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Design,Synthesis And Photocatalytic Performance Of Cadmium Sulfide Heterojunctions

Posted on:2022-11-09Degree:MasterType:Thesis
Country:ChinaCandidate:Z H LiFull Text:PDF
GTID:2491306770493994Subject:Inorganic Chemical Industry
Abstract/Summary:PDF Full Text Request
In recent years,with the rapid economic and social development,human beings have overexploited and utilized energy,especially fossil fuels,which has caused serious ecological and environmental problems.Therefore,it is imperative to research and develop new renewable clean energy.As a secondary energy source,hydrogen energy has the advantages of high fuel calorific value,abundant raw material sources,and no pollution of oxidation products.It is considered as one of the most ideal environmentally friendly energy sources to replace fossil fuels.Among various hydrogen production methods,semiconductor photocatalysis technology can directly utilize solar energy to produce hydrogen by water splitting reaction,which shows broad application prospects in solving energy and environmental problems.The design and development of new high-performance semiconductor materials is the core of photocatalysis technology.Among all kinds of semiconductor materials,CdS has strong visible light absorption ability and suitable conduction band position,which makes it an ideal catalyst for photo-splitting water for hydrogen production.However,its photocorrosion and high carrier recombination rate reduce the photocatalytic efficiency.In view of the above problems,CdS is adopted as the research object in this paper.A series of CdS-based composite photocatalysts with novel structure are synthesized by means of constructing heterojunction,introducing vacancy defect,and controling hollow structure,thererby improving the performance of photo-splitting water for hydrogen production significantly.The specific research contents of this paper as follows:(1)The porous heterostructures of S-deficient Co S/CdS hexagonal nanoplates(HNPs)were fabricated for the first time through a self-template approach combined with a solvothermal process.The Z-scheme charge transfer pattern of the Co S/CdS HNPs heterojunction was proposed by band structure analysis,scanning Kelvin probe microscopy and·OH radical measurements.These unique Co S/CdS HNPs demonstrated excellent photocatalytic activity and stability for the H2 evolution reaction(HER)under visible-light(λ>400 nm)irradiation.And its optimal HER rate is as high as 39.29mmol·h-1·g-1,approximately 152,112,and 51 times that of Co S,CdS,and 3 wt%Pt-loaded CdS,respectively.The exceptional HER capability of Co S/CdS HNPs heterojunction could be attributed to their outstanding visible-light harvesting capability,efficient Z-scheme charge separation,and abundant H2 evolution active sites.(2)A series of ZnS/CoSx-CdS heterojunctions with hollow polyhedral structure were synthesized by solvothermal method combined with cation exchange reaction using ZnCo metal-organic framework structure as sacrificial template.The Z-scheme charge transfer pattern of the Zn S/Co Sx-CdS composite was proposed by band structure analysis,scanning Kelvin probe microscopy and·OH radical measurements.The photocatalytic test results under visible-light(λ>400 nm)irradiation showed that Zn S/Co Sx-CdS has the HER rate is as high as 32.62 mmol·h-1·g-1,and apparent quantum yield of 13.3%and 11.6%at 400 and 420 nm,respectively.The excellent photocatalytic activity of Zn S/Co Sx-CdS is related to the following reasons:Firstly,the hollow polyhedron structure is beneficial to multiple reflection and scattering of incident light and improves the capture efficiency of light.Secondly,the Z-scheme charge transfer pathway effectively promotes the separation efficiency of photogenerated charge.In addition,the Zn-vacancy and S-vacancy not only enhance the light absorption but also provide the capture sites for holes and electrons to enhance charge separation.(3)The Cd1-xZnxS@CdCN2 concentric circular nanosheet synthesized by oil bath reaction was used as precursors.A unique Cd1-xZnxS@CdS-Ni(OH)2(CZxS@CdS-Ni(OH)2)composite photocatalyst was synthesized by in-situ sulfidation and photodeposition strategy,in which Cd CN2 was converted into CdS through sulfidation reaction,while Ni(OH)2 cocatalyst was loaded on CZxS central particles through photodeposition reaction.The photocatalytic test results under visible-light(λ>400 nm)irradiation showed that the highest hydrogen production rate is 34.94 mmol·h-1·g-1 of CZxS@CdS at x=0.25(CZ0.25S@CdS).Moreover,after photodeposition of Ni(OH)2,the hydrogen production rate of CZ0.25S@CdS-Ni(OH)2 is further significantly increased to 77.66 mmol·h-1·g-1.The study shows that the type II heterojunction is formed between CdS and CZ0.25S,and the p-n heterojunction is formed between CZ0.25S and Ni(OH)2.The synergistic effect of the two heterojunctions can effectively promote the spatial separation of photogenerated charge,thus greatly improving the efficiency of photo-splitting hydrogen production water.In addition,the CZ0.25S@CdS-Ni(OH)2 composite has good hydrogen evolution stability under prolonged visible light irradiation.
Keywords/Search Tags:cadmium sulfide, heterojunction, vacancy defect, hollow structure, photocatalytic hydrogen evolution
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