Degradation of ofloxacin, amoxicillin and tetracycline antibiotics using magnetic core-shell MnFe2O4@C-NH2 as a heterogeneous Fenton catalyst

Magnetic core-shell MnFe2O4@C and MnFe2O4@C-NH2 nanoparticles were successfully prepared by hydrothermal synthesis and well characterized by a variety of characterization methods. The carbon layers with a uniform thickness of about 2 nm could be clearly seen on the MnFe2O4 surface. The catalytic activity of these heterogeneous catalysts was estimated by the degradation of antibiotics. Ofloxacin (OFX), amoxicillin (AMX) and tetracycline (TC) were used as representative antibiotics. It was found that TC was the most refractory compound among the studied antibiotics. Compared to MnFe2O4, MnFe2O4@C and MnFe2O4@C-NH2 presented higher catalytic activity in the antibiotics and TOC removal. The enhanced catalytic activity of MnFe2O4@C-NH2 was ascribed to the carbon shell and the introduction of -NH2. The carbon shell enlarged the specific surface area, reduced the aggregation of magnetic nanoparticles and prevented the leaching of metal. The introduction of -NH2 enhanced the electron density of carbon shell and more electrons are transferred from carbon to the metal oxide, and thus more Mn2+ and Fe2+ species are produced. Based on the results of XPS and ESR spectra, a plausible mechanism for the generation of active species was proposed. MnFe2O4@C-NH2 was evaluated in the treatment of the mixed antibiotics solution. The results showed that the COD removal efficiency after 180 min of reaction was 63.8% and the corresponding BOD5/COD increased from 0.012 to 0.36. Finally, MnFe2O4@C-NH2 showed a high stability in the heterogeneous Fenton oxidation of the mixed antibiotics solution.