Adsorption and catalytic degradation of phenol in water by a Mn, N co-doped biochar via a non-radical oxidation process

A modified biochar material (Mn/C-KOH) was synthesized from chitosan using KOH and MnCl2 as the activators via a one-pot pyrolysis process. The characterization suggested that the two activators promoted its textural properties, led to a surface area of 1223 m2/g and modified the surface chemical groups. Mn/C-KOH with a Mn-doping dosage of 0.27 wt% was an adsorbent and outstanding catalyst for removing phenol via peroxydisulfate (PDS) activation. A 55% adsorption rate of phenol was achieved within 10 min at a concentration of 30 mg/L. A 95% degradation rate and a 75% mineralization rate of phenol (30 mg/L) were obtained through the activation of PDS (200 mg/L). And, the catalytic degradation system could tolerate a wide pH range from 3 to 9. The intrinsic pyridinic N and C-C/C--C groups of the chitosan-derived biochar played dominant roles in the adsorption. The simultaneous activation of KOH and MnCl2 enhanced the proportion of C--O groups of Mn/C-KOH, and C--O groups served as the catalytic active sites for PDS activation. The electron transfer and 1O2- mediated non-radical processes that were induced by the formation of a dioxirane intermediate between Mn/C-KOH and PDS were responsible for the phenol degradation. This work offers a modification for the biomass-derived catalysts and is beneficial to the understanding of non-radical mechanism in AOPs.