Enhancing permeability of polyamide nanofiltration membranes via aqueous organophosphorus co-reactant assisted interfacial polymerization

Nanofiltration membranes' performance hinges on their ion sieving and water permeability, which are affected by the crosslinking degree, uniformity, thickness, and microstructure of the active layer. Additive control offers a promising approach for optimizing membrane properties. This study presents a novel approach to improve water permeance of nanofiltration membranes by introducing organophosphorus end-capping reagents ((2-aminoethyl) triphenyphosphonium bromide (ATPB), (3-aminopropyl) triphenylphosphonium bromide (ATPPB), and 2-(diphenyphosphino) ethylamine (DPPE)) as co-reactive additives in the aqueous phase during interfacial polymerization. These reagents influenced the amine monomer's diffusion behavior, leading to a more homogeneous and potentially thinner polyamide (PA) layer, as demonstrated by molecular dynamics (MD) simulations. By regulating this process, we effectively modified pore characteristics, charge density distribution, and structural properties of the PA layer, all through a straightforward one-step method. The ATPB-0.015 membrane emerged as the optimal choice due to its excellent performance, characterized by a nodular buried structure, a water permeance of 16.3 L m⁻² h⁻¹ bar⁻¹, and a high Na₂SO₄ rejection (98.5 %). In addition, the amide and phosphorus units on the ATPB-0.015 membrane surface facilitated the removal of 97.48 % of Escherichia coli through hydrogen bonding and electrostatic interaction, enhancing its anti-bacterial property. Anti-fouling tests employing bovine serum albumin (BSA) and humic acid (HA) as foulants revealed that the ATPB-0.015 membrane demonstrated a faster recovery ratio than the control membrane, primarily attributed to its enhanced surface hydrophilicity. This study demonstrates a facile method for designing nanofiltration membranes with controlled structure and functional performance characteristics.