Modification Of Titanium Dioxide-Based Photocatalysts By Doping:a First Principles Study

Photocatalytic materials, based on Titanium dioxide (TiO2), have its excellent properties, such as high photocatalytic activity, chemical and thermal stability, non-toxicity and low cost, and has a broad application prospect in water splitting, solar cells and environmental protection fields. However, A wide band gap (rutile structure:3.0eV, anatase structure:3.2eV) makes pure TiO2have a poor visible light utilization. In addition, the electrons and holes in compound also reduce the pure TiO2photocatalytic efficiency in certain extent. Therefore, by doping to reduce the bandgap of TiO2and prevent the compound of electrons and holes has become an important means of regulating the photocatalytic performance of TiO2and gradually has drawn people’s great attention.By the first principles calculation based on density functional theory method, This paper systematically studied the electronic structure and absorption properties of doped systems and, from a microscopic view, revealed the mechasim of reducing the bandgap of TiO2by doping and preventing the compound of electrons and holes. The main research contents and results are as follows:(1) By density functional theory plus U(GGA+U) method, we calculated the electronic structure and absorption properties of (Nb+Sb, C) doped rutile TiO2. In (Nb+Sb, C) doped rutile TiO2, we use a niobium(Nb) atom and a antimony (Sb) atom to replace Ti in the pure TiO2, at the same time, we use a carbon atom to replace O in the pure TiO2. This substitution doping system is not be mentioned in the previous research work which is our work innovations. The bandgap of (Nb+Sb, C) doped rutile TiO2is only1.8eV, which can absorb visible light well and improve the photocalatic activity of pure TiO2. We predicted that (Nb+Sb, C) doped rutile TiO2will be a good photocatalysts.(2) By GGA+U method, we calculated the electronic structure and absorption properties of (N, Sn) doped anatase TiO2and also calculated the system of Sn-,(N, Sn) doped and (2N, Sn) doped anatase TiO2. This substitution doping system theory research has not been reported. We found that the Sn doping and (N, Sn) doping can not reduce the bandgap of pure anatase TiO2. However, the (2N, Sn) doping which two adjacent O atoms are replaced by two N atoms and any Ti atom is replaced by Sn atom make a significant reduction of band gap. Instead, the (2N, Sn) doping which the two O atoms are located far away are replaced by N atoms just make a little reduction of bandgap. This is due to the former doping produced the N-N copuling which is the reason of the bandgap reduction. Our theoretical results provided a reasonable explanation for the previous experimental work that N-Sn codped TiO2showed obvious photocatalytic activity.(3) By GGA+U method, we calculated the electronic structure of F doping concentration of anatase TiO2and TiO2(101). The theoretical research about this has not been reported. We found that, F doing bring out more electronics phenomenon and make the electronics of systems unbalance. As F doping cncentration increases gradually, the phenomenon of the electronics unbalance is more and more serious, which caused the lattice defects. Thus, increase its visible light absorption rate and improve the photocatalytic activity of TiO2. The corresponding theoretical results bring the experimental work a certain guiding significance.