Insights into electrochemical peroxymonosulfate activation on a robust stepwise-grown Co₃O₄/CNT/NF anode for antibiotic degradation

Electrochemical peroxymonosulfate (PMS) activation offers a promising pathway to combat antibiotic contamination, but electrode instability and poorly understood mechanisms of anodic activation remain significant challenges. Herein, a robust nickel foam supported carbon nanotube and Co₃O₄ (Co₃O₄/CNT/NF) monolithic anode was constructed via in-situ stepwise growth and employed for efficient PMS activation to degrade antibiotics. Based on the excellent conductivity, dispersion, and anchoring properties of carbon nanotubes, the Co₃O₄/CNT/NF anode achieves 96.78% tetracycline (TC) removal within 60 min (5 mA cm^-2 current density, 1 mM PMS), with the anodic potential decreased to 0.75 V. Moreover, cobalt ion leaching was dramatically reduced by 66.67% (0.17 mg l ^-1 vs. 0.51 mg l ^-1 CNT-free electrode). Results from single and dual-chamber experiments indicate that anodic PMS activation contributes approximately 45.31% to the overall TC degradation efficiency. EPR and radical quenching experiments revealed a degradation pathway dominated by non-radical processes, with singlet oxygen (¹O₂) as the primary reactive oxygen species (contributing 66%), followed by sulfate radicals (SO₄·⁻) and hydroxyl radicals (·OH). This study underscores the critical role of electrode design in stabilizing active sites and elucidates the dominant non-radical mechanism in anodic PMS activation.