Hydrogel supported positively charged ultrathin polyamide layer with antimicrobial properties via Ag modification

Positively charged nanofiltration (NF) membranes are essential for an efficient separation of cations. However, the water permeance is limited by the thickness of polyamide (PA) selective layer caused by the rapid diffusion rate of the aqueous monomers in interfacial polymerization (IP). Here, the use of a Kevlar hydrogel interface is demonstrated, to achieve an ultrathin PA layer with high water permeability through the interaction of Kevlar hydrogel and polyethylenimine (PEI) during the IP reaction. The ultrathin PA layer reduces the water transport resistance, and the Kevlar hydrogel provides a three-dimensional transport network, greatly enhancing the water transport efficiency. When used for separation of cations, the water permeance of Kevlar-based NF membranes was measured to be 10.9 LMH bar⁻¹, outperforming the state-of-the-art polyethersulfone (PES)-based positively charged NF membranes. Furthermore, silver nanoparticles (AgNPs) were used for modification of the PA layers via in situ chemical reduction of silver. The modified membrane exhibits a high bacteriostatic rate (99.99%) for live Escherichia coli (E. coli) bacteria. The Ag modification has almost no effect on the water permeance and salt rejection. Combining Kevlar based NF membrane with biocidal AgNPs endows the prepared membrane with dual functionality: high water permeance and antibiofouling ability. The diversity of hydrogel and Ag modification makes this strategy a potentially universal approach for the preparation of ultra-thin antibacterial membranes for heavy metal removal and water softening.