Preparation And Photocatalytic Performance Of CdZnS Composites

With the development of socity,the rapidly growing energy demands and the increasinglyingly serious problem of environmental pollution have raised widespread concerns about the development of renewable and sustainable energy cources to replace tradition fossil fuels.Hydrogen?H₂?have been considered as a potential fuel owing to its high combustion efficiency,renewable and environmentally-friendly combustion production.Water splitting over semiconductor is a simple and effective method for H₂evolution,which is considered to have a propective prospect in the storge and utilization of solar energy.However,the photocatalytic water splitting reaction of the most catalysts is difficult due to the slow surface reaction kinetics,unsutible energy band position,and low efficiency of charge separatopn.Therefore,it is necessary to design the efficient photocatalysts for H₂ production.CdZnS?CZS?photocatalyst have attracted extensive attention,owing to its relatively narrow band gap and outstanding light harvesting.In this paper,the CZS-based composite catalysts are prepared by simple hydrothermal and the photocatalytic activity of the composites is investigated.The main results include the following aspects:?1?The porous Al₂O₃ with surface oxygen vacancies was successfully prepared via solution combustion,and the CZS/Al₂O₃ composite structure was formed by the hydrothermal method.The XPS results confirms that the existence of oxygen vacancy on the surface of Al₂O₃.The TEM results shows that CZS and Al₂O₃ form a close interface,which is helpful for the rapid transfer of photogenerated charges.The oxygen vacancies on the surface of Al₂O₃ can act as electron traps to capture photo-generated electrons,resulting in the separation efficiency of photo-generated electron-hole pairs.And we exploed the effects of the oxygen vacancies on the performance of composite structures for photocatalytic H₂ production.It was found that when the molar ratio of CZS to Al₂O₃ was 5:3,the CZS/Al₂O₃ composite structure exhibit the best photocatalytic H₂ evolution rate of 31.63 mmol·g^-1·h^-1.?2?The introduction of the cocatalyst can decrease the overpotential for H₂evolution,promote the separation of photo-generated charge,and provide the reactives,thereby promote the photocatalytic activity of the catalyst.CZS/Ni₂P composite structure was prepared by two-step hydrothermal method.CdZnNiS sample was firstly synthesized and then CZS/Ni₂P composite structure was prepared via surface phosphating reaction.A close contact interface was formed between CZS and Ni₂P through two-step hydrothermal method.The XPS results shows that the formation of Ni-S bonds on the interface between Ni₂P and CZS to provide a channel for electron transfer,thereby promote the separation of photo-generated charge.During the photocatalysis processing,Ni₂P can be act as electron traps to capture photo-generated electrons from CZS and provide proton reduction sites,thereby improve the photocataltic performance.With the introduction of Ni₂P,the photocatalytic activity of the composite structure has been significantly improved.When the loading of Ni₂P is 0.3 mol%,the photocatalytic H₂ evolution rate can reach 41.26 mmol·g^-1·h^-1.?3?Co₃O₄ is typical p-type semiconductor with excellent optical properties.Therefore,it seems quite promising to couple Co₃O₄ and CZS to form p-n heterojunction to obtain high photocatalytic H₂ production performance.In order to further improve the photocatalytic activity of p-n heterojunction,loading suitable cocatalysts to enhance the separation of photo-generated charges is an effective approach.Ni₂P/CZS/Co₃O₄composite structure was successfully prepared based on three-step hydrothermal method.The TEM results shows the formation of the Ni₂P/CZS/Co₃O₄ ternary heterostructure.The CZS/Co₃O₄ heterostructure can effectively promote the separation of charges.The Ni₂P loaded on the surface of CZS can be act as electron traps to attract the photo-generated electrons from CZS and provide proton reduction sites.