Preparation And Photocatalytic Performace Of ZnS-based Nancomposite Photocatalysts

Semiconductor photocatalysts has played a huge role in the field of environmental governance, especially in the degradation of organic pollutants in water by virtue of their environment-friendly and energy-saving features. Among them, ZnS have attracted much attention due to their unique properties and excellent performance. However, ZnS has a wide band gap and can only absorb UV light, which limits its practical applications. Recently, to improve the photocatalyitc activity by dopping and integrating has become one of the popular topics in the field of semiconductor photocatalysts.In this thesis, metal sulfide semiconductor photocatalysts were chosen as the research topics. Semiconductor composites such as CdS/ZnS nanosheets, Co、Mn-doped ZnS nanospheres and ZnO/CdS/ZnS nanospheres were prepared via solvothermal method, ion exchange and calcined technology. Photochemical properties of these nanocomposites were studied. It includes three sections as follows:(1) Preparation and Photocatalytic Performace of CdS/ZnS nanosheets:ZnS(en)0.5 precursor were prepared by solvothermal method. CdS/ZnS nanosheets were synthesized by a hydrothermal and cation exchange method. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (UV-DRS) and transmission electron microscopy (TEM) were used to characterize the compositions, structures, morphologies and properties of CdS/ZnS nanosheets. XRD results showed that the crystals obtained were CdS/ZnS nanocomposites rather than a physical mixture of ZnS and CdS. Furthermore, SEM image showed that the product exhibits a sheet-like structure. The photodegradation experiments of MO solution were carried out under visible irradiation with CdS/ZnS nanosheets as photocatalyst. Results demonstrated that CZ0.8 has the best photocatalytic performance. The decolorization efficiency of 50mL MO solution (10mg/L) would reach 99% after 60min under visible light with 10mg of CZ0.8 as photocatalyst.(2) Preparation and Photocatalytic Performace of Co-, Mn-codoped ZnS nanospheres:Firstly, Mn-doped ZnS nanospheres were prepared by a one-pot solvothermal synthesis; then, ion-exchange method was used to synthesize Co、Mn-codoped ZnS nanocomposites. The nanocomposites was characterized using XRD, UV-Vis and SEM, respectively. As seen in a SEM image, Co、Mn-codoped ZnS nanospheres have the diameter of about 400nm. The photocatalytic activity was evaluated by the photocatalytic decolorization of MO aqueous solution under visible-light irradiation with Co、Mn-codoped ZnS nanocomposites as photocatalyst. Results indicated that the nanocomposites exhibit the best photocatalytic performance. The decolorization efficiency of 50mL MO solution (3mg/L) would reach 96.65% after 90min with 20mg of the nanocomposites as photocatalysts.(3) Preparation and Photocatalytic Performace of ZnO/CdS/ZnS nanocomposites:ZnO/CdS/ZnS nanocomposites were prepared by a solvothermal method, followed by calcination treatment and ion exchange. The structure and properties were characterized by SEM, XRD, XPS and UV-Vis. SEM image shows that the product is nearly spherical with narrow size distribution. The photocatalytic activity was evaluated by the photocatalytic decolorization of MO aqueous solution under visible-light irradiation with ZnO/CdS/ZnS nanocomposites as photocatalyst. Results show that ZnO/CdS/ZnS nanocomposites exhibit the best photocatalytic performance. The decolorization efficiency of 50mL MO solution (10mg/L) would reach 96.8% after 60min with 20mg of the nanocomposites as photocatalyst.