Synthesis and PHOTOCATALYSIS STUDY of BROOKITE PHASE TITANIUM DIOXIDE NANOPARTICLES Radhika Bhave Clemson University, Rbhave@Clemson.Edu

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1-2007 SYNthesis AND PHOTOCATALYSIS STUDY OF BROOKITE PHASE TITANIUM DIOXIDE NANOPARTICLES Radhika Bhave Clemson University, [email protected]

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This Thesis is brought to you for free and open access by the Theses at TigerPrints. It has been accepted for inclusion in All Theses by an authorized administrator of TigerPrints. For more information, please contact [email protected]. SYNTHESIS AND PHOTOCATALYSIS STUDY OF BROOKITE PHASE TITANIUM DIOXIDE NANOPARTICLES

A Thesis Presented to the Graduate School of Clemson University

In Partial Fulfillment of the Requirements for the Degree Master of Science Material Science and Engineering

by Radhika Bhave May 2007

Accepted by: Dr. Burtrand I. Lee, Committee Chair Dr. Jian Luo Dr. Michel Drews

ABSTRACT

Titanium dioxide is mainly being used as a white pigment in the paint industry. It is also being used as a delustrant in fibers. Nanofabrication of TiO 2 makes it useful in variety of other important applications like photocatalysis, self-cleaning coatings, fog proof glass and water purifier. This is one of the reasons for large amount of research being done in synthesis of TiO 2 and its applications in various fields. Titanium dioxide,

TiO 2 or titania mainly exists in three crystalline polymorphs namely; anatase, rutile and brookite. Anatase and rutile phases have been explored thoroughly. Comparatively less work is done on the synthesis and applications of brookite phase TiO 2 nanoparticles.

The main goal of this research work is to synthesize brookite phase TiO 2 nanoparticles, characterize these particles by various techniques, estimate the photoactivity of the powder and apply the powder as a scratch resistant coatings. The work was divided into three parts.

Chapter 2 deals with the synthesis of brookite phase TiO 2 particles by ambient condition sol (ACS) process. The brookite particles formed were checked for phase purity and calculation of crystallite size by X-ray diffraction (XRD), phase morphology by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and thermal analysis. Calcination of the particles showed complete phase change from brookite phase to rutile by 600°C iii

Chapter 3 consists of investigation of the photoactivity of brookite phase TiO 2 nanoparticles. UV-Vis absorption spectra for non-calcined and calcined brookite nanoparticles showed absorption characteristics in the visible region. Decrease in degradation rate of methyl orange was observed with increase in calcination temperature and decrease in the surface area of the powders. Comparison of three phases determined the brookite phase to have fastest degradation rate after particular time of UV exposure.

Chapter 4 involves the basic application of these nanoparticles as scratch resistant coatings using a binder material. A new binder material was developed. The coatings had good adhesion to the glass substrate used. A simple scratch test was done to determine the scratch resistance of the binder and the coatings. The brookite phase TiO 2 nanoparticles had better adhesion and scratch resistance compared to the Degussa P25 powder (approximately 85% anatase and 15% rutile).

DEDICATION

This thesis is dedicated to my mother Sharmila Bhave and my father

Chandrashekhar Bhave. They have supported me in every stage of my life, have been a continuous source of encouragement and without them I would have never achieved this goal. I would also like to dedicate this work to my husband Amit who stood by me in difficult times and was always supportive. My sister Rashmi always provided me with the smile and I am blessed to have such a wonderful sister. I also dedicate my work to her.

ACKNOWLEDGEMENTS

First, I would like to thank my advisor Dr. Burtrand I. Lee. With his enthusiasm, his inspiration, and his confidence he helped me achieve my goal. I will be forever grateful for his incredible support, encouragement and guidance in conducting my research and in writing this thesis. He encouraged me to write research papers and brought out the good research work that I did. Without his help and guidance this work would not have been possible. Thanks Dr. Lee! Thanks for being my advisor and helping me flourish through this rough path.

I would also like to acknowledge my committee members Dr. Jian Luo and Dr.

Michel Drews for their assistance and recommendations and for reviewing my work in such a short time.

I would take this opportunity to thank Dr. Kathleen Richardson for giving me financial support from Fall 2004 to Fall 2006. I would also like to thank the department of Materials Science and Engineering and the staff for being very kind and helpful, Dr.

Gary Lickfield for his help. I would specially like to thank Kim Ivey for always helping me through all sorts of situations. I have learnt a lot of things from you. Thanks Kim!

I would also like to express gratitude to my undergraduate teachers Prof. Bapat,

Prof. Kher who believed in me and inspired me to go for my master’s degree. vi

I appreciate my group members Sujaree, Chris, Elliott, Ravi, Hiroki, Gopi, Prem and Venkat for their kind words and suggestions that helped me complete this thesis. I would also like to thank Dr. Jin Hwang and Dr. Ashraf Ali for their suggestions.

I extend my thanks to my friends Neha, Utpal, Gayatri, Kaveri, Ninad, Sonia,

Gauri, Nitendra, Swapna, Lalit and Abhijit in Clemson and Meenal, Pradnya, Apurva,

Rohit and Aditya in India. I would also like to thank my parents, my sister and my husband for continuous love and support.

TABLE OF CONTENTS

Page

TITLE PAGE...... i

ABSTRACT...... ii

DEDICATION...... iv

ACKNOWLEDGEMENTS...... v

LIST OF TABLES...... vii

LIST OF FIGURES ...... viii

PREFACE...... xi

CHAPTER

1. INTRODUCTION ...... 1

2. SYNTHESIS OF BROOKITE PHASE TITANIUM DIOXIDE NANOPARTICLES...... 8

Abstract...... 8 Introduction...... 9 Experimental...... 10 Results and Discussion ...... 15 Conclusions...... 27

3. INVESTIGATION OF PHOTOCATALYTIC BEHAVIOUR OF BROOKITE NANOPARTICLES ...... 28

Abstract...... 28 Introduction...... 29 Experimental...... 31 Results and Discussion ...... 33 Conclusions...... 43

Table of Contents (Continued)

Page

4. APPLICATION OF TiO 2 AS SCRATCH RESISTANT COATINGS ...... 44

Abstract...... 44 Introduction...... 45 Experimental...... 46 Results and Discussion ...... 49 Conclusions...... 54

FUTURE WORK...... 55

REFERENCES ...... 56

LIST OF TABLES

Table Page

1 Samples prepared with varying experimental condition...... 12

2 Samples prepared under varying water to isopropanol ratios and varying pH conditions ...... 13

3 Properties of TiO 2 nanoparticles for various calcination...... 17

4 Properties of TiO 2 nanoparticles after calcination...... 33

5 Materials used for coating preparation ...... 46

LIST OF FIGURES

Figure Page

2- 1 Structure of TiO 6 octahedra ...... 1

2 Formation of bond by two octahedral...... 2

3 Rutile formation...... 3

4 Crystal structure of rutile ...... 3

5 Anatase formation...... 4

6 Crystal structure of anatase...... 4

7 Brookite formation...... 5

8 Crystal structure of brookite ...... 5

9 Phenomenon of photocatalysis ...... 7

10 Experimental setup for the synthesis of brookite phase TiO 2...... 11

11 XRD pattern of as-prepared brookite phase TiO 2 nanoparticles ...... 15

12 XRD patterns of the calcined brookite phase TiO 2 nanoparticles ...... 16

13 (a) SEM micrograph of as-prepared particles...... 18

13 (b) TEM micrograph of as-prepared particles ...... 18

13 (c) TEM micrograph of the as prepared samples at atomic scale...... 19

13 (d) TEM micrograph showing magnified atomic scale image...... 19

14 (a) As-prepared brookite nanoparticles...... 20

14 (b) TiO 2 nanoparticles calcined at 200°C ...... 20

14 (c) TiO 2 nanoparticles calcined at 400°C ...... 21

List of Figures (Continued)

Figure Page

14 (d) TiO 2 nanoparticles calcined at 600°C ...... 21

15 TGA curve of the as-prepared sample ...... 22

16 XRD patterns of powders prepared at 83°C for different refluxing times ...... 23

17 Effect of HCl concentration on the phase content ...... 25

18 SEM micrograph of brookite particles prepared with HPC...... 26

19 (a) UV-Vis absorption spectra of mixed phase crystallite powders...... 34

19 (b) UV-Vis absorption spectra for brookite samples...... 35

20 Degradation of methyl orange with respect to time...... 36

21 (a) Color change of methyl orange for T100 ...... 37

21 (b) Color change of methyl orange for T200...... 37

21 (c) Color change of methyl orange for T300 ...... 38

21 (d) Color change of methyl orange for T400...... 38

21 (e) Color change of methyl orange for T500 ...... 39

21 (f) Color change of methyl orange for T600...... 39

22 Degradation of methyl orange as a function of surface area ...... 40

23 (a) Comparison of degradation rate after 30 minutes ...... 41

23 (b) Comparison of degradation rate after 60 minutes ...... 42

23 (c) Comparison of degradation rate after 90 minutes ...... 42

24 (a) Structural formulae of TMOS...... 46

24 (b) Structural formulae of GPTS ...... 46

List of Figures (Continued)

Figure Page

25 Flowsheet showing the fabrication of TiO 2 coating ...... 47

26 Setup for scratch test...... 48

27 Binder, brookite TiO 2 and P25 after curing (0.5 wt. %)...... 49

28 (a) Binder before scratch test (Mag. 200X)...... 51

28 (b) Binder after scratch test (Mag. 200X)...... 51

29 (a) P25 before scratch test, 1.5 wt. % (Mag. 200X)...... 52

29 (b) P25 after scratch test, 1.5 wt. % (Mag. 200X)...... 52

30 (a) Brookite coating before scratch test, 1.5 wt. % (Mag. 200X) ...... 53

30 (b) Brookite coating after scratch test, 1.5 wt. % (Mag. 200X) ...... 53

PREFACE

Goal of this work was to synthesize brookite phase titanium dioxide nanoparticles, evaluate their properties as a photocatalyst and use them in scratch resistant coatings. This work was divided into three parts. The first part deals with the synthesis and characterization of brookite phase titanium dioxide nanoparticles, by ambient condition sol (ACS) process. Certain experimental parameters were varied to check the effect on the phase change and to optimize the experimental conditions. The second part deals with investigation of the photoactivity of the brookite powders and use of brookite as a photocatalyst. The third part is to indicate a simple application of the brookite powder as a scratch resistant coating where the adhesion and scratch resistant properties were studied.

CHAPTER 1

INTRODUCTION

Titanium dioxide structure

Titanium dioxide, TiO 2 or titania exists in both crystalline and amorphous forms.

Titanium dioxide mainly exists in three crystalline polymorphs namely, anatase, rutile and brookite. These three polymorphs have different crystalline structure. Anatase and

Rutile have tetragonal structure, whereas brookite is orthorhombic [1-8].

Anatase and brookite are metastable phases, whereas rutile is the most stable phase. Brookite and anatase convert to rutile when they are calcined at higher temperatures. The phase transition temperature varies with the method of preparation of

2- the powders. All of these phases consist of TiO 6 octahedra. Fig. 1 above shows the

2- structure of TiO 6 octahedra. The octahedral has center atom of titanium surrounded by six oxygen atoms.

2- Fig. 1 Structure of TiO 6 octahedra 2

For the formation of titanium dioxide crystal, first two octahedron condense together to form a bond as shown in Fig. 2. Then position of the third octahedra determines the phase that will be formed.

Fig. 2 Formation of bond by two octahedra

Rutile has a tetragonal structure, the octahedron join in such a way that they form a linear chain and so just two of the twelve edges of the octahedra are connected. The linear chain is joined by sharing of corner oxygen atoms. Fig. 3 shows the formation of rutile by joining of two edges of the octahedra. Fig. 4 shows the crystal structure of rutile.

Anatase also has a tetragonal structure. In this case, there is no corner oxygen sharing. Four edges are shared per octahedra. Fig. 5 shows the formation of anatase. Fig.

6 shows the crystal structure of anatase.

Brookite has orthorhombic crystal structure. In the brookite formation there is sharing of three edges of the octahedra. Fig. 7 shows the formation of brookite structure.

Fig. 8 shows the crystal structure of brookite.

Fig. 3 Rutile formation

Fig. 4 Crystal structure of rutile

Fig. 5 Anatase formation

Fig. 6 Anatase crystal structure

Fig. 7 Brookite formation

Fig. 8 Crystal structure of brookite

Brightness and high refractive index of the titanium dioxide powder make it useful in applications like paints and pigments. It is being employed as a pigment to provide whiteness and opacity to products like paints, coatings, plastics, papers, inks, foods and most toothpaste. It is also being used as a pigment and thickener in cosmetic and skin care products. Almost every sunblock contains titanium dioxide because of its high refractive index and its resistance to discoloration under ultraviolet light. This enhances its ability to protect the skin from ultraviolet light. Hence, this pigment is being used extensively in plastics and other applications for its UV resistant properties where it acts as a UV reflector.

Photocatalytic properties and applications of TiO 2

Titanium dioxide is a photocatalyst under ultraviolet light. It has recently been discovered that it is also active in the visible light region with the addition of dopants like nitrogen, carbon and some metallic dopants such as iron, lanthanum, and copper.

The strong oxidative potential of the positive holes oxidize water to create hydroxyl radicals. It also oxidizes organic material directly. Titanium dioxide is thus added to paints, cements, windows, tiles or other products for sterilizing, deodorizing and anti-fouling properties. Titanium dioxide is a potential component to be used as a source of energy because it can carry hydrolysis as a photocatalyst. The hydrogen thus collected by breaking of water into hydrogen and oxygen, could be used as a fuel.

Photocatalysis

Photocatalysis is a reaction which uses light to activate a substance which modifies the rate of a chemical reaction without being involved itself. Fig. 9 shows the phenomenon of photocatalysis.

Fig. 9 Phenomenon of photocatalysis

Photocatalyst

Semiconductors are being used as a photocatalyst because they have a small band gap between the conduction band and the valence band. For the photocatalysis process to proceed, semiconductors need to absorb energy equal to or more than its energy gap, by shifting of electrons from the valence band to the conduction band. This movement of electrons generates negatively charged electron and positively charged hole pairs.

CHAPTER 2

SYNTHESIS AND CHARACTERIZATION OF BROOKITE PHASE

TiO 2 NANOPARTICLES VIA AMBIENT CONDITION

SOL (ACS) PROCESS

Abstract

Nanocrystalline brookite phase titanium dioxide particles have been prepared under ambient condition sol (ACS) process. Titanium tetrachloride was used as precursor in water with co-solvent isopropanol in hydrochloric acid as the reaction catalyst. The formed gel mass was peptized and crystallized under refluxing condition. The refluxing temperature of 83°C with the refluxing time of 15 hours led to the formation of brookite phase. Lower refluxing temperature of 70°C gave a mixture of rutile and anatase, and higher refluxing temperature of 100°C gave mixture of rutile and brookite. Calcination of brookite powders at different temperatures resulted in phase change and different phase compositions.

X-ray diffraction (XRD) technique was used to identify the phase purity and to determine the crystallite size of the powders. The surface area was measured by BET surface area analyzer Scanning electron microscopy and transmission electron microscopy has been used to examine the morphology of the particles. The morphology of the particles was determined by scanning electron microscopy and transmission electron microscopy. The effect of various parameters such as temperature of refluxing, time of refluxing, water to alcohol ratio, and pH of the sol on the phase obtained was also 9 investigated. Hydroxy propyl cellulose was added as a surface modifier to give uniform particle size along with higher surface area.

Introduction

Titanium dioxide, TiO 2 or Titania mainly exists in three crystalline polymorphs namely, anatase, rutile and brookite. The three polymorphs of titania have different crystalline structure. Anatase and rutile have tetragonal structure, whereas brookite is orthorhombic in nature [1-8].

Banfield et al. [9, 10, 11] discussed the size effect on the phase obtained, the thermodynamic effect and the polymorphic phase transformation behavior of TiO 2 nanoparticles. They stated that the transformation rate was faster with the decrease in the particle size. Thermodynamically anatase phase is more stable then the rutile phase when the particle size is below 14 nm.

Zhu et al. [12] also studied the size effect on the phase transition sequence of

TiO 2 nanoparticles. They observed that anatase, brookite and rutile phases were stable with particle size less than 4.9 nm, between 4.9 and 30 nm and above 30 nm respectively.

TiO 2 is generally synthesized by processes like thermolysis, hydrothermal synthesis and sol-gel process [1-4]. Anatase and rutile have been of interest to many researchers for long time [13, 14]. The properties and applications of brookite phase are comparatively new. Much less attention has been given to the properties and applications of this phase due to the difficulty in producing pure brookite particles.

Zheng et al. [15, 16] synthesized and characterized brookite TiO 2 as the major phase by hydrothermal method using titanium sulfate and titanium tetrachloride as the precursors. Titanium tetrachloride gave pure brookite at pH 8.

Lee et al. [17] synthesized pure brookite at low temperatures by hydrolysis of

TiCl 4 using HNO 3 solution. The presence of HNO 3 was considered to be very important in the formation of pure brookite nanoparticles. It was also seen from the literature that hydrothermal synthesis was necessary to obtain brookite as major phase [18-24].

Here we synthesize brookite phase by ambient condition sol (ACS) process. The formed brookite phase is then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), BET surface area analysis and thermogravimetric analysis. Effect of experimental parameters like temperature and refluxing time, addition of surface modifier, effect of hydrochloric acid on the phase obtained, morphology and particle size of the powders were also investigated.

Experimental

Procedure

Brookite phase TiO 2 nanoparticles were prepared by ACS process [25, 26].

Titanium tetrachloride (99.6% TiCl 4, Alfa Aesar) was used as a precursor with a molar concentration of 0.1 M. This was done by diluting the sol with addition of de-ionized water. Hydrochloric acid was added as a reaction catalyst. Isopropanol was added as a co-

11 solvent. The resulting precursor gel was then peptized at 83°C for 15 hours to give a homogeneous sol. The experimental setup is shown in Fig. 10 below.

Fig. 10 Experimental setup for the synthesis of brookite phase TiO 2

Calcination of the 1g of TiO 2 nanoparticles was carried out in porcelain crucibles at temperatures of 200°C, 300°C, 400°C, 500°C and 600°C for 2 hours in air atmosphere in using Thermolyne 1400 oven.

A set of experiments with varying parameters like temperature and time of refluxing, hydrochloric acid concentration and addition of hydroxypropyl cellulose as surface modifier were conducted. The influence of these experimental parameters on the

properties and the resultant phase obtained was studied for the series of TiO 2 samples that have been prepared. All the samples were prepared with water to isopropanol ratio of 1:2, except unless specified. Sols with varying water to isopropanol ratio were treated with

NH 4OH to obtain pH of 9 and the effect of pH was studied. The details of the powders prepared and their processing conditions are given in the Tables 1 and 2.

Table 1 Samples prepared with varying experimental conditions

TiO 2 Temperature Reaction Phase/Phases

Samples (°C) Time (hr) Identified

T1(a) 70 5 Anatase, Rutile

T1(b) 70 10 Anatase, Rutile

T1(c) 70 15 Anatase, Rutile, Brookite

T1(d) 70 20 Anatase, Rutile, Brookite

T2(a) 83 5 Rutile, Brookite

T2(b) 83 10 Brookite, Rutile

T2(c) 83 15 Brookite

T2(d) 83 20 Brookite, little Rutile

T3(a) 100 5 Anatase, Rutile, very little Brookite

T3(b) 100 10 Anatase, Rutile, little Brookite

T3(c) 100 15 Rutile, Brookite

T3(d) 100 20 Rutile, Brookite

Table 2 Samples under varying water to isopropanol ratio and varying pH conditions

Sample Water to Temp. pH Reaction Phase/Phases

ID isopropanol °C Time (hr) Identified

T2(e) 1:1 83 2 15 Rutile, Anatase

T2(f) 1:1.5 83 2 15 Brookite, Rutile

T2(c) 1:2 83 2 15 Brookite

T2(g) 1:3 83 2 15 Brookite

T2(h) 1:1 83 9 15 Rutile, Anatase

T2(i) 1:1.5 83 9 15 Rutile, Anatase

T2(j) 1:2 83 9 15 Rutile, Anatase, Brookite

TO2(k) 1:3 83 9 15 Rutile,Anatase

Characterization

The powders were dried at 100°C, then crushed and then checked for phase purity

[27] by room temperature X-ray diffraction (XDS 2000, Scintag PAD V using CuK α with wavelength ( λ) of 0.15406 nm). The crystallite size of the particles was determined from broadening of the peak by the Scherrer’s equation.

. d = 0.9 λ (1) β.Cos( θ) where, d = crystal size,

β = full width half maxima of the peak of interest

(121) for brookite, (110) for anatase and (101) for rutile

θ = diffraction angle

The phase content of the powders is calculated from integrated intensities of anatase (101), rutile (110) and brookite (121) peaks represented by A A, A R and A B. The mass fraction of rutile (W R), anatase (W A) and brookite (W B) was calculated from equation 2 (a), (b) and (c) and K A and K B are coefficients with values 0.886 and 2.721

[11]:

The morphology of the particles was studied with scanning electron microscopy

(SEM) and transmission emission microscopy (TEM). SEM samples were prepared by placing 2 drops of TiO 2 sol on carbon tape attached to a brass stub. The liquid was allowed to evaporate. An air gun was applied to blow off excess TiO 2 particles. To prepare TEM samples, a milligram of TiO 2 particles were dispersed in isopropanol by grinding in an agate mortar. A copper grid with supported thin carbon film was dipped into the suspension, removed and dried on a filter paper. Hitachi HD2000 and Hitachi

9500 HRTEM were used for getting the SEM and TEM micrographs.

Thermogravimetric analysis (TGA) was conducted on a 2950 Hi-Res

Thermogravimetric analyzer for the temperature range of room temperature to 900°C, in air at rate of 10°C/minute. The Brunauer-Emmett-Teller (BET) surface area was determined by N 2 physisorption using a Micromeritics ASAP 2020 automated system. A

0.3-0.5 g of the powder sample was degassed in the Micromeritics ASAP 2020 at 100 °C for 3 hours prior to analysis. The powders were analyzed using N 2 adsorption at -196 °C.

Results and Discussion

X-ray diffraction (XRD)

The brookite phase TiO 2 nanoparticles were measured for phase purity by XRD. Fig. 11 shows the XRD pattern for the as prepared TiO 2 nanoparticles.

350 B(120)(111)

300

250

200

150 Intensity B(320) B(121) B(231) B(221)

100 B(112)

0 20 30 40 50 60 2 Theta

Fig. 11 XRD pattern of brookite phase TiO 2 nanoparticles prepared by ACS process

The phase change from brookite to rutile is seen from Fig. 12 which shows the

XRD patterns for the powders calcined at various temperatures.

(a) As prep. (b) 200°C R(110) (c) 300° C (d) 400°C (e) 500°C (f) 600°C

R(211) R(101) B(231) B(120) B(111) B(120) B(121) Intensity (a.u.) Intensity (f) (e) (d) (c) (b) (a) 20 30 40 50 60 2 Theta

Fig.12 XRD patterns of the calcined brookite phase TiO 2 nanoparticles

The as-prepared powders have brookite as the dominant phase. Powders calcined at 200°C have similar results. Rutile phase content increases at 300°C calcination. The rutile phase dominates at 500°C and there is complete transition to rutile phase at 600°C.

The transformation is directly from brookite phase to rutile phase, with no presence of anatase phase. The physical properties of TiO 2 nanoparticles before and after calcination temperature are shown in table 3.

Table 3 Physical properties of TiO 2 nanoparticles for various calcination temperatures

TiO 2 Cal. Phase composition Crystal size Surface Pore

samples temp, (%) nm area, volume,

°C B R B R m2/g cm 3/g

T100 100 90 10 5 12 170 0.101

T200 200 83 17 5 18 195 0.116

T300 300 79 21 7 19 123 0.127

T400 400 71 29 10 24 83 0.128

T500 500 29 71 18 36 58 0.119

T600 600 - 100 - 47 25 0.080

Particle Morphology

The morphology of the as prepared brookite particles can be seen from the Fig.

13. The particle size of the as-prepared powder is approximately 10 nm. The particle size and morphology is affected by the calcination temperature. As observed from Fig. 14, size of particles increases from about 10 nm for as-prepared powder to about 50 nm after calcination at 600°C.

Fig. 13 (a) SEM micrograph of aggregated as-prepared particles

Fig. 13 (b) TEM micrograph of aggregated as-prepared particles

Fig 13 (c) TEM micrograph of the as prepared samples

at atomic scale (scale = 20 nm)

Fig. 13 (d) TEM micrograph showing magnified

atomic scale image (scale = 5 nm)

Fig. 14 (a) As-prepared brookite nanoparticles

Fig. 14 (b) TiO 2 nanoparticles calcined at 200°C

Fig. 14 (c) TiO 2 nanoparticles calcined at 400°C

Fig. 14 (d) TiO 2 nanoparticles calcined at 600°C

Thermal Analysis

Fig. 15 shows the TGA curve of the as-synthesized powder. The weight loss was exhibited in the temperature range of 20 to 400°C. The weight loss of 9.9 % in the temperature range of 20 to 200°C corresponds to the loss of adsorbed water and weight loss of about 6 % in the temperature range of 200 to 400°C is due to the removal of hydroxyl groups and/or organic residues such as alkoxy groups.

102

100

Weight loss (%) loss Weight 88

0 200 400 600 800 1000 Temperature ( oC)

Fig. 15 TGA curve of the as-prepared sample

Effect of Refluxing time and Temperature

A series of samples with water to isopropanol ratio of 1:2 have been synthesized at refluxing temperatures 70°, 83°, 100° with varying refluxing times from 5 – 20 hrs.

The details of the sample preparation conditions are given in Table1. The pH of all the samples was maintained at 2 for consistency of comparison. The XRD pattern in Fig. 16 shows the crystallized phases for the samples refluxed for 5, 10, 15 and 20 hrs at 83°C. It took refluxing temperature of 83°C and refluxing time of 15 hours to yield brookite nanoparticles. Brookite with rutile impurity was also obtained at refluxing time of 20 hours as indicated in Fig. 16, with an increase in the crystallite size.

B(120) B(111) B(320) R(110) B(231) B(220)(211) B(121) B(012)

( d )

( c )

Intensityu.) (a. ( b )

( a )

20 30 40 50 60 2 theta (degree)

Fig. 16 XRD patterns of powders prepared at 83°C for different refluxing times

(a) 5 hours (b) 10 hours (c) 15 hours (d) 20 hours

Effect of hydrochloric acid (HCl)

Yu et al. [28] studied the effect of acidic and basic hydrolysis catalysts on the microstructure and photoactivity of titania. The acidic conditions gave crystalline titania particles and also enhanced the growth of brookite particles, whereas the basicity suppressed the formation of crystalline phase and the formation of brookite phase.

Lee et al. [29] studied the effect of HCl concentration on change in the crystalline state of TiO 2. They obtained 50 volume percent of brookite phase with the concentration of HCl to be between 4.9 and 6.4M.

The effect of acidic and basic condition was studied by changing the pH of the sol. Table 2 gives the details of the different pH values and the effect of pH on the brookite phase obtained. It was observed that acidic conditions were necessary for the formation of brookite phase. NH 4OH was added to the sol to get pH 9. There was no brookite phase present under any conditions of refluxing time. Rutile was the major phase obtained.

The reactions were carried out from adding no hydrochloric acid in the sol, to adding about 0.6 M HCl. At HCl concentration of 0.3M brookite phase was obtained. At no HCl addition to the sol, the refluxed sol did not precipitate properly, and the obtained powder was amorphous. With the HCl concentration of 0.15M, the powder was crystalline, but the major phase was anatase. Concentration of 0.45M brookite was the major phase with rutile as a byproduct. 0.6M concentration of HCl gave rutile as the major phase though the brookite was still present. At the concentration of 1.35M pure rutile was obtained.

Fig. 17 shows the effect of HCl concentration on phase content of the TiO 2 nanoparticles obtained. These results confirm that the presence of hydrochloric acid was necessary for the synthesis of pure brookite phase.

100

60 (c) (b) 40

Phase Content (%) Content Phase 20

0 (a) 0.1 0.2 0.3 0.4 0.5 0.6 HCl concentration (M)

Fig. 17 Effect of HCl concentration on the phase content

(a) Anatase ( ●), (b) Rutile ( ▲), (c) Brookite ( ■)

Effect of Hydroxypropyl Cellulose (HPC)

Two sets of experiments were done to understand the effect of HPC as surface modifier, on the particle morphology. In the first one the normal experimental conditions were applied with refluxing temperature of 83°C and the refluxing time of 15 hours. The sol was then dried on a carbon stub and the morphology of the particles was observed by

SEM.

In the second set of experiments, all the experimental parameters were kept the same, except that 0.02g/ml of HPC was added at the start of the experiment. Addition of

HPC decreases the agglomeration of the particles and thus the surface area of the particles is slightly increased. Fig. 18 shows the morphology of brookite particles with

HPC. The micrograph shows that the particle size was much smaller than the as prepared particles. There was increase in the surface area of the nanoparticles from170 m 2/g to

198 m 2/g with presence of HPC.

Figure18 SEM micrograph of brookite particles prepared with HPC

Conclusions

Pure brookite phase titanium dioxide nanoparticles were successfully synthesized by ACS process. The powders were characterized by XRD for phase purity, SEM and

TEM for particle morphology, TGA, BET surface area. The powders were calcined at different temperatures. There was a phase change from brookite to rutile with the calcination of the powder to 600°C. There was also increase in the average particle size with increase in the calcination temperature.

The effect of the experimental conditions on the phase synthesized was studied.

The refluxing time and temperature had a very vital role in controlling the particle size and phase. The increase or decrease in the temperature, above or below 83°C added phase impurity to the pure brookite nanoparticles. Acidic nature of the sol was necessary for obtaining brookite phase. Hydroxypropyl cellulose can also be added as a surface modifier to get smaller particles and higher surface area of the particles.

CHAPTER 3

PHOTOCATALYTIC ACTIVITY OF BROOKITE PHASE

TiO 2 NANOPARTICLES

Abstract

Brookite phase TiO 2 nanoparticles with about 10 nm particle size were synthesized by ambient condition sol (ACS) process. Calcination of the brookite phase particles at different temperatures resulted in phase change and different phase compositions which were identified by X-ray diffraction (XRD) in the previous chapter.

The surface area of the particles was analyzed by BET surface area analyzer.

Spectroscopic measurements were taken for the calcined powders on UV-Vis spectrometer, showing the onset of band-gap transition shifted to the visible region (410 nm). The effects of the calcination temperature and the surface area of the TiO 2 nanoparticles on the photocatalytic degradation of the methyl orange under ultraviolet

(UV) illumination were studied. It was observed that higher the surface area faster the degradation. Increase in the calcination temperature decreased the rate of degradation of methyl orange, with increase in the particle size and decrease in the surface area of the particles. Anatase, brookite and rutile were compared for the rate of photocatalytic degradation and brookite gave fastest degradation among the three phases.

Introduction

The heterogeneous photocatalytic property of TiO 2 is described very well in the past [30-33]. Due to desirable properties of titanium dioxide like water insolubility, non- toxic nature [34], photoactivity it has gained lot of interest in the fields like photocatalysis [35, 40, 41], photo-electrodes [36-38], gas sensors [39] and water purification.

The photocatalytic degradation of organic pollutants by TiO 2 [42] has proven to be an excellent application of the material [43-45]. The degradation of various organic dyes and the comparison of the degradation rate have been convenient way to examine the effectiveness of the catalyst material [46-50].

Kinetics of photodecolorization of methyl orange by TiO 2 catalyst was studied by

Chyuan et al. [51]. They observed that the initial decolorization rate increased and decreased with the calcination temperature, till 800°C. They also observed that there was increase in the reaction rate with increase in rutile content during the phase change from anatase to rutile, upto a critical value of rutile, above which the reaction rate was inversely affected.

The photoreduction of methyl orange sensitized by colloidal TiO 2 was studied by

Brown et al. [52]. In steady-state conditions maximum reduction rate occurred at pH 4.7 in absence of O 2 and shifted to pH 3.0 with presence of O 2. Due to rapid reduction of O 2 compared to unprotonated dye. Li et al. [34] studied the photocatalytic degradation of methyl orange by TiO 2-coated activated carbon. They concluded that the coating of activated carbon gives higher degradation rates in water phase than the uncoated TiO 2.

Sol-gel synthesis of TiO 2 nanoparticles, photocatalytic degradation of methyl orange in aqueous TiO 2 suspension and the effect of phase composition on the

30 degradation was studied by Yang et al. [53]. According to the authors presence of single phase (anatase) gave the highest degradation rate.

Anukunprasert et al. [54] studied the effect of anatase phase morphology, i.e. crystallite size prepared by microemulsion technique on the photocatalytic decomposition of phenol. The smallest crystallites possessed the highest surface area and thus had the fastest photocatalysis rate in the degradation of phenol. However the results could not explain the effect of surface area on the degradation rate.

Ozawa et al. [55] studied the photocatalytic activity of anatase-brookite mixed phase composite. They observed that mixed phase of brookite and anatase showed better results than the single phase anatase and higher crystallinity gave higher photoactivity.

These results were obtained due to the junction effect between anatase and brookite.

Bakardjieva et al. [56] observed the transformation of brookite TiO 2 to rutile and studied the correlation between microstructure and photoactivity. They reported that mixed phase sample of brookite, anatase and rutile gave the best photoactivity.

Kominami et al. [57] prepared brookite type TiO 2 nanoparticles by solvothermal synthesis and checked the correlation between photocatalytic activity and physical properties of TiO 2. They studied the effect of calcination temperature of brookite TiO 2 on the photodecomposition of acetic acid, 2-propanol and silver sulfate evolving CO 2, H 2 and O 2 respectively. They concluded that the brookite type TiO 2 has potential to be a good photocatalyst.

Experimental

Catalyst particle preparation

The procedure for preparation of brookite phase nanoparticles is described in detail in the Chapter 2. Briefly, brookite phase nanoparticles were prepared using titanium tetrachloride (99.6 % TiCl 4, Alfa Aesar) as a precursor. The molar concentration of titanium tetrachloride at 0.1 M was dissolved in water as the co-solvent with isopropanol and hydrochloric acid as the reaction catalyst. The resulting precursor gel was then peptized at 83°C for 15 hours to give a homogeneous sol. The sol was then centrifuged and dried in the oven at 100°C to obtain as-prepared brookite phase TiO 2 nanoparticles. Calcination of the TiO 2 nanoparticles at temperatures of 200°C, 300°C,

400°C, 500°C and 600°C for 2 hours in air was carried out.

Characterization

The BET surface area of the TiO 2 nanoparticles was determined by N 2 physisorption using a Micromeritics ASAP 2020 automated system. A 0.3-0.5 g of the catalyst sample was degassed at 100 °C for 3 hours prior to analysis. The analysis was done using N 2 adsorption at -196 °C. Ultraviolet-visible spectra in reflectance mode were obtained from a GretagMacbeth Color i5 spectrometer across a UV-Vis range of 360 to

750 nm. The spectrometer was typically used to analyze fiber samples and hence was retrofitted to handle compacted powder samples using a small conical sample holder.

Equation 3 was used to convert the percent reflectance values obtained to percent absorbance values.

%A = 2 – log (%R) (3)

The photocatalytic degradation of methyl orange by TiO 2 nanoparticles was measured by the Unicam 5625 UV-Vis spectrophotometer.

Photocatalytic activity

The photocatalytic degradation of methyl orange by TiO 2 powder under UV illumination was investigated in order to investigate the photocatalytic activity of the

-5 TiO 2 nanoparticles. A 100 ml of 2 × 10 M methyl orange solution was targeted. The dried 0.2 g TiO 2 powders were dispersed in the methyl orange solution and stirred magnetically for 30 minutes in the dark. The UV light source (Spectroline black light lamp) with a wavelength of 365nm and power wattage of 182W was used.

The initial pH of the solution was kept constant at 5 by addition of dilute hydrochloric acid, if necessary. The samples were continuously stirred during the UV exposure. Aliquots of the solution were withdrawn at regular intervals of 15 minutes, to determine the change in methyl orange concentration during the UV exposure. The solution withdrawn was filtered for separating the TiO 2 nanoparticles. The clear transparent solution was analyzed by UV-Vis spectroscopy after filtration on a 0.02 µm filter paper. Concentration of methyl orange was measured from the resulting spectra at wavelength of 490 nm.

The photocatalytic degradation rate of the three phases was compared using anatase and rutile powders to compare to as-prepared brookite powder. The anatase powder had slightly lower surface area than the brookite powder and rutile had very low surface area, due to its very big particle size.

Results and Discussion

Characterization of TiO 2 catalyst

Table 4 shows the effect of calcination temperature on the properties of TiO 2 nanoparticles. The surface area data for the different calcination temperatures suggests that with the increase in the calcination temperature there is decrease in the surface area.

However, there seems to be increase in surface area from 100 to 200°C calcination, which must be due to some of the adsorbed sites occupied by impurities like residual isopropanol, in the as-prepared nanoparticles that are being freed at 200°C calcination.

Table 4 Properties of TiO 2 nanoparticles after calcination at various temperatures

TiO 2 Calcination Crystal Surface Pore

samples temp, phase area, volume,

°C m2/g cm 3/g

T100 100 Brookite 170 0.101

T200 200 Brookite 195 0.116

T300 300 Brookite + Rutile 123 0.127

T400 400 Brookite + Rutile 83 0.128

T500 500 Rutile + Brookite 58 0.119

T600 600 Rutile 25 0.080

UV-Vis spectra

The UV-Vis spectra of calcined powders by Tseng and his co-workers [58] are shown in Fig 19 (a). They prepared ultraviolet and visible light responsive titania-based photocatalysts. They calcined the powders at various temperatures. The as-prepared phase was anatase. Under controlled calcination temperature of 200°C to 250°C they obtained mixed phases of anatase, rutile and brookite crystallite structure. The increase in the calcination temperature increased the amount of rutile content and crystalline structure completely transformed to rutile at 600°C.

Fig 19 (a) UV-Vis absorption spectra of mixed phase crystallite TiO 2 powders [ref. 58]

It can be seen from the Fig 19 (a) that the spectrum of 200°C calcined TiO 2 had no obvious absorption edge and absorption continued above 800 nm and leads to strong visible light absorption. They concluded that the existence of mixed lattice structure was important reason for the visible light absorption. Also, they showed that the visible light absorption decreased considerably for calcination above 300°C.

The UV-Vis reflectance spectra of the calcined brookite powders are shown in

Fig. 19 (b). It was observed that the visible light absorption for T200 and T300 powders was very high and had no particular absorption edge till wavelength of 750 nm. The absorption of all the other powders was comparatively less. The T600 powder also showed some absorption in visible light region.

1.2 T600

T500 1.0 T400

0.8 T100

0.6 T200 T300 0.4 Absorbance Absorbance

0.2

0.0 400 500 600 700 Wavelength (nm)

Fig 19 (b) UV-Vis absorption spectra for brookite samples

Fig. 12 shows the XRD graph of the powders calcined at different temperatures.

The XRD patterns show brookite powders to have smaller crystallite size compared to rutile that was formed at 600°C calcination. The high absorption of visible light T200 and

T300 powders can be due to higher surface area, smaller particles and presence of mixed phases [58] and suggests photoactivity of these powders in the visible light region.

Photocatalytic degradation of methyl orange in aqueous

brookite phase TiO 2 suspensions

Fig. 20 shows the rate of degradation of methyl orange for the non-calcined and calcined brookite powders. It was observed that the T200 powder had the fastest degradation rate, which then decreased with increase in the calcination temperature. The as-prepared T100 nanocrystalline TiO 2 particles were strongly hydrated and thus a further thermal treatment at 200°C increased the photocatalytic properties of the powder (T200).

100 No Titania T600 T500 80 T400

T300 20 T100

T200 0

Undegraded methyl orange (%) orange methyl Undegraded 0 10 20 30 40 50 60 70 80 Time (min.)

Fig. 20 Degradation of methyl orange with respect to time

Fig. 21 shows the photographs of the Color changes observed for the methyl orange solution during UV exposure. It can be seen that the T400, T500 and T600 powders did not give a complete Color change even after UV exposure of 150 minutes, whereas the T200 powder gave the fastest Color change after 45 minutes of UV exposure followed by 90 minutes for T100 and 120 minutes for T300 powders.

Fig. 21 (a) Color change of methyl orange for T100

Fig. 21 (b) Color change of methyl orange for T200

Fig. 21 (c) Color change of methyl orange for T300

Fig. 21 (d) Color change of methyl orange for T400

Fig. 21 (e) Color change of methyl orange for T500

Fig. 21 (f) Color change of methyl orange for T600

The effect of surface area on degradation rate after 75 minutes of UV exposure is shown in Fig. 22. It can be clearly seen that the degradation rate of methyl orange is inversely proportional to the surface area of TiO 2 nanoparticles till the surface area is above 100. Later the decrease in surface area does not decrease the surface area considerably. As seen from table 4, powders calcined above 300°C had surface area less than 100 m 2/g and the dominating phase was rutile. Hence, it can be said that the presence of brookite phase and higher surface area have a mixed effect on the higher degradation rate of methyl orange.

100

20 Undegraded Methyl Orange Orange Methyl % Undegraded

0 0 50 100 150 200 Surface Area (m 2/g)

Fig. 22 Degradation of methyl orange as a function of surface area

Comparison of rate of degradation of methyl orange in aqueous

anatase, brookite and rutile phase TiO 2 suspensions

Fig. 23 (a), (b), (c) show the comparison of the photocatalytic degradation of the three phases namely anatase, brookite and rutile after 30, 60 and 90 minutes of UV exposure. It was observed brookite particles showed the fastest rate of degradation followed by anatase and then by rutile. This can be due to smaller particle size and higher surface area of the brookite nanoparticles. Research from the past [10, 59] shows that brookite nanoparticles have smaller particle size and so have higher surface area and hence faster degradation rate.

110 Anatase

105 Rutile

100 Brookite

65 Undegraded methyl orange(%) methyl Undegraded 60 0 5 10 15 20 25 30 35 Time (min.)

Fig. 23 (a) Comparison of degradation rate after 30 minutes

120 Anatase

Rutile

100 Brookite

20 Undegraded(%) orangemethyl 0 0 10 20 30 40 50 60 70 Time (min.)

Fig. 23 (b) Comparison of degradation rate after 60 minutes

120 Anatase

Rutile 100 Brookite

20 Undegradedmethylorange(%) 0 0 20 40 60 80 100 Time (min.)

Fig. 23 (c) Comparison of degradation rate after 90 minutes

Conclusions

As the calcination temperature increases the particle size increases and the surface area decreases. With increase in the calcination temperature, there was decrease in the rate of methyl orange degradation. With higher surface area of the particles, there is an increase in the catalyst active sites. This increases the probability of the electrons and holes to reach the surface and react with methyl orange giving a faster degradation. The degradation rate of methyl orange decreased when powders were calcined above 300°C and the decrease in surface area did not change the rate of degradation. This can be due to increase in the rutile and decrease in brookite phase content. This shows that the brookite

TiO 2 nanoparticles are good photocatalysts in the UV region.

The UV-Vis absorbance spectra of the brookite powders calcined at various temperatures indicate that T200 powder shows absorption in the visible light region.

These powders have a potential to be used in visible light region. The comparison of degradation rate of methyl orange for the three phase’s anatase, rutile and brookite shows that brookite phase has the fastest degradation rate. This can be due to higher surface area and lower particle size of the brookite nanoparticles.

CHAPTER 4

APPLICATION OF TiO 2 AS SCRATCH RESISTANT COATINGS

Abstract

One of the applications for brookite phase TiO 2 is scratch resistance coatings.

These coatings can be also applied to windows or glass panes for protection from UV light. A primary level attempt has been made to show the application of the powder as coating. Semi-transparent coatings were formed by dispersion of as-prepared brookite phase TiO 2 nanoparticles in a binder material.

The organic-inorganic sol was ultrasonicated and then stirred for 12 hours, then coated and cured at temperature of 120°C for 4 hours. TiO 2 coatings with different weight percent were prepared. These coatings were studied for properties like adhesion and scratch resistance. A commercial titania powder, Degussa P25 was used as a reference and similar coatings were fabricated. It was observed that the coatings prepared from Degussa P25 powder had very bad adhesion and the coating cracked after curing.

The brookite coatings showed nearly no scratches at 1.5 weight % loading.

Introduction

Organic-inorganic nanocomposite coatings for desirable applications as glass, tile, porcelain and granite with the properties like scratch and impact resistance, good adhesion and long term durability are based on the simple epoxy groups of

(3-glycidoxypropyl)trimethoxysilane (GPTS) molecules[60-65].

Mackenzie et al. [66] studied the physical properties of sol-gel coatings. They stated that for sol-gel coatings, there is a possibility of applying oxide coatings with practically all types of chemical compositions.

Coatings with GPTS and methyltrimethoxy silane (MTMS) were prepared by

Hwang et al. [67] and surface modified TiO 2 nanoparticles were dispersed in the sol. The coatings had good scratch resistance and adhesion. The main application of the coating was as a UV-protector. There was no loss of adhesion even after the UV test period of 20 weeks. There was improvement in the coating properties when multilayer applied to any substrate [68].

Here, we show the basic preparation of organic-inorganic coating with brookite phase TiO 2 nanoparticles dispersed in the organic sol. The basic properties of the binder and of the coatings were to be durable in terms of having good adhesion, good scratch resistance and in some cases good transparency. The coatings should not decompose when exposed to UV. Appearance of the brookite coatings was semi-transparent. There was no crack formation after the fabrication of the coatings and even after curing at

120°C for 4 hours. The adhesion and scratch resistant properties of the coatings were investigated.

Experimental

Materials

Table 5 Materials used for coating preparation

Materials Source Chemical Physical Formula properties

3-glycidoxypropyl-tri(methoxy)silane Gelest C9H20 O5Si M.W. 236.34 (GPTS) b.p. 120.

Tetramethyl orthosilicate Alfa C4H12 O4Si M.W. 155.22 (TMOS) Aesar b.p. 121.

Degussa P25 Aerosil (TiO 2) Particle size (Anatase + Rutile) 21 nm

Titanium Dioxide Synthesized (TiO 2) Particle size (Brookite) by ACS 10 nm

Fig. 24 (a) Structural formulae of TMOS

Fig. 24 (b) Structural formulae of GPTS

Procedure

3 mol of GPTS and 5 mol of TMOS were prehydrolyzed with ethanol at room temperature for 3 hours by continuous stirring. After stirring for 5 minutes acetic acid was added to maintain the pH at 4. Brookite nanoparticles (refer chapter 2) were added to the organic sol as 0.5 wt. %, 1.0 wt. % and 1.5 wt. % of the organic sol. Organic- inorganic sol was ultrasonicated for 1 hour and later magnetically stirred for 12 hours.

Sol was then dip-coated on sterilized glass substrates. The coatings were then cured at

120°C for 4 hours. Fig. 25 shows the flowsheet explaining the fabrication of the TiO 2 coatings. Degussa P25 powder was used as a reference and similar weight % coatings were prepared. The volume of Degussa P25 was more than the volume of brookite.

Binder properties with no TiO 2 particles in the coating were also checked.

Fig. 25 Flowsheet showing the fabrication of TiO 2 coating

Characterization

The coatings were checked for adhesion properties and scratch resistance by a very simple method. The adhesion of the coatings was checked by visual inspection of the coatings after curing.

For the scratch test, weight of 200g was applied to the coating and the coatings were forced out with a particular speed. Fig. 26 shows the experimental setup for the scratch test.

Fig. 26 Setup for scratch test

Optical microscopy was used to observe the structure of the coatings before and after the scratch test.

Results and Discussion

Adhesion

Binder showed good adhesion and formed a clear, crack free coating. Brookite particle coatings showed good adhesion for all the wt. %. Adhesion was comparatively poor for the Degussa P25 samples and it got worst with the increase in the wt. % of the powder. It can be due to poor wetting of the coating.

Fig. 27 shows the visibility test for adhesion of the coatings after curing. P25 coatings were falling off and not properly adhered to the glass substrate, whereas the brookite coatings showed good adhesion and it was rather difficult to remove the coatings from the glass substrate.

Fig. 27 Binder, brookite TiO 2 and P25 (0.5 wt. %)

It can be clearly seen that the binder coating was transparent, brookite coating was semi-transparent and degussa P25 coatings were cracked and not properly adhered to the glass substrate. The whitening of the P25 coatings was also observed. The semi- transparency of the brookite phase coatings can be due to the agglomerate of the powder.

The non-uniform dispersion of the particles can also lose the transparency of the coating.

Scratch resistance

Fig 28 (a) and (b) shows the optical micrograph of the binder before and after scratch test at magnification of 200X. Fig. 29 (a) and (b) show the optical micrograph of P25 coatings, with 1.5 wt. % of powder, before and after scratch test at magnification of

200X. Fig. 30 (a) and (b) show the optical micrograph of brookite coatings, with 1.5 wt.

% of powder, before and after scratch test at magnification of 200X. The darker areas in the brookite coatings are the hollow pores formed due to non-uniform dispersion of particles.

Fig. 28 (a) Binder before scratch test (Mag. 200X)

Fig.28 (b) Binder after scratch test (Mag. 200X)

Fig 29 (a) P25 coating before scratch test, 1.5 wt. % powder (Mag. 200X)

Fig 29 (b) P25 coating after scratch test, 1.5 wt. % powder (Mag. 200X)

Fig 30 (a) Brookite coating before scratch test, 1.5 wt. % powder (Mag. 200X)

Fig 30 (b) Brookite coating after scratch test, 1.5 wt. % powder (Mag. 200X)

The binder coating showed very little scratch resistance and it improved with addition of brookite particles. The 1.5 wt. % of brookite particle coatings showed nearly no scratches as compared to P25 coatings which had lot of scratches. The scratch resistance of the coatings can be further increased by higher loading of the brookite nanoparticles. Further research of the fabrication and testing of the coatings will give better estimation of the properties.

Conclusions

Binder material showed good adhesion properties. Brookite phase TiO2 nanoparticles were embedded in the silane based organic sol. Adhesion and scratch resistance properties of these coatings were found to be better than the P25 coatings. The bad adhesion and scratch resistance of the P25 coating can be caused due to poor wetting, higher loading of powder and bad dispersion. This can be improved by ball milling.

The comparison of the coatings should be done by volume % and not weight %, because it might be one of the reasons for poor quality of coating. It can be noted that further study of these coatings can give positive results for the use of brookite nanoparticles as coatings on the windows, tiles and glass panes and also the use of coatings as UV protector.

FUTURE WORK

Based on the results, the following works are recommended for future research:

1. Phase composition analyzed by XRD can be confirmed by using Raman

Spectroscopy.

2. Investigating the effect of refluxing time on the phase composition of the precipitated

powder and relating them to the thermodynamic stability.

3. Normalizing the conditions for degradation of methyl orange with respect to surface

area and phase composition.

4. Investigating the degradation rate of methyl orange by brookite powder in the visible

light region.

5. Testing the durability hardness of the TiO 2 coatings with selected binder under

practical conditions.

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