Photocatalytic degradation of Naproxen and methylene blue: Comparison between ZnO, TiO2 and their mixture

Photocatalytic (PC) methods based on advanced oxidation processes have shown great potential for removal of water pollutants. Oxide semiconductors stand out as the most promising materials for UV-mediated photodegradation of persistent pollutants in wastewater. Although an immense number of studies have appeared so far concerning the PC activity mostly of TiO2 but also of ZnO, the efficiency of these and other mixed oxides in degrading a wide range of organic pollutants has not yet been extensively explored. In this work we compare the efficiency of ZnO, TiO2 and the 2ZnO-TiO2 mixed crystal prepared by mechanochemical solid-state treatment, to decompose a pharmaceutical (Naproxene) and a dye (methylene blue) compound. The phase morphology, composition, specific surface area and crystalline structure of the nanopowders were characterized in detail. The photocatalytic activity of ZnO under UV irradiation was systematically higher than the other materials. The activity of the mixture was found to depend on the type of the analyte molecule, being, however, higher than that of pristine TiO2 nanoparticles.