Construction And Photocatalytic Hydrogen Evolution Performance Of CdS-based Heterostructure Catalysts

Solar water splitting is a green clean technology to mediate the increasing energy crisis and environmental pollution,and the preparation of catalysts is the key to this technology.CdS has a good optical response to visible light due to its narrow band gap.However,the rapid electron-hole recombination and serious inherent photocorrosion limit its application.Therefore,in this paper,CdS/oxide,CdS/sulfide and CdS/oxide/sulfide heterostructures have been constructed from the perspective of electronic structure and band matching.The as-prepared heterostructures not only prolong the lifetime of photogenerated electrons and holes,but also expand the photo response range of CdS.As a result,high rate of photocatalytic hydrogen production was achieved.TiO₂/Ti₂O₃ heterostructures consisting of in situ grown TiO₂ nanotubes with mixed anatase and rutile phases on bulk Ti₂O₃ materials were fabricated through hydrothermal treatment,acid washing and calcination processes.Then a impregnation method was used to construct TiO₂/Ti₂O₃/CdS heterostructures.Attribute to the synergistic effect of the TiO₂,Ti₂O₃ and CdS,the absorption of sunlight,transfer of photogenerated carriers and photocatalytic hydrogen evolution activity were greatly enhanced.The rate of photocatalytic hydrogen evolution can reach 1.90 mmol·g-1·h-1.CdS/Co?OH?2 nanocomposites were fabricated through a hydrolysis-precipitation process of 2-methylimidazole and Co²⁺,and subsequent calcination of the CdS/Co?OH?2 nanocomposites in the inert atmosphere leaded to CdS/CoO heterostructures.The introduction of CoO can effectively enhance the light absorption,prolong the carrier lifetime,and improve the photocatalytic performance of CdS/CoO heterostructures.Meanwhile,the rate of photocatalytic hydrogen evolution of the CdS/CoO-1h heterostructures can reach a rate of 6.45 mmol·g-1·h-1 without using any noble metal cocatalyst under visible light irradiation.Moreover,the XPS,XANES and theoretical simulation results indicated that the Co-S bond formed between CdS and CoO greatly contributes to enhance the ability of photocatalytic hydrogen production.CdS/NiS and CdS/Cu₇S₄ heterostructures were prepared by one-step hydrothermal and ion exchange methods,respectively.In addition,the introduction of g-C₃N₄ can effectively enhance the absorption of sunlight and improve the stability of the catalysts.The NiS can greatly improve the response of CdS in the visible region,while the presence of Cu₇S₄ further extended the absorption range into the NIR light region because of the plasmonic absorption of Cu₇S₄.In addition,by adjusting the content of NiS and Cu₇S₄ with CdS,the hydrogen evolution on heterostructures can be effectively tuned and the hydrogen evolution rates can be as high as 3.10 and 3.60 mmol·g-1·h-1 without using any noble metal cocatalyst.The impregnation method and ion exchange method were promoted for fabricating H-TiO₂/CdS/Cu_2-xS heterostructures with highly dispersed ultrafine??4 nm in diameter?CdS and Cu_2-xS nanoparticles on H-TiO₂ nanobelts.In addition,the CdS/Cu₇S₄/CdMoO₄ heterostructures were prepared successfully through the method of ion exchange.Both the H-TiO₂/CdS/Cu_2-xS and CdS/Cu₇S₄/CdMoO₄ heterostructures can absorb ultraviolet,visible and near-infrared light due to their special band gaps.To further confirm the efficient separation of charge carriers,the behavior of charge trapping and separation in heterostructures were compared by the photoelectrochemical tests.It was found that the tuned bandgap alignments in CdS/Cu₇S₄/CdMoO₄ heterostructures enable efficient separation of photogenerated charge carriers,leading to high rate of hydrogen evolution of 16.55 mmol·g-1·h-1.In summary,CdS-based heterostructures can effectively enhance the absorption of sunlight and promote the separation and transport of carriers,which can provide scientific basis for the design of efficient semiconductor heterostructure photocatalysts.