Study On Electronic Structures And Optical Properties Of VIB And VIA Codoped TiO₂

Anatase TiO₂ is a kind of semiconductor with stable structure,non-toxic,strong photocatalytic activity and hydrophilicity,which is widely used in environmental governance,green energy,solar cells and other major fields.In order to solve the problem of large band gap and low optical quantum efficiency of anatase TiO₂,we use first-principles software based on density functional theory to study the optical and electronic properties of VIB and VIA co-doped TiO₂ systematically.This paper mainly explores the basic methods and mechanisms of modulating band gap and improving light absorption,thereby increasing photocatalytic efficiency.Specifically,the formation energy,geometric structure,electronic structure and optical properties of the doped structure are studied.The main research results are as follows:（1）The volume of TiO₂ after doping of VIA atoms expands significantly with increasing atomic number of VIA atoms.VIA atoms introduce impurity energy levels at the top of valence band,which are mainly hybridized by S＿3p,Se＿4p,Te＿5p and O＿2p orbitals,respectively.The band gap decreases with increasing atomic number of VIA atoms,and the absorption range of light is also expanded to the visible light region,which improves utilization rate of light,thereby improving the photocatalytic activity.（2）In the structures of VIB atoms single doping TiO₂,the introduction of VIB atoms leads to impurity levels at the bottom of the conduction band,which are hybridized by Cr＿3d,Mo＿4d,W＿5d and Ti＿3d orbitals,respectively.The band gap increases with the increasing atomic number of doping atoms,and the band gap of W@TiO₂ is larger than that of pure TiO₂.The existence of impurity level is the reason that the light absorption range extends to infrared light,which improves utilization rate of light,thereby improving the photocatalytic activity of TiO₂.Cr@TiO₂ has the best light absorption ability in the structures of VIB atoms doping TiO₂.（3）The volume expansion of W,Mo and Cr co-doped TiO₂ with VIA atoms is obvious with the increase of the order number of VIA atoms.Cr＿3d,Mo＿4d and W＿5d electronic states introduce impurity states at the bottom of conduction band.VIA atoms introduce impurity states at the top of valence band with S＿3p,Se＿4p and Te＿5p electronic states,respectively.The band gap decreases with the increase of VIA atomic number.Among them,the light absorption ability of Cr co-doped structures,increases with the increasing atomic number of VIA atoms in the 200 nm～430 nm region.The light absorption ability of co-doped structures of W and Mo increases with the increasing atomic number of VIA atoms in the360 nm～500 nm region.In the region of 360 nm～500 nm,the light absorption ability of VIB atoms and Te doped structures is WTe@TiO₂>Mo Te@TiO₂>Cr Te@TiO₂,which increases with the increasing atomic number of VIB atoms.In the wavelength range of 350 nm～800nm,the red shift of WTe@TiO₂ structure is the most obvious,which is the best absorption ability of these doped structures.