DFT Study Of Influence Of Extra Electric Field On The Electric Structure And Optical Properties Of TiO₂ And Doped TiO₂?001?Surface

TiO₂ photocatalysis has been studied and developed for many years.It has not been widely used in industry due to the low utilization rate of sunlight,although it has made great achievements.How to extend the photo catalytic ability of TiO₂ from the UV region to the visible region is still a hotspot and difficulty of the international research in nowadays.Semiconductor photocatalysis can promote the separation of photogenerated electron and hole by using extra electric field,and improve the photo catalysis efficiency.On the other hand,the optical absorption edge will be widened and red-shifted due to the Franz-Keldysh effect produced by extra electric field,which can enhance sunlight utilization and photocatalytic reaction.The recombination of photogenerated electron and hole and low utilization efficiency of sunlight are the main factors which limit the photocatalytic efficiency in the photocatalytic reaction.The photoelectric catalysis provides a feasible direction for solving these two problems,which is expected to be the most promising and most useful photo catalysis technique.In this paper,the influence of the applied electric field on the electronic structure and optical properties of TiO₂,TiO₂?001?,C-TiO₂?001?and Cr-TiO₂?001?was studied by using the first-principle based density functional theory,the main results are as follows:?1?The electric structure and optical properties of the bulk TiO₂ under the action of the z-direction electric field.As the electric field increases from 0 V/A to 0.25 V/A,the energy gap gradually decreases to 0 eV,and the conduction band moves toward the Fermi level,and all levels are widened.The band structure collapses and the Ti-O in Z-direction breaks when the applied electric fieldstrength continues to increase to 0.28V/A.The optical properties ofTiO₂ are better in the near ultraviolet region?100 nm to 380 nm?,while relatively poor in visible light?380 nm to 650 nn?without extra electric field.Under the action of an applied electric field,the absorption range ofTiO₂ is extended to the visible light region,and the intensity of optical absorption in the visible light region is increased.?2?The electric structure and optical properties of TiO₂?001?surface under external electric field.As the electric field intensity increases from 0 V/A to 0.3 V/A,the valence band moves toward the Fermi level and the electron activity increases,the optical absorption in the near ultraviolet region increases,but the absorption side does not shift to long wavelength.The optical absorption in the near-visible region is weakened as the electric field intensity increases.?3?The electron structure and optical properties of C-TiO₂?001?surface under external electric field.With the addition of C,a new impurity level is introduced in the band gap region and band gap decreases,resulting in the shift of optical absorption to the visible region.As the electric field intensity increases from 0 V/A to 0.08 V/A,the valence band moves toward the Fermi level,the responsiveness of C-TiO₂?001?to visible light increases and the probability of occurrence of photoelectric effect increases.The optical properties in the near ultraviolet and visible light regionare enhanced.When the electric field intensity is 0.06 V/A,the optical absorption in the visible region is the best.?4?The electron structure and optical properties of Cr-TiO₂?001?surface under external electric field.With the doping of Cr,a new impurity level is introduced in the bandgap region.The conduction band is close to the Fermi level,and the band gap is reduced,resulting in the redshift of the optical absorption side.As the electric field intensity increases from 0 V/A to 0.3 V/A,the DOS curve does not change,but the responsiveness to visible light increases,and the light absorption in the near ultraviolet region increases.However,the effect of the applied electric field on the surface of Cr-TiO₂?001?in the visible region is not obvious.It is found by analysis and comparison of the effects of external electric field on the optical properties of C-Ti02?001?and Cr-TiO₂?001?that the optical absorption of non-metallic C doped TiO₂?001?surface in the near ultraviolet region is better than that of metal element Cr doped TiO₂?001?surface under external electric field.