Activation of peroxymonosulfate by a core-shell structured carbon-encapsulated cobalt ferrite (CoFe2O4/CoFe@C) for bisphenol S removal: Temperature-dependent structure and degradation mechanism elucidation

As a popular additive for polycarbonate plastic production, bisphenol S (BPS) has raised significant risk concerns as a suspected endocrine disruptor. The activation of peroxymonosulfate (PMS) can provide an efficient solution. In this work, a carbon-encapsulated cobalt ferrite (CoFe2O4/CoFe@C) was prepared for PMS activation and BPS removal. A unique interaction of oxide and carbon was observed during calcination in N2, which led to a temperature-dependent catalyst structure and activity. At the optimal 500 degrees C, the amorphous carbon shell was partially graphitized and further reduced the oxide core to form zero-valent CoFe. The structure was thoroughly characterized by SEM, TEM, XRD, FTIR, Raman, EIS, TGA, and XPS. The catalyst (100 mg/L) rapidly removed 99.8% of BPS in 20 min (kobs = 0.199 min-1) with 2 mM of PMS. The reaction parameters were optimized, including catalyst dosage, PMS concentration, temperature, and pH. Remarkably, the catalyst worked well in alkaline conditions, removing 91.6% of BPS in 20 min at pH 11, with low leaching of Co (0.14 mg/L) and Fe (0.02 mg/L). Additionally, its environmental adaptability was assessed by considering co-existing ions, water matrixes, different pollutants, TOC removal, and catalyst regeneration. High efficiency and robustness were observed during these tests. Furthermore, the scavenging and probing experiments suggested SO4 center dot-, 1O2, and high-valent metal-oxo species as reactive species. The degradation pathway was proposed based on the transformation products identified by HPLC-MS. The ECOSAR and TEST programs indicated an overall decreased trend in toxicity. In summary, the CoFe2O4/CoFe@C catalyst shows promising prospects for treating BPScontaminated wastewater.