A comparative study on the activation of persulfate by mackinawite@biochar and pyrite@biochar for sulfamethazine degradation: The role of different natural iron-sulfur minerals doping

• Activation of PS by FeS@BC and FeS 2 @BC was compared. • FeS@BC had better catalytic performance than FeS 2 @BC. • FeS@BC has larger specific surface areas, abundant micropores, higher defect degree. • Surface C = O, Fe(II), and S-thiophene groups of FeS@BC accounted for PS activation. • S 2− /S n 2– species and graphene structure of FeS 2 @BC accounted for PS activation. In this work, two novel heterogeneous catalysts were prepared by loading natural mackinawite (FeS) and pyrite (FeS 2 ) particles into peanut shell-derived biochar (i.e., FeS@BC and FeS 2 @BC), and the persulfate (PS) activation processes by these two composites for sulfamethazine (SMT) degradation were systematically examined. After doping natural iron-sulfur ores, the catalytic removal performance of the above two composites were 37.2%–80.0% and 31.0%–35.2% higher than those of their respective original minerals and primitive biochar. Simultaneously, FeS@BC had better catalytic performance than FeS 2 @BC. The larger specific surface areas, abundant micropores, higher defect degree, better conductivity and FeS crystals favored the release of more iron, resulting in higher reaction stoichiometric efficiency (RSE) value, excellent catalytic activity, and enhanced SMT mineralization. In the FeS@BC/PS system, surface ketonic groups (C = O), Fe(II), and highly active S-thiophene groups all accounted for PS activation. In the FeS 2 @BC/PS system, C = O groups, Fe(II), highly reductive S 2− /S n 2– species, and graphene structure participated in the catalytic reaction. The electron-rich S-thiophenic groups, S 2− /S n 2– species, and ketonic moieties could act as electron donors, prompting the regeneration of Fe(II) in the lattice (≡Fe(II)) and solution (Fe 2+ ) by direct or indirect electron transfer. In view of the higher catalytic activity of FeS@BC, we further investigated different influencing factors on SMT degradation, activation mechanism, and degradation pathway of SMT in the FeS@BC/system. Overall, this study would fill the gap in the research on the difference in the catalytic activity of catalysts prepared by loading different natural iron-sulfur minerals onto biochar for persulfate activation.