Preparation And Photocatalytic Properties Of Semiconductor Photocatalyst With Visible Light Response

The approach for improving photocatalytic efficiency by restraining the recombination of charge carrier and extending the photoresponse to the low energy region is a hot issue of semiconductor photocatalytic area at present.In this paper,the research progress of semiconductor photocatalysts was summarized and reviewed and two kinds of new photocatalysts with high photocatalytic activity were reported.The visible-light responding region of semiconductor ZnS with wide-bandgap was extended by doping Cadmium ions and the photoinduced charges separation of nano-composites CdS@TiO₂ was promoted by "shell" TiO₂ coating on the "core" CdS were described here in a detail way.The photocatalyst Cd_xZn_1-xS and CdS@TiO₂ were synthesized employing precipitate-hydrothermal or hydrolysis under the assist of ultrasonic irradiation method respectively.The as-prepared samples were characterized by X-ray diffraction(XRD),Transmission electron microscopy(TEM),UV-Vis diffuse reflectance spectroscopy(DRS) Scanning electron microscope(SEM)and Photoluminescence spectra (PL).The photocatalytic activity of the products were evaluated by the photocatalytic decomposition of methyl orange(MO)under visible light (λ＞390nm).Cd_xZn_1-xS photocatalyst was synthesized by a novel and simple chemical approach involved in precipitate-hydrothermal processes with alloy structure and the crystallite sizes were in the range of 25-35nm. The lattice structure gradually changed from hexagonal to cubic with increasing percentage of Zn in the ternary compound Cd_xZn_1-xS.The UV-Vis and PL spectra indicated that the optical properties of the obtained nanocrystals could be continuously modulated by tuning their compositions.The positions of absorption edges,band edge emission and deep level emission of Cd_xZn_1-xS all shifted towards the longer wavelength with the increase of Cd content.Cd_xZn_1-xS also showed the high photocatalytic activity in degradation of MO under visible light, and the remnant ratio was 3%～13%for 1 h far better than commercial photocatalyst P25.At last,photocatalytic degradation process of MO with Cd_xZn_1-xS as photocatalyst under visible light irradiation was investigated by UV-Vis spectra.CdS@TiO₂ photocatalyst was synthesized by sonochemical method with core-shell structure and the nano-composite sizes were in the range of 25-35nm.The core CdS was synthesized by hydrothermal method and then the shell TiO₂ nanocrystals were derived via Sol-gel technology.The presence of a small quantity of polyethyleneimine(PEI)on the surface of the CdS nanocrystals facilitated this coating process due to remarkablely increasing the isoelectric point(IEP)of CdS.The thickness of TiO₂ layer with clear interface and smooth surface were easily controlled by adjusting the ultrasonic irradiation time and the amount of precursor in contrast with other methods.The nano-composite CdS@TiO₂ exhibited excellent photocatalyic property as been measured by degradation of MO in the visible light region,which was mainly due to the effective separation of photoinduced charges.