Visible-light-driven photocatalytic removal of antibiotics by newly designed C3N4@MnFe2O4-graphene nanocomposites.

Newly designed magnetic g-C3N4/MnFe2O4/graphene (C3N4@MnFe2O4-G) composites with enhanced photocatalytic activity were successfully synthesized. The photocatalytic behavior of C3N4@MnFe2O4-G was assessed in photo Fenton-like degradation of antibiotic pollutants, including metronidazole, amoxicillin, tetracycline and ciprofloxacin, using persulfate (S2O82-) as an oxidant under visible light illumination. The C3N4@MnFe2O4-G composites show a superior catalytic activity with 94.5% removal of metronidazole that was almost 3.5 times as high as that of the pure g-C3N4, which could be attributed to the synergistic promoting effect of the favorable adsorptivity, enhanced light absorption intensity, high migration efficiency of charge carriers and longer lifetime of separated electron-hole pairs derived from the formation of the heterojunction between the g-C3N4 and MnFe2O4. Moreover, the self-redox properties of iron and manganese atoms in MnFe2O4 induced by S2O82- were particularly beneficial for the generation of SO4-. The quenching tests and electron spin resonance (ESR) display that h+, O2-, SO4- and OH are responsible for the antibiotics decomposition. The heterogeneous photocatalyst could be easily recovered by an extra magnetic field and reused several times without any obvious deterioration in catalytic activity. According to the investigation of active species and identified intermediates, the possible photocatalytic mechanism and reaction pathways have been proposed.