Photocatalytic activities of europium (III) and niobium (V) co-doped TiO2 nanopowders synthesized in Ar/O2 radio-frequency thermal plasmas

Europium (III) and niobium (V) co-doped TiO2 nanopowders were synthesized in Ar/O-2 radio-frequency thermal plasmas by pyrolyzing aqueous precursors that contained various concentrations of Eu3+/(Eu3+ + Nb5+ + Ti4+) = 0-0.5 at.% and Nb5+/(Eu3+ + Nb5+ + Ti4+) = 0-1.0 at.%. Phase identification was performed by X-ray diffraction (XRD), particle morphology was observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), and UV-vis absorption spectra were determined by UV-vis spectroscopy. The photocatalytic activities under UV and visible light irradiations were both evaluated by bleaching 20 mu M of a methyl orange aqueous solution. All the resulting powders had a phase composition of anatase (30-66 nm crystalline size) (major phase: similar to 80% mass proportion) and rutile (56-94 nm crystalline size) polymorphs, with a relatively wide particle size distribution from several nanometers (faceted crystallites) to similar to 100 nm (spherical particles). The photocatalytic activities dominated by oxygen defects in the TiO2 host lattice for the powders prepared with identical doping concentrations of Eu3+ and Nb5+ were both superior under UV and visible light irradiations over those obtained with different doping amounts. More interestingly, the co-doped powder exhibited an improved photocatalytic performance under 600-700 nm visible light illumination than the Eu3+-doped TiO2 and P25 commercial powders. (c) 2014 Elsevier B.V. All rights reserved.