Synergistic adsorption and singlet oxygenation of humic acid on alkali-activated biochar via peroxymonosulfate activation

Humic acid (HA), as a represent of natural organic matter widely existing in water body, dose harm to water quality and human health; however, it was commonly treated as an environmental background substance while not targeted contaminant in advanced oxidation processes (AOPs). Herein, we investigated the removal of HA in the alkali-activated biochar (KBC)/peroxymonosulfate (PMS) system. The modification of the original biochar (BC) resulted in an increased adsorption capacity and catalytic activity due to the introduction of more micropores, mesopores, and oxygen-containing functional groups, particularly carbonyl groups. Mechanistic insights indicated that HA is primarily chemically adsorbed on the KBC surface, while singlet oxygen (¹O₂) produced by the PMS decomposition served as the major reactive species for the degradation of HA. An underlying synergistic adsorption and oxidation mechanism involving a local high concentration reaction region around the KBC interface was then proposed. This work not only provides a cost-effective solution for the elimination of HA but also advances our understanding of the nonradical oxidation at the biochar interface.