Sludge-derived biochar toward sustainable Peroxymonosulfate Activation: Regulation of active sites and synergistic production of reaction oxygen species

Abstract

Active sites on the surface of heterogeneous catalysts accounted for the generation of reactive oxygen species (ROS) from peroxymonosulfate (PMS) toward organic degradation. In this study, the surface chemistry of sewage sludge-derived biochar (SSB) was regulated by controlled pyrolysis and SSB was used for PMS activation and oxidation of antibiotic ciprofloxacin (CIP). SSB-20–120 achieved high CIP removal efficiencies in both batch test (94.2%) and continuous column test (96.3%) with PMS. The species and contents of Fe, N and O as active sites on SSB and their relationships with generated ROS (SO4•−, •OH, and 1O2) for CIP degradation were comprehensively identified. Fe(0), –OH, C = O and the pairwise interaction among Fe(0), Fe(II) and Fe(III) were responsible for SO4•− generation. Besides, pyrrolic N, graphitic N and the co-effect among pyridinic N, pyrrolic N and graphitic N exerted positive effects on •OH and SO4•− generation simultaneously. Meanwhile, Fe(II), Fe(III), pyrrolic N, graphitic N, lattice O with –OH, lattice O with C = O, the interactions among Fe(0), Fe(II) and Fe(III) as well as pyridinic N, pyrrolic N and graphitic N contributed to the production of •OH coupling with 1O2. Moreover, SO4•− and 1O2, as well as the co-effects of •OH with SO4•− and •OH with 1O2 were in favor of CIP degradation. This research provided new insights into the biochar synthesis, structure evolution, and the generation mechanism of reactive oxygen species from PMS activation. Outcomes are beneficial to sewage sludge utilization and developing low-cost catalysts for wastewater remediation.