Rapid activation of peroxymonosulfate by Co₁Fe₂/B-MXene membrane for removal organic pollutants

The combination of membrane filtration technology and peroxymonosulfate (PMS)-driven advanced oxidation processes (AOPs) presents a viable approach for eliminating refractory organic contaminants in aqueous environments. In this study, boron-doped MXene-supported CoFe nanoparticles (denoted as Co₁Fe₂/B-MXene) powder was synthesized via a novel one-step molten salt etching strategy. This innovative approach simultaneously achieves the etching of the MAX phase, boron doping, the in-situ formation of CoFe alloy nanoparticles, and their firm immobilization onto the MXene support in a single thermal treatment process, overcoming the limitations of conventional multi-step procedures. The Co₁Fe₂/B-MXene membrane was subsequently fabricated through vacuum filtration. The membrane was characterized using X-ray diffraction, Brunauer-Emmett-Teller surface area analysis, scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Compared to the undoped Co₁Fe₂/MXene membrane, the B-doped Co₁Fe₂/B-MXene membrane achieved complete degradation of Acid Orange 7 (91 % vs 100 %) under a high flux of 210 ± 10 L m^-2·h^-1·bar^-1 (LMH/bar), with an extremely short residence time of only 13.38 ± 0.005 ms. Electrochemical analysis revealed that B doping facilitates charge migration and enhances catalytic performance. The Co₁Fe₂/B-MXene membrane exhibited nearly complete catalytic efficiency (close to 100 %) over a broad pH range of 3-6.5, demonstrating excellent catalytic activity toward various pollutants, strong tolerance to ionic interference, and remarkable self-cleaning capability. During 24 h of continuous operation, the membrane maintained a pollutant degradation efficiency above 90 % along with stable water flux. Quenching experiments and EPR spectroscopy verified that singlet oxygen (¹O₂) acts as the dominant reactive oxygen species. Finally, the degradation pathways of AO7 within the Co₁Fe₂/B-MXene membrane/PMS system were elucidated through high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis.