Active sites on a catalyst surface play an overwhelming role in reactive oxygen species production in advanced oxidation processes. However, the possible interaction among different active sites for oxidant activation was ignored, leading to inaccurate understanding of the active sites contribution. Herein, C═C and C═O sites were constructed by lignin pyrolysis and KOH/KBH4 modification for investigation of possible interactions on peroxomonosulfate (PMS) activation. Indispensable synergy was found between C═C and C═O sites on the LG-KOH-300 surface, of which the catalytic activity was 2.24 times higher than that of LG-300 with one single type site. Furthermore, fewer toxic intermediates were obtained in the LG-KOH-300/PMS system. The LG-KOH-300 catalyst with synergistic sites exhibited strong anti-interference ability and good stability for treating wastewater containing CO32– and H2PO4–. Additionally, PMS was more conducive to be adsorbed to synergistic C═C and C═O sites under a higher adsorption energy (Eads = −3.27 eV). The free energy of the spontaneous reaction between intermediates (i.e., *OH and *SO4) and PMS at the synergistic site was low, leading to easy desorption of intermediates and production of SO4•– rather than 1O2. As a result, the dominant species was SO4•– (contribution rate >97.9%) with synergistic C═C and C═O. Overall, this study provided new insights into the active sites interactions, beneficial for guiding the catalysts design and application in the treatment of emerging contaminants in a Fenton-like system.

Indispensable Synergy between C═C and C═O Sites in Biochar for Peroxomonosulfate Activation and Sulfamethoxazole Degradation