Structural and electronic properties of iodine-doped anatase and rutile TiO2

The structural and electronic properties of iodine-doped (I-doped) anatase and rutile TiO2 were investigated based on the density functional theory (DFT) calculations. The results indicate that substitutional iodine (I) for Ti-doped anatase TiO2 has a much more efficient and stable photocatalyst than the pristine TiO2. The density of states analysis shows that I 5p states mix with Ti 3d states and O 2p states move to high energy region and induce band gap narrowing, which is responsible for absorption edge red-shift. Interestingly, for substitutional I for O model, it is predicted theoretically that the blue-shift of absorption edge phenomenon can be measured in experiment. On the other hand, for I-doped rutile TiO2, its red-shift microscopic mechanism is similar to the configuration in anatase but an indirect band gap reduces its photocatalytic efficiency. For substitutional I for O model, the electronic structures indicate that the nature of red-shift is ascribed to I 5p states. We also analyzed the different photocatalytic activities based on the crystal structure of TiO6 distortion and their different band structure characteristics. The calculated formation energy indicates that it is difficult for substitutional I for O to appear in the experiment. The analysis can explain well the experimental observations and tentatively give some new concepts.