Crystalline TiO2 nanoparticles were synthesized by hydrolysis of titanium (IV) isopropoxide (TTIP) in the Aerosol OT (AOT)－cyclohexane microemulsion at controlled temperature. The influence of various reaction conditions, such as mixing energy ( ), [AOT] concentration (W), [TTIP] concentration (R), temperature (T), and aging (t) on the particle size were investigated. The nano-TiO2 particles were characterized for specific surface area (Brunauer-Emmett-Teller, BET) in addition to X-ray diffraction (XRD) and X-ray spectroscopy (XPS) as to determine the particle size, crystalline state, chemical composition, surface charge, and binding energy. The photocatalytic activity was assessed using methylene blue as probe.
Results showed that the particle size was in the range from 13.7 to 31.4 nm based on BET measurements. The size of the particle grows with mixing energy until log ( ) = 2.02; further increase in mixing rate caused particle breakup. In micelle solution, the particle size decreased with increase in W. In true solution the particle size increased with W. However, increase in R increased the particle size which reached a maximum value at a critical value of log R = -0.26, then decreased upon further increase in R. The activation energy (Ea) was calculated using Arrenhius plot and a value of -5.96 and -2.17 kJ mol-1 was obtained. Results of particle size analysis from XRD and BET were consistent with each other. Crystalline pattern was proved to be anatase. Furthermore, the photocatalytic activity appeared to optimum with particle size between 22.0-25.1 nm and best crystalline pattern.
Titanium dioxide (TiO2) synthesized using the thermal hydrolysis method in our laboratory was used as the photocatalyst in this study to degrade low concentration phenol in aqueous solution. A 150 mL batch reactor was used to carry out the degradation of 0.385 mM phenol solution (pH = 6.5) in room temperature (25 oC) with 0.5 g L-1 TiO2 and irradiated with 10.8 mW cm-2 light intensity for 8 hours. Major intermediate products include hydroquinone (HQ) with the highest quantity followed by catechol (CA), p-benzoquinone (BQ), resorcinol (RES); tri-hydroquinone (THQ) is the secondary intermediate. The by-products consist of 6 organic acids including the six-carbon trans, trans-muconic acid (t,t-MA), the four-carbon maleic acid (MA), the three-carbon propionic acid (PA), the two-carbon oxalic acid (OA) and acetic acid (AA) as well as the one-carbon formic acid (FA). Among these acids, oxalic acid is the most abundant followed by formic acid; the six-carbon t,t-MA is one of the by-products with a lagged formation period. The pathway of intermediate product formation was mathematically calculated and simulated using first-order reaction kinetics models. The reaction rate constants were statistically calculated using functions provided in Microsoft Excel 2003; the simulated results show that the predicted and measured concentrations of the reactant and products in samples collected at various times are consistent.

TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS I
ABSTRACT II
TABLE OF CONTENTS IV
LIST OF TABLES VII
LIST OF FIGURES VIII

Chapter 1 INTRODUCTION 1
1.1 Preparation of crystalline nanosize titania by microemulsion 1
1.2 Intermediates and kinetic modeling on photocatalytic degradation of phenol 3

Chapter 2 LITERATURE REVIEW 6
2.1 Characteristics of TiO2 6
2.2 Preparation of TiO2 7
2.2.1 Thermal hydrolysis technique 7
2.2.2 Hydrothermal processing 8
2.2.3 Sol-gel method 9
2.2.4 Microemulsion technique 10
2.3 Fundamentals of photocatalysis 11
2.4 Degradation mechanisms 13
2.4.1 Langmuir-Hinshelwood mechanism 13
2.4.2 Delplot technique 15
2.5 Decolorization of dyes 15
2.6 Decomposition of phenol 16
2.7 Application of solar energy in the photocatalysis 16
2.8 Toxicity of intermediates 18
2.9 Particle size effect 19

Chapter 3 MATERIALS AND METHODS 23
3.1 Preparation of crystalline nanosize titania by microemulsion 23
3.1.1 Reagents and materials 23
3.1.2 Synthesis 23
3.1.3 Physical characterization 24
3.1.4 Photocatalytic experiments 25
3.2 Intermediates and Kinetic modeling on photocatalytic degradation of phenol 26
3.2.1 Reagents 26
3.2.2 Laboratory synthesis of titanium oxide powder 27
3.2.3 Analyzing physical characteristic of the synthesized titanium dioxide 27
3.2.4 Photocatalytic reaction 29
3.2.5 Analysis of reactant 29
3.2.6 Calibration of the kinetic model 30

Chapter 4 RESULTS AND DISCUSSION 33
4.1 Preparation of crystalline nanosize titania by microemulsion 33
4.1.1 Characterization of XRD and XPS 33
4.1.2 Effect of mixing energy 34
4.1.3 Effect of W 35
4.1.4 Effect of R 35
4.1.5 Effect of temperature 36
4.1.6 Effect of aging 37
4.1.7 Photocatalytic activity 37
4.2 Intermediates and kinetic modeling on photocatalytic degradation of phenol 48
4.2.1 Physical characteristics of the synthesized titanium dioxide 48
4.2.2 Photocatalytic activity of synthesized titanium dioxide 50
4.2.3 Identification of products 51
4.2.4 Investigation of the reaction mechanism 53
4.2.5 Reaction kinetics and reaction rate constants 55

Chapter 5 CONCLUSIONS 69
5.1 Preparation of crystalline nanosize titania by microemulsion 69
5.2 Intermediates and kinetic modeling on photocatalytic degradation of phenol 70
5.3 Recommendations 71

REFERENCES 73
Curriculum Vitae 87

LIST OF TABLES
Page
Table 4.1 Summary of experimental conditions and prepared nanosize titania 39
Table 4.2 Degradation of phenol and production of intermediates with initial phenol concentration = 0.385 mM, Vo = 150 mL, [Synthesized-TiO2] = 0.5 g L-1, pH = 6.5, Temperature = 25 oC, Io = 10.8 mW cm-2 at 254 nm @ 2 cm 59
Table 4.3 Concentrations of organic acids at various reaction times with initial phenol concentration = 0.385 mM, Vo = 150 mL, [Synthesized-TiO2] = 0.5 g L-1, pH = 6.5, Temperature = 25 oC, Io = 10.8 mW cm-2 at 254 nm @ 2 cm 60
Table 4.4 The calculated pseudo-first-order rate constants for reaction network in Figure 4.13 61


LIST OF FIGURES
Page
Figure 2.1 Schematically illustrated mechanism of photocatalysis 22
Figure 3.1 Schematic plot of photocatalytic reactor 32
Figure 4.1 X-ray diffraction patterns 40
Figure 4.2 X-ray photoelectron spectroscopy (XPS) patterns of 25.1 nm 41
Figure 4.3 Relation between mixing energy and particle size 42
Figure 4.4 Relation between AOT concentration (W) and particle size 43
Figure 4.5 Relation between TTIP concentration (R) and particle size 44
Figure 4.6 Arrhenius plot of log (d) particle size versus 103(1/T) 45
Figure 4.7 Relation between aging (days) and particle size 46
Figure 4.8 Relation between photocatalytic degradation rate (R) and particle size 47
Figure 4.9 XRD pattern of synthesized-TiO2 62
Figure 4.10 SEM photograph of synthesized-TiO2 63
Figure 4.11 Comparison of phenol conversion under various experimental conditions at different irradiation times for the degrading phenol in aqueous solution (Experimental conditions: Vo = 150 mL, [Phenol]o = 0.5 mM, [Synthesized-TiO2] = 0.5 g L-1, pH = 3, Temperature = 25 oC, Io = 10 mW cm-2 at 365 nm @ 2 cm; 50 mW cm-2 at 254 nm @ 2 cm.) 64
Figure 4.12 Selectivity (molar ratio of product produced to phenol reacted) of various products vs. phenol conversion 65
Figure 4.13 Selectivity (molar ratio of acid produced to phenol converted) of organic acids produced vs. phenol conversion 66
Figure 4.14 Proposed main reaction pathway network for phenol oxidation in UV/TiO2 system 67
Figure 4.15 Comparison of calculated and measured concentration changes of phenol treated and intermediates produced in UV/TiO2 system 68

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