Enhanced heterogenous photo-Fenton degradation of tetracycline in aqueous medium by visible light responsive sulphur dopped zinc ferrite nanoparticles

Tetracycline (TC) is a common antibiotic that is eco-toxic and readily develops bacterial resistance, so it must be removed from the water system. Herein, first-time non-metal (Sulphur) dopped Zinc Ferrite (S-ZnFe₂O₄) was prepared through a single-step calcining process to study the tetracycline removal performance from water. The effects of catalyst dose, initial pH, co-existing anions, and H₂O₂ concentration on tetracycline removal were explored. The related degradation kinetics were studied using various models with experimental data, and it turned out that S-ZnFe₂O₄ exhibited an optimum tetracycline removal efficiency of 95.41% after 70 min, which is much better than the majority of Photo-Fenton catalysts. Furthermore, the electron paramagnetic resonance (EPR) analysis and quenching studies revealed that hydroxyl radicals (^•OH) and hole (h⁺) production led to fast tetracycline degradation in the Vis/S-ZnFe₂O₄/H₂O₂ system. In particular, the S-ZnFe₂O₄ demonstrated superparamagnetic properties and high stability, enabling effective catalysis recovery and utilization via an external magnetic field. Based on the degradation products identified by liquid chromatography-mass spectrometry (LC-MS), three possible degradation pathways of TC were proposed in the Vis/S-ZnFe₂O_4/H₂O₂ system. In addition, a significant amount of mineralization was found as total organic carbon (TOC) removal efficiencies were 84.4% within 70 min. The toxicity evaluation with activated sludge showed that the TC solution toxicity increased during the first 30 min, but later on significantly decreased as the oxidation proceeded. This work indicates the S-ZnFe₂O₄ nanoparticles and gives a new outlook for photo Fenton degradation to reduce the amount and toxicity of antibiotics (TC) effectively in water supplies.