation of Aspergillus niger on tile coated with
T iO 2, T iO 2+ PH F (B atch #111) .......................................... ............................................... 74

4-19 Reusability test: photocatalytic inactivation of Aspergillus niger on TiO2, TiO2-PHF
(Batch #111) coated tiles (12-hour UVA exposure) ............................................... 75

4-20 Reusability test: photocatalytic inactivation of Aspergillus niger on TiO2, TiO2-PHF
(Batch #111) coated tiles (12-hour UVA exposure) ............... ............. ...................... 76









3.5.2 Optimization of PHF/TiO2 Nanocomposite on Grout Surface

The preparation of TiO2-PHF and TiO2 coatings was described in section 3.2.2. After

the coatings were dry, dye Procion red MX-5B was applied upon the coating following the

procedure described in section 3.2.4. Different PHF/TiO2 at 0.02, 0.01 and 0.05 were

prepared. The preparations of TiO2-PHF and TiO2 coatings were the same as the procedure

described in section 3.5.2a. UV/Vis spectroscopy was utilized to measure the dye degradation

and the detailed measurement and calculation of dye degradation was mentioned in section

3.4.5.

3.5.3 Effect of TiO2 Concentration at Optimum PHF/TiO2 Ratio

A mass of 5 g of grout powders were weighted and placed in 25 mL glass beakers,

followed by adding 2.5 mL of different concentration of TiO2-PHF suspension (in deionized

water, PHF/TiO2=0.01), giving the final concentration of TiO2 at 1000, 10000 and 50000

mg/L7, respectively. In addition, a control without PHF was also set up using the same

procedure. The preparations of grout-TiO2-PHF and grout-TiO2 were specified in Table 3-2

and 3-3, respectively. After that, grout slurry containing TiO2 and PHF was further mixed and

coated on glass slides following the procedure described in section 3.2.2. After the coatings

were dry, dye Procion red MX-5B was applied upon the coating following the procedure

described in section 3.2.4. UV/Vis spectroscopy was utilized to measure the dye degradation

and the detailed measurement and calculation of dye degradation was mentioned in section

3.4.5.

3.5.4 Recovery ofAspergillus niger from Different Surfaces Coated upon Tiles

Recovery of Aspergillus niger from different surfaces was carried out, including TiO2

anatase, TiO2 anatase-PHF, TiO2 rutile and SiO2 (3 different types), which were coated upon

the front side of tiles. All the particles listed above were weighted and suspended in deionized


SThey can be also reported as 0.1 wt%, 1 wt% and 5 wt% respectively

35









The synthesized PHF (#II) was also used for the TiO2-PHF nanocomposite optimization by

using UV/VIS reflectance to measure dye degradation. Figure 4-8 indicates that, after 6 hours,

the optimum ratio of PHF to TiO2 for photocatalytic performance is present at 0.01 and 0.02, and

dye degradation (47% and 48%) is almost two times faster than TiO2 alone (25%). The result

was confirmed from One-Way ANOVA and Tukey-Kramer test (a=0.05) that it is significantly

different between the optimum ratio and TiO2 alone. The result after 12-hour UVA exposure

indicated that the overall photocatalytic reaction became slower, but the ratio at 0.01(61% dye

degradation) still manifests the optimum performance, which is by a factor of 1.2 times

enhancement under statistical test confirmation. At the measurement of 24 hours, the

photocatalytic enhancement (73-74%) reduced much closed to TiO2 alone (66%). Ratio at 0.02

still showed 1.1 times enhancement compared to TiO2 alone. To sum up, both measurement

techniques optical microscope and UV/VIS reflectance spectroscopy consistently reflected the

optimal ratio of PHF to TiO2 is near 0.01-0.02.

4.2.4 Effect of TiO2 Concentration at Optimum PHF/TiO2 Ratio

The performance of dye degradation for optimum TiO2-PHF nanocomposite was also

compared to higher concentration TiO2 coating prepared from 10000 and 50000 mg/L

suspension, as measured by UV/VIS reflectance spectroscopy. In Figure 4-9, as the

concentration of TiO2 coating decreased from 50000 mg/L to 1000 mg/L, dye degradation

diminished as expected, from 47% to 30.8%. However, the optimum TiO2-PHF nanocomposite

exhibited approximately 2 times enhancement (61.6%) of dye degradation compared to TiO2

(1000 mg/L) alone, and its photocatalytic reaction rate was even faster than 50000 mg/L TiO2

coating. However, this enhancement induced by PHF was not observed at 10000 mg/L and

50000 mg/L TiO2-PHF even though they were under the same ratio of PHF to TiO2. In the case

of 10000 mg/L TiO2-PHF nanocomposite, it did not show any enhancement in dye degradation

47









photocatalytic activity. Secondly, some of the PHF possibly attached to the grout or tile surface,

also resulting in less amount of PHF available for TiO2. Thirdly, the difference between aqueous

and "dry" system may also contribute to the shift of optimal ratio. Aqueous TiO2 photocatalysis

is more sensitive to shading effect because UVA needs to travel through a large amount of water

molecules to reach suspended TiO2 particles, and TiO2 particle itself can also block UVA from

reaching particles underneath. In addition, high concentration of PHF can also induce shading

effect, so less amount of PHF in water is allowed in order to outcompete the shading effect.

However, in "dry" system (humidity was controlled at between 80-85%), water molecule is

much less, and TiO2 is arranged horizontally as thin film on surfaces. Therefore the amount of

PHF can increase to a certain point that still outcompetes the shading effect.

Many studies have been conducted on the enhancement of TiO2 thin film photocatalysis,

and metals, such as silver, gold and other transition metals, were frequently applied as dopants to

enhance TiO2 photocatalysis (Song et al. 2001, Arabatzis et al. 2003a, Arabatzis et al. 2003b,

Herrmann et al. 1997, Arpac et al. 2007, Somekawa et al. 2008). Comparison between TiO2

photocatalytic enhancements on surface films was made and listed in Table 4-5. Table 4-5

showed that TiO2 films were used to expose to aqueous dye in all studies, and no similar studies

used TiO2 films that were exposed to air, so this may be the first study utilizing photocatalytic-

enhanced surface upon which dye was deposited. In aqueous media while water is readily

available, hydroxyl radicals are produced faster than in air. Accordingly, the duration of UVA

exposure in parallel studies is shorter than this study.

Sol-gel processes for manufacturing TiO2 films was applied in all the studies listed except

TiO2-PHF nanocomposite in this study, which is self-assembly. The photocatalytic activity

manifests 1.1-3 times enhancement depending on different dopants. The best enhancement (3 x)









Table 4-1. Mean particle size of PHF batch #11 at different concentrations
Concentration Mean volume size Mean number size Mean surface area size
(mg/L) (nm) (nm) (nm)
1 3.39 3.31 3.36

10 3.40 3.32 3.37
100 3.33 3.25 3.51

1000 3.38 3.31 3.36


Table 4-2. Elemental composition of PHF batch #II, as determined by XPS
Element %

C 68.40
O 27.00

Na 1.90

Si 2.20
N 0.60



Table 4-3. Carbon bonding states within PHF batch #11
Carbon Area of peak % Carbon

Nonoxygenated carbon (C) 19941.43 61.37

Monooxygenated carbon (C-OH) 10944.09 33.68
Dioxygenated carbon (RO-C-OH) 1607.39 4.95




Table 4-4. Functional groups of PHF batch #11
Functional groups Numbers

OH 20

RO-C-OH 3

Na 2









the experiment conducted in section 4.3.2. In addition, there is no significant difference between

TiO2-PHF and TiO2 in terms of inactivation rate coefficient (as confirmed by student's t-test,

a=0.05)

4.3.4 Discussion

This unexpected result of PHF batch II, which is unable to enhance the photocatalytic

inactivation, is probably due to several reasons: the first reason might be the aging of synthesized

PHF, as reported previously by Krishna (2006). The aging of PHF may cause instability of the

molecular structure of PHF, so PHF losses its electron scavenger ability. The interval between

the dye degradation experiment and the microbial inactivation study is approximately 8 months,

during which the molecular structure of PHF may change. Compared with the molecular

structure deduced from XPS spectrum, the first measurement of PHF batch #11 indicated that

there are 17 hydroxy groups and 3 hemiketal groups attached to the fullerene cage, while the

second measurement (after 8 months) showed that the number of hydroxyl group and hemiketal

group are 12 and 9, respectively. The change of molecular structure possibly change the ability

of PHF to scavenge electrons.

For PHF batch #III, it showed significant enhancement ofphotocatalytic inactivation.

However, the enhancement diminishes as extended exposure time to UVA. Although PHF can

act as an electron scavenger, enhancing the photocatalytic performance of TiO2 at the beginning,

PHF itself may also undergo photochemical transformation under UVA, resulting in the

decreasing inactivation rate. Similar trend was also observed in dye degradation study. In

addition, there are two studies indicating that PHF can be mineralized under UVA or sunlight

exposure (Kong et al. 2009, Hwang and Li 2010).

The reusability study indicated that the photocatalytic performance of either coatings

decreases. This may be due to the fact that the debris of Aspergillus niger from previous

53









pipetted onto the grout surface, gently spread using a pipette, and allowed to dry in a 50C

oven (Fisher Scientific Isotemp 500 series) for 2 hours.

3.2.3 Dye Coating on Grout

A volume of 100 IL dye solution (100 mg/L) was pipetted onto coated or bare grout

and gently spread using a pipette. The dye was allowed to dry in a 500C oven for 2 hours.

3.2.4 Photocatalytic Coatings on Tiles

Ceramic tiles were examined as substrates for Aspergillus niger inactivation. The tile

dimensions were 2.5 cmx2.5 cmx0.5 cm. Tiles were white with a smooth but not glossy

finish on both front and back. Adhesive was present at the back side. The front side was used

as the solid substrate upon which photocatalytic coatings were deposited. Tiles were initially

immersed in a full strength Clorox solution (Clorox Company) overnight to remove adsorbed

organic compounds and then were rinsed thoroughly with deionized water, followed by 30-

minute sonication to remove any particle coatings on the surface. Finally, tiles were

autoclaved at 1200C and 16 bar for 15 minutes. The tiles were reused throughout the

Aspergillus niger inactivation experiment, and prepared every time with the same cleaning

procedures described above. The preparations of two different coatings (TiO2-PHF and TiO2)

were the same as the procedures for coating preparations on grout. Uncoated tiles (i.e., with

no photocatalyst) were used as negative controls. A volume of 0.4 mL of TiO2-PHF or TiO2

suspension was deposited over the tile surface and allowed to dry under a laminar flow hood.

3.3 Microbes

3.3.1 Culturing and Enumeration of Aspergillus niger

Asperigillus niger spores were obtained by inoculating potato dextrose agar with one

loop of stock culture and incubating at 37 C. After 7 days of incubation, mycelia and spores

covered the agar surface. Fungal spores were scraped from the mycelia and suspended in

sterile deionized water.









in this plastic bin. The UV/VIS reflectance was measured after 0, 3, 6, 12 and 24 hours of

exposure.

3.4.7 Measurement of the Size and Size Distribution of Aspergillus niger

During the experiment of recovering Aspergillus niger from surface, the size and size

distribution of Aspergillus niger was measured by Coulter LS13320, which is a technique

based on laser diffraction. The Coulter LS230 measures particle sizes from 40 nm to 2,000

[lm by laser diffraction. It is based on the principle that particles scatter and diffract light at

certain angles based on their size, shape, and optical properties. A 750 nm diode laser is used

for analysis in the size range from 400 nm to 2 mm. The beam passes through filters as well

as projection and Fourier lenses and is spatially recorded onto 126 photodiode detectors. The

particle size, shape, and optical properties of the particles control the spatial variation of the

diffracted beam. The calculations assume the scattering pattern is due to single scattering

events by spherical particles (Particle Engineering Research Center 2009). Following the

procedure described in section 3.3.4, a volume of 19 mL of Aspergillus niger suspension was

pipetted to the sampler of Coulter LS13320. Suspension was circulated into the detector of

this machine by a pump, which is set at a medium speed. Each sample was read 3 times by

the detector, and each reading time is 1 minute.

3.5 Experimental Procedures

3.5.1 Selection of TiO2 Concentration for Surface Coating on Grout

Different concentrations of TiO2 coating were prepared on grout to identify the TiO2

concentration which does not significantly change the surface appearance of grout. TiO2

suspensions at concentrations of 1000 mg/L, 10000 mg/L and 50000 mg/L were prepared,

followed by coating a volume of 0.3 mL of the TiO2 suspensions on grout surfaces, as

described previously. The difference of surface coating was compared through images taken

by a digital camera.









Scientific Isotemp 500 series). PHF-D20 solution was pipetted into a clean, dry NMR tube to

fill up 1/3 capacity of the tube, and then sealed with a polyethylene cap. 1H NMR spectra was

measured with a Varian VXR 300 spectrometer at a frequency of 300MHz.

3.4.4 Light Absorption by Surface Dye

Light adsorption by Procion red MX-5B on grout surface was measured using Perkin-

Elmer Lambda 800 with PELA-1000 Reflectance Spectroscopy Accessory) at wavelengths of

512 nm, at which adsorption of MX-5B Procion Red dye is greatest. The detector of this

instrument responds to reflective light from the surface and electronically converts this

information to absorbance.

The PELA-1000 is an external integrating sphere diffuse reflectance accessory

connecting to Perkin-Elmer Lambda 800. The PELA accessory, mainly composed of an

optics chamber and an integrating sphere, is designed to measure the reflectance or

transmittance of solids, powders, or other small objects. The theory of reflectance

measurement is based on the Kirchoff equation:

a(A) + T(1) +p(1) = 1 (3-2)

where a(k) = fraction adsorption at wavelength X, Tz() = fraction transmittance and p(X) =

fraction reflectance.


During the reflectance measurement, the reflectance and scattered radiation are

collected in the integrating sphere. The reflectance measured from the integrating sphere is

much more accurately described as reflectance factor (in unit %R), which is a term referring

to reflectance of a surface relative to that of a perfect diffuser. In the measurement of MX-5B

Procion Red dye on grout surface, a thick coating of TiO2 on a glass slide was utilized as a

reference for baseline correction. TiO2 with a high concentration of coatings exhibit

extremely white color on surface, which can be utilized as reference for 100% reflectance.









Table 3-2. Reagent volumes of grout, TiO2 and PHF mixture
Description


TiO2 concentration mg/L



1000
10000
50000


Table 3-3. Reagent volumes of grout, TiO2 mixture
Description


TiO2 concentration mg/L


Grout (g)



5


2.5 mL of given
concentration of
TiO2-PHF
suspension
(PHF/TiO2=0.01)

0.3


Mixture


Grout (g)


2.5 mL of given
concentration of TiO2
suspension


1000 5 0.3
10000 5 3
50000 5 15



Table 3-4. Reagent volume of particle suspension and Procion red MX-5B
Volume of Volume of Volume of
Total Volume
particle Procion red deionized water
/mL
suspension /mL MX-5B /mL /mL

Positive control
(W/O particle)

TiO2 futile
0.9 28.65
(1000 mg/L)

Geltech silica 0.45 30
0.9 28.65
(1000 mg/L)

Negative control
(TiO2 anatase 0.9 28.65
1000 mg/L)


Mixture









3.5.6 Photocatalytic Inactivation of Aspergillus niger

After knowing the optimum ratio of PHF to TiO2 (0.01), the nanocomposite was used

to evaluate the photocatalytic inactivation of Aspergillus niger. The PHF used in the

inactivation experiment are batch II PHF and commercial PHF (BuckyUSA, Houston, TX).

The preparation of TiO2-PHF nanocomposite on tile surface follows the procedure described

in section 3.2.4. Tiles coated with SiO2 suspension were also prepared as a photocatalytically

inactive control.

A volume of 0.2 mL ofAspergillus niger suspension (2-3 x 105 spores/mL) was

inoculated on the coated tile surface. Thus the initial concentrations ofAspergillus niger on

each tile surface ranges from 6400 to 9600 spores/cm2. Tiles were dried in dark under a

laminar flow hood for 24 hours. After that, the photocatalytic inactivation experiment was

carried out at the same system as dye degradation experiment, which is described in section

3.4.7. Every two tiles were collected in 0, 3, 6, 12, 24 hours, respectively. The remaining

spores on each collected tile were recovered following the procedure in section 3.3.2. The

enumeration procedures of the recovered spores were carried out following the procedure in

section 3.3.1.

For data processing, the calculation of %inactivation at given times is according to the

equation described above.

%Inactivation = t-c0 x 100% (3-5)
Co

where Ct is the number of colonies after exposing to UVA at a given time; Co is the

number of colonies before exposing to UVA.

The survival ratio of Aspergillus niger was calculated as the ratio of the number of

viable spores of Aspergillus niger after exposing to UVA at a given time to the number of

viable spores before exposing to UVA. The inactivation rate coefficient was calculated by









CHAPTER 2
LITERATURE REVIEW

2.1 TiO2 Photocatalysis

The semiconductor, TiO2, is an excellent photocatalyst due to its wide availability,

biocompatibility and high chemical stability. The photocatalytic splitting of water on TiO2

electrodes was first demonstrated by Fujishima and Honda (1972). Extensive studies have been

conducted to improve our understanding of the mechanisms and principles of photocatalysis as

well as to enhance TiO2 photocatalytic efficiency. TiO2 photocatalysis has been applied for

oxidizing persistent organic pollutants and inactivating microorganisms. Principal applications of

TiO2 photocatalysis are water and air purification, sterilization and cancer therapy (Fujishima et

al. 2000).

TiO2 particles can be applied for environmental control in two ways: suspending TiO2

particles in water or air and immobilizing TiO2 or TiO2 particles on surfaces exposed to water or

air. Many studies have been carried out using suspended TiO2 particles to oxidize organic

contaminant in aqueous systems or air (Yamazaki et al. 2001, Alberici and Jardim 1997). This

method requires energy to maintain TiO2 particles in suspension and separation of photocatalyst

from suspension prior to discharge of treated effluent. TiO2 immobilization as a thin, surface film

can overcome these limitations. Interest in nanocrystalline TiO2 porous film has been growing in

recent years, as the nanoporous structure of these films yield higher photocatalytic activities

because of high surface area (Yu et al. 2002, Fretwell and Douglas 2001). Wang et al. (1997)

proposed light-induced amphiphilic surfaces (TiO2 polycrystalline films) that, upon UV

irradiation, form hydrophilic and oleophilic microstructures that have antifogging and self-

cleaning properties.









CHAPTER 5
CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH

This study demonstrated the ability ofPHF acting as an enhancer for TiO2 photocatalysis

on surfaces. Based on the procion red MX-5B dye degradation experiments, TiO2-PHF

nanocomposite coatings manifested significant enhancement (2 times faster) of dye degradation

compared to TiO2 coatings. It was also found that the enhancement of dye degradation is

strongly dependent on the ratio of PHF to TiO2. There are ratios from 0.01-0.02 at which the

optimal photocatalytic performance can be achieved.

Bacterial and fungal spores are resistant to traditional disinfection techniques, such as

heating and mild chemical treatment. TiO2 photocatalysis is able to completely mineralize

bacterial and fungal spores and it has been reported to be safe and used as commercial products

as coating for years. However, high efficiency photocatalysis usually requires thick TiO2 coating,

which is not cost-effective and also obscures the appearance of surface upon which TiO2

particles are deposited on. Hence, the findings of this research using PHF to enhance TiO2

photocatalysis (in low concentration) show potential applications for microbial destruction on

surfaces. A prototype based on tile-grout system for Aspergillus niger inactivation has been

developed and tested. TiO2-PHF nanocomposite coatings also showed significant enhancement

compared to TiO2 coatings within 12-hour exposure to UVA.

However, there are some potential limitations that may not be resolved in this study,

preventing the applications of TiO2-PHF nanocomposite, and it need further research to resolve

these issues.

Firstly, it is not clear that how the molecular structure of PHF correlates to the electron

scavenger ability, which may associate with the stability of PHF structure. Xing' s (2004) study

indicated that hemiketal group is the impurity group of PHF, and this functional group can cause
















Differential Number (Average)
PHF $av


0 375 pm to 2000 pm
Number 100%
Mean 940 pm
Median 4782 pm
SD 4 547 pm
din 3460 pm
dJ 9 504 pm




















2 4 6 8 10 2C 40 60 100 200 400 600 1000 2000
Particle Diameter (pm)


04 0B 1


Differential Number (Average)
Nonecatalysts $av


E 375 pm to 2000 pm
Number 100%
Mean 4 623 pm
Median 3 886 pm
SD 3 368 pm
din 2 204 pm
ds 7 547 pm




















2 4 6 b 10 20 40 60 100 200 400 600 1000 2000
Particle Diameter (pmr)


Figure 4-11. Particle size of Aspergillus niger, as measured by lazer diffraction (Coulter LS13320)


04 06 1




































2010 Wei Bai









energy of the emitted electron as measured by the instrument and D is the work function of

the spectrometer.

A wafer was utilized as substrate for X-ray Photoelectron Spectroscopy (XPS). XPS

Analysis was performed with an XPS/ESCAPerkin-Elmer PHI 5100ESCA system, followed

by curve fitting for C s spectrum with Grams 7.01 software (Thermo Fisher Scientific,

Waltham, MA). Compared to other electron configuration spectrum of carbon (C2s, C2p), the

C1s spectrum exhibits the highest resolution, which facilitates subsequent analysis.

3.4.3 Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) is a technique that takes advantage of magnetic

properties of certain nuclei, such as 1H or 13C, to identify the structure of organic molecules.

The NMR experiment includes placing a sample in a strong magnetic field (Bo) to distinguish

the nuclei according to the quantum number Iz, followed by applying a second magnetic field

(B1) at the frequency (resonance frequency) corresponding to the energy difference between

spin states of this nuclei. The energy difference is dependent on the gyromagnetic ratio (a

constant of a given nuclei) and the magnetic field Bo. Due to the electron cloud surrounding

nuclei, which can induce shielding6 or deshielding effects, the nuclei in different positions

within a molecule may not correspond to the exact magnetic field (Bo), leading to variation of

resonance frequency. This phenomenon is termed as chemical shift, which can be exploited

to identify the chemical structural of organic molecules (Lambert 1987).

The natural abundance of 1H isotope is 99.985%, which can create high sensitivity and

result in fast detection during an 1H NMR experiment. Thus 1H NMR is readily used in

chemical characterization of organic molecules. PHF was dissolved in 98% D20 in a 20 mL

scintillation vial to obtain a concentration of 200 mg/L. The NMR tubes were triple rinsed

with deionized water and acetone, and left to completely dry in a 50 C oven (Fisher


6 Shielding, is a measure of the ability of the electrons to alter the magnetic field (Bo) (Lambert 1987)

31









valence band holes that react with H20 to form hydroxyl radicals. Arabatzis (2003b) used Ag+ as

dopant in TiO2 thin film to degrade methyl orange. This modification of TiO2 thin films

enhanced the rate of photocatalysis about three times relative to the rate achieved without Ag+

dopant.

Extension of TiO2 photocatalytic activity to the visible light range is another active

research area. Visible light photocatalysis can be achieved by doping TiO2 with various elements

such as C, N, F, P and S to create a band gap in TiO2 that absorbs visible light. Nitrogen doping

is recognized as the most effective method, because it can effectively narrow the band gap of

TiO2 by substituting the 2p state ofN for the 2p state of O, resulting in bonding states below the

O 2p valence band (Asahi et al. 2001).

Carbon nanotubes and fullerenes have recently been evaluated for enhancing TiO2

photocatalysis. Lee et al. (2005) coated multi-wall carbon nanotubes (MWNTs) with TiO2. The

authors hypothesized that MWNTs can trap photoexcited electrons due to their unique electronic

properties and large specific surface area. TiO2-coated MWNTs inactivated bacterial spores at

twice the rate of TiO2 alone. Krishna et al. (2006, 2008) utilized polyhydroxyl fullerenes mixed

with TiO2 in aqueous solution to enhance photocatalytic rates. Electron paramagnetic resonance

spectroscopy was used to detect the generation of hydroxyl radicals (Krishna et al. 2008). Results

indicated that the concentration of hydroxyl radicals was increased by 20% to 60% through use

of a nanocomposite of TiO2 and PHF in comparison to TiO2 alone. Dye degradation and E. coli

inactivation experiments also indicated higher rates of photocatalysis with the TiO2-PHF

nanocomposite as compared to TiO2 alone.

2.5 Application of TiO2 Thin Films for Environmental Control

TiO2 has been extensively investigated for the photocatalytic purification of water and

wastewater. TiO2 photocatalytic thin films have also shown promise for elimination of gas-

20



































To my family











100%

90%

80%

70%

S60%

S50%

40%

30% I

20%

10%

0%
3 6 12 24
Time (hour)

DTiO2 TiO2+PHF W SiO2


Figure 4-15. Photocatalytic inactivation ofAspergillus niger on tile coated with TiO2, TiO2+PHF (Batch #111) and SiO2

One-Way ANOVA and Tukey-Kramer test at 3, 6, 12 and 24 hours were conducted at a=0.05 to validate the experimental
result, respectively.









LIST OF TABLES

Table page

3-1 Reagent volumes for TiO2/PHF mixtures I ........................................................... 39

3-2 Reagent volumes of grout, TiO2 and PHF mixture.........................................40

3-3 R agent volum es of grout, TiO 2 m ixture ........ ....... ........ ..............................................40

3-4 Reagent volume of particle suspension and Procion red MX-5B ........... ...............40

4-1 Mean particle size of PHF batch #11 at different concentrations................................... 55

4-2 Elemental composition of PHF batch #II, as determined by XPS ................................. 55

4-3 Carbon bonding states w within PH F batch #11 ....................................................................... 55

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4-5 Comparison of photocatalytic activity between different enhancer................................ 56









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Full Text

PAGE 5

Aspergillus niger Aspergillus niger Aspergillus niger

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Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger

PAGE 8

Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger

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Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger

PAGE 10

Aspergillus niger

PAGE 12

E.coli

PAGE 13

Aspergillus niger Aspergillus niger Aspergillus niger

PAGE 15

2.1 TiO2 Photocatalysis

PAGE 16

2.2 Mechanism of TiO2 Photocatalysis 2.3 Methods for Preparing TiO2 Coatings

PAGE 17

c h

PAGE 19

2.4 Enhancement of TiO2 Photocatalysis

PAGE 20

E. coli 2.5 Application of TiO2 Thin Films for Environmental Control

PAGE 21

Escherichia coli Pseudomonas aeruginosa Staphylococcus aureus Enterococcus faecium Candida albicans 2.6 Polyhydroxy Fullerenes (PHF)

PAGE 22

2.7 Fungi

PAGE 23

Aspergillus niger

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3.1 Chemicals, Reagents and Biological Culture Media 3.1.1 Phosphate -Buffered Saline 3.1.2 Polyhydroxy Fullerenes ( PHF)

PAGE 26

3.1.3 Titanium Dioxide (TiO2) Suspension 3.1.4 Procion Red MX -5B 3.1.5 Culture Media for Aspergillus niger Aspergillus niger

PAGE 27

3.2 Coatings 3.2.1 Grout Preparation 3.2.2 Photocatalytic Coating on Grout

PAGE 28

3.2.3 Dye Coating o n Grout 3.2.4 Photoca talytic Coatings o n Tiles Aspergillus niger Aspergillus niger 3.3 Microbes 3.3.1 Culturing a nd Enumeration of Aspergillus niger Asperigillus niger

PAGE 29

Aspergillus niger 3.3.2 Recovery of Aspergillus niger from Tiles Aspergillus niger Aspergillus niger Aspergillus niger

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Aspergillus niger 3.4 Characterization 3.4.1 S ize Measurement 3.4.2 X-r ay Photoelectron Spectrosco py = 5\5\ 5X5X5X5X 5X5X5X5X

PAGE 31

3.4.3 Nuclear Magnetic Resonance

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3.4.4 Light Absorption b y Surface Dye ( ) + ( ) + ( ) =1

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3.4.5 Measurement o f Destruction of the Dye ( Proc ion Red MX -5B ) o n Grout A= log1 Percentage reflectance % Dye degradation =(A0 A( background ) (At A( background )) A0 A( background ) 100% 3.4.6 Exposure o f Surfaces to UVA

PAGE 34

3.4.7 Measurement of the Size and Size Distribution of Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger 3.5 Experimental Procedures 3.5.1 Selection o f Ti O2 Concentration for Surface Coating o n Grout

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3.5.2 Optimization of PHF/TiO2 Nanocomposite o n Grout Surface 3.5.3 Effect o f Ti O2 Concentration a t Optimum PHF/TiO2 Ratio 3.5.4 Recovery of Aspergillus niger from Different Surfaces Coated u pon Tiles Aspergillus niger

PAGE 36

Aspergillus niger 3.5.5 Dye Degradation i n Aqueous Particle Suspension Aspergillus niger

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3.5.6 Photocatalytic Inactivation of Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger % 5<5< 5<5<5<5<5<5< 5<5<5<5<5<5<5<5< = 5a5a 00 100 % Aspergillus niger Aspergillus niger

PAGE 38

3.5.7 Evaluation of t he Reusability of TiO2-PHF Nanocomposite Coating Aspergillus niger Aspergillus niger Aspergillus niger 3.6 Statistical A nalysis Aspergillus niger

PAGE 41

a b c

PAGE 42

4.1 Characterization of Polyhydroxy Fullerenes 4.1.1 Size a nd Size Distribution

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4.1.2 Chemical Characterization 4.1.2.1 X -ray photoelectron spectroscopy

PAGE 44

4.1.2.2 Nuclear Magnetic Resonance Spectroscopy

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4.2 Photocatalytic Dye Degradation o n Grout Surface 4.2.1 Selection o f Ti O2 Concentration for Surface Coating o n Grout 4.2.2 Full Spectrum Scanning of Procion Red MX -5B o n Grout Surface 4.2.3 Optimization of PHF/TiO2 Nanocomposite o n Grout Surface

PAGE 47

4.2.4 Effect of TiO2 Concentration a t Optimum PHF/TiO2 Ratio

PAGE 48

4.2.5 Discussion

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4.3 Photocatalytic Inactivation o f Fungi o n Tile Surface 4.3.1 Recovery of Aspergillus n iger from Different Surfaces Coated o n Tiles Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergi llus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger

PAGE 51

Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger 4.3.2 Photocatalytic Inactivation of Aspergillus niger Aspergillus niger Aspergillus niger

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Aspergillus niger Aspergillus niger Aspergillus niger Aspergillus niger 4.3.3 Evaluation of t he Reusability o f Ti O2-PHF Nanocomposite Coating

PAGE 53

4.3. 4 Discussion Aspergillus niger

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Aspergillus niger

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AWavelength (nm)

PAGE 64

% Dye degradationTime (hour)

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% Dye degradation W/ PHF W/O PHF

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Aspergillus niger CFU

PAGE 67

Aspergillus niger

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Aspergillus niger Aspergillus niger Recovery

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Log(Ct/C0)Time (minutes)

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Aspergillus niger Log(Ct/C0)Time (hour)

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Aspergillus niger % InactivationTime (hour)

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Aspergillus niger log(Ct/C0)Time (hour)

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Aspergillus niger log(Ct/C0)Time (hour)

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Aspergillus niger % InactivationTime (hour)

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Aspergillus niger log(Ct/C0)Time (hour)

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Aspergillus niger log(Ct/C0)Time (hour)

PAGE 77

Aspergillus niger

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