Theoretical Study On Photocatalytic Activity Of Double-anion Codoped SnS₂ Nanosheet

The development of renewable,environmental,friendly,and clean energy has attracted intensive interest of scientific researchers in the field of materials science in recent decades because of the energy crisis and environmental pollution issues.Hydrogen is one of the most excellent energy carriers,and the use of semiconductor photocatalysts to decompose water for hydrogen production is one of the important ways to effectively solve energy and environmental problems.In recent years,two-dimensional materials have triggered much attention because of the large surface areas providing more active sites for photocatalytic reactions,and the short migration distance of carriers.Among them,the low toxicity,environmentally friendly and earth-abundant semiconducting SnS₂ nanosheets have been successfully synthesized by solvothermal technique.However,the wide band gap limit the visible light absorption,and the band edge positions is unfavorable for oxidation and reduction processes for decomposition of water,which has limited the photocatalytic activity of SnS₂ nanosheets.The foreign elements doping is an effective way to reduce the band gap,modulate the band structure,and expand the visible light absorption range.In this paper,the first-principles calculations based on the density functional theory have been adopted to explore the photocatalytic activity of anionic modoped（N and P）and codoped（N-N,N-P,and P-P）SnS₂ nanosheet,so as to design a highly active photocatalyst.The main research work is listed as follows:1.The defect formation energies of all anionic doped and codoped systems have been studied.The results show that the defect formation energies of all doped systems decrease monotonically with the decrease of the chemical potential of S.The P-P codoped system has the lowest defect formation energy under S-poor condition.2.The electronic structures of all doped systems have been investigated.The results of analysis indicate that anionic doping（N and P）and codoping（N-N,N-P,and P-P）can effectively reduce the band gap of SnS₂ nanosheet,but these unoccupied impurity states acting as electron-hole recombination centers have been introduced above the Fermi level,which will increase the recombination rate of photogenerated charge carriers and suppress the photocatalytic efficiency.P-P codoped system gives a band gap reduction without introducing unoccupied impurity states.3.The band edge positions and optical properties of the P-P codoped system have been further investigated.Although P-P（ii）codoping can reduce the band gap,the valence band edge（the conduction band edge）is more negative than the oxidation potential of H₂O/O₂（the reduction potential of H⁺/H₂）.Therefore,this system is not suitable for hydrogen evolution through photocatalytic water splitting.P-P（i）codoping has not only suitable band gap but also appropriate bandedge positions,which overcomes the disadvantage that the pristine SnS₂ nanosheet is not beneficial for hydrogen production.In addition,P-P（i）codoping also has a wide visible light absorption range.4.The effect of doping concentration on the defect formation energy,electronic structure,bandedge positions and optical properties of the P-P（i）codoped system have been investigated.The results show that the change of defect formation energy and bandgap of P-P（i）codoped system are small at a lower doping concentration.Interestingly,there is no unoccupied impurity states in the band gap.In addition,this system has suitable bandedge positions and good optical absorption behavior.The above results indicate that P-P（i）codoping is a promising photocatalyst for visible light photocatalytic water splitting for hydrogen production.Finally,we hope that our findings could provide experimental researchers with some valuable information to design highly active and efficient photocatalysts.