[Sunflower-Straw-Derived Biochar-Enhanced Fe(Ⅲ)/S₂O₈^2- System for Degradation of Benzoic Acid]

Fe(Ⅱ) activation persulfate (PS) is an effective method of degradation of organic pollutants, but the undesirable Fe(Ⅲ)/Fe(Ⅱ) cycle has become a restrictive factor in the Fe(Ⅱ)/PS system. The effects of sunflower-straw-derived biochar (SFBC) on an Fe(Ⅲ)/S₂O₈^2- system and the subsequent degradation of benzoic acid (BA) in water were systematically investigated. The characterization results of SFBC showed that it has a porous structure, consists of amorphous carbon, and has an abundance of surface functional groups and persistent free radicals (PFRs). The effects of critical parameters, including the initial pH, PS concentration, and dose of SFBC were also investigated. The results indicated that the degradation rate of BA in the SFBC/Fe(Ⅲ)/S₂O₈^2- system was significantly higher than that in the Fe(Ⅲ)/S₂O₈^2- system and SFBC system. The degradation efficiency of BA reached 100.00% with SFBC, BA, PS, and Fe(Ⅲ) concentrations of 2.0 g·L^-1, 10.0 mg·L^-1, 2.0 mmol·L^-1, and 1.0 mmol·L^-1, respectively, an initial pH of 3.0, and a reaction time of 90 min. Free radical quenching experiments and EPR studies demonstrated that SO₄^-· and ·OH were involved in the SFBC/Fe(Ⅲ)/S₂O₈^2- system, and the SO₄^-· was the main radical for the BA degradation. Reuse and real water matrix effects experiments suggested that SFBC had good stability and practical applicability. Mechanism analysis revealed that PFRs and-OH as the electron donor reacted with Fe(Ⅲ) to generate Fe(Ⅱ), which then activated PS for highly efficient oxidation of BA.