First Principles Studies On The Photocatalytic Properties Of Two-Dimensional G-C₆N₆/GaTe And SiAs/SnS₂ Van Der Waals Heterojunctions

Since the 21st century,in order to alleviate the serious problems of fossil fuel shortage and environmental pollution,the human energy structure needs to be transformed urgently,and the development and utilization of sustainable and clean energy is crucial.Hydrogen energy is attracting attention as a new generation of green energy that is used for energy production without emitting carbon dioxide or other harmful substances.Among the various ways of producing hydrogen,the use of solar energy to produce hydrogen by hydrolysis through catalysts is considered to be the most promising technology at present.Compared to bulk photocatalysts,two-dimensional photocatalysts exhibit superior properties,shortening the diffusion distance of photogenerated electron-hole pairs and expanding the specific surface area.However,their photocatalytic performance is still limited due to factors such as the limitation of the light absorption range and the compounding of photogenerated carriers on the surface.The construction of two-dimensional van der Waals heterojunctions is an effective strategy to improve the photocatalytic performance of two-dimensional materials.Among them,the energy band structure of type II heterojunctions arranged in staggered intervals can promote the separation of photogenerated carriers and improve visible light photoabsorption.Therefore,the study of two-dimensional heterojunction photocatalysts is of great significance in the new era of development.In our study the electronic structure and optical properties of g-C₆N₆/Ga Te and Si As/Sn S₂ van der Waals heterojunctions are investigated in depth using a first-principles approach based on density function theory,and their application prospects in the field of photocatalysis are explored.The main results are as following.（1）The electronic structures of monolayer g-C₆N₆ and Ga Te materials were analysed.Three types of two-dimensional g-C₆N₆/Ga Te heterojunction models were constructed based on symmetry,and the most stable structures were selected for electronic and optical property calculations.The results show that the g-C₆N₆/Ga Te heterojunction is a type II heterojunction with a built-in electric field formed at the interface and a potential difference,which is conducive to the effective separation of photogenerated electron-hole pairs.At the same time,the band edge position also straddles the redox potential,satisfying the basic conditions for the photolytic water reaction.The hydrogen production efficiency of the g-C₆N₆/Ga Te heterojunction is significantly improved compared to that of monolayer g-C₆N₆ and Ga Te.Furthermore,we find that biaxial strain can effectively modulate the electronic structure of the g-C₆N₆/Ga Te heterojunction,which in turn leads to a red-shift in its optical absorption spectrum and improves the light absorption capability of the heterojunction in the visible region.（2）The electronic structure and optical properties of the Sn S₂and Si As monolayer were carefully studied.Six types of two-dimensional Si As/Sn S₂ heterojunction models were constructed by translation,and the most stable stacking model was selected to carry out photocatalytic performance studies.It show that Si As/Sn S₂ heterojunctions are indirect semiconductors with interleaved energy bands.An internal electric field is formed at the interface.During photodissociation of water,under the combined effect of the built-in electric field and energy band bending,photogenerated carriers migrate according to the Z-type charge transfer model and participate in the reaction using a strong redox potential,which improves the photocatalytic efficiency.the light absorption capacity of the Si As/Sn S₂ heterojunction is significantly enhanced compared to that of monolayer Si As and Sn S₂.In addition,the Si As/Sn S₂ heterojunction exhibits superior ability to desorb H₂ and O₂.The biaxial strain resulted in a reduced band gap of the Si As/Sn S₂ heterojunction,which facilitated the compounding of photogenerated carriers at weak redox potentials;the tensile strain also increased the charge transfer and the light absorption coefficient in the visible region of the heterojunction.It was also found that the strained heterojunction maintained a good redox capacity at different p H values.