Photocatalytic performance of iron (III) and niobium (V)-codoped TiO2 nanopowders synthesized by a radio frequency thermal plasma process

Iron (III) and niobium (V)-codoped TiO2 nanopowders have been synthesized by Ar/O2 RF thermal plasma. Phase composition, morphology, and photocatalytic performance of the plasma-generated powders have been investigated by the combined means of XRD, FE-SEM/TEM, and UV–vis absorption spectroscopy. Rutile formation in the plasma-produced phase composition of anatase and rutile was promoted by Fe3+ addition but was inhibited by Nb5+ doping. The resultant powders consisted of a majority of fine crystallites (several nanometers) and a small portion of coarse particles (~ 100 nm). In comparison with TiO2 singly doped with 0.1 at.% of Fe3+, photocatalytic reactivity of codoped TiO2 was improved at 2.0 at.% of Nb5+ but was depressed at 6.0 at.% under the UV irradiation, indicating that UV-induced photocatalytic capability was dominated by Nb5+ doping concentration. In contrast to the case of 1.0 at.% of Fe3+ single addition, the codoped sample obtained the decreased photocatalytic performance with increasing Nb5+ content under the visible light irradiation, due to the low visible light absorption resulting from a broadened band gap.