Theoretical insights into sulfonamide chain length effects on polyamide-based reverse osmosis membranes

Polyamide (PA)-based reverse osmosis (RO) membranes are pivotal in water treatment due to their superior separation performance and cost-effectiveness. Nevertheless, challenges such as membrane fouling and the permeability-selectivity trade-off limit their efficiency. This study employs molecular dynamics simulations and density functional theory to systematically investigate the influence of sulfonamide chain length on the performances of PA-based RO membranes. Three sulfonamide-modified PA membranes (M-AESA(n), n = 2, 4, 6) were constructed to assess morphology, hydrophilicity, water transport dynamics, antifouling behavior, and salt resistance. Results demonstrate that increasing sulfonamide chain length enhances membrane roughness, hydrophilicity, and fractional free volume, correlating with improved water diffusion coefficients and flux. Notably, M-AESA(4) exhibits optimal antifouling capability owing to weakened interfacial interactions with calcium alginate foulants. All modified membranes retain robust salt rejection under simulated conditions. These findings provide molecular-level insights into the design of high-performance PA-based membranes, bridging theoretical predictions with practical membrane optimization strategies.