Iron-based metal organic framework (Fe-MOF)-doped sesame stalk biochar enhances antibiotic degradation: Important role of free radicals and comparison of multiple degradation processes

A novel iron-based metal organic framework-doped sesame stalk biochar (Fe-MOF@SBC) composite was successfully synthesized using sonication and used for the degradation of sulfamethoxazole (SMX), norfloxacin (NOR), erythromycin (ERY) and tetracycline (TC) in aqueous solution. The characterization results indicated that Fe oxide was successfully loaded on the biochar. The Fe-MOF@SBC composite presented a porous structure enriched in micropores and mesopores. Adsorption mechanisms, including pore filling, π–π electron donor–acceptor (EDA) interactions, hydrophobic interactions, hydrogen bonding and electrostatic interactions, and the catalytic effect of the Fe-MOF@SBC composite facilitated antibiotic degradation. Specifically, single-layer and multilayer adsorption occurred, and abundant oxygen-containing functional groups were involved in the degradation of NOR, which might be one reason for the high degradation rate of NOR by the Fe-MOF@SBC composite. Scavenging experiments combined with electron paramagnetic resonance (EPR) analysis indicated that free radicals such as •OH, O2−• and 1O2 played vital roles in the degradation of SMX, NOR, ERY and TC. Furthermore, the proposed degradation pathways and possible intermediates of SMX, NOR, ERY and TC were identified, which indicated that the adsorption properties and free radical (•OH, O2−• and 1O2) activity of the Fe-MOF@SBC composite strongly promoted the removal of SMX, NOR, ERY and TC.