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 CoFe 2 O 4 catalyst was fabricated to activate hydrogen peroxide (H 2 O 2 ) to degrade aqueous doxycycline (DC). Batch experiments investigated the influence of different factors such as CoFe 2 O 4 dosage, H 2 O 2 dosage, contaminant concentration and pH on DC elimination. Remarkably, the results showed that 1.2 g/L CoFe 2 O 4 with 10 mM H 2 O 2 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 EPR illustrated abundant hydroxyl radicals ( OH) were produced in the surface CoFe 2 O 4 /H 2 O 2 system swiftly and that was the dominant active oxygen species in the degradation of DC. The valence changes of Co 3+ /Co 2+ and Fe 3+ /Fe 2+ appeared on the surface of CoFe 2 O 4 provided many electrons to participate in the process of activating H 2 O 2 . 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.