Study On Photocatalytic Properties Of Zn_xCd_1-xS Quantum Dots And Their Composites Photocatalysts

In recent years,with the continuous increase of social population and the development of industry,the excessive consumption of fossil fuels and the increasing concentration of CO₂have caused serious energy crisis and environmental pollution.Photocatalytic H₂ production has been considered as a promising technology to solve energy crisis and environmental pollution problems.Photocatalytic H₂ production is driven by solar energy,and H⁺is converted to H₂ on the surface of the photocatalyst.Zn O,a traditional semiconductor photocatalyst,has a boarder bandgaps of 3.2 e V,which widely limits the practical application of Zn O.Therefore,it is urgent to develop visible light response semiconductor photocatalysts.Zn_xCd_1-xS is a solid solution photocatalyst that responds to visible light.The bandgaps can be adjusted by changing the the ratio of the Zn and Cd,which can further affect its phtocatalytic performance.Namely,Zn_xCd_1-xS solid solution has a high conduction band position,which endows the photocatalytic electrons high reduction ability that can reduce the H⁺into H₂,or CO₂ into hydrocarbon fuel.However,Zn_xCd_1-xS suffer from faster photocatalytic electrons and holes recombination rate,resuting in a low photocatalytic performance.Thus,on the one hand,we can reduce the particle size of photocataltsts.When the particle size is less than its Bohr radius,the ZCS QD can be obtained.As the particle size decreases,the transfer distance of photogenerated carriers from the interior to the surface will decrease,reducing the recombination of photogenerated electrons and holes and improving the separation efficiency.On the other hand,quantum dots have high interface energy.Thus,the single quantum dots can easily reunite,which can lose the advangtage of quantum dots.Constructing heterojunction is a promising method to improve the separation and transfer efficiency of photogenerated carriers,increase the absorption capacity of light,and broaden the light absorption range.Importantly,loading ZCS QD onto two-dimensional nanosheets can form 0D/2D heterojunction photocatalyst,which can make the ZCS QD more stable.The main research contents are as follows:1.Synthesizing the ZCS QD and Zn_xCd_1-xS relative samples（ZCS RS）used for photocatalytic H₂-production.Oil-soluble ZCS QD was synthesized by a hot injection method using the Zn O and Cd O as material,octadecene as solvent,oleic acid as protective agent.Finally,water solubility ZCS QD was obtained by ligand exchange.At the same time,the ZCS RS was synthesized by the traditional co-precipitation.After that,study on the effect of semiconductor photocatalyst particle size on photocatalytic H₂-performance.The experimental results demonstrate that ZCS QD shows excellent photocatalytic H₂-production performance.It indicates that the partical size of semiconductor photocatalyst plays an important role in improving photocatalytic performance.2.WO₃ nanosheets were obtained by electrostatic assisted ultrasonic exfoliation method.ZCS QD was deposited on the surface of WO₃ nanosheets by calcination method to form ZCS QD/WO₃ S-scheme heterojunction used for photocatalytic CO₂reduction.The interaction between the ZCS QD and WO₃ nanosheets is conductive to the stability and dispersion of ZCS QD.More importantly,the S-scheme heterojunction formed between ZCS QD and WO₃ nanosheets is beneficial for the transfer and separation of electrons and holes at the interface.Thus,comparing with WO₃ nanosheets and ZCS QD,the ZCS QD/WO₃ composite shows the enhanced photocatalytic CO₂ reduction performance.