Then, the Cr-doped system can serve as a remarkably better photocatalyst. Ti7MnO16, Ti7FeO16, Ti7CoO16, Ti7NiO16, and Ti7AgO16. The IELs occur in the middle of the band gap, namely the
intermediate level. They may reduce the energy required for electron transition, lower the threshold of photoexcitation, and thus expand the optical absorption spectrum without reducing the energy of electrons or holes. The electrons in the VB can be excited to the IELs and then subsequently excited to the CB by the visible light irradiation. So, IELs are beneficial for extending the sensitive light wavelength. The result gives a good explanation of the red shift [31–34]. However, for these find more kinds of IELs, high impurity doping concentration might form a recombination center for photoexcited electron–hole pairs and results in a decrease in the quantum yield for the photocatalytic reactions . Therefore,
we must control the doping concentration to avoid them to act as Quisinostat datasheet the recombination center of photo-generated electrons and holes. Ti7CuO16. The IELs are located above the VB and partially overlap with the VBM. These kinds of IELs could act as trap centers for photoexcited holes, which can also reduce the recombination rate of charge carriers . The holes generated in the VB produce an anodic photocurrent. Because the Cu t 2g level is close to the VB, the holes easily overlap in highly impure media . Ti7ZnO16 and Ti7YO16. The IELs are located at the top of the VB and completely mixed with the O
2p states to form a new VBM (seen in Figures 3, 4, and 5). The band gaps of Zn- and Y-doped anatase TiO2 are narrowed to 2.69 and 3.15 eV, respectively, and smaller than that of pure TiO2, Buspirone HCl which is consistent with the experimental data on the red shift of the absorption edge [35, 36]. Figure 5 Calculated band structure. (a) Zn-doped anatase TiO2; (b) Y-doped anatase TiO2. Ti7ZrO16, Ti7NbO16. The IELs are not situated at band gap. The electronic structure of Zr-doped TiO2 exhibits similar to that of pure TiO2. Therefore, we can infer that the t2g level due to Zr does not contribute to the photo-response. Similarly, the band gap of Nb-doped anatase TiO2 is larger than that of undoped TiO2 by 0.09 eV, which may result in a blue shift of the absorption edge. Formation energy We analyzed the relative difficulty for different transition metal doping into anatase TiO2 using impurity formation energies, which is a widely accepted method. First-principles calculation for the relative stability of metal-doped TiO2 can help us understand the formation of the doped structures and provide useful guidance to prepare samples.