A photocatalytic approach in micro arc oxidation of WO3-TiO2 nano porous semiconductors under pulse current

Since ultraviolet (UV) irradiation cannot be applied for a long time in practical applications, it is necessary to develop a narrow band gap photocatalyst to decompose environmental pollutants under visible irradiation. In this research, (WO3)(x)-(TiO2)(1-x) nano-porous layers were fabricated by micro arc oxidation (MAO) and influence of the electrical current type on their physical and chemical properties was investigated. Morphological studies, performed by SEM technique, revealed that pore size and roughness decreased with the frequency and increased with the duty cycle. The pulse-grown layers had a finer structure when compared to those fabricated under direct current. XRD and XPS results showed that the layers consisted of anatase, rutile, and tungsten oxide phases. Applying pulse current resulted in higher anatase relative contents. Band gap energies of the MAO-grown TiO2 and WO3-TiO2 layers were respectively measured as 3.14 and 2.96 eV. The layers fabricated under pulse current exhibited higher photoactivity under ultraviolet and visible illuminations as compared to the layers grown under direct current. Methylene blue (MB) was used as a model material to examine photocatalytic performance of the layers. Maximum MB-photodegradation reaction rate constants over the pulse-synthesized WO3-TiO2 layers were measured as 0.0269 and 0.0129 min(-1) for ultraviolet and visible irradiations. For layers grown under direct current, the rate constants were lower, i.e. 0.0228 and 0.0099 min(-1) respectively. (C) 2011 Elsevier B.V. All rights reserved.