Controlled synthesis and surface modification of titanium dioxide
Abakay, Ayça (2012) Controlled synthesis and surface modification of titanium dioxide. [Thesis]
Official URL: http://192.168.1.20/record=b1416993 (Table of Contents)
TiO2 nanoparticles were synthesized with simplified sol-gel method using water as solvent and Titanium tetraisopropoxide as precursor. The synthesized materials were characterized by Dynamic Light Scattering (DLS), Simultaneous Thermal Analysis (STA), X-Ray Diffraction (XRD) and C13 Nuclear Magnetic Resonance Spectroscopy (NMR). These characterization methods provide valuable information to understand crystal type and size of nanoparticles, effect of synthesis parameters, change in particle size of TiO₂ sols, thermal behavior and pH dependence of particles. The effects of synthesis conditions such as water:precursor molar ratio, amount of acid catalyst, amount of chelating agent, reaction temperature and time on properties of TiO₂ particles were investigated. High water:precursor molar ratio ensures small particle size and stable particles in aqueous suspension of TiO₂. Additionally, increasing acid amount results in smaller particle size and stable particles with higher surface potential. Results clearly show that acid catalyst has crucial effect on particle synthesis and it is not possible to obtain particles without acid catalyst. In this work acetic acid was used as chelating agent and according to obtained results fine particles can be obtained with higher acetic acid. Reaction temperature and time also serve for smaller size and stable particle. However, effects of these parameters are not significant compared to other parameters. Isoelectric point of TiO₂ sols was measured between pH 5 and 6. Lower and higher pH values result in stable sols which is needed condition for smooth applications. Additionally, it was observed that significant change in particle size occurs after synthesis reaction TiO₂ sol samples. This change was associated to uncompleted reactions of precursor and C13 NMR was used to understand this behavior. XRD patterns of samples showed that anatase crystal particles were obtained for samples on which calcinations process was not applied. Furthermore, it is determined with XRD measurements that water:precursor molar ratio does not have effect on crystal structure of the particles. Phase transition from anatase to rutile crystal phase was determined between 500 and 600°C. Simultaneous thermal analysis of TiO₂ sample support this phase transition temperature value. Surface modification of TiO₂ nanoparticles was done with aminopropyl triethoxysilane and modified particles were characterized by Fourier transform infrared spectroscopy (FTIR), STA and Elemental Analysis. Effects of modification conditions such as modifier concentration, TiO₂ concentration and reaction time were investigated. Increasing concentration of modifier has significant effect on amount of surface modification. On the other hand, above certain concentration amount of grafted amino silane is not affected. These results were verified with STA and Elemental Analysis. When TiO₂ concentration increases, reaction between surface OH group and alkoxy group of modifier increases and higher mass loss is observed in thermal analysis due to degradation of grafted organic materials. Moreover, longer reaction time results in higher coverage of modifier on the surface of the particle.
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