Preparation And Photocatalytic Water Splitting Properties Of Actinomorphic ZnO/Au/CdS Nanocomposites

As a clean energy,hydrogen(H₂)has the advantages of abundant reserves,high combustion value and pollution-free products,and it is known as the"ultimate energy"of the 21st century.It is an ideal way for H₂ generation by photocatalytic water splitting by using semiconductor materials as catalysts.A variety of photocatalytic water splitting for H₂ generation technologies based on semiconductor materials have been developed.As a direct band-gap semiconductor,zinc oxide(ZnO)is a potential photocatalytic material due to its advantages of low exciton binding energy,high electron mobility,simple preparation process,low cost and pollution-free.However,the band gap of ZnO is about 3.3 e V,and its light absorption range is limited to the ultraviolet region,accounting for only about 5%of the solar spectrum.In order to broaden the range of light response,reduce the recombination of photogenerated carriers and improve the efficiency of hydrogen production from water splitting,a novel actinomorphic ZnO/Au/CdS nanocomposite catalyst is prepared in this thesis.The deposition of cadmium sulfide(CdS)broaden the photo-response range of ZnO,the introduction of Au nanoparticles is used as a cocatalyst to reduce the recombination of photogenerated carriers at the interface of ZnO/CdS and further enhance the photocatalysis activity.In this thesis,the crystallinity,morphology,optical properties and photocatalysis activity of actinomorphic ZnO/Au/CdS ternary nanocomposites are characterized and measured detailly.The specific research contents are as follows:(1)The actinomorphic ZnO nanorods are synthesized by chemical water bath method and CdS nanoparticles are deposited by successive ionic layer adsorption and reaction method.Detailed characterizations and measurements are employed to investigate the crystal structure,morphology,optical properties and photocatalytic water splitting performance of the samples.The results show that the CdS is successfully deposited on the surface actinomorphic ZnO nanorods,compared with the pure ZnO,the light absorption range is broadened from uv region to visible region,the light absorption edge red shifts to 530 nm,and the intensity of light absorption increase with the increase of the layer number of CdS sensitization.When the CdS sensitization layers is 5 cycles,the photocatalytic water splitting performance of actinomorphic ZnO/CdS nanocomposite is 346.0?mol/g/h,which is 15 times than that of pure ZnO.The enhanced photocatalytic performance of actinomorphic ZnO/CdS nanocomposite is attributed to the expansion of the light absorption range,and the step energy level structure formed between ZnO/CdS interface promotes the separation of electron-hole pairs,resulting in improved photocatalytic performance.(2)In order to further reduce the recombination of photogenerated carriers at the ZnO/CdS interface,Au nanoparticles are introduced into the interface of ZnO/CdS by photo-deposition method.The crystallinity,morphology,composition,optical properties and photocatalytic water splitting performance are characterized and measured detailly.The results show that the photocatalytic activity of actinomorphic ZnO/Au/CdS nanocomposites are significantly enhanced after the introduction of Au nanoparticles at the interface of ZnO/CdS,and the gas generation rate is 502.2mol/g/h,which is 22.5 and 1.5 times than that of the pure ZnO sample and ZnO/CdS sample,respectively.The enhanced photocatalytic activity is attributed to the improved light absorption capacity,electron separation and transfer efficiency simultaneously.