Study On Preparation And Photocatalytic Performance Of Ultrathin CoAl-LDHs-based Heterojunction

As a kind of clean and renewable energy,solar energy has extraordinary value and significance for semiconductor photocatalysis research.Layered double hydroxide（LDHs）is an important 2D layered material,which has been widely used in the field of photocatalysis.The accumulation or even agglomeration of LDHs will affect the overall performance and application range.Therefore,stripping LDHs into ultrathin nanosheets can make use of the nanosheet structure of LDHs as effectively as possible,thereby improving the photocatalytic performance.Although ultrathin LDHs show better photocatalytic activity than bulk LDHs,there are still problems such as easy recombination of electron-hole,low electron utilization,and low photocatalytic efficiency.The general 2D ultrathin heterojunction has weak interface bonding force and is not an ideal material for converting solar energy into chemical energy.In order to solve the above problems,this paper proposes to construct an ultra-thin CoAl-LDHs-based heterojunction with strong interfacial bonding force.The design combines the positively charged ultrathin CoAl-LDHs nanosheets with the negatively charged ultrathin ZnIn₂S₄,C₃N₄ nanosheets,and uses electrostatic interactions to form a strong interface combination.The mechanism of the improvement photocatalytic performance is also explored.Ultrathin CoAl-LDHs nanosheets were prepared by swelling method,solvothermal method and inverse microemulsion method.Among them,the swelling method could obtain the best ultrathin CoAl-LDHs（0.7 nm-2.1 nm）,and has the advantages of simple operation and environmental friendliness.On this basis,the ultrathin CoAl-LDHs/ZnIn₂S₄ heterojunctions were synthesized by in-situ method,showed excellent photocatalytic activity for hydrogen production.The hydrogen production rate of CoAl-LDHs/ZnIn₂S₄（1:2）photocatalyst was 1563.64μmol·g^-1·h^-1 was about 4.6 times of ZnIn₂S₄,646 times of CoAl-LDHs,and 9.7 times of CoAl-LDHs/ZnIn₂S₄（bulk）.The results showed that the formation of new Co-S_x bond at the interface of ultrathin CoAl-LDHs/ZnIn₂S₄ heterostructures,the successful construction of Z-type heterostructure and the formation of built-in electric field conducive to the separation of photogenerated carriers were the mechanisms to improve the photocatalytic performance of hydrogen production.Ultrathin CoAl-LDHs nanosheets were prepared by swelling method,ultrathin C₃N₄nanosheets were prepared by two-step calcination method,and ultrathin CoAl-LDHs/C₃N₄heterojunction was prepared by mechanical stirring method,which exhibited excellent photocatalytic degradation CPX activity.The degradation rate of CoAl-LDHs/C₃N₄（1:2）was68%,which was about 1.3 times of CoAl-LDHs and 2.7 times of C₃N₄.The results showed that the successful construction of ultrathin CoAl-LDHs/C₃N₄ typeⅡheterojunction,broadening the light response range of a single catalyst,and improving hydrophilicity were important factors for the photocatalytic performance improvement.