Investigation Of Photocatalytic Hydrogen Evolution Of Metal Sulfides In Multiple Systems Based On Charge Separation

With the rapid development of industrialization,people’s transitional exploitation of traditional fossil energy has caused a serious energy crisis and environmental pollution.The development of clean,renewable new energy sources is on the agenda and has received a lot of attention from the scientific community.Hydrogen energy,due to its combustion without carbon emissions and high energy density,is considered a potential alternative to fossil energy.Photocatalytic hydrogen production technology has great potential among many ways to produce hydrogen because it is green,low-carbon and cheap,and its core lies in photocatalysts.To this end,this paper is devoted to the preparation of excellent,stable and inexpensive photocatalysts for efficient photocatalytic hydrogen production from water.The efficient photocatalytic decomposition of water for hydrogen production is achieved by constructing a heterojunction strategy,a synergistic strategy of co-catalyst-induced heterojunction,and introducing a low overpotential core-shell structure co-catalyst.The following work has been mainly carried out:1.The construction of S-scheme heterojunctions is considered as an effective strategy to improve the photocatalytic activity of single-component photocatalysts.In this work,Cu MOF/CdS composite photocatalysts were successfully prepared using the principle of electrostatic self-assembly.The hydrogen precipitation performance of the20%Cu MOF/CdS composite photocatalyst under visible light(4017μmol g^-1 h^-1)was 3.34times higher than the hydrogen production rate of pure CdS(1202μmol g^-1 h^-1).The analysis and investigation of the catalyst structure,chemical composition and photoelectrochemical properties led to the conclusion that the efficient hydrogen precipitation was mainly attributed to the reduction of CdS agglomeration and S-scheme heterojunction formation by the high specific surface area Cu MOF.The formation of S-scheme heterojunction between the contact interface of CdS and Cu MOF hinders the recombination of photogenerated electrons and holes and improves the effective charge separation and transfer rate,thus significantly enhancing the photocatalytic hydrogen production capacity.2.The construction of heterojunction photocatalysts is considered to be an important means to promote effective photogenerated electron-hole separation.However,it is inevitable that the photocatalysts have poor light absorption ability,relatively small chance of capturing H⁺,and the stability needs to be improved.In this work,a non-precious metal co-catalyst Cu₃P was introduced on the basis of the successful construction of p-n heterojunctions by Ni O and CdS to promote charge separation while expanding the light absorption capacity and increasing the chance of H⁺capture,thus enhancing the photocatalytic hydrogen precipitation activity and stability.The overall photocatalytic performance was improved by continuously optimizing the loading of Ni O and Cu₃P.Satisfactorily,the hydrogen precipitation rate of the composite photocatalyst 15NC@Cu-10in 10 vol%lactic acid solution was 15612.0μmol g^-1 h^-1 with an apparent quantum efficiency of 10.4%using a 5 W LED lamp as the light source.XPS analysis confirmed the direction and path of electron transfer.This synergistic strategy of co-catalyst modification of p-n heterojunctions provides a unique insight into the preparation of efficient and stable photocatalysts,and also expands the applications of MOFs and their derivatives in the field of photocatalysis.3.Photocatalysts generally suffer from low charge separation efficiency and single catalytic reaction system for adapting system,which seriously hinder the industrial development of photocatalytic hydrogen production technology.In this work,the core-shell structured non-precious metal co-catalyst Co S_X/Ni Co-LDH was designed by surface sulfidation and acid etching using ZIF-67 as a template.When coupled with CdS,the hydrogen precipitation rate of the 3%Co/Ni Co/CdS composite photocatalyst in anhydrous ethanol reached 20.67 mmol g^-1 h^-1 under visible light（λ≥420 nm）irradiation,which was59 times higher than that of pristine CdS.It exhibited excellent hydrogen precipitation rate and cycling stability even after 20 h of continuous light exposure.Furthermore,the3%Co/Ni Co/CdS composite catalyst also showed good hydrogen precipitation performance in Na₂S/Na₂SO₃ and lactic acid systems.Fluorescence,Uv-vis diffuse reflection and photoelectrochemical tests show that the coupling of CdS with Co S_X/Ni Co-LDH not only accelerates the effective charge transfer but also greatly broadens the absorption range of CdS to visible light.As a result,the hydrogen precipitation activity of the composite photocatalyst was significantly improved.