Understanding electronic and optical properties of anatase TiO2 photocatalysts co-doped with nitrogen and transition metals

Abstract

This paper describes an investigation into the general trend in electronic properties of anatase TiO2 photocatalysts co-doped with transition metals and nitrogen employing first-principles density functional theory. Fourteen different transition metals (M), including Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, and Cd, have been considered. The characteristic band structures of the co-doping systems involving the transition metal series are presented. Our results indicate that the absorption edges of TiO2 are shifted to the visible-light region upon introduction of dopants, due to the reduced conduction band minimum (CBM) and the formation of impurity energy levels (IELs) in the band gap. These IELs are primarily formed from (a) the anti-bonding orbitals of the M-O (M indicates the doped transition metal) bonds, (b) the unsaturated nonbonding d orbitals of the doped transition metal (mainly d(xy), d(yz), and d(xz)), and (c) the Ti-O bonding/Ti-N anti-bonding orbitals of the bond next to the doped transition metal. When the valence d electrons of the doped metal are between 3 and 7, all three types of IELs appear in the band gap of the (M, N) co-doped systems. For systems doped with a metal of more than 7 valence electrons, only types (a) and (c) of IELs as well as the unoccupied pz state of N are observed. Based on our analysis, we propose that the co-doping systems such as (V, N), (Cr, N), and (Mn, N), which have the IELs with a significant bandwidth, are of great potential as candidates for photovoltaic applications in the visible light range.

Porous (001)-faceted Zn-doped anatase TiO2nanowalls and their heterogeneous photocatalytic characterization

“…15 XPS analysis as shown in Fig. 45 This in turn lowers the energy required to photoexcite the electron from the VB. This will further enhance the surface energy for several orders higher, producing more reactive surface to facilitate active O 2 c adsorption on the surface.…”

Enhancing photocatalytic properties of rutile TiO2 by codoping with N and metals – Ab initio study

“…Long and English [47] reported that among the investigated systems (N or C; TM ¼ Ta, Hf, Fe)-codoped anatase TiO 2 , only (N, Ta)-codoping case narrows the band gap significantly by up to 0.48 eV. Meng et al [44] indicated that (V, N), (Cr, N) and (Mn, N) codoped anatase TiO 2 , with the impurity energy levels of a significant bandwidth in the band gap, are of great potential as candidates for photovoltaic applications in the visible light range. Long and English [54] used hybrid density functional theory calculations to investigate (N, Si)-codoped TiO 2 and found that codoping produces a larger band gap narrowing compared to monodoping with the same elements.…”

Characterization and photocatalytic activity of SiO2, FeOx coatings formed by plasma electrolytic oxidation of titanium

“…7b). The detailed information about the composition and E g is shown in the Table. Incorporation of Fe atoms into the anatase crystal lattice leads to hybridization of the non-bonded d electrons of Fe with the Ti\ \O bonding orbitals [33]. This results in the emergence of new energy levels near the bottom of the conduction band and an effective electron transfer under visible light.…”