Sea Urchin-like NiCo₂O₄ Catalyst Activated Peroxymonosulfate for Degradation of Phenol: Performance and Mechanism

How to efficiently activate peroxymonosulfate (PMS) in a complex water matrix to degrade organic pollutants still needs greater efforts, and cobalt-based bimetallic nanomaterials are desirable catalysts. In this paper, sea urchin-like NiCo₂O₄ nanomaterials were successfully prepared and comprehensively characterized for their structural, morphological and chemical properties via techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), among others. The sea urchin-like NiCo₂O₄ nanomaterials exhibited remarkable catalytic performance in activating PMS to degrade phenol. Within the NiCo₂O₄/PMS system, the removal rate of phenol (50 mg L^-1, 250 mL) reached 100% after 45 min, with a reaction rate constant k of 0.091 min^-1, which was 1.4-times higher than that of the monometallic compound Co₃O₄/PMS system. The outstanding catalytic activity of sea urchin-like NiCo₂O₄ primarily arises from the synergistic effect between Ni and Co ions. Additionally, a comprehensive analysis of key parameters influencing the catalytic activity of the sea urchin-like NiCo₂O₄/PMS system, including reaction temperature, initial pH of solution, initial concentration, catalyst and PMS dosages and coexisting anions (HCO₃^-, Cl^-, NO₃^- and humic acid), was conducted. Cycling experiments show that the material has good chemical stability. Electron paramagnetic resonance (EPR) and quenching experiments verified that both radical activation (SO₄^•-, ^•OH, O₂^•-) and nonradical activation (¹O₂) are present in the NiCo₂O₄/PMS system. Finally, the possible degradation pathways in the NiCo₂O₄/PMS system were proposed based on gas chromatography-mass spectrometry (GC-MS). Favorably, sea urchin-like NiCo₂O₄-activated PMS is a promising technology for environmental treatment and the remediation of phenol-induced water pollution problems.