The Study On Modification And Photocatalytic Performance Of CdS Semiconductor Materials

With the overuse of fossil fuels,environmental pollution and energy shortages have become the two major challenges that may affect the sustainable development of economy.It is imminent to solve these challenges.Since the phenomenon was found that H₂ and O₂ could be produced on TiO₂ photocatalyst for the first time by Japanese researchers under ultraviolet light irradiation,many research scholars continue to explore and find out new photocatalysts to solve environmental and energy problems,such as TiO₂,ZnO,Cu₂O,CuO,ZnS,CdS,CuS,BiVO₄,Ag₃PO₄ et al.Among them,CdS is far the most charming one because it is a direct semiconductor and responds to visible light with band gap of approximately 2.4 eV.Its valence band and conduction band position is 1.8 eV and-0.6 eV,respectively.And its conduction band position is more negative than the standard hydrogen-0.4 eV,which is satisfied with CdS of photocatalytic hydrogen production.But the serious photocorrosion and high recombination rate of photogenerated charge are two major factors affecting its performance.Some specific works have been done to resolve these two drawbacks.1.CdS and Pal/CdS composites photocatalysts were prepared by co-precipitation method.SEM images show that Pal/CdS composite materials were core-shell structure.Under visible light irradiation,their photocatalytic performance was evaluated by the degradation of organic dyes.The results show that the 0.5 Pal/CdS(m_Pal/m_CdS = 0.5)composite exhibits the best photocatalytic activity than others in the present study and excellent photo-stability.The addition of Pal alleviates the agglomeration of CdS nanospheres,provides more reactive sites for photocatalysts and improves separation and transfer efficiency of electron-hole.2.The MoS₂/CdS composites with different mass ratios were prepared by hydrothermal and solvothermal method.All samples were characterized by XRD,SEM,TEM,UV-vis DRS and so on.The performance of production hydrogen was tested with lactic acid as sacrificial agent under visible light irradiation.Among these composite materials,5 wt% MoS₂/CdS possesses the highest rate of H₂ and was about 6300 ?mol/h,which is about seven times than that of pure CdS.PL,PC and EIS measurements proved that the photoinduced charge in 5 wt% MoS₂/CdS composite is easier to separate than that of the pure CdS.The cycle test experiment confirmed that this composite material has an excellent cycle stability.3.CdS,Co₃O₄/CdS photocatalysts were synthesized by co-precipitation method at various mass ratios of Co₃O₄ and characterized by XRD,UV-vis DRS,SEM,TEM,PL and so on.We evaluated photocatalytic activitiy of samples for splitting water into hydrogen in 0.5 M Na₂S/Na₂SO₃ aqueous solution under visible light irradiation.Among the photocatalysts with various compositions,the maximum rate of H₂ obtained from 3 wt% Co₃O₄/CdS sample was about 1270 ?mol/h,which was increased up to about 3.5 times than that of the pure CdS.PL and EIS measurements demonstrated that p-n heterojunction suppresses charge recombination,improving interfacial charge transfers,consequently enhancing the photocatalytic activity for H₂ evolution.