Insight into degradation mechanism of sulfamethoxazole by metal-organic framework derived novel magnetic Fe@C composite activated persulfate

Highlights: • Novel porous carbonized MOF derivate Fe@Cs are fabricated for the first time. • Different pyrolysis temperature endows Fe@Cs diverse iron phases and magnetism. • The core-shell Fe@C-800 possesses strong ferromagnetic properties for recycling. • Fe@C-800/PS system displays high RSE of 20.9% compared to Fe²⁺/PS systems. • SMX degradation includes both radical and non-radical mechanisms. Novel Fe@C composites derived from metal-organic framework (MOF) were synthesized. Being subject to pyrolysis under different temperatures endows these Fe@Cs diverse physical-chemical properties, including morphology, crystal structure, defect level, magnetism, and most importantly, iron phase composition. Fe@C-800 consists mainly of Fe₃C and α-Fe, thus possesses strong ferromagnetic properties, which imparts the ability to be separated and recycled. Its catalytic activity towards the activation of persulfate (PS) and the decomposition of sulfamethoxazole (SMX) was found to be the best among all the Fe@Cs, and this activity can be regenerated by simple heat treatment. Given the mixed form of iron and N-doped carbon, α-Fe/Fe₃C species provide electrons for PS to decompose and generate sulfate radical (SO₄·⁻), hydroxyl radical (·OH), and superoxide radical (O₂·⁻), initiating the radical pathway for partial SMX degradation. The positively charged C atoms on PS bonded Fe@C, as well as the conversion of O₂·⁻ give rise to the generation of singlet oxygen (¹O₂), which was responsible for the non-radical pathway for SMX degradation. As a consequence, SMX was degraded to intermediates through five degradation pathways, and finally mineralized to inorganic molecules. The results indicate that Fe@C-800 has great potential to serve as a promising activator for persulfate-mediated environmental remediation.