Photo-Fenton reaction for the degradation of sulfamethoxazole using a multi-walled carbon nanotube-NiFe₂O₄ composite

In this study, magnetically recyclable spinel nickel ferrite (NiFe₂O₄) and multi-walled carbon nanotubes (MWCNTs) incorporated NiFe₂O₄ (NiFe-CNT) composite with different CNT contents were successfully synthesized by one-step hydrothermal treatment. The photo-Fenton efficiency of the synthesized materials was assessed by the degradation of recalcitrant sulfamethoxazole (SMX) under ultraviolet (UV)-A and visible light. The efficiency of poorly active NiFe₂O₄ was significantly enhanced by the incorporation of 25 wt% CNT, and complete degradation of SMX (5 mg/L) was achieved within 2 h using NiFe-CNT composite (0.025 g/L) in the presence of H₂O₂ under UV-A light. Higher mineralization (total organic carbon (TOC) removal = 68%) was obtained in case of NiFe-CNT composite than bare NiFe₂O₄ (TOC removal = 39%). The effects of catalyst dosage, SMX concentration, H₂O₂ concentration, and pH on the degradation of SMX were investigated in order to identify the optimized reaction conditions. No leaching or degradation of MWCNTs was observed in the reaction solution and iron leaching from the composite was also under permissible limits. Photocurrent and Electrochemical Impedance Spectroscopy studies were performed to check the effective charge separation. The improved photocatalytic activity of the NiFe-CNT composite reflects (1) the synergy effect between NiFe₂O₄ and MWCNTs, (2) effective charge separation that retards the recombination of photogenerated charges, and (3) the generation of more reactive oxidation species (especially [rad]OH radicals). Moreover, ease of separation due to the significant magnetic properties of the NiFe-CNT composite provides an efficient method to treat recalcitrant organic pollutant.