Preparation And Visible Light Photocatalytic Properties Of Co₉S₈-based Transition Metal Sulfide Composites

The semiconductor photocatalytic technology driven by solar energy has been in-depth research and development since its proposal,and has shown great potential in alleviating the current environmental and energy crisis.So far,semiconductor materials for photocatalysis have been extensively developed and researched.Among them,transition metal sulfides have excellent photoelectrochemical properties and have received widespread attention.However,problems,such as high electron-hole pair recombination rate,greatly reduce its photocatalytic activity.In order to improve the catalytic performance of the photocatalyst,it can be optimized by constructing heterojunction composite structure,element doping,supporting co-catalyst,adjusting its morphology and structure,dye sensitization and other strategies.Among them,the supporting co-catalyst can increase reaction active sites,provide more electron transport channels,accelerate charge transfer and separation,and thereby improve photocatalytic activity.Precious metal promoters are expensive,and the development of non-precious metal promoters is of great significance.As a cheap and efficient transition metal sulfide promoter,Co₉S₈ has excellent photoelectrochemical properties,so it has received more and more attention.This thesis is dedicated to the design and preparation of Co₉S₈-based transition metal sulfide photocatalytic materials,and to improve the photocatalytic performance of the materials by adjusting the morphology,MOFs derivation,element doping,and building heterojunctions.The main work is as follows:（1）N,S-doped carbon nanotubes （CSCNS） embedded with Co₉S₈ nanoparticles were prepared by the method derived from MOFs,and ZnIn₂S₄ nanosheets（ZIS）were loaded on the surface of the CSCNS-ZIS composite material by the oil bath method.Under visible light irradiation,the hydrogen production performance of CSCNS-ZIS composite material was studied.After ZnIn₂S₄ nanosheets were grown in CSCNS,the hydrogen production performance was significantly improved.The hydrogen production rate of the best ratio composite material 5%-CSCNS-ZIS was 2409.2μmol·h^-1·g^-1,which was about 5.5 times higher than that of pure ZnIn₂S₄.After a series of characterization,the results showed that the Co₉S₈nanoparticles and N and S-doped carbon in the derivative were beneficial to charge transfer and separation as a co-catalyst,and the doping of S in the carbon material was beneficial to improve the light absorption efficiency and enriched Derivatives containing folds and particles,and the support of flake-shaped ZnIn₂S₄ all provide a large number of reactive sites.At the same time,the heterojunction structure formed by the composite accelerated the separation of photogenerated carriers,so the CSCNS-ZIS composite had excellent photocatalysis Hydrogen production performance.In addition,we also carried out a photocatalytic cycle experiment on the material,and the results showed that the composite material had good cycle stability.Finally,the photocatalytic mechanism of the system was studied.（2）Cd_0.85Zn_0.15S nanorods were synthesized by solvothermal method,and then Co₉S₈particles were loaded onto the Cd_0.85Zn_0.15S nanorods to form a one-dimensional heterojunction.Then the hydrogen production and degradation performance tests were carried out under visible light irradiation.The photocatalytic performance of Cd_0.85Zn_0.15S nanorods loaded with Co₉S₈particles was greatly improved.The optimal ratio of the composite material Cd_0.85Zn_0.15S-Co₉S₈-15%photocatalytic hydrogen production rate was 19.15 mmol·g^-1·h^-1,which was 4.5 times and 1915 times the hydrogen production rate of Cd_0.85Zn_0.15S and Co₉S₈.The degradation rate of tetracycline,a typical antibiotic,could reach 85%within 15 minutes.The research results showed that:Co₉S₈ as a co-catalyst improved the light absorption performance of the system and increases the reactive sites;excellent electrical conductivity could quickly lead out the photogenerated charge;the heterojunction formed with Cd_0.85Zn_0.15S could efficiently separate photogenerated electrons-hole pairs reduce the recombination efficiency of photo-generated electron-hole pairs,so the composite material had high-efficiency photocatalytic performance.Finally,the photocatalytic charge transfer mechanism,the Z-type heterojunction charge transfer mechanism,was proposed.The charge transfer path was confirmed to conform to the Z-type structure by photoreduction deposition of Pt,and the reason for the system’s high-efficiency photocatalytic performance was obtained.By designing two Co₉S₈-based transition metal sulfide materials,the application of non-noble metal promoter Co₉S₈ was explored.The prepared material had excellent photocatalytic performance,with important research significance and value for the development of new,efficient,inexpensive photocatalysts.