Trends In Non-metal Doping Of The SrTiO₃ And NaTaO₃?001? Surface:A Hybrid Density Functional Study

Photocatalytic technology can be used in field of solar energy to produce H₂,specially from water splitting and degradation of organic pollutants,which is considered to be a very broad prospect to solve the environmental pollution and energy shortage problems.Developed photocatalytic material contributes to the development of photocatalytic technology,however,the vast majority of materials have been developed are relatively wide band gap,resulting in photocatalytic reaction surface occurring absorbs only in the ultraviolet range.Therefore,it is one of the most important tasks for scientists to develop a photocatalyst with visible light response and improve the utilization of solar energy.SrTiO₃ has better photocatalytic activity,and it has received wide attention in photocatalytic technology,but it has been limited its practical application because of its wide band gap?3.2eV?.If the band gap can be reduced,broaden its range of light absorption and improve their photocatalytic activity for water splitting under visible light,so can greatly improve its practical value.In this paper,density functional theory?DFT?and mixed HSE06 method,calculats and analyzs non-metallic element doping on SrTiO₃?100?surface of the band gap changes,as well as the doping effect on the photocatalytic oxidation.The doping elements are C,N,F,Si,P,s,Cl,Se,Br and I.Our mainly research content is that use PBE and HSE two methods to calculate the ten kinds of non-metallic element doping defects in SrTiO₃?001?surface system situation,including of formation energy,the local geometric structure and density of states.The results obtained are as follows:Doped SrTiO₃?001?surface of the obtained results are as follows:1.The choice of a unit cell model,we analyze the contains five atomic layers and seven layers of atoms doped doping.Through the calculation of two kinds of models of defect formation energies,in the end we find out that have little effect on the size of the model of system geometry and electronic properties.So starting from the energy point of view,the main work of this thesis is to study with five layers of atoms of the unit cell.2.On the doping position,we considered the doping in the surface layer and the second layer of SrTiO₃?001?surface.By comparing the formation energy and the electronic structure of each doped system and other related knowledge,the analysis shows that:in the energy,for most of the X doping system,the anion in the top layer is more favorable than the sub layer.There are relative smaller atomic radius of atom x?x = C,N and F?tending to replace the O atoms of the TiO₂-terminated surface,and the greater atomic radius of the atoms X?X = P,S,Cl,Se and Br?priority to replace the O atom of the SrO-terminated surface.Therefore,this article is mainly to study doping in the first layer of the terminal surface.3.Pure TiO₂ surface terminal can not only help absorb visible light,but also help improve the ability of photo-oxidation.?1?C,Si and P elements doped systems creates localized state separation between the CBM and VBM,that could act as recombination centers,which is unfavorable to photocatalysis.?2?S or Se elements doped systems induce new associated track with S3P or Se4P bandgap,which should substantially reduce the energy of electrons excited from a desired track into the CBM,but due to the local nature of the new track,it may accelerate the carrier recombination.?3?N,Br,and I element doped systems can not only extend the absorption edge into the visible region,but also improve the photo-oxidation and or the photoreduction ability.Systematic theoretical investigation has been performed for NaTaO₃?001?surface doped with nonmetal elements X?X=C,N,F,Si,P,S,Cl,Se Br and I?to evaluate the effect of doping on the band structure.The findings are as follows:1.The doping is energetically more favorable on the NaO termination than the TaO₂ termination.2.The absorption band edge of NaTaO₃?001?surface terminated with TaO₂ is in the visible region.For C and P-doped systems,some impurity states are localized in the middle of the band gap,which are detrimental to photocatalysis because the gap states can act as recombination centers to limit the efficiency of semiconducotrs.Doping with isovalent elements?S and Se?introduces new states near to VBM,which may reduce the required energy of exciting electrons from occupied states to CBM and reslut in the red-shift of absorption band edge.As to N and I-doped surfaces,the band gaps essentially decrease compared with the clean NaTaO₃?001?surface,and the absorption edge moves from the UV to visible light range.