| Two-dimensional molybdenum disulfide is a transition metal sulfide,which has excellent electrical and optical properties.The van der Waals heterojunction formed with other two-dimensional materials can be used as a photocatalytic material to effectively inhibit photo-generated carrier recombination.In recent years,there have been few reports on the research of inducing the catalytic reaction of total hydrolysis by doping 3d transition metal elements into Mo S2.In this article,we will select transition metal elements Co and Fe doped into monolayer Mo S2 and related heterostructures to explore whether further improve the photocatalytic efficiency of the material,and improve the imbalance of hydrogen evolution and oxygen evolution reactions in the photocatalytic reaction.Based on the first principles,we use Co and Fe to dope the single-layer Mo S2 and Mo S2/WSe2,Mo S2/WS2,Mo S2/Mo Se2 three related heterostructures respectively,and calculates the energy band of each doping system.Electrical and photocatalytic properties such as structure,density of states,light absorption spectrum,band edge position,etc.The main research results of the thesis are as follows:（1）Based on the first-principles method density functional theory,the model structure of single-layer Mo S2 and Mo S2/WSe2,Mo S2/WS2,Mo S2/Mo Se2 related heterojunctions is first constructed,and the CASTEP calculation module in the Materials Studio software is used to analyze each Model structure optimization.The formation energies of single-layer Mo S2doping systems under different environments and the formation energies of different heterojunction doping systems under different interlayer spacing were calculated,and the optimized structure model was finally obtained.（2）Based on the optimized stable structure,the paper calculated the Co-Mo S2,Fe-Mo S2single-layer doping system at 2.08%,3.70%and 8.33%doping concentration,as well as Mo S2/WSe2,Mo S2/WS2,Mo S2/Mo Se2.The electrical properties of the heterojunction doped system,such as the band structure and the density of states.The results show that,compared with before doping,the band gap value of the doped material is less than 0.65e V,and the impurity energy level is introduced,which is similar to the band performance of other transition metal elements doped in the literature.In order to avoid that the band gap calculated by the PBE hybridization functional is too small to affect the accuracy of the band edge position,each doping system adopts the HSE06 hybridization functional method to finally obtain the conduction band bottom and valence band that actually participate in the hydrogen evolution and oxygen evolution reaction.The top difference all meets the 1.23 e V required by the photocatalytic material,showing the potential of the photocatalytic material for total water decomposition.（3）Based on the density functional theory of the first-principles method,the paper studies the photocatalytic properties of monolayer Mo S2 and its related heterojunction doped systems.Through analysis of the light absorption coefficient,it is found that the doping of transition metals Co and Fe can enhance the material’s utilization of visible light.When the wavelength is 800nm,the light absorption coefficient when the Co doping concentration is8.33%is the most obvious improvement compared with the intrinsic Mo S2.When sunlight is used as a light source,for single-layer Mo S2 and its related heterojunctions,the doping of Co and Fe makes the material’s absorption of sunlight significantly improved,which helps to improve the photocatalytic efficiency of the material.（4）Based on the calculation results of the HSE06 hybridization functional for the energy band,the paper analyzes the position of the band edge of each doping system relative to the vacuum energy level.The results show that the band edge position of the single-layer Mo S2doped with different concentrations of Co and Fe is improved.When the Co and Fe doping concentrations are 3.70%and 8.33%,respectively,the band edge position improves the photocatalytic ability while improving the photocatalytic performance.The imbalance of hydrogen evolution and oxygen evolution capacity in the intrinsic state is improved.On this basis,applying compressive strain to the material can further improve the photocatalytic properties.In the heterojunction doping system,Fe-Mo S2/WS2 is a Type-I structure type.The photogenerated electrons recombine at the interface,but it still effectively extends the life of most photogenerated carriers.The other heterojunctions are all Type-Ⅱ-PN structures.The photo-generated holes and electrons are retained in the valence band and conduction band of different materials,respectively,to inhibit the recombination of photo-generated carriers and greatly improve the reaction activity. |
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