Antibacterial and desalting behavior of forward osmosis membranes engineered with metal ions

The current Covid-19 aggravates membrane biofouling issue caused by bacteria and viruses which are widely present in water. Herein we synthesized a series of polyamide (PA)-based membranes engineered with distinct metal ions (Cu2+, Fe3+) via one-step metal-ligand ligation for forward osmosis (FO) separation. The antibacterial and desalting behavior of membrane were investigated by systematically varying the influential factors including the charge status, complexation ability and antibacterial mechanism of metal ions as well as testing conditions. All the newly synthesized membranes exhibit better performance with markedly increased water permeability and selectivity. Therein the Fe3+ − membrane increases water fluxes by 93% (FO mode) and 112% (PRO mode) relative to the nascent PA membrane with 0.5 M NaCl as the draw solution. Both Cu2+ and Fe3+ on membrane surface dramatically improve the membrane bactericidal efficacy against Escherichia coli via destroying the bacterial phospholipid layer. Remarkably, the metal ions on membrane surface are easily regenerated after being consumed by bacteria by simply immersing the membranes into the corresponding nitrate solutions. The separation performance and antibacterial properties of the regenerated membranes are comparable to those of the fresh membranes. When using brine from reverse osmosis process as the draw solution, the Fe3+ membrane recovers water from brackish water up to 70% higher than the nascent PA membrane. This study provides a practical strategy to develop FO membrane with sustainable antibacterial activity and desalination performance.