Synergistic multiple active species for catalytic self-cleaning membrane degradation of persistent pollutants by activating peroxymonosulfate

Recently, the development of dual functional catalytic membrane for the synergistic degradation and filtration of persistent pollutants has attracted considerable attention in environmental remediation. Herein, novel CoFe alloy and CoFe₂O₄ nanoparticles encapsulated in N-doped microtube composites (CoFe-NMTs) were firstly fabricated through in-situ pyrolysis of simple-source Prussian blue analogues (PBA). As expected, this unique structure not only inhibited the nanoparticles agglomeration, but also provided a "highway" that accelerated the Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺ redox cycles. Therefore, CoFe-NMT-800 (0.1 g/L, pyrolyzed at 800 °C) achieved over 90% tetracycline (TC, 30 mg/L, 0.1821 min^-1) removal after 30 min at a wide pH (2.55-9.55) by coupling with peroxymonosulfate (PMS, 0.3 g/L), which dramatically outperformed the majority of the reported catalysts (such as Co₃O₄, CoFe alloy, CoFe₂O₄ and N-doped carbon nanotubes, etc.). Additionally, CoFe-NMTs-800 also exhibited excellent catalytic activity in the existence of inorganic anions (Cl^-, HCO₃^- and H₂PO₄^-) and natural organic matters (humic acid (HA)). Subsequently, CoFe-NMTs-800 was immobilized into polyvinylidene fluoride (PVDF) membrane as catalytic self-cleaning membrane via applying phase-inversion technology. It was found that CoFe-NMTs-800/PVDF membrane not only maintained high removal efficiency for TC degradation (over 90%) in TC/HA coexistence system, but also effectively eliminated the adverse effect of membrane fouling. Besides, the fabricated membrane also showed desirable reusability and neglectable metal leaching (0.003 mg/L Fe and 0.015 mg/L) with almost constant flux after five cycles. The quenching experiments and electron paramagnetic resonance (EPR) results clearly indicated that sulfate radicals (SO₄^-), hydroxyl radicals (OH and singlet oxygen (¹O₂) were responsible for TC degradation and SO₄^- was a major contributor. Significantly, this work was very meaningful to construct novel catalytic self-cleaning membrane for water purification.