Sulfate radical-induced transformation of trimethoprim with CuFe2O4/MWCNTs as a heterogeneous catalyst of peroxymonosulfate: mechanisms and reaction pathways

Trimethoprim (TMP), a typical antibiotic pharmaceutical, has received extensive attention due to its potential biotoxicity. In this study, CuFe2O4, which was used to decorate MWCNTs via a sol-gel combustion synthesis method, was introduced to generate powerful radicals from peroxymonosulfate (PMS) for TMP degradation in an aqueous solution. The results showed that almost 90% of TMP was degraded within 24 min with the addition of 0.6 mM PMS and 0.2 g L-1 CuFe2O4/MWCNTs. The degradation rate was enhanced with the increase in initial PMS doses, catalyst loading and pH. A fairly low leaching of Cu and Fe was observed during the reaction, indicating the high potential recyclability and stability of CuFe2O4/MWCNTs. Electron paramagnetic resonance analysis confirmed that the CuFe2O4/MWCNT-PMS system had the capacity to generate OH and SO4-, whereas quenching experiments further confirmed that the catalytic reaction was dominated by SO4-. A total of 11 intermediate products of TMP was detected via mass spectrometry, and different transformation pathways were further proposed. Overall, this study showed a systematic evaluation regarding the degradation process of TMP by the CuFe2O4/MWCNT-PMS system.