Activation of peroxymonosulfate by chemically modified sludge biochar for the removal of organic pollutants: Understanding the role of active sites and mechanism

Abstract Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) are promising tools for wastewater treatment. However, the production of high-efficient PMS activator from low-cost material still needs further improvement for practical application. Herein, we reported a series of sludge-derived biochar as catalysts for PMS activation and subsequent degradation of organic pollutants such as acid orange 7, rhodamine B, methylene blue, methyl orange, and their combination. Chemical treatment (e.g., NH4OH, KOH, or HCl treatment before, after, or both before and after pyrolysis) and various pyrolytic conditions were employed for synthesizing sludge biochar based-catalysts. Our best as-synthesized catalyst exhibited excellent performance in oxidative degradation of recalcitrant organics in PMS/acidic media, which was superior to many previously reported carbocatalysts. A non-radical process performed by pyridinic N was the dominant catalytic mechanism, while pyrrolic N, activated C(+) and surface area supported the adsorption of pollutants. A significant correlation between reaction rate constant and dye adsorption suggested that the non-radical oxidation process influenced by both pollutant adsorption and PMS activation. This study not only provides a facile rote of efficient sludge valorization, but also gives new scientific insight into the specific role of N species and other functional groups of carbocatalysts in PMS-based AOPs.