Cobalt-ferrite functionalized graphitic carbon nitride (CoFe2O4@g-C3N4) nanoconfined catalytic membranes for efficient water purification: performance and mechanism

Abstract

Membrane-based nanoconfinement catalysis combined with advanced oxidation processes (AOPs) and membrane filtration can efficiently and rapidly remove organic pollutants. Herein, cobalt-ferrite-doped graphitic carbon nitride (CoFe₂O₄@g-C₃N₄) nanoconfined catalytic membranes were fabricated to activate peroxymonosulfate (PMS) for efficient water purification with the rapid degradation of pollutants. The catalytic membrane was highly efficient in degradation of various pollutants including pharmaceuticals, dye and phenol and achieved a 100% removal efficiency of the model pollutant ranitidine (5 mg L⁻¹) within a retention time of 54.6 ms. The CoFe₂O₄@g-C₃N₄ membrane/PMS system achieved a degradation first-order rate constant of 0.088 m s⁻¹ (5280 min⁻¹), which is 10⁴–10⁶ times higher than those of traditional AOP systems. Electron paramagnetic resonance spectroscopy and quenching experiments indicated that hydroxyl and singlet oxygen species were the main contributors to pollutant degradation. Density functional theory (DFT) calculations revealed that charge was transferred from g-C₃N₄ (0.247e) to CoFe₂O₄ and then from CoFe₂O₄ (1.611e) to PMS (−1.858e) in the CoFe₂O₄@g-C₃N₄/PMS system with its free energy of −5.64 eV, which indicated that the PMS dissociation on the CoFe₂O₄@g-C₃N₄ heterojunction was spontaneous. The Fe(II)/Co(III) redox cycle and the promotion of electron transfer by the heterojunction induced high stability (42 h) and efficient catalytic capacity for the CoFe₂O₄@g-C₃N₄ membrane/PMS system. The as-obtained CoFe₂O₄@g-C₃N₄ membrane expands a new pathway for membrane-based nanoconfinement catalysis and also provides a promising scheme for water treatment.