The Study On Photocatalytic Properties Of Two-dimensional GeS Materials

With the progress of society,the energy structure dominated by fossil fuels is increasingly showing its drawbacks.This also makes environmental pollution and energy shortage becoming one of the main problems facing human society.Since science and technology have developed rapidly,fossil fuels are increasingly being replaced by clean energy and renewable energy.Using solar energy to produce clean,renewable energy and decompose pollutants through efficient,economic,and pollution-free photocatalytic technology is an effective method that can validly solve energy shortage and environmental pollution at the present stage.In recent years,two-dimensional materials have attracted widespread attention due to their unique properties.They have been increasingly used in photocatalysis.Among them,GeS,as a two-dimensional material with high carrier mobility,high light absorption efficiency and nice stability.It has excellent potential in the research of photocatalytic hydrogen production and pollutant degradation.However,the sizeable indirect bandgap of monolayer GeS limits the absorption range of sunlight,and its limited oxidation ability also leads to the difficulty of realizing photocatalytic water decomposition and oxygen generation reaction.Therefore,the development of monolayer GeS materials as high-efficiency photocatalysts for photocatalytic reactions requires further control.In this thesis,single-layer GeS is used as the research object,and density functional theory calculations are used to try to adjust its electronic structure and improve its photocatalytic performance through appropriate means,including applying stress,constructing heterojunctions,etc.,so as to make it more suitable for photocatalytic reaction.The main results are as follows:(1)Two kinds of GeS monolayers were constructed into a heterojunction system to improve the catalytic efficiency of the structure.After combining two GeS monolayers with different phases to form a heterojunction system,a smaller bandgap can be obtained than that of a single component.Simultaneously,the energy required for the direct electron transition was close to the indirect bandgap of the heterojunction,so the light absorption of the composite system can be expanded to the visible light range,and the solar energy utilization rate of the material can be improved.(2)The internal electric field of a single layer of GeS was used to promote the photocatalytic reaction.There were vertical and parallel internal electric fields in different phases of GeS monolayers.Combining the two electric fields can promote the transfer of photogenerated electrons and holes to the surface active sites of different layers,thereby reducing the probability of electron-hole recombination and improving the photocatalytic quantum efficiency of heterojunction materials.(3)The construction of heterojunction has improved the oxidizability in single-layer GeS.The formation of heterojunction between two layers of GeS with different phases effectively improved the problem of insufficient oxidation capacity existing in previous single GeS layer.As a result,the photogenerated electrons and holes transferred to different layers have enhanced oxidation and reduction capabilities,respectively,which can realize the complete decomposition of photocatalytic water.(4)Applying biaxial reverse stress to the single-layer GeS material could improve the properties of the single-layer GeS and promote photocatalytic efficiency.Considering that the biaxial reverse stress may be applied in the experiment,the GeS single layer material properties would change after the biaxial reverse stress was applied to the GeS single layer.The energy of the system was lower and therefore more stable when the tension and compression stresses were applied in the two axes respectively than when the tension and compression stresses were applied in the two axes simultaneously.Besides,under this kind of stress,the bandgap of the GeS single layer was slightly reduced,and the position of the band edge has been adjusted,which was more suitable for the catalytic reaction compared with the original single-layer GeS material.