Enhanced Thin-Film Composite Nanofiltration Membranes via Substrate Pore Structure Engineering: Performance and Mechanistic Insights

Substrate pore size is a key factor influencing the structure and performance of polyamide thin-film composite (TFC) membranes, yet its constitutive relationship and mechanism remain unclear. In this study, we systematically elucidate its critical influence on the selective layer, separation performance, and kinetics of water molecule transport of TFC membranes by employing a combination of experimental investigations and molecular dynamics (MD) simulations. The experimental results revealed the formation of a thinner and less cross-linked polyamide layer on the substrate with larger pore size, leading to a high water permeance of 35.4 L m^-2 h^-1 bar^-1. In contrast, the smaller-pore-size substrate promoted the formation of a polyamide layer with more uniformly distributed pore size, resulting in better solute/solute selectivity (erythromycin/NaCl selectivity = 426). MD simulations confirmed the significant influence of substrate pore size on mass transfer in the TFC membrane. This study offers both fundamental insights and a methodological framework for the targeted design of high-performance TFC nanofiltration membranes by substrate pore size optimization.