A review of anionic, cationic and co-dopants in titanium dioxide (anatase) and its effect on band gap

Titanium dioxide (TiO2) is a semiconductor material that has excellent optical, electronic and photocatalytic properties in various applications. But the wide band gap of anatase (eV3.2) has reduced its optical and electronic properties under visible light. For this reason, this gap needs to be narrowed, and one of these methods is contamination by various elements. The aim of this study was to investigate the effect of various cationic, anionic and common contaminants on the band gap and optical properties of anatase. Alternative type contamination at the site of oxygen atoms (anionic contamination) has shown that the addition of carbon to the structure in addition to reducing the band gap leads to the formation of intermediate levels below the Fermi surface and the presence of these levels in improving light absorption in the visible area he does. In contrast, the addition of sulfur atoms instead of oxygen leads to the mixing of O 2p and S 3p states, and with the addition of contaminant concentrations, the band gap gradually decreases. The important point about the concentration of nitrogen pollutants, which is one of the most important anionic pollutants, is that at concentrations higher than 1.4%, it leads to the creation of intermediate levels in the forbidden gap in areas close to the Fermi surface and increases the recombination of charge carriers. Be. In cationic contaminants, the contaminant is replaced at the site of the titanium atom. Contamination of intermediate elements has created semi-solid impurity levels in the restricted area and at the same time has reduced the band gap. In addition, iron pollutants in the presence of oxygen depletion have reduced the gap to eV1.94, which is the most effective compared to other pollutants. Common contamination in anatase is considered to improve the band gap and reduce the recombination of charge carriers, and this leads to the addition of impurity levels above the capacity strip and below the conduction band, and in some applications such as photocatalytic processes can provide optimal performance.