First-principles Study Of S And Cr Co-doped Anatase TiO₂

China is a country with a large population and a large consumption of resources.It is unrealistic to rely on nature to degrade a large quantities of waste discharged by production and living.Many organic compounds are almost impossible to be degraded via visible,and a large number of photocatalysts are urgently needed to accelerate their degradation.How to improve the optical property of titanium dioxide by visible light has been a hot topic in the photocatalytic field.In this thesis,the first principle calculation method based on the density functional theory was used to study the properties of anatase titanium dioxide single doped and co-doped with chromium and sulfur.The electronic structure and optical property of the doping system are studied systematically using CASTEP.In the study,at the concentrations of 4at.%,8at.%and 12at.%,Cr and S^2-are doped in anatase titanium dioxide in the form of substitution.The energy band structure and optical properties of titanium dioxide with different doping concentrations,different doped elements and their proportions,and different doping models were calculated.The calculation results show that:Atoms doped at different positions have different impacts on the energy band structure and optical property of anatase titanium dioxide.With the increase of Cr³⁺concentration,the band gap of TiO₂ decreases obviously.When the concentration is 12at.%,the impurity energy level is connected with the conduction band,the band gap is sharply narrowed,and the light absorption intensity increases significantly.With the increase of sulfur concentration,the impurity energy level changes little,the band gap decreases slowly,and the light absorption intensity increases slightly.Chromium is the preferred doping element to improve the light absorption intensity.As the concentration of doped elements changes,not only the peak value of density of states increases,but also the the number and position of the peak change,leading to the change of the number and position of the impurity energy level,resulting in the change of the band gap and ultimately affecting the optical properties.Chromium is the most sensitive element in this regard.?8at.%Cr+4at.%S?-TiO₂ is the best constituent of Cr/S doped anatase titanium dioxide among all the doping models studied in this thesis,its Light absorption edge is greater than850nm.The analysis of energy band structure shows that the band gap has a great influence on the light absorption intensity.The impurity energy level which is not mixed with valence band or conduction band,especially the impurity level in the middle of the gap band,has little influence on the light absorption intensity,but it can make the light absorption edge redshift.The calculation work in this thesis provides a theoretical basis for understanding and improving the photocatalytic performance of Cr/S co-doped anatase titanium dioxide system.