Effects Of Oxygen Vacancies On The Electronic Structure And Photocatalytic Activity Of Pure And C(N)-doped Anatase Titanium Dioxide

Many studies have shown that it is easy to generate oxygen vacancies in pure, C-doped andN-doped TiO₂in a reducing atmosphere or in a vacuum, but a lot of controversies still exists about theeffects of oxygen vacancies on the electronic structures and photocatalytic activity of various systems. Sothis issue deserves further study. In this paper, the following three parts have been carried out usingstandard density functional theory: the effects of oxygen vacancies on the electronic properties andphotocatalytic activity of pure anatase TiO₂; the effects of oxygen vacancies on the electronic propertiesand photocatalytic activity of C-doped anatase TiO₂; the effects of oxygen vacancies on the electronicproperties and photocatalytic activity of N-doped anatase TiO₂.By the calculation and analysis of formation energies of C-doped and N-doped TiO₂containingoxygen vacancies, we found that oxygen vacancies prefer to reside in the vicinity of impurity ions incompensation doping system （i.e. the number of excess electrons released by oxygen vacancies is equal tothe number of holes introduced by acceptor impurities）.The electron density difference and Mulliken population analysis have shown that the two excesselectrons released by an oxygen vacancy don’t localize near the oxygen vacancy. In pure TiO₂, the twoelectrons are mainly located around the three titanium ions linked with the oxygen vacancy; in C-dopedTiO₂, they are mainly located in the Carbon ion and three titanium ions linked with the Carbon ion; inN-doped TiO₂, they are mainly located in the two Nitrogen ions and five titanium ions linked with theNitrogen ions.For C-doped and N-doped TiO₂containing oxygen vacancies, Carbon and Nitrogen impuritiescan introduce band-gap states, and oxygen vacancies don’t introduce any additional band-gap state.However oxygen vacancies can significantly lower these impurity levels in energy, which can reduce thecarrier recombination probability and is very beneficial to the improvement of TiO₂’s photocatalyticactivity.The main effects of oxygen vacancies on the electronic properties of C-doped TiO₂and N-dopedTiO₂are similar to the phenomenon appearing in conventional compensated donor-acceptor co-doping TiO₂, which can eliminate some deeper impurity levels introduced by single impurity and lower therecombination probability of photo-generated carriers to some extent. This offers a fresh idea to understandthe effects of oxygen vacancies on the electronic properties and photocatalytic activity of C-doped TiO₂andN-doped TiO₂.