Hierarchical porous biochar for persulfate activation: Non-radical pathway for rapid degradation of organic pollutants

The development of efficient, low-cost, and environmentally friendly catalysts has the potential to significantly enhance the persulfate-based advanced oxidation technology for wastewater treatment. In this study, chitosan gel was ultilized as the biomass to be pyrolyzed by two-step pyrolysis method at 600 °C and 800 °C to produce biochar (BC-800). Results from the SEM, TEM, BET, Raman, and XPS characterizations showed that the BC-800 had a surface area of 1748 m2/g and a hierarchical pore structure with co-existing macropores, mesopores, and micropores, as well as an obvious graphitic carbon, pyridinic N, and graphitic N configurations. The prepared biochar was found to activate persulfate (PS) for rapid degradation of 2,4-dichlorophenol, with 90% of pollutants removed in 5 min due to the excellent mass transfer facilitated by the abundant pores. Chemical quenching experiments, EPR detection, and electrochemical analysis indicated that the degradation process was triggered by a nonradical pathway, in which the biochar acted as an electron transfer shuttle between the oxidant and pollutant. This electron transfer mechanism not only enabled the degradation system have a wide pH range for application, but it also demonstrated high resistance to inorganic anions in the aquatic environment. This research is expected to enhance the preparation method of hierarchical porous biochar and provide effective technical support for the biochar-activated PS for water purification.