Hydrogel-coated polyamide nanofiltration membranes for seawater ion separation

Abstract

In this study, a fully aromatic thin-film composite (TFC) polyamide layer was prepared on a porous polyethersulfone substrate via interfacial polymerization and subsequently coated with a glutaraldehyde (GA)-cross-linked polyvinyl alcohol (PVA) hydrogel to form a TFC PVA composite. Compared with two commercial nanofiltration (NF) membranes (NF270 and TS80), the hydrogel coating increased transport resistance and modified ion separation behavior. Consequently, the seawater permeate flux of the TFC PVA membrane decreased (2.2 L m⁻² h⁻¹ at 4 bar) following hydrogel coating, while rejection of major ions increased (Na⁺ and K⁺: 40–46%; Ca²⁺ and Mg²⁺: 67–74%). Moderate boron rejection (45%) was also observed at natural seawater pH without chemical adjustment, while commercial NF membranes NF270 and TS80 showed negligible boron rejection. Although membrane permeability decreased following hydrogel coating, stable operation was maintained over 38 h of continuous filtration relative to the uncoated TFC membrane. These combined mechanisms confer unique separation characteristics, highlighting the TFC PVA membrane's potential for use in targeted ion-removal tasks in resource recovery and removal of ions in pretreatment of high salinity water.