First-principles Study On Photocatalytic Mechanism Of Two-dimensional Metal Sulfide Heterojunctions

Hydrogen energy is a clean energy which can solve the problems of energy shortage and environmental pollution.So,it is important to study how to efficiently produce hydrogen.Using photocatalyst to decompose water is an effective way to obtain hydrogen.Two-dimensional（2D）heterojunctions could separate photogenerated carriers effectively and realize efficient hydrogen production.In thesis,the first-principles calculation method is used to carry out theoretical research on the electronic structure and photocatalytic performance of 2D metal sulfide heterojunctions based on transition metal disulfides（TMDs）and group-Ⅲ monochalcogenides and analyse the effects of biaxial strain,external electric field and atomic adsorption on the heterojunction performance.The results show that the heterostructures have potential application value for efficient hydrogen production.The specific research content is as follows:（1）Study on the electronic structure and photocatalytic properties of GaSe/ZrS₂heterojunction.Heterojunction is constructed using monolayer GaSe and ZrS₂.The calculation results of lattice mismatch,binding energy and phonon spectrum show that the heterojunction has good stability.The calculation results of band arrangement and built-in electric field show that GaSe/ZrS₂ heterojunction is a direct Z-scheme heterojunction which can not only effectively separate photogenerated carriers but also improve the redox capacity of carriers.The comparison results of the edge position and the redox potential of water show that GaSe/ZrS₂ heterojunction can achieve overall water splitting.The mobility of the electrons in this heterostructure is as large as 1450.38 cm²V^-1s^-1along the zigzag direction.Moreover,GaSe/ZrS₂ heterojunction has excellent absorption coefficients in both visible and ultraviolet ranges.The biaxial strain,external electric field and atomic adsorption（Se and Zn）can significantly regulate the electronic structure of the heterojunction and the biaxial strain can significantly enhance the light absorption capacity of the heterojunction.The results show that the direct Z-scheme GaSe/ZrS₂heterojunction has excellent photogenerated carrier mobility,light absorption capacity and photocatalytic overall water splitting capacity.（2）Study on the electronic structure and photocatalytic properties of InSe/XS₂（X=Zr/Hf）heterojunctions.The monolayer InSe and XS₂ are used to construct the heterojunctions.The lattice mismatch and binding energy are calculated to prove that the two heterojunctions have good stability.The results of band arrangement and built-in electric field show that InSe/XS₂ heterojunctions are direct Z-scheme heterojunctions.InSe/ZrS₂ heterojunction and InSe/HfS₂ heterojunction can achieve overall water splitting when compressive strain is applied,and when the strain reaches±4%,the arrangement can be changed from type-II to type-I.In addition,the heterojunctions have extremely high light absorption coefficients which can reach 2×10⁵ cm^-1 in the visible light.The application of compression strain can significantly improve the light absorption in the range of visible light and infrared light which could improve the utilization rate of solar energy.The results show that the direct Z-scheme InSe/ZrS₂ heterojunction and the InSe/HfS₂heterojunction have excellent light absorption coefficients and their photocatalytic ability can be optimized by strain,they both have good application potential in photocatalytic water splitting.