CoTiO₃ immobilized on nickel foam for degradation of levofloxacin via peroxymonosulfate activation: Electron transfer pathways and degradation mechanism

Although sulfate radical-based advanced oxidation processes (SR-AOPs) have shown significant potential for pollutant degradation, persistent challenges such as catalyst recycling and the inadequate exposure of active sites in existing powdered catalysts have severely hindered their degradation efficiency. In this study, CoTiO₃ was successfully immobilized on nickel foam (CoTiO₃/NF) using a straightforward consecutive immersion pyrolysis method to activate peroxymonosulfate (PMS) for the degradation of levofloxacin (LFX). Compared to the TiO₂/NF/PMS and Co₃O₄/NF/PMS systems, the CoTiO₃/NF/PMS system exhibited an impressive LFX degradation efficiency of up to 99.3% within 8 min. Furthermore, the formation of Co-O-Ti bonds significantly reduced cobalt (Co) ion leaching to less than 0.15 mg/L after 20 cycles, while maintaining reusability with a 95.0% removal efficiency after the same number of cycles, as confirmed in a pilot-scale study. Density functional theory (DFT) calculations indicated that the unique Co-O-Ti structure enhances electron transfer to PMS through a “conducting bridge” mode, facilitating O-O bond cleavage and the generation of more reactive oxygen species (^•OH, O₂^•−, SO₄^•−, and¹O₂). The primary degradation intermediates of LFX were identified using liquid chromatography-mass spectrometry (LC-MS), and potential degradation pathways were proposed. Additionally, the ecotoxicity of the degradation products was assessed using ECOSAR software. This research presents a promising solution to overcome the limitations of powdered catalysts for sustainable wastewater treatment.