Defect Control And Heterostructure Formation Of AgInS₂ Quantum Dots And Photocatalytic Hydrogen Production Performance

Using photocatalytic decomposition of water to produce hydrogen and preparing hydrogen instead of non-renewable fossil energy is a hot research topic in the field of photocatalysis.I-III-VI quantum dot AgInS₂（AIS）quantum dot is an environment-friendly semiconductor nanocrystal,which has the advantages of non-toxicity,high defect tolerance and adjustable energy band structure.However,the problems of easy recombination of photo-generated carriers and low quantum yield hinder its development in the field of photocatalysis.Based on the understanding of the current research situation and how to solve the existing problems,this paper studies the construction of heterojunction and the control of surface defects.The main research contents of this paper are as follows:AgInS₂quantum dots have high defect tolerance,which allows multiphase existence,therefore,the photocatalytic hydrogen evolution efficiency can be enhanced by controlling defects,size or phase structure.In this work,ultra-small AgInS₂quantum dots with clear exciton absorption were prepared in water by reverse thermal injection method for the first time.After coarsening at 95℃or 135℃,AgInS₂growth based on directional assembly or rapid aggregation was observed respectively,and the tetragonal-orthorhombic phase transition occurred through aggregation growth.The phase change of AgInS₂was observed by studying the phase transition kinetics.Ultraviolet-visible absorption spectrum confirmed that the double absorption edge of t-o heterojunction can enhance the absorption of visible light.PL spectra show that the separation or transfer of carriers in this t-o junction is improved,and the t-o junction exhibits excellent photocatalytic hydrogen evolution performance,with a rate of 1022μmol·g^-1·h^-1,and the PHE rate is 51.1 times that of t-AIS or 3.8 times that of o-AIS.In this study,the photocatalyst with high hydrogen yield was designed by constructing heterojunction,which provided a new idea for designing ternary alloy quantum dots with strong coupling interface.The surface engineering of AgInS₂provides an effective photocatalytic hydrogen evolution platform for zinc alloy AgInS₂which can adjust the band gap.Understanding the relationship between the band gap related defects,zinc alloy and Zn S shell is very important for designing effective photocatalyst.The growth kinetics of GSH-coated AgInS₂quantum dots involving the size and defect evolution and the PHE rate of the catalyst corresponding to the growth kinetics were studied.Combined with structural characterization,PL analysis show that these planar defects constructed by directional assembly are the main reasons for strengthening PHE.In order to stabilize or passivate the defects of AIS,TGA-assisted zinc alloying and zinc sulfide deposition were further designed,and ZAIS quantum dots with zinc alloy and AIS@Zn S and ZAIS@Zn S nanocrystals with core-shell structure were obtained respectively.PL and photocurrent show that the carrier separation or transfer in ZAIS is effectively improved,and the carrier separation or transfer in Zn S with core-shell structure is obviously reduced.ZAIS shows an excellent PHE rate of 2.01 mmol·g^-1·h^-1,which is 3.6 times higher than AIS quantum dots and 11.8 times higher than AIS@Zn S PHE efficiency of 0.17 mmol·g^-1·h^-1.Based on the analysis of energy band structure,the decrease of PHE of AIS@Zn S or ZAIS@Zn S can be attributed to the passivation of related defects caused by DB.This work provides a new idea for designing the core-shell structure or the visible light photocatalytic performance enhanced by alloyed ternary quantum dots.