Theoretical Study On Electronic Structure And Photocatalytic Properties Of Two Dimensional Janus M₂XY/ZnO Heterojunction

With the global energy crisis intensifying,it is crucial to develop and utilize sustainable and clean energy sources.Hydrogen energy is currently attracting a lot of attention from researchers as a green energy source.Since Fujishima and Honda first used the semiconductor material titanium dioxide（Ti O₂）to photocatalyze hydrogen production in 1972,hydrogen production by solar energy via semiconductor materials has become an important route to hydrogen production.The development of highly efficient catalysts for hydrolysis under visible light is now a key issue in the field of green energy research.The composite of photogenerated carriers severely affects the performance of photocatalysts,and type-II van der Waals heterostructures can effectively solve this problem and extend the carrier lifetime.Therefore,this thesis predicted efficient type-II van der Waals g-Zn O/Ga₂SSe heterojunctions and g-Zn O/In₂SSe heterojunction photocatalysts based on density flooding theory,and analyzed their optical,electrical and heterojunction interface properties.Firstly,the electronic structures of monolayer g-Zn O and Ga₂SSe were investigated.Based on the asymmetry of Janus monolayer Ga₂SSe,different Se and S atoms may have an effect on the stability of the heterojunction.six different stacking models of g-Zn O/Ga₂SSe heterojunction were constructed,and the most stable structure was selected to analyze the electronic structure and optical properties computationally.The computational results show that g-Zn O/Ga₂SSe heterojunctions are direct band-gap semiconductors with type II energy band structure,in which the redox reactions of photo-generated electrons and holes occur in different layers.Due to the suitable band gap and band edge positions,the g-Zn O/Ga₂SSe heterojunction can achieve water splitting at different p H levels（0<p H<14）,and the heterojunction has better light absorption performance and significantly enhanced hydrogen production efficiency in the visible region compared with g-Zn O and Ga₂SSe monolayers.In addition,it was found that biaxial strain regulates the band gap value and edge position of g-Zn O/Ga₂SSe heterojunctions.Therefore,g-Zn O/Ga₂SSe heterojunction is an efficient hydrolysis photocatalyst with promising applications.Secondly,the electronic structure and optical properties of In₂SSe and g-Zn O/In₂SSe heterostructures were studied in depth,and six different g-Zn O/In₂SSe heterostructure stacking models were also constructed.Based on the most stable stacking model,the electronic and optical properties were calculated and analyzed.The results indicate that the g-Zn O/In2SSe heterojunction is a direct bandgap semiconductor with a type II energy band structure,which allows for the spatial separation of photo-generated electrons and holes,suggesting that the carrier complexation inside the heterojunction is reduced and the carrier lifetime can be effectively extended.There are significant differences in the photocatalytic water decomposition performance of g-Zn O/In₂SSe heterojunctions under different p H media.The g-Zn O/In₂SSe heterojunction satisfies the conditions for photocatalytic hydrogen production in a strongly acidic environment at p H=0 and in a neutral environment as the acidity decreases to p H=7,while the photocatalytic hydrogen decomposition reaction can no longer be performed in an alkaline environment at p H>7.g-Zn O/In₂SSe heterojunction has significantly improved light absorption in the visible region compared to g-Zn O and In₂SSe monolayers.Compared with g-Zn O and In₂SSe heterojunctions,the light absorption performance of heterojunctions in the visible light region is significantly improved,The hydrogen production efficiency is significantly enhanced and meets the minimum critical value for industrial applications.The electronic structure of g-Zn O/In₂SSe heterostructure is regulated by biaxial strain.The g-Zn O/In₂SSe heterojunction can serve as a potential photocatalyst under visible light.Finally,the g-Zn O/Ga₂SSe heterojunction and the g-Zn O/In₂SSe heterojunction were com pared.the g-Zn O/Ga₂SSe heterojunction can catalyze water decomposition under more complex p H conditions,while the g-Zn O/In₂SSe heterojunction can only catalyze water decomposition under acidic and neutral conditions.Compared to the g-Zn O/Ga₂SSe heterojunction,the g-Zn O/In₂SSe heterojunction has a stronger visible light absorption range and intensity,and has a greater solar hydrogen production conversion efficiency,meeting the minimum critical value for industrial applications.It is possible to produce on a large scale in industry.