Activating peroxymonosulfate with MOF-derived NiO-NiCo₂O₄/titanium membrane for water treatment: A non-radical dominated oxidation mechanism

Traditional peroxymonosulfate (PMS) catalytic membranes dominated by radical pathways often face interference from complex components in water bodies. Herein, we employed a controlled electro-deposition technique to coat a Ni-Co metal-organic framework (MOF) precursor onto titanium hollow fiber membrane (THFM), followed by high-temperature calcination to synthesize a MOF-derived NiO-NiCo₂O₄/THFM (M-NNCO-THFM) PMS catalytic membrane. Then, the M-NNCO-THFM filtration integrated with PMS activation (MFPA process) for water treatment. Experimental results demonstrated that the M-NNCO-THFM MFPA process successfully achieved complete phenol (PE) removal via a non-radical-dominated degradation pathway, involving singlet oxygen (¹O₂) and electron transfer, while exhibiting wide pH adaptability and exceptional stability in complex water matrices. Mechanism analysis revealed that the electron transfer process was significantly enhanced by the MOF-derived heterojunction structure, which increased the flat-band potential from 0.39 eV to 0.56 eV, thereby facilitating efficient electron transfer for PE removal. The non-radical ¹O₂ pathway was primarily due to the cycling of metal valence states (Ni²⁺/Co³⁺), leading to the reduction of Co²⁺ and its reaction with PMS, resulting in the generation of reactive species. Furthermore, electrochemical measurements indicated that the M-NNCO-THFM exhibited lower charge transfer resistance and enhanced charge transfer efficiency compared to non-MOF-derived NNCO-THFM, corresponding to the superior catalytic performance and electrochemically active surface area of M-NNCO-THFM.