High-efficiency removal of tetracycline by carbon-bridge-doped g-C₃N₄/Fe₃O₄ magnetic heterogeneous catalyst through photo-Fenton process

Carbon-bridge-modified malonamide (MLD)/g-C₃N₄ (CN) was prepared by copolymerization of MLD with urea and melamine and loaded with Fe₃O₄ for the high-efficiency removal of tetracycline (TC) in water under photo-Fenton. The prepared catalysts were characterized by SEM, TEM, N₂ adsorption–desorption analysis, XPS, XRD, and FTIR, which proved that the modification method successfully introduced the C bridge into the carbon nitride molecular system and increased the structural defects of the catalyst. The Carbon-bridge-modified MLD/CN/Fe₃O₄ also had good visible-light response and charge-separation and transport abilities in the photoelectrochemical test. Degradation results showed that the photo-Fenton degradation of TC reached 95.8%, and the mineralization rate was 55.7% within 80 min at 80 mM H₂O₂ dosage, 0.5 g/L catalyst dosage, and near-neutral pH by 0.8MLD/CN/Fe₃O₄. Moreover, the oxidation products and mineralization pathways of TC were explored by LC-MS. Toxicity analysis indicated low environmental threat of the intermediates in TC mineralization. EPR analysis and H₂O₂ decomposition efficiency analyses showed an improvement in the H₂O₂ decomposition performance of 0.8MLD/CN/Fe₃O₄. This work could provide a valuable insight for the application of heterogeneous photo-Fenton technology in wastewater treatment.