Catalytic degradation of mefenamic acid by peroxymonosulfate activated with MWCNTs-CoFe2O4: influencing factors, degradation pathway, and comparison of activation processes.

Abstract

The cobalt ferrite loaded on multi-walled carbon nanotubes (MWCNTs-CoFe2O4) was synthesized and used as a novel catalyst for the degradation of mefenamic acid (MFA) in the presence of peroxymonosulfate (PMS). The results showed that MWCNTs-CoFe2O4 has higher catalytic performance in the activation of PMS and degradation of MFA compared with MWCNTs, Co2+, Fe2+, and CoFe2O4. The highest kinetic constant rate (0.0198 min-1) and MFA degradation (97.63%) were obtained at pH = 7, PMS = 4 mM, catalyst = 500 mg/L, MFA = 10 mg/L, and time = 150 min. MFA degradation accelerated with increasing PMS and catalyst dosage but decreased by initial pH. The influence of different anions and water matrix on the catalytic system was investigated, and the results explained a decrease in the MFA rate in the presence of the interfering substances. Scavenging experiments showed that both sulfate radical anion (SO4•-) and hydroxyl radical (•OH) were effective on MFA degradation, but SO4•- had a greater effect on the degradation of MFA. In addition, the stability and recyclability of MWCNTs-CoFe2O4 were evaluated in the consecutive reaction cycle; the MFA degradation rate reached 89.75% after 4 cycles of reaction. The MFA degradation products were identified by gas chromatography-mass spectrometry (GC-MS) and their degradation pathway was suggested. Finally, a comparison was conducted among the methods used for PMS activation, and the results showed that the cobalt ferrite-based catalyst has high degradation efficiency. However, ultrasound, heat, and ultraviolet (UV) processes can be used to improve the degradation rate of the MWCNTs-CoFe2O4/PMS system at different reaction times.