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. Alkaline activation enhanced the adsorption and catalytic performance of biochar. The localized concentration of 1O2 around the interfacial layer facilitated the oxidation of enriched HA. [Display omitted]