Photocatalytic performance of iron (III) and niobium (V)-codoped TiO ₂ 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.