Degradation of sulfamethoxazole by Co3O4-palygorskite composites activated peroxymonosulfate oxidation

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 mu M 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 center dot- and center dot 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.