Synthesis And Characterization Of Highly Self-dispersed Titanium Dioxide With Superior Photocatalytic Activity

Nanoscaled TiO2with excellent physicochemical properties has been led to many promising applications in areas ranging from photocatalysis, photovoltaics and sensors to sunscreens and paints. Nowadays, many applications require TiO2nanoparticles could disperse in the liquid medium stably. However, nanoparticles tend to accumulate due to their high surface energy. Surface modification is a common method to enhance their dispersion property, but results in the photocatalytic activity decrease. Therefore, it is important to develop new methods to synthesize TiO2nanoparticles with high dispersibility and photocatalytic activity.In this thesis, we report a nonaqueous sol-gel method to synthesize highly self-dispersed TiO2nanocrystals with superior photocatalytic activity. The as-prepared sample was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption measurements. The resulting sample was pure anatase TiO2with high crystallinity. The size of the TiO2nanoparticles was uniform and about10nm. The stability of the TiO2dispersion was evaluated by the change rate of transparency and Zeta potential. It was found that the as-prepared TiO2could well self disperse in different solvents without adding any dispersant. We also proposed a possible mechanism of this interesting dispersibility as follows. During the formation process of titanium dioxide, high concentration of titanium alkoxide significantly retarded the growth of nanoparticles and solvothermal condition contributed to its good crystallinity. In addition, the as-prepared titania particles appeared to be positively charged. The inner shell of charge and the outer ionic atmosphere formed the electrical double layer. There was a repulsive interaction between the charges of the electric double layers on neighbouring particles. Therefore, both the small particle size and electric double layers made the TiO2nanoparticles well dispersed in solution.The sample exhibited high photocatalytic activity on the degradation of RhB solution under visible light. The visible light photocatalytic activity of the sample could be attributed to the following reasons. First, the carbonaceous species on the TiO2surface was able to absorb visible light as a photosensitizer. It also might act as an impurity of TiO2to form interface states that effectively lower the band gap. Second, carbonaceous species on the surface of the TiO2reduced the recombination rate of CB electrons and VB holes. Finally, large surface area of TiO2was also a key factor in high photocatalytic activity.