First-Principles Study On Two-Dimensional Wide Band Gap Semiconductor-Based Van Der Waals Heterojunction Photocatalyst

Photocatalysis utilizes solar energy to split water into renewable clean energy hydrogen energy,which is expected to solve the increasingly serious energy shortage and environmental pollution problems caused by the abuse of non-renewable energy.Two-dimensional wide band gap semiconductor-based materials have been widely used in the field of photocatalysis to prepare van der Waals heterojunction photocatalysts because of their large specific surface area,excellent stability and ability to participate in tuning the bandgap of composites.The purpose of this paper is based on the first-principle calculation of density functional theory,taking the two-dimensional wide band gap semiconductor-based materials like h BN and Si C as the substrate and the existing feasible photocatalytic materials as the research object-to reveal the mechanism of improving the performance of van der Waals heterojunctions,find out the effective means to reasonably regulate the photocatalytic performance and induce the feasible scheme of constructing high efficiency van der Waals heterojunction photocatalyst.The paper aims to provide theoretical guidance and train of thought reference for experimenters to construct high efficiency van der Waals heterojunction photocatalyst.The main contents and results of this paper are as follows:（1）The Ce O₂（111）/h BN structure is constructed,and it is found that the band gap of the heterojunction is obviously lower than that of its single component.The band arrangement accords with the characteristics of typeⅡheterojunction,which can effectively separate the electrons and holes in the interface,enhance the absorption capacity of visible light and improve the efficiency of photocatalytic hydrogen evolution.In addition,the Ce O₂（111）/h BNC structure obtained by doping two C atoms in the h BN structure further reduces the band gap and expands the optical absorption range.This work shows that the photocatalytic hydrogen evolution efficiency of Ce O₂（111）/h BN van der Waals heterojunction is better than its Ce O₂（111）and h BN monolayer,and it is also helpful to understand the mechanism of photocatalysis.It has a certain reference value for practical application.（2）The Pt Se₂/h BN structure is constructed,and it is found to be a type I heterojunction by analyzing the electronic properties of the structure.Combined with the research in the previous chapter,the Pt Se₂/h BNC heterojunction obtained by doping two C atoms into the h BN structure belongs to the typeⅡheterojunction,which can effectively realize the spatial separation of electrons and holes,restrain the photogenerated carrier recombination and improve the photocatalytic performance.This structure has good carrier mobility and is an ideal photocatalyst.This study reveals the possible mechanism that the structure has better oxygen evolution capacity,which paves the way for the actual design of more solar energy-driven high-performance photolysis catalysts.（3）The Mo Si Ge N₄/Si C structure is constructed,and 12 kinds of heterostructures with high symmetry are constructed according to different stacking methods,four of which show excellent stability.It is found that these heterojunctions are Z-scheme heterojunctions,which not only have good light absorption efficiency,but also show excellent photocatalytic hydrogen evolution performance.One of the stable configurations shows excellent photocatalytic hydrogen evolution performance,and the Gibbs free energy is only-0.038 e V.This study further enriches the theoretical research pedigree of MA₂X₄ series materials and points out the direction for further rational design of photocatalysts.