Exploiting Highly Anti-Fouling and Biofouling Activity through in-Situ Growth of Silver-Based MOFs on Zwitterion Incorporated TFC Polyamide Membranes

In this work, the surface of the polyamide (PA) forward osmosis (FO) membrane was modified with zwitterions followed by the in-situ growth of silver-based metal-organic frameworks (Ag-MOFs). First, the zwitterion 3-bromopropionic acid is grafted to the membrane surface using an initiator solution; then, the in-situ growth of Ag-MOFs is obtained by immersing the membranes in a metal solution followed by a ligand solution treatment. The successful surface functionalization is verified through surface characterization techniques. The contact angle measurements indicate an enhanced membrane wettability. The transport performance of the membranes is evaluated in a forward osmosis setup, in terms of water and salt transport parameters. The results show roughly 50% higher water flux than that of pristine membranes, with no significant change in salt selectivity. In order to investigate the antibacterial activity of the membrane, confocal, colony-forming unit (CFU), and scanning electron microscopy (SEM) tests were employed. The results show an over 77% increase in the bacterial inhibition rate of the modified membrane over the pristine membrane. The SEM images of the modified membrane treated with E. coli confirms the deterioration of bacteria cell. The long-term fouling and biofouling tests of the membranes reveal that the highest water flux drop for sodium alginate and E. coli do not exceed 25% and 20%, respectively. This proves the promising antifouling and anti-biofouling properties of the membranes. Finally, the stability of the membrane was tested over the measurement of silver ion release in 30 days. All modified membranes suggest negligible depletion of silver, confirming the strong immobilization Ag-MOFs on the surface of modified membranes.