Biochar-activated persulfate for organic contaminants removal: Efficiency, mechanisms and influencing factors

Turning biomass into biochar as a multifunctional carbon-based material for water remediation has attracted much research attention. Sawdust and rice husk were selected as feedstock for biochar (BC) production, aiming to explore their performance as a catalyst to activate persulfate (PS) for degrading acid orange 7 (AO7). There was an excellent synergistic effect in the combined BC/PS system. Sawdust biochar (MX) showed a faster and more efficient performance for the AO7 degradation due to its abundant oxygen functional groups, compared to rice husk biochar (DK). In the BC/PS system, AO7 was well decolorized and mineralized. Based on the two-dimensional correlation analysis method, the azo conjugation structure and naphthalene ring of AO7 molecule changed first then benzene ring changed during the reaction. Moreover, AO7 decolorization efficiency increased with the increase of PS concentration and biochar dosage, and the deacrease of pH. Biochar deactivated after used twice. When the biochar reached its adsorption equilibrium of AO7, the AO7 could not be degraded in the BC/PS system. SO4− and OH participated in the reaction together and OH played the main role in activating PS to AO7 decolorization based on the radical scavengers experiment. All of results indicate using biochar to activate PS for degradation of AO7 contaminated water is a promising method. [Display omitted] •AO7 was well decolorized and mineralized in BC/PS system.•Biochar activation ability depended on its surface functional groups.•AO7 molecule degraded followed the order of azo conjugation = naphthalene ring > benzene ring.•Factors affecting AO7 degradation in BC/PS system were investigated.