Epitaxially grown MOF membranes with photocatalytic bactericidal activity for biofouling mitigation in desalination

Abstract

In this study, we demonstrated the antifouling MOF membrane via the in-situ growth of metal azolate framework-4 (MAF-4) on polyethersulfone (PES) substrates and then epitaxial growth of MAF-7. The basal MAF-4 layer, which was confirmed to bind to the substrate by chelation, was flawless to ensure the desalination performance. The upper MAF-7 shell, which was confirmed to possess crystal characteristics and leave an unbound nitrogen atom, was hydrophilic and smooth to subserve the membrane permeability and antiadhesion. The as-prepared MAF-7@4/PES membrane exhibited exceptional salt rejection (98.7% for NaCl) and preferable permeability (1.24 L m−2 h−1 MPa−1), along with a flux decline ratio of 22.4% by employing bovine serum albumin (BSA) as the model foulant. The synergy of MAF-4 and MAF-7 enhanced the photocatalytic activity of membranes probably imputed to the almost perfect lattice match at the junction interface of epitaxial growth, leading to a bactericidal rate of nearly 100%. The main bactericidal mechanism was proved to be massive detected reactive oxygen species (•OH, H2O2 and •O2−) generated under visible light, rather than the role of leached metal ions and ligand precursor as recognized. Finally, the significant reduction in flux loss and the inhibition of biofilm formation in dynamic filtration indicated MAF-7@4/PES membrane had the potential for the application of desalination with a prominent antifouling property.