Activation of persulfate by CO2-activated biochar for improved phenolic pollutant degradation: Performance and mechanism

Environment-friendly and low-cost catalysts are important for persulfate based advanced oxidation processes. In this study, we reported a CO2-activated biochar (AC) as a low-cost and efficient catalyst for persulfate (PS) activation and the degradation of phenol and chlorophenols. The AC950 showed the best catalytic performance for PS with an oxidant utility of 0.5 mol/mol oxidant/h/g with an activation energy of 15.86 kJ/mol owing to its large surface area, rich surface defects, and well-modified oxygen functional groups. In contrast to a radical-based mechanism, this novel biochar/persulfate system works through a non-radical mechanism that includes singlet state oxygen generation and an electron transfer reaction pathway. The major degradation intermediate of the phenolic pollutant was identified to be benzoquinone; moreover, amongst chlorophenols, the para-chlorine substituent was the first to degrade. The durability of the catalyst was low, it was deactivated primarily because of the oxidation of the carbon surface, and thermal regeneration was determined to be efficient for its recovery. Furthermore, HCO3− and HPO42− were found to considerably inhibit the performance of the catalytic oxidation system.