Nature of Nitrogen-Doped Anatase TiO₂ and the Origin of Its Visible-Light Activity

Abstract

Nitrogen doped anatase TiO 2 is studied by using hybrid density functional theory (DFT) calculations. It is shown that under typical experimental conditions, nitrogen prefers to substitute at a Ti-site and bond to two or three neighboring oxygen ions, forming nitrite or nitrate molecules. This leaves one Tivacancy and under-coordinated oxygen ions which produces a large electron density of states at the valence band edge, with localized characters slightly extending into the pristine TiO 2 band gap, due to an altered local electrostatic potential and orbital interactions. We suggest that this large electronic density of states at the valence band edge is responsible for the enhanced sub-gap tail absorption observed in Ndoped anatase TiO 2 and hence the visible-light photocatalytic activity. IntroductionTitanium dioxide (TiO 2 ) is one of the most promising photocatalyts and has been intensively studied over the past few decades 1-3 . The main drawback of TiO 2 is that it does not absorb sunlight efficiently due to its large band gap. The measured optical band gaps of two common polymorphs, rutile and anatase, are ~3.0 eV 4,5 and ~3.4 eV 5,6 respectively, which limits their use for solar energy conversion. Therefore considerable efforts have been devoted in order to make TiO 2 active under visible light, which comprises the major part of the solar spectrum.

Biocompatibility and antibacterial activity of nitrogen-doped titanium dioxide nanoparticles for use in dental resin formulations

“…Consistent with literature reports, [18][19][20][21] nitrogen doping of TiO 2 resulted in absorption extending well into the visible range of wavelengths. The extent of absorption in the visible range of wavelengths was concentration dependent.…”

“…34 Other reports indicate that the bulk material bandgap does not significantly shift, and that the absorption of blue light is instead the result of a variety of states at the valence band edge attributed to titanium-site vacancies and undercoordinated oxygen ions. 19,21 Generally, nitrogen doping by substitution into the crystal structure results in lower energy states closer to the original bandgap, while doping by chemisorption and interstitial incorporation results in deeper trap states. This has generally been found to be dependent on the synthetic method and the concentration of nitrogen precursor, with lower concentrations resulting in substitution and higher concentrations resulting in chemisorption and interstitial doping.…”

“…16 Another self-healing composite material was developed using breakable capsules of unreacted monomers, which has shown promising healing characteristics. 17 Recent research has shown that the light absorption of TiO 2 can be shifted to the visible range by doping with a variety of atoms, including nitrogen, [18][19][20][21] fluorine, 22 copper, 23 and silver, 24 resulting in a new class of visible light active materials. This is of particular interest in the development of novel dental materials for two reasons: exposure of gum tissue to blue light is preferable to cytotoxic UV light 25 and most of the dental offices are already equipped with blue light sources used to cure photoactive composite dental resins.…”

Self‐Compensation in Transparent Conducting F‐Doped SnO2

“…The hybrid functional PBE0 developed by Adamo and Barone was used in order to combat the self‐interaction error and thus allowed for an accurate description of the band gap of SnO 2 . Hybrid functionals were consistently shown to provide improved calculations of both geometry and electronic structure, and PBE0 was shown to predict these properties for tin‐based TCOs with a high degree of accuracy . PBE0 incorporates 25% of exact Fock exchange to the PBE (Perdew, Burke, and Ernzerhoff) formalism.…”

The influence of nitrogen doping on the electronic structure of the valence and conduction band in TiO2

“…They calculated the DOS by using density functional theory to compare the anatase TiO 2 structure with substitutional nitrogen, interstitial nitrogen or oxygen vacancy induced by N doping. On the other hand, Chen & Dawson (2015) performed their research assuming different nitrogen substitution sites in TiO 2 . As a result, the calculated DOS relates to nitrogen substitution at a Ti site and formation of nitrite or nitrate molecules.…”