Photocatalytic properties of TiO <inf>2</inf>/WO <inf>3</inf> coatings formed by plasma electrolytic oxidation of titanium in 12-tungstosilicic acid

Abstract

In this paper, we have investigated photocatalytic properties of TiO 2/WO 3 coatings formed by plasma electrolytic oxidation (PEO) of titanium in 12-tungstosilicic acid water solution and compared with photocatalytic activity of pure TiO 2 coatings. The photocatalytic activity of the coatings is evaluated by measuring the degradation of methyl orange under simulated sunlight conditions. Photocatalytic activity of TiO 2/WO 3 coatings varied with duration of PEO process and higher photoactivity is obtained for a shorter process time. Photocatalytic activity of TiO 2/WO 3 coatings is related to morphology and phase and elemental composition of coatings. The oxide coatings morphology is strongly dependent on PEO time. The elemental components of the coatings are Ti, W and O. The oxide coatings are partly crystallized and mainly composed of WO 3 and anatase. Decrease in the number of microdischarge channels and agglomeration of particles on the surface leads to a decrease in photocatalytic activity. The reduction of the photocatalytic activity with increased time of PEO process is accompanied with the increase of WO 3 concentration on the coatings' surface. Diffuse reflectance spectroscopy has shown that coatings enriched with tungsten oxide exhibit significant red shift with respect to the pure TiO 2 coatings. TiO 2/WO 3 coatings with improved catalytic activity, compared to pure TiO 2 coatings, are grouped around energy band gap of 2.6eV. The results of PL measurements of TiO 2/WO 3 coatings are in agreement with photocatalytic activities. The increase of PL intensity corresponds to decrease of photocatalytic activity of the coatings, indicating fast recombination of electron-hole pairs. © 2012 Elsevier B.V.