Degradation of sulfamethoxazole by Co3O4-palygorskite composites activated peroxymonosulfate oxidation

Abstract In this study, a simple hydrothermal method was used to synthesize Co3O4-palygorskite composites. Transmission electron microscopy, X-ray spectroscopy and X-ray diffraction analysis showed that Co3O4 nanoparticles with diameters of approximately 3–5 nm were uniformly distributed on the surface of palygorskite fibers. Co3O4-palygorskite composites were outstanding catalyst for activating peroxymonosulfate (PMS) to degrade the antibiotic sulfamethoxazole (SMX). Complete removal of 30 μM SMX at pH 3–5 was achieved with doses of 0.3 mM PMS and 125 mg/L Co3O4-palygorskite composites. The composites exhibited higher catalytical activity than unsupported Co3O4. The removal rate of SMX was accelerated under acidic conditions (pH 3–5), while was significantly inhibited under basic conditions (pH 11–12). Radical quenching tests revealed that SO4 − and OH were responsible for the degradation. The oxidative degradation was initiated at either isoxazole or aniline moiety of the SMX molecule. Using solid phase extraction-liquid chromatography-time-of-flight-tandem mass spectrometry, a total of six transformation products formed from benzene ring hydroxylation, S-N bond cleavage, aniline moiety oxidation and coupling reactions were identified. Based on the products, three transformation pathways are proposed for the catalytic degradation of SMX in the Co3O4-palygorskite/PMS system.