Abstract
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 a 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, evaluated by 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 Escherichia 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 ions over 30 days, confirming the stable immobilization of Ag-MOFs on their surface.
Highlights
As an emerging technology, forward osmosis (FO) is attracting significant interest for numerous applications, such as desalination and wastewater treatment.[1−3] its fouling behavior is considered better than that of pressure-driven processes,[4] fouling and biofouling remain limiting factors to the effective implementation of FO.[5]
ATR-FTIR spectroscopy of the membrane surface showed the peaks typically associated with aromatic polyamide and suggested the presence of bromopropionic acid (BPA) zwitterions on the modified surface through a characteristic peak associated to C O stretching of the carboxyl group; see the Supporting Information, Figure S1, for further information
This study evaluated the synergistic effect of silver-based Metal−organic frameworks (MOFs) and hydrophilic zwitterions to sustainably tackle fouling and biofouling in thin-film composite (TFC) membrane applications
Summary
Forward osmosis (FO) is attracting significant interest for numerous applications, such as desalination and wastewater treatment.[1−3] its fouling behavior is considered better than that of pressure-driven processes,[4] fouling and biofouling remain limiting factors to the effective implementation of FO.[5]. Oxygen-containing functional groups belonging to BPA may act as appropriate sites to retain silver ions, which leads to the stability of the Ag-MOFs and their binding to the membrane surface.[37] Based on the data from the 30 day silver release experiment and on the typical tangential feed flow rate in FO and RO modules, the concentration of silver in the final concentrate stream of a cross-flow system would be
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