Preparation And Catalytic Activity Of Nanoscale Metal Oxides Photocatalysts Having C₆₀ Or Graphene

Both air purification and degradation of organic pollutants in waste water can be achived by means of light-to-chemical energy conversion realized by photocatalysis. As one of the most widely researched materials, TiO₂ possesses many kinds of advantages, such as lower cost, non-toxicity, no photocorrosion, good stability and strong oxidative capacity. But some disadvantages limit its application. For example, the quantum transfer efficiency of TiO₂ is very low, and visible light cannot be utilized due to its large band gap. In order to explore the photocatalysts with higher activity, the modification of TiO₂ is studied, furthermore, alternative materials are also attempted. It is found that ZnO is another one of the best photocatalysts.In this thesis, TiO₂ and ZnO were modified by C6o and graphene with special structural characteristics and photoelectrochemical properties, respecitively. The purpose was to realize the efficient separation of photoinduced electron/hole pairs and to improve the photocatalytic activity of TiO₂ and ZnO.Anatase TiO₂ nanoparticles loaded with different mass fractions of C₆₀ were synthesized in a hydrothermal process using water soluble C₆₀ and TiO₂ colloid as precursors. The photocatalytic activity of the C₆₀/TiO₂ nanocomposites as investigated by using p-nitrophenol as a model pollutant under UV and visible light irradiation, respectively. The results showed that the TiO₂ loaded with C₆₀ possessed higher photocatalytic activity than pure anatase TiO₂, and an optimal mass fraction of C₆₀ in TiO₂ was about 0.5wt%. The results of photoluminescence spectra, solid diffuse UV-vis spectra suggested that C₆₀ could transfer electrons and promoted the separation of photoinduced electron-hole pairs. Furthermore, the photocatalytic degradation mechanism of the C₆₀/TiO₂ nanocomposites was discussed, which was considered as a catalyzed photoreaction. By the comparison of photocatalytic degradation efficiency with 0.5wt% C₆₀/TiO₂ as a photocatalyst after various recycles, it was found that the photocatalyst was well stable. In addition, the nanocomposite of water-soluble C₆₀ and anatase TiO₂ was prepared by adsorption method. The degradation activities of the C₆₀/TiO₂ prepared by the two methods were compared using PNP as a model contaminant. The results showed that the C₆₀ in the C₆₀/TiO₂ prepared by adsorption method was profitable for photoelectrons transferring towards C₆₀ relative to that prepared by hydrothermal process, which made the C₆₀/TiO₂ prepared by adsorption method display higher photocatalytic activity. However, the stability of the catalyst prepared by adsorption method was worse because the C6o on the surface of TiO₂ easily falled off.The x%C₆₀/ZnO nanorods composites with vavious amounts of C6o were synthesized in the hydrothermal processes without any template. The results of XRD and TEM showed that the C6o of certain amounts in ZnO had little effect on the crystal and morphology of ZnO. In addition, the photocatalytic activity of the C₆₀/ZnO nanocomposites was investigated by using rhodamine B as a model pollutant under visible light irradiation. The results showed that the C6o in the C6o/ZnO photocatalysts was served as a photo-electron trap, facilitated transfer of photoinduced electrons, and inhibited recombination of electrons with RhB+.Subsequently, the photocatalytic activity of ZnO was improved by loading with C₆₀-Compared with pure ZnO nanorods, the adsorbance of the x%C₆₀/ZnO nanorods to rhodamine B increased significantly. Perhaps, it was another reason for the enhanced photocatalytic activity of the x%C6o/ZnO nanorod photocatalysts. Combined the result of photocatalysis with that of photoluminescence spectra, it was demonstrated that the degradation of rhodamine B was a self-sensitized photoreaction process with the C₆₀/ZnO composite as a photocatalyst. Importantly, the stability of the C₆₀/TiO₂ photocatalyst is high, and the degradation efficency of RhB can still reach 90% after being recycled for seven times.With graphene and TiO₂ colloid as precursors, nanocomposites of graphene and anatase TiO₂ were prepared in a solvothermal process. The results of IR spectra showed that the carboxylic groups were produced in the structures of graphenes during thermally reduced graphite oxide, which made graphene interacte with TiO₂ more easily. It was benefit for the separation of electron/hole pairs. The photocatalytic activity of the graphene loaded anatase TiO₂ was investigated by using rhodamine B as a model pollutant under UV light irradiation. The results showed that the loading amounts of graphene had great influence on the photocatalytic activity of TiO₂. It is profitable for improving the photocatalytic activity of TiO₂ by loading proper amounts graphene in TiO₂, and an optimal mass fraction of C₆₀ in TiO₂ was about 0.5wt%. Combined with the result of photoluminescence spectra, it was suggested that the graphene can serve as electron traps and promote the electron/hole separation of TiO₂.