Enhanced Peroxymonosulfate Activation via Non-radical Pathways by CoFe2O4 Anchored on N and S co-doped Carbon Nanotubes.

Abstract

Developing highly efficient catalysts to activate peroxymonosulfate (PMS) via non-radical pathways for water decontamination is desirable, yet achieving this via green and scalable methods remains challenging. Herein, we report highly dispersed CoFe₂O₄ nanoparticles anchored on N and S co-doped commercial-grade carbon nanotubes (CoFe₂O₄-N/S-CNT; abbreviated as CFO-N/S-CNT), prepared by a simple, solvent-free route involving mechanical grinding and low-temperature calcination, for tetracycline (TC) degradation. Under optimal conditions, the CFO-N/S-CNT/PMS system achieves 96% TC removal with an observed rate constant (k_obs) of 2.03 min^-1, corresponding to 35.6-, 27.4-, and 2.78-fold enhancements relative to CFO/PMS (0.057 min^-1), N/S-CNT/PMS (0.074 min^-1), and CFO-CNT/PMS (0.73 min^-1), respectively. Quenching tests, electron paramagnetic resonance (EPR), and electrochemical measurements reveal that PMS activation over CFO-N/S-CNT proceeds primarily via non-radical pathways, involving singlet oxygen (¹O₂) generation and an electron-transfer pathway (ETP). Density functional theory (DFT) calculations indicate that a moderate PMS adsorption strength on CFO-N/S-CNT enables efficient electron withdrawal from TC, thereby promoting the ETP, while adsorption-induced O-H bond elongation in PMS lowers the barrier for ¹O₂ generation. In line with the non-radical regime, CFO-N/S-CNT delivers consistently high TC removal in diverse and chemically complex water matrices. This work offers mechanistic insights for the design of non-radical PMS catalysts and demonstrates a practical, scalable strategy based on commercial nanomaterials.