Preparation And Photocatalytic Activity Of MoS₂/CdS-based Composites

In recent years, with the growth of worldwide industy, the severe environmental pollutions and energy crisis have become a major concern of society. Due to its high energy content and environmental friendliness, much attention has been focused on solar energy. Semiconductor photocatalysis technology is an important area for the useage of solar energy. Cadmium sulfide（CdS） is a typical combination of the Ⅱ B- Ⅵ A semiconductor material, and its band gap is 2.4 eV, which could be excited by visible light, and has good photocatalytic properties. However, bare CdS photocatalyst usually suffers from photocorrosion. Some researches have demonstrated that the combination of MoS₂/CdS can effectively improve the photocatalytic performance of CdS. In this thesis, a series of research has been done on the MoS₂/CdS-based composites:（1） MoS₂/CdS/TiO₂ nanocomposites were synthesized via solvothermal method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron micrograph, X-ray photoelectron spectroscopy, photoluminescence spectra, Ultraviolet–Visible diffuse reflectance spectroscopy, and photocatalytic measurement. Enhanced visible light photoresponse, higher efficiency of charge carriers separation, and improved photocatalytic degradation of methylene blue were confirmed for MoS₂/CdS/TiO₂ nanocomposites. It was observed that the highest degradation rate was achieved for MoS₂/CdS/TiO₂ nanoparticles（24%） prepared at 180 oC when exposed to visible light illumination for 80 min relative to CdS/TiO₂（20%） and TiO₂（15%）. This work demonstrates that synergetic effect of MoS₂ and CdS in which it proves to be an effective choice for improving the utilization of visible light of TiO₂-based materials.（2） ZnO nanorod was successfully prepared by solvothermal method, and then the MoS₂/CdS/ZnO composites were synthesized via hydrothermal method. The material’s phase composition and morphology were characterized by XRD, XPS, SEM and TEM, and the light absorption intensity of samples’ was test by UV-vis DRS. Moreover, the photocatalytic activity was also test by degradation MB under visible light irradiation. The results showed that the degradation efficiency of CdS/ZnO was about 1.3 times than that of pure Zn O, while the MoS₂/CdS/ZnO composites was 2 times than that of ZnO. The result indicated that CdS and ZnO modified MoS₂ had higher photocatalytic activity.（3） CdS photocatalysts loaded with Ag2 S and MoS₂ as dual co-catalysts were prepared via a one-step in-situ hydrothermal method using CdCl2·2.5H₂ O, H₂MoO₄, AgNO₃·9H₂O, and CS（NH₂）2 as the raw materials. The as-prepared photocatalysts were characterized by XRD, SEM, TEM, XPS, PL, UV-vis DRS. The highest photocatalytic degradation rate was achieved for Ag2S/MoS₂/CdS composites（87%） compared to MoS₂/CdS composites（66%） and CdS（62%） under visible light illumination for 60 min. The recycled photocatalytic experiments show that the photocatalytic stability of CdS was improved with the introduction of Ag2 S and MoS₂. The improved photocatalytic performance of Ag2S/MoS₂/CdS composites can be ascribed to the red shift of absorption edge, enhanced light absorption intensity, and the increased separation of the photoinduced electron-hole pairs, which was attributed to the synergetic effect of MoS₂ and Ag2 S on CdS. It was proven that Ag2 S and MoS₂ can act as effective dual co-catalysts to enhance the photocatalytic degradation activity of CdS.