The Preparation And Photocatalytic Hydrogen Production Of ZnS@ZnO Heterostructure And Zn-In-S Solid Solution

Heterostructure and solid solution are two forms to improve the separation efficiency of photoinduced electrons and holes,thereby enhance the photocatalytic performance of water splitting.Here,two-dimensional ZnS@ZnO core-shell heterostructure and Zn_1-xCr_xIn₂S₄ solid solution were synthesized to investigate its influence on the performance of photocatalytic hydrogen production.?1?Two-dimensional Z-scheme ZnS@ZnO heterostructure with highly ordered ZnO core and highly disordered ZnS shell was prepared by a simple hydrothermal method,using ZnO nanosheet as a template and Na₂S as a sulfur source.The zinc interstitials were successfully introduced to ZnS@ZnO photocatalysts,and the photocatalysts were used for photocatalytic hydrogen production by water splitting.As shown from the result of transmission electron microscope?TEM?and high-resolution transmission electron microscope?HRTEM?,the ZnS@ZnO composite were successfully synthesized in core-shell structure,with highly ordered Zn O core and highly disordered ZnS shell.The separation of charge carriers can be promoted by this structure,thereby contributes to the improvement of photocatalytic hydrogen production efficiency.The existence of zinc interstitials was determined by X-ray photoelectron spectroscopy?XPS?,fluorescence spectra?PL?,and electron paramagnetic resonance?EPR?.Interstitial zinc was introduced for the balance of atoms volume when the oxygen atom on the surface of ZnO nanosheets replaced by larger sulfur atoms.The ZnS@ZnO core-shell structures with different ZnS shell thicknesses were obtained by changing the ratio of ZnO to Na₂S from8:1 to 6:1 and 4:1.It found that the photocatalytic hydrogen production activity was highest when the ratio of ZnO to Na₂S was 6:1,and the thickness of ZnS shell is ca 8 nm.The defect concentration and the numbers of active sites can be changed by changing the reaction temperature and time,which affects the photocatalytic hydrogen production efficiency.The optimal reaction temperature and the optimal reaction time are 60?and 6 h,respectively.Moreover,it was purposed that the Z scheme with ordered/disordered heterogeneous junction between ZnO and ZnS contributes to improving photocatalytic hydrogen production.This work provides an avenue for preparing heterostructure photocatalysts in combination with defect engineering.?2?A series of Zn_1-xCr_xIn₂S₄?x=0,0.15,0.25,0.45,1?solid solution were synthesized by one-step hydrothermal method,and were applied to photocatalytic hydrogen production.The Zn_1-xCr_xIn₂S₄ solid solution with regular morphology were synthesized when reaction temperature was 200?and at a stoichiometric ratio.The polyhedron morphology of photocatalyst was changed with the increase of chromium content.The regular hexagon of ZnIn₂S₄ solid solution were synthesized when x is 0.The regular octahedron of Zn_0.75Cr_0.25In₂S₄solid solution were synthesized when x is 0.25.The regular hexahedron of CrIn₂S₄ solid solution were synthesized when x is 1.The UV-Vis diffuse absorption spectrum?UV-Vis DRS?showed that the Zn-Cr-In-S solid solution were localized surface plasmonic material.Zn-Cr-In-S solid solution exhibited broadened visible-light absorption and charge separation efficiency due to the surface plasmon effect.Therefore,Zn-Cr-In-S solid solution exhibited higher hydrogen production activity than ZnIn₂S₄ solid solution.In particular,the Zn_0.75Cr_0.25In₂S₄ solid solution showed highest photocatalytic hydrogen production for the highest charge carrier separation efficiency.In conclusion,ZnS@ZnO heterostructure and Zn_1-xCr_xIn₂S₄ solid solution exhibited enhanced charge carrier separation efficiency,thus contributed to the improvement of photocatalytic hydrogen production.