Fabrication And Photocatalytic Performance Of Polyoxometalates/Cadmium Sulphide Composite Catalysts

Photocatalysis is a new type of catalytic technology that effectively converts solar energy into renewable energy.Its development not only helps to reduce dependence on fossil fuels,but also promotes the use of clean energy.Therefore,the development and rational use of photocatalysis will be the focus of future research in the field of energy chemistry and is key to achieving sustainable development goals.A wide variety of catalysts have been investigated.Polyoxometalates are of interest due to their excellent electron storage and transport capabilities,as well as their redox properties.In this paper,the discussion concentrates on polyoxometalates（POMs）based composite photocatalysts,which have unique structural features and strong oxidation properties and are easy to prepare.However,when polyoxometalates is used as a homogeneous catalyst alone,the photogenerated carriers complex faster,resulting in a lower conversion efficiency to solar energy.Therefore,in order to suppress the complexation of photogenerated carriers,this paper combines polyoxometalates with a semiconductor materials to form two composite photocatalysts,thereby increasing the charge separation efficiency and thus significantly improving the photocatalytic efficiency.The CdS@POMs and POMs@CdMOF@CdS composite photocatalysts were prepared mainly by microwave synthesis as well as hydrothermal synthesis.The photocatalytic performance of the prepared composite photocatalysts was tested and a series of characterisations were carried out under visible light irradiation,and their photolytic aquatic hydrogen and photo-oxidation of cyclohexene performance were mainly investigated.Details of the study are as follows:（1）CdS@POMs binary composite photocatalysts were prepared by loading POMs onto the surface of CdS nanosheets using a facile microwave synthesis method.Under visible light irradiation,the highest hydrogen production rate of 5.7 mmol/g/h was achieved in 6 hours with the CdS@PMo₁₂ composite catalyst,which is nearly 6 times higher than that of the pure CdS semiconductor catalyst.The composite of CdS and POMs accelerates the separation of photogenerated carriers and thus significantly improves the performance of photolytic hydrogen production.（2）POMs@CdMOF@CdS composites encapsulating different Keggin-type polyoxometalates were prepared by a hydrothermal method.By optimising the reaction conditions,the PMo₁₂@CdMOF@CdS composite catalyst encapsulating PMo₁₂exhibited excellent performance in the photooxidation of cyclohexene to epoxycyclohexane,with a maximum yield of 89%in 24 h using 5 mg of catalyst,cyclohexene（0.5 mmol,51μL）,isobutyraldehyde（1 mmol,91μL）,and dichloroethane（4 m L）,with a maximum yield of 89% in 24 h.