Effective strategy for UV-mediated grafting of biocidal Ag-MOFs on polymeric membranes aimed at enhanced water ultrafiltration

Ultrafiltration membranes with antifouling and antibacterial properties are greatly beneficial for all industrial applications and to supply safe water worldwide. Improving these properties while maintaining both high productivity and high water quality remains a challenge. This work proposes the surface functionalization of an ultrafiltration membrane obtained via UV-initiated grafting polymerization of acrylic acid (AA) and silvercontaining metal–organic frameworks (Ag-MOFs), with the goal to achieve combined bactericidal and hydrophilic properties. The effectiveness of different modification pathways is evaluated, including Ag-MOFs blending into the AA solution followed by grafting, as well as in-situ synthesis of Ag-MOFs over the surface of AA-grafted membranes, with in-depth characterization of the resulting materials. The steady-state water fluxes with a feed water laden with organics are improved from two to three-fold for the functionalized membranes compared to the commercial one, while the rejection of macromolecules is maintained at greater than 99%. Significantly, fouling is partly reversible with all enhanced surfaces: the flux recovery ratio following cleaning varies between 3.8% and 20% compared to near zero for the pristine membrane. Noteworthy bacterial inactivation reaches up to 90% for E. coli and 95% for S. aureus, respectively, for surface-grafted membranes. Silver leaching and surface characterization analyses indicate a strong immobilization of Ag-MOFs on membranes and imply long-lasting antimicrobial as well as antifouling activities

In-Situ Ag-MOFs Growth on Pre-Grafted Zwitterions Imparts Outstanding Antifouling Properties to Forward Osmosis Membranes

In this study, a polyamide forward osmosis membrane was functionalized with zwitterions followed by the in-situ growth of metal-organic frameworks with silver as metal core (Ag-MOFs) to improve its antibacterial and antifouling activity. First, 3-bromopropionic acid was grafted onto the membrane surface after its activation with N, N-diethylethylenediamine. Then, the in-situ growth of Ag-MOFs was achieved by a simple membrane immersion sequentially in a silver nitrate solution and in a ligand solution (2-methylimidazole), exploiting the underlying zwitterions as binding sites for the metal. The successful membrane functionalization and the enhanced surface wettability were verified through an array of characterization techniques. When evaluated in forward osmosis tests, the modified membranes exhibited high performance and improved permeability compared to pristine membranes. Static antibacterial experiments, appraised with confocal microscopy and colony-forming unit plate count, resulted in a 77% increase in the bacterial inhibition rate due to the activity of the Ag-MOFs. Microscopy micrographs of the E. coli bacteria suggested the deterioration of the biological cells. The antifouling properties of the functionalized membranes translated into a significantly lower flux decline in forward osmosis filtrations. These modified surfaces displayed negligible depletion of silver ion over 30 days, confirming the strong immobilization of Ag-MOFs on their surface