Rapid degradation of aqueous doxycycline by surface CoFe2O4/H2O2 system: behaviors, mechanisms, pathways and DFT calculation

Heterogeneous Fenton technology is considered to be an effective method to solve the issues of antibiotic pollutants. In this study, a highly active surface exposed CoFe2O4 catalyst was fabricated to activate hydrogen peroxide (H2O2) to degrade aqueous doxycycline (DC). Batch experiments investigated the influence of different factors such as CoFe2O4 dosage, H2O2 dosage, contaminant concentration and pH on DC elimination. Remarkably, the results showed that 1.2 g/L CoFe2O4 with 10 mM H2O2 could quickly remove 92% DC of 20 ppm under neutral pH conditions in 10 min, and after 5 cycles, the removal of DC still remained above 85%. DMPO-X signals captured by EPA illustrated abundant hydroxyl radicals ('OH) were produced in the surface CoFe2O4/H2O2 system swiftly and that was the dominant active oxygen species in the degradation of DC. The valence changes of Co3+/Co2+ and Fe3+/Fe2+ appeared on the surface of CoFe2O4 provided many electrons to participate in the process of activating H2O2. Density functional theory (DFT) calculation was conducted to reveal preferable sites of different atoms on DC for radicals attacking. Combined with LC-MS analysis, two possible degradation pathways were proposed.