Efficient degradation of organic pollutants with a sewage sludge support and in situ doped TiO 2 under visible light irradiation conditions

TiO2 is considered to be the most promising candidate for photocatalytic organic pollutant degradation, however, it suffers from a large band gap, which means that it is active only in the UV region. Thus, in recent decades, a considerable amount of research has investigated how to expand the optical absorption spectrum of TiO2 into the visible region. In this study, we developed a new approach that used sewage sludge as the support and dopant to construct a bimodal-pore composite visible-light-driven TiO2 photocatalyst (SS-Ti-700). The design was based on a mesoporous assembly of the organic and inorganic compounds in the sewage sludge, which served as the scaffold templates; a SiO2–TiO2 nanostructure, which has been demonstrated to have markedly high photocatalytic activity; and the in situ doping of TiO2 with transition metals (Fe, Cu, and Cr) originating from the sewage sludge, which significantly enhances visible-light absorption. Kinetic analysis showed that this arrangement exhibited rapid p-nitrophenol degradation and mineralization under visible light irradiation conditions. The possible reaction mechanism was explored by ESR spectroscopy. Our protocol demonstrates a new approach for the potential environmentally benign reuse of sewage sludge and provides a facile, cost-effective, and eco-friendly approach for synthesizing TiO2-based mesoporous photocatalysts.