First-Principles Study Of N、F Doped And N/F Codoped Anatase TiO₂

Anatase TiO2 semiconductor material becomes the most research value and development prospects of environmental photocatalysis materials, because of its safe non-toxic, low cost, stable chemical properties and corrosion resistance, etc. The activity of titanium dioxide are limited, due to its large band gap, can only absorb less than 387 nm wavelength ultraviolet light to generate the photocatalysis, which accounts for only a small part of the ultraviolet light in sunlight. So, in recent years, there are many research scholars keen to research how to improve the photocatalytic activity of TiO2. One of the most concern is heterogeneous elements doping. It contains metal elements doping, nonmetallic elements doping, as well as two metals co-doping, metal and nonmetal co-doping and two kinds of nonmetal co-doping. In this paper,we chose two nonmetal elements of nitrogen and fluorine, We studied the electronic structure of pure anatase TiO2,anatase TiO2 doped with N or F and anatase co-doped with N and F from the first principles calculation method based on density functional theory.At first,we studied pure anatase TiO2 with two kind of approximate methods,LDA and GGA.We found that the calculation results with GGA agreed with the experiment data more better. But due to the well-known DFT always underestimated the width of band gap, we adopt GGA+U method for correction. We tested three different value of U and through calculation results to choose the best one.Then the best value will be used in the following calculation all.Next,we construct a 2x2x2 anatase titanium dioxide model to study the activity of N-doping anatase TiO2 and F-doping anatase TiO2.Doping concentrations are 2.1% and 1.05%,respectively,through N/F instead of oxygen.The results showed that:N-doping can improve the photocatalytic activity by introducing the impurity level,however,F-doping can narrow band gap,which lead to the red shift of absorption wavelength.After studied the effects of different elements doping, we studied the influence of different concentration of doping modification. We construct three kinds of unit cell model,2×2×1、2x2x2、3x2x2,respectively.The type and number of impurity atoms are same,two nitrdgen atoms instead of two oxygen atoms and one fluorine atom instead of one oxygen. Thus three different doping concentrations of model are be made(N:4.2% F:2.1%; N:2.1% F:1.05%;N:1.4% F:0.7%).It is important to keep the position of the impurity atom is relatively consistent,so the affect of doping position is eliminated.We come to the conclusion:co-doping can integrated the advantages of single doping,achieve a better effect;the anatase TiO2 photocatalytic activity along with the increase of doping concentration.