Design And Synthesis Of S-Scheme Heterojunction Catalysts Constructed From Metal Sulfides And Layered Bimetallic Hydroxides And Their Photocatalytic Hydrogen Evolution

The aim of this paper is to design and prepare efficient photocatalytic materials for the construction of an efficient photo-induced decomposition of water for hydrogen production.The related research work was mainly carried out in the following aspects:（1）CdS and layered double hydroxides are the hot materials for photocatalytic hydrogen evolution reaction due to their unique structure and excellent performance.Here,CdS/NiCo LDH catalyst with S-scheme heterogeneous is successfully prepared by the method of electrostatic self-assembly.Compared with CdS,the hydrogen evolution performance over the appropriate CdS/NiCo LDH is increased by 3.6 times.This is because the tight coupling of the contact interface between CdS and NiCo LDH and the matching of the band gap structure improve the transmission efficiency of photogenerated electrons.Ultraviolet-visible and photoluminescence experiments have proved that the separation efficiency of electrons and holes,the light absorption intensity and the charge lifetime of the composite catalyst have been greatly improved.Additional series of characterization prove the possible S-scheme heterojunction mechanism of CdS/NiCo LDH photocatalytic hydrogen evolution.（2）High-performance and noble metal-free MoO₃/Cd_0.8Mn_0.2S nanocomposites were synthesized via a simple direct physical mixing process.Consequently,from the many characterization methods,the obtained MoO₃/Cd_0.8Mn_0.2S composites exhibited excellent photocatalytic hydrogen production performance and stability.The enhanced photocatalytic activity of the MoO₃/Cd_0.8Mn_0.2S catalyst could be ascribed to the close contact interfaces and well-matched band structure of MoO₃and Mn_0.8Cd_0.2S,which is beneficial to the transport and separation of photonic excitons.Besides,the hydrogen production performance of the MoO₃/Cd_0.8Mn_0.2S composite catalyst was 1.7 times higher than that of the pure MoO₃.Based on the results of time-resolved fluorescence（TRPL）and electrochemical measurements,the possible S-scheme heterojunction mechanism of the photocatalytic hydrogen evolution of MoO₃/Cd_0.8Mn_0.2S was proposed.This work has contributed to the transformation of solar energy into chemical energy.（3）ZnCdS/NiAl hydrotalcite S-scheme heterojunction with highly effective photocatalytic hydrogen evolution activity was devised and prepared by a simple solution-based mixing way.Layered double hydroxide（LDH）,also called hydrotalcite-like compound,is composed of adjustable metal cations and exchangeable anions between layers.The hydrogen evolution performance of ZnCdS/NiAl LDH is about 7 times that of ZnCdS and 130 times that of NiAl LDH.Because the rod-shaped ZnCdS and the layered NiAl LDH can construct close interface contact.This interface contact helps to accelerate charge transfer,thereby achieving more effective photocatalytic hydrogen evolution.The S-scheme ZnCdS/NiAl LDH heterojunction catalyst shows excellent hydrogen evolution and good stability,which not only gets benefits from the prominent performances of the cob-like ZnCdS and the layered NiAl LDH but also the matching bandgap structure for them.The configuration of the S-scheme ZnCdS/NiAl LDH heterojunction catalyst accelerates the rapid charge movement and inhibits the recombination of charge carriers,thereby greatly enhancing visible-light-driven water splitting,which is corroborated by the PL spectrum,I-T,LSV,EIS,Mott Schottky and UV-vis DRS studies,etc.（4）NiO and Co_1.29Ni_1.71O₄were generated in situ by oxidizing and calcining NiCo LDH to erect an S-scheme heterojunction heterogeneous catalyst.The composite catalysts have thinner flakes and some of the flakes are porous,which can provide more active sites for the reaction.The amount of hydrogen released by composite catalysts is 3 times that of NiCo LDH.This in-situ generation method will allow NiO and Co_1.29Ni_1.71O₄to establish a close relationship,form a built-in electric field,and build an S-scheme heterojunction.NiO and Co_1.29Ni_1.71O₄have good band structure and band gap position matching.S-scheme heterojunction composite catalysts has the best light absorption intensity and photocurrent response,the smallest electronic impedance and good electron and hole separation efficiency,thereby improving the performance of photocatalytic hydrogen evolution.It was confirmed by a large number of characterization studies.