Study On The Two-dimensional Composite Materials For Regulation And Photocatalytic Performance

In recent years,semiconductor-mediated photocatalysis technology has received widespread attention,and it has broad development prospects in solving energy and environmental problems worldwide.Since solar energy is inexhaustible,the conversion of solar energy into environmentally friendly,high-energy-density hydrogen energy through photocatalytic water splitting is of great significance to the realization of sustainable development of mankind.In order to improve the efficiency of photocatalysis,the design and synthesis of a new high-efficiency photocatalyst is the key.Among the photocatalysts with various morphologies,two-dimensional(2D)semiconductor materials have become a hot spot in photocatalysis research,and they show many unique structural advantages,such as shortened photo-generated charge migration distance from bulk to surface,increased specific surface area,and more catalytic active sites on the surface,and so on.In addition,metal sulfide semiconductors with narrow band gaps have been widely used in photocatalytic reactions due to their adjustable electronic,optical,and physical and chemical properties.As a typical metal sulfide semiconductor,the layered structure of ZnIn₂S₄has good visible light absorption and a suitable energy band position for the photolysis of water to produce hydrogen.However,similar to other sulfide semiconductors,pure ZnIn₂S₄severely weakens the efficiency of photolysis of water to produce hydrogen due to the high charge recombination rate and photo-corrosion problems.In order to solve the above problems,we designed and synthesized a series of ZnIn₂S₄-based nanocomposites through strategies such as morphology control,heteroatom doping,heterostructure building,and co-catalyst modification,so as to broaden the light absorption range,promote charge separation,and increase catalysis.The purpose of the active site,thereby achieving a significant improvement in photocatalytic performance.The specific research is as follows:(1)A unique 2D tandem heterojunction is constructed for the first time,which is composed of ultra-thin Cd_xZ_n1-xIn₂S₄nanosheets,rectangular Cd S nanosheets and defect-rich MoS₂few-layer nanosheets.The study found that the electron transfer channels existing in the Cd S/Cd_xZn_1-xIn₂S₄and Cd_xZn_1-xIn₂S₄/MoS₂2D series heterojunctions effectively promote the transfer and spatial separation of photo-generated charge carriers.In addition,this 2D tandem heterojunction Cd_xZn_1-xIn₂S₄-Cd S-MoS₂had excellent light-trapping ability and abundant active sites derived from MoS₂promoter.The photocatalytic test showed that the optimized C_0.15ZIS-5C-3M composite(5 wt%Cd S,3 wt%MoS₂)exhibited a photocatalytic hydrogen evolution reaction(HER)of up to 27.14 mmol·h^-1·g^-1,and the apparent quantum yield(AQY)under?=400 nm monochromatic light irradiation was 19.97%.In addition,C_0.15ZIS-5C-3M composite material showed good long-term hydrogen evolution stability.(2)In order to improve the photocatalytic activity of ZnIn₂S₄,we grew Cd-doped ZnIn₂S₄nanosheets(C_0.15ZIS)on reduced graphene oxide(RGO)nanosheets,and then further loaded Ni₂P cocatalyst to prepare a ternary RGO/C_0.15ZIS-Ni₂P composite photocatalyst.The study found that Cd doping broadens the visible light absorption range of ZnIn₂S₄,and the Schottky junction formed between C_0.15ZIS,RGO and Ni₂P effectively promotes the transfer and separation of photo-generated charges.In addition,the Ni₂P cocatalyst provided a large number of active sites for the hydrogen production reaction.Benefiting from the above advantages,the composite material exhibited excellent visible light-driven photolysis water hydrogen production activity.Under optimized conditions,the highest hydrogen production rate of 2%-RGO/C_0.15ZIS-3N(2wt%RGO and 3wt%Ni₂P)nano-heterojunction was 14.56mmol·h^-1·g^-1,where the apparent quantum yield(AQY)under ?=400 nm monochromatic light irradiation reached 10.94%.In addition,cyclic and long-term hydrogen evolution reaction(HER)tests showed that RGO/C_0.15ZIS-Ni₂P had good photocatalytic stability.(3)We first grew Cd_0.15Zn_0.85In₂S₄(C_0.15ZIS)nanosheets on MXenes(MNs)nanosheets,and then further grew WS₂promoters by solvothermal method,successfully fabricating 2D/2D/2D semiconductor nanoheterojunctions.The study found that C_0.15ZIS and MNs and WS₂formed Schottky junctions and I-type heterojunctions respectively,which significantly promoted the transfer and separation efficiency of photo-generated charges.In addition,the defective WS₂cocatalyst could provide abundant catalytic active sites for hydrogen production reactions.Therefore,under visible light irradiation,the structure-optimized 3MNs/C_0.15ZIS-4W(3wt%MNs and 4wt%WS₂)composite exhibited a hydrogen production rate as high as31.29 mmol·h^-1·g^-1,and the apparent quantum yield(AQY)under?=400 nm monochromatic light irradiation reached 23.25%.In addition,the MNs/C_0.15ZIS-WS₂composite exhibited good cycling and long-term hydrogen production stability in the photolysis of water reaction.