Induction plasma-sprayed photocatalytically active titania coatings and their characterisation by micro-Raman spectroscopy

Undoped TiO2 (anatase) powder was deposited by induction plasma spraying (IPS) varying the plasma power, the carrier gas (argon) flow rate and the powder feed rate according to statistical design of experiments (SDE) methodology. In addition, anatase powders doped with varying amounts of V, Nb or Ta oxides were deposited by suspension plasma spraying (SPS) using reactive induction plasma spray (IPS) technology. The microstructure, crystallinity and anatase-rutile ratio of the coatings were studied by surface mapping with micro-Raman scanning spectroscopy and grazing-incidence X-ray diffraction (GIXD), and their photocatalytic activity was tested utilising the photocatalytie decomposition reaction of 4-chlorophenol in aqueous solution under UV irradiation. The rates of pH change (-dpH/dt) were compared with those of standard Degussa P-25 coatings. It was found that the photocatalytic activity of the samples showed a reasonable correlation with the phase content and the plasma processing conditions. In particular, the activity of coatings doped with 4 at.% of either Nb or Ta exceeded those of standard Degussa P-25 coatings. (c) 2005 Elsevier B.V. All rights reserved.