The Preparation And Properties Of TiO₂ Hollow Sphere-based Photocatalyst

As we all know, water pollution is becoming more and more serious. Semiconductor materials have received widely attention for its excellent photocatalytic performance. As one of the most important semiconduct photocatalysts, TiO2 possesses several advantages, for instance low cost, high chemical stability, environmental benign and resistance to photocorrosion and has been widely used in a variety of fields. However, it still suffers from rapid recombination of charge carriers and low light utilization efficiency. These factors have become the barriers of putting TiO2 into practical application. The hollow nanostructure allows multiple reflections of incident light, making efficient utilization of light energy. Moreover, coupling these hollow nanostructured materials with other materials is an effective strategy for the separation of electron-hole pair and contributing to further improvement of the photocatalytic activity. The thesis is devoted to couple hollow nanostructured TiO2 matrix with SnO2 and graphene(GR) respectively. Main research work includes the following aspects:(1) Multilayer TiO2@SnO2 hollow nanostructures have been successfully synthesized via a simple approach employing the template-assisted and hydrothermal methods. And the samples were characterized by XRD, SEM, TEM, EDS,N2 adsorption/desorption and UV-Vis DRS. The photocatalytic properties of the composite were investigated through the degradation of methyl orange solution under ultraviolet light irradation. The composites have the following advantages: multilayer core/shell structure can contribute to the enhancement of reflections and scattering of incident light. The preferable matchable band potentials between TiO2 and SnO2 lead to high separation efficiency of photoinduced electron and hole pairs. It is easy to separate the synthesized micrometer sphere from the catalytic reaction system owing to its large size. The porous structure which is ascribed to accumulation of small particles, can provide larger specific surface area and then be conductive to the enrichment of organic pollutant molecules at the interface. All above mentioned make the multilayered TiO2@SnO2 hollow nanostructures exhibit higher photocatalytic performance than TiO2 hollow sphere and P25. The results demonstrated that the molar ratio of Ti(SO4)2 to SnSO4 plays important roles in the composition and morphology of the products, and calcining temperature directly affected the crystallinity and the crystal type, and then influence the photocatalytic performance. The photocatalytic reaction rate of multilayered TiO2@SnO2 hollow nanostructures,which obtained at calcination temperature is 750 ℃ when molar ratio of Ti(SO4)2 to SnSO4 is 1.12:1, is 3.45 times higher than that of TiO2 hollow spheres and 5.65 times higher than that of P25.(2) Micro-sized TiO2 hollow spheres partially wrapped with reduced graphene oxide(GR) have been synthesized via a simple hydrothermal method. The results demonstrated that the –CON groups were formed during the synthesis process. The morphology, structure and optical properties of samples were characterized by XRD, SEM, Raman, FTIR, XPS, PL and UV-Vis DRS. The results showed that graphene oxide has been effectively reduced via hydrothermal process. The prepared hybrid composites could be used as photocatalysts for selective reduction of 4-nitroaniline and showed excellent photocatalytic performance. It was mainly attributed to the efficient nanostructures, resulting in the obvious improvement of interfacial charge separation and transfer efficiency, adsorptivity of reactants and light harvesting. Furthermore, the amount of graphene has a direct impact on the photocatalytic performance of composites and the optimum content of graphene is 3%. The photocatalytic reaction rate of TiO2 hollow spheres/3%GR(TiO2 HS/3%GR) is 1.6 times higher than that of TiO2 hollow spheres and 20 times higher than that of P25. Meanwhile, selective reductions of other aromatic nitro compounds such as 2-nitroaniline and 2,4-dinitroaniline were also performed, which demonstrste the photoactivity enhancement is general. Moreover, the photocatalytic performance is still good during four successive recycling tests for reduction of 4-nitroaniline over TiO2 HS/3%GR under simulated sunlight irradiation.