Cobalt doped titanate nanosheets with oxygen vacancies: A high-efficiency catalyst for PMS activation with magnetic recyclable property

The design of multifunctional catalysts for peroxymonosulfate (PMS) activation is crucial for advanced oxidation processes. Herein, we synthesized cobalt-doped sodium titanate nanosheets (Co-doped TNS) with enriched oxygen vacancies to activate PMS for 4-chlorophenol (4-CP) decomposition. Incorporating cobalt ions into the TiO 6 crystal lattice enhanced structural stability, preventing cobalt leaching after the reaction. Oxygen vacancies, generated through calcination under a reducing atmosphere, facilitated electron transfer and promoted the formation of active species. The intrinsic magnetism imparted by cobalt doping enabled efficient catalyst recovery using an external magnet. The optimized Co-doped TNS exhibited exceptional PMS activation performance, achieving nearly 100 % 4-CP removal within 60 min (k = 0.065 min⁻¹). Critically, high degradation efficiency (>90 %) was sustained even in the presence of commonplace ions and across diverse water matrices, with the catalyst demonstrating broad pH adaptability from acidic to alkaline conditions. Quenching experiments, along with electron paramagnetic resonance (EPR) spectra, indicated that sulfate radicals (SO 4 •- ) were the main oxidants, with notable support from superoxide radicals (•O 2 - ), hydroxyl radicals (•OH), and singlet oxygen ( 1 O 2 ). Furthermore, density functional theory (DFT) calculations validated the enhanced adsorption of PMS on the Ti-Co center and the oxygen vacancy site in Co-doped TNS, as well as the augmented electron transfer from Co-doped TNS to the PMS molecule. This work presents a novel multifunctional catalyst design strategy that effectively integrates high catalytic activity, structural stability, and practical magnetic recoverability for efficient and sustainable water purification.