Study On The Preparation And Photocatalytic Properties Of Nano-composites Based On ZnO

In recent years, environmental pollution problems become more and more serious. Photocatalytic technology is one of the effective ways to solve the problems. Semiconductor photocatalyst is payed more attention due to its excellent properties. As photocatalyst, ZnO is the most widely used by researcher, but ZnO is a wide band gap semiconductor with strong photosensitiveness, strong oxidation ability and stable chemical property, also it is nontoxic and easy to synthesize. Nevertheless, limited visible light spectrum and the fast recombination of the electron-hole pairs restrict the applications in photocatalysis. But compositing narrow band gap semiconductor materials on the surface of ZnO can improve the photocatalytic activity. CdS is considered to be one of the most suitable sensitizers for ZnO, in particular, it has a high optical absorption coefficient and a similar lattice of ZnO.In this thesis, a two-step process is proposed for the fabrication of ZnO/CdS core-shell nanocomposites. Firstly, hydrothermal process was used to grow ZnO nanowires on the Si substrates. We systemically studied the effect of ZnO seed, hydrothermal conditions. In addition, we fabricated ZnO nanowires with an aspect ratio of 35 which were vertically aligned to the Si substrate. Secondly, ion-exchange reaction was employed to prepare ZnO/CdS core-shell nanocomposites. We researched the effect of ion exchange time and solution concentration on the structure and optical performance of ZnO/CdS core-shell nanocomposites. Finally, the photocatalytic properties of ZnO/CdS core-shell nanocomposites were also studied. It was confirmed that the ZnO/CdS core-shell nanocomposites exhibit improved photocatalytic performance compared to bare ZnO. The degradation rate of the nanocomposites under UV light increased about 50%.