Preparation Of Ⅱ-Ⅵ Quantum Dots-based Nanocomposites And Their Application In Photocatalytic Hydrogen Production

The massive use of fossil fuels,the increasing demand for energy and the resulting environmental pollution have brought serious problems to our lives.Photocatalytic hydrogen production is an effective way to alleviate and solve this problem.In this paper,a series of composite photocatalysts were obtained by modifying different semiconductor materials withⅡ-Ⅵquantum dots（QDs）.The photocatalytic water splitting performance of the composite photocatalysts was studied,the structure,composition and photoelectrochemical properties of the composite photocatalyst were investigated,and the mechanism of the enhanced photocatalytic performance was explored.The research content mainly included the following parts:（1）In-MIL-68 with hexagonal prism morphology was synthesized and calcined at500°C to obtain hollow In₂O₃ nanorods.Then,using MPA as a stabilizer,aqueous Cd_0.67Mo_0.33Se QDs was synthesized and decorated on the surface of In₂O₃ to form Cd_0.67Mo_0.33Se/In₂O₃ hollow nanotubes,and their photocatalytic hydrogen production performance was studied.Compared with In₂O₃ and Cd_0.67Mo_0.33Se,Cd_0.67Mo_0.33Se/In₂O₃ possessed stronger light absorption ability,higher photocurrent response density and faster electron-hole separation efficiency.When the concentration of Cd_0.67Mo_0.33Se was 0.01 M,the obtained Cd_0.67Mo_0.33Se/In₂O₃-2 performed the best photocatalytic activity,and its H₂ production rate within 6 h was 78468.82μmol·g^-1,14.5 and 3.9 times higher than pure In₂O₃ and Cd_0.67Mo_0.33Se,respectively.Meanwhile,Cd_0.67Mo_0.33Se/In₂O₃ exhibited great cycling stability.（2）CuInS₂ microflowers were prepared by solvothermal method,and its surface was decorated with CdSe QDs to obtain CdSe/CuInS₂ composite photocatalyst with p-n heterojunction structure.And the photocatalytic hydrogen production performance of CdSe/CuInS₂ was also discussed.By adjusting the concentration of CdSe,it was found that the prepared CdSe/CuInS₂-3 had high photocatalytic hydrogen production activity(10610.37μmol·g^-1·h^-1),and the AQE value at 420 nm reached 48.97%.The construction of p-n heterostructures enhanced the photocatalytic hydrogen production activity,promoted the light absorption capacity,accelerated electron transfer,and reduced the recombination of photoinduced electrons and holes.CdSe/CuInS₂ with high stability and good cyclability was beneficial to the application of photocatalytic hydrogen production.（3）An efficient ZnSe/Cu_0.08Zn_0.92S composite photocatalyst was fabricated by element doping and the construction of heterostructure.Due to the synergistic effect of Cu element doping and the internal electric field of the heterostructure,the light absorption range of ZnSe/Cu_0.08Zn_0.92S was expanded and the electron transfer was facilitated,which was conductive to the separation and transfer of photogenerated electrons and holes.Meanwhile,the directional migration of photogenerated electron effectively inhibited their recombination with holes,thereby enhancing the photocatalytic hydrogen production capacity of ZnSe/Cu_0.08Zn_0.92S.When the ZnSe concentration was 0.01 M,the as-prepared ZnSe/Cu_0.08Zn_0.92S-2 achieved the best photocatalytic hydrogen production efficiency（11.4492 mmol/g,AQE=66.89%at 420nm）and exhibited good cycling stability.