Development of WO3-incorporated porous ceramic coating: A key role of WO3 nanoparticle concentration on methylene blue photodegradation upon visible light illumination

Abstract

In this study, we synthesized WO3/TiO2 nanocomposites by incorporating WO3 nanoparticles (NPs) into TiO2-based coatings produced via plasma electrolytic oxidation (PEO) on pure Ti. We investigated their effectiveness for the photodegradation of methylene blue (MB) under visible light. We analyzed the morphology, chemical composition, and optical properties of the PEO coatings using various techniques, including scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, UV–Vis diffuse reflectance, and photoluminescence spectroscopy. The addition of WO3 NPs led to a finer microporous structure and a higher specific area. Furthermore, the phase analysis of the oxide coatings revealed that the WO3 NPs were inertly incorporated into the oxide coating and prevented the formation of rutile at higher concentrations. All coatings were found to be hydrophobic in nature with contact angles higher than 89°, except for the coating containing 2 g/L WO3 NPs, which had a contact angle of 41.32°. Increasing the concentration of WO3 NPs in the composite coatings from 0 to 3 g/L led to a decrease in the optical band gap energy of the coating from 3.02 to 2.9 eV. The PEO coating with 2 g/L WO3 NPs showed the highest photocatalytic activity (PA) (83%), which was 1.8 times higher than that of the WO3-free coating. This improvement in PA could be attributed to the formation of a hydrophilic heterojunction that can effectively separate electron/hole pairs. Moreover, the optimal coating retained its reusability even after being used three times. We fully investigated the influence of photocatalytic parameters such as pollutant concentration, pH, and light intensity. Extensive scavenger tests also indicated that holes and hydroxyl radicals played a major role in MB degradation. We established the MB photodegradation mechanism based on Mott-Schottky and DRS (Diffuse Reflectance Spectroscopy) results.