Electronic and optical properties study on Fe−B co-doped anatase TiO₂

Highlights: • We calculate (Fe, 2B) compensated co-doped TiO₂ using density functional theory. • The (Fe, 2B) compensated co-doping is more energetically favorable. • The gap states modify the electronic structures, resulting in bandgap narrowing. • The electron transfer realizes the charge compensation, forming strong Fe−B bond. • The optimal band gap is found to be about 2.13 eV after compensated co-doping. - Abstract: We investigate the density of states and optical properties for Fe, 2B and (Fe, 2B) doped TiO₂ with DFT calculations. The calculated results reveal mono-doping introduces midgap states which are half-occupied and easy to become the recombination centers of charge carriers, thus inhibiting the enhancement of photocatalystic activity. The coupling of 2p-3d states in the (Fe, 2B) compensated co-doped TiO₂ makes gap states couple with the valence bands edge, thus greatly causing the band gap narrowing and higher visible light absorption. Moreover, the gap states cannot become recombination centers of the photoexcited carriers, thus promoting the separation of electron-hole pairs, prolonging the lifetime of carriers. The analysis of electron density indicates more electrons from Fe transfer to adjacent B, realizing the charge compensation and forming a stronger Fe−B bond. Therefore, the (Fe, 2B) compensated co-doped TiO₂ exhibits the higher visible-light photocatalystic activity than those of pure and solely doped TiO₂.