Characterization of Paramagnetic Species in N-Doped TiO₂ Powders by EPR Spectroscopy and DFT Calculations

Abstract

Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations are combined for the first time in an effort to characterize the paramagnetic species present in N-doped anatase TiO2 powders obtained by sol-gel synthesis. The experimental hyperfine coupling constants are well reproduced by two structurally different nitrogen impurities: substitutional and interstitial N atoms in the TiO2 anatase matrix. DFT calculations show that the nitrogen impurities induce the formation of localized states in the band gap. Substitutional nitrogen states lie just above the valence band, while interstitial nitrogen states lie higher in the gap. Excitations from these localized states to the conduction band may account for the absorption edge shift toward lower energies (visible region) observed in the case of N-doped TiO2 with respect to pure TiO2 (UV region). Calculations also show that nitrogen doping leads to a substantial reduction of the energy cost to form oxygen vacancies in bulk TiO2. This suggests that nitrogen doping is likely to be accompanied by oxygen vacancy formation. Finally, we propose that the relative abundance of the two observed nitrogen-doping species depends on the preparation conditions, such as the oxygen concentration in the atmosphere and the annealing temperature during synthesis.

Influence of the chemical synthesis on the physicochemical properties of N-TiO2 nanoparticles

“…These centres (labelled as N i O • ) are paramagnetic and were identified via Electron Paramagnetic Resonance (EPR) spectroscopy [7][8][9].…”

Evidence for TiON sputtered surfaces showing accelerated antibacterial activity under simulated solar irradiation

“…Increasing the sputtering times from 1 to 5 min in Fig. 3 lead to TiON samples with a higher optical absorption (Subramanian et al, 2011) due to the introduction of Ninterstitial sites doping the TiO 2 with O-vacancies (Valentin et al, 2005). This in turn leads to a larger amount charge transfer sites in the visible region (Lin et al, 2005;Lee et al, 2009 …”

High Selectivity of Visible-Light-Driven La-doped TiO2 Photocatalysts for NO Removal

“…For non-metal ion dopants, substitution of p block elements (B, C, N, F, S, P and I) either at Ti 4+ and O 2-sites is an appealing option to tailor the bandgap absorption to the visible-light region, with a robust interfacial charge carrier transfer process (Devi and Kavitha, 2013). For instance, N-doping TiO 2 (N-TiO 2 ) generates the visible light response because of the occupied N 2p states above the VB edge, while the transition from the occupied π* character N-O localized state results in a visible light response for N-TiO 2 (Di Valentin et al, 2005). On the other hand, many transition metal ions have been introduced into titania to extend the visible absorption, which is attributed to the charge transfer transition between the d electrons of the dopant and CB (or VB) of TiO 2 .…”