Insights into the photocatalytic behavior of carbon-rich shungite-based WO3/TiO2 catalysts for enhanced dye and pharmaceutical degradation

Carbon-rich shungite-based WO3/TiO2 catalysts were synthesized by a solvothermal method. The morphological, structural, optical and physical features of the catalysts were characterized by XPS, FTIR, Raman spectroscopy, SEM and UV-Vis diffuse-reflectance spectroscopy (DRS). The photocatalytic performance of the catalysts was investigated for the degradation of Orange II dye and pharmaceuticals under UV-A irradiation. SEM images show that the shungite surface is completely covered with WO3/TiO2 particles. Raman and XPS analyses demonstrate that the carbon-rich shungite is well-incorporated with the WO3 and TiO2. UV-Vis DRS indicates enhanced visible-light absorption and a lowered band gap (2.83 eV) for the catalysts. The degradation degree of Orange II increases with increasing shungite ratio, which is ascribed to a combined effect of adsorption and photocatalysis, and the improved light absorption and easy transfer of photogenerated holes and electrons across the interface of W/Ti. Mechanism studies indicate that the pi-pi conjugation between a dye molecule and the aromatic bonds of carbon materials are more dominant rather than columbic interactions, and that center dot O-2(-) is the main species in Orange II degradation. However, the Orange II degradation efficiency is lowered in drinking water due to the photo-generated hole (h(+))-scavenging effects by organic matter and salts and their competing adsorption with the target pollutant in the active sites on the catalyst surface. This work provides a possible use of the carbon-rich shungite as a natural carbon resource for the fabrication of carbon-based photocatalysts.