Construction Of Modified Two-dimensional Co-catalyst/CdZnS-based Schottky Junctions And Their Performance And Mechanism For Photocatalytic Hydrogen Evolution

"Energy crisis"and"environmental pollution"have become the two major issues of common concern and urgent to be solved around the world in which faced by the development of today’s society.One of the effective ways to solve these problems are to produce clean energy instead of traditional fossil fuels through green and advanced technologies,reduce carbon emissions and retardation global environmental pollution through their production and use,and thus achieve the transformation of the country’s energy structure and sustainable economic and social development.Among many emerging environmental technologies,semiconductor photocatalytic hydrogen production is recognized as one of the most environmental friendly technologies because it can directly utilize and convert solar energy into green chemical energy,otherwise,the hydrogen produced by this method called"green hydrogen"with no carbon emission during the production process.And in the co-catalyst/photocatalyst composite system,which is becoming more and more mature in current research,the loading of the co-catalyst will inevitably lead to the formation of some other interfaces and junctions between the semiconductor and co-catalyst,which is not conducive to the interfacial migration of photogenerated carriers.Therefore,after mastering the basic principles,application prospects and scientific problems of photocatalytic hydrogen production from semiconductor materials.The exploration of co-catalysts with efficient interfacial charge transfer capability,high activity as well as high stability is of great practical significance for the design of high-performance composite photocatalytic systems for photocatalytic hydrogen evolution.Based on the above analysis,we select 2D structure WS₂ and MXene phase Ti₃C₂T_x as template co-catalysts in the process of constructing composite system photocatalysts,and explore the gaps in current research,i.e.,the bulk phase and surface modification respectively,to enhance its ability for the rapid charge transfer in complex catalytic systems as a co-catalyst and to summarize their methods and regularly guide their future applications.The main research contents and conclusions were summarized as follows:（1）Co-WS₂ nanosheets were successfully synthesized by a simple one-step hydrothermal method.The variation of the XRD diffraction peaks and the lattice micro-strain of the（100）crystal plane proved that Co²⁺was successfully doped into the active（100）plane of WS₂ with a high exposed surface area.And it was shown by PL and TRPL analysis that the electron transfer from CZS to Co-WS₂ was faster than that from CZS to WS₂.Compared with CZS and 7%WS₂/CZS,the HER efficiency of 7%（Co-WS₂）/CZS was improved by 9.3 and 1.3 times,respectively.The results of DFT calculations also showed that doping Co²⁺into the（100）plane of WS₂could change the surface charge density and increase the charge density near Co²⁺in the（100）crystal plane,and the synergistic effect of the two aspects made Co-WS₂ more suitable than WS₂ as a non-precious metal-based co-catalyst to improve HER efficiency.The good chemical and physical structural stability of 7%（Co-WS₂）/CZS was also demonstrated by cyclic H₂ evolution experiments and XRD,SEM,and TEM tests.（2）Non-precious metal-based Ti₃C₂-A_x co-catalysts with high catalytic activity were prepared by a simple sonication method,and surface-active Ti-S bonds introduced AET to the Ti₃C₂T_x surface,replacing-F/-O passivation groups in the surface.The catalytic activity of the CZS/Ti₃C₂-A₄₀ Schottky junction was significantly improved compared with that of CZS and CZS/Ti₃C₂T_x.The H₂ evolution rates were5.8 and 1.9 times higher than those of the pristine Cd_0.4Zn_0.6S and CZS/Ti₃C₂T_x,respectively,and were superior to all reported CZS-based composite catalysts.Experimental and theoretical results show that the improved photocatalytic hydrogen production activity is attributed to the internal electric field formed at the Schottky junction interface,which facilitates the unidirectional transfer of electrons,and the Schottky barrier can effectively inhibit the recombination of electron-hole pairs,resulting in a more efficient carrier separation.