In situ growth of an ultrathin Cu/g-C3N4 coating over SBA-15 for catalytic wet air oxidation of pollutants under extremely mild conditions

Abstract

Catalytic wet air oxidation (CWAO) is a very promising technology for the elimination of various refractory pollutants, but to activate dioxygen under mild conditions is a great challenge. In this research, we report a series of Cu_x/CN_y@SBA catalysts to activate dioxygen for CWAO of phenols and antibiotics under mild conditions. The catalysts were prepared by in situ growth and dispersion of g-C₃N₄ and Cu species over the SBA-15 surface. Characterization by HRTEM, EDS, XRD, FT-IR, and XPS showed that the formed ultrathin g-C₃N₄ coating over the surface of SBA-15 provided abundant locations to embed the Cu species and thus more active sites were generated. UV-vis DRS characterization proved that the synergetic effect between Cu species and the SBA-15-dispersed g-C₃N₄ greatly enhanced the ability to activate dioxygen. It was found interestingly that superoxide radicals (˙O₂⁻) were the dominating active species at low temperature, while both ˙O₂⁻ and hydroxyl radicals (˙OH) became the active species at high temperature during the CWAO of phenol. Among the catalysts tested, Cu₁/CN_3.3@SBA-N demonstrated the highest activity, affording 100% phenol removal and more than 90% chemical oxygen demand (COD) removal, even at 90 °C and atmospheric dioxygen pressure. Modification of the SBA-15 surface with KH-550 could remarkably improve the recycling stability of the catalyst. These findings provide new insights for the development of highly effective catalysts for the activation of dioxygen, particularly in the field of CWAO wastewater treatment.