A green strategy for porous biochar fabrication with superior capacity for peroxydisulfate activation to degrade sulfadiazine: the cooperative role of C-sp3 and specific surface area

Metal-free porous biochars are popularly utilized as catalysts for peroxydisulfate (PDS) activation. The enhancement effect of PDS activation of porous biochars fabricated by employing both hard template and alkali metal activating agent has not been explored completely. In addition, the role of the inherent carbon defect in PDS activation has not been clearly elucidated. Hence, a series of carbonaceous catalysts were fabricated using a sole template (KCl), a sole activating agent (Na 2 S 2 O 3 ) or a combination of template and activating agent (KCl/Na 2 S 2 O 3 , KCl/KHCO 3 , KCl/NaHCO 3 , and KCl/Na 2 C 2 O 4 ), to systematically investigate the effect of specific surface area (SSA) and intrinsic defect of porous biochar on its PDS activation ability. The biochar synthesized by KCl and Na 2 S 2 O 3 (SK-C) exhibited the optimum degradation performance. The SK-C was found to possess an interconnected hollow cage with three-dimensional mesh structure showing the largest surface area, pore volume and C- sp 3 edge defect content among all the catalysts, which explained its paramount catalytic ability. The SSA and C- sp 3 content together can determine the catalytic performance in a quantitative relationship. The single electron transfer pathway from SDZ to inner-sphere bound SK-C/PDS* was the protagonist of pollutant oxidation. The degradation intermediates were detected and recognized and their toxicities were evaluated. This study for the first time comprehensively identified the synergistic effect between the SSA and inherent defects on improving the catalytic performance of biochar for PDS activation to removal contaminants. Graphical Abstract Highlights Several porous biochars with various surface area and defect degree were fabricated. These catalysts were used for peroxydisulfate activation to degrade sulfadiazine. The catalyst made by employing Na 2 S 2 O 3 and KCl exhibited the optimum performance. The surface area and C- sp 3 together determined quantitatively the catalytic effect. The single electron transfer from organic to inner-sphere catalyst/peroxodisulfate* was dominant.