Breaking rate-limiting steps in a red mud-sewage sludge carbon catalyst activated peroxymonosulfate system: Effect of pyrolysis temperature

Abstract

The active sites on biochar surface could be increased via pyrolysis of sewage sludge (SS) with mixing red mud (RM), improving its catalytic activity effectively. Pyrolysis temperature plays an important role in the regulation of active sites on the catalyst surface. Herein, the RM-SS carbon-based catalysts (RSDBC) were prepared under different pyrolysis temperatures to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. It was found that the rate-limiting step (first oxidation stage) of the RSDBC-500/PMS system could be broken by increasing the pyrolysis temperature from 500 °C to 700 °C, leading to a 1.9-fold increase in SMX degradation efficiency within 120 min. Furthermore, the specific surface area (SSA) and the content of CO, defects, Fe(II), pyridinic N, and graphite N sites of RSDBC increased during the elevation of temperature (500-700 °C), thereby facilitating PMS activation and active species production. The breakage of the rate-limiting step provided the theoretical basis for the optimal preparation of sludge biochar-based catalysts, which is beneficial to promote the application of RSDBC/PMS system in wastewater treatment.