Co-solvent-assisted interfacial polymerization toward one-step synthesis of dense polyester NF membranes for natural surface water treatment

Achieving dense polyester (PE) nanofiltration (NF) membranes through in-situ conditioning for effective surface water purification has remained a significant technical challenge. In this work, the weaker-polarity ethyl acetate was employed as a co-solvent. The reaction between polyhydroxy maltitol and trimesoyl chloride was regulated through a co-solvent-assisted interfacial polymerization (CAIP) strategy. CAIP effectively promoted molecular diffusion and subsequently enhanced the miscible phase layer, resulting in a distinct ridge-and-valley morphology atop the support after the two-stage IP reaction. The ordered ridge-and-valley structure endowed the resultant membrane with remarkable electronegativity and hydrophilicity. The optimal PEM-3 membrane exhibited ideal water permeance and Na₂SO₄ rejection (20.5 L m^-2 h⁻¹ bar⁻¹ and 91.1 %). The dense PE NF membranes efficiently removed organic matter from natural surface water while retaining specific mineral ions (Ca²⁺ and Mg²⁺). This study provides a universal method for tailoring dense PE membranes for producing healthy drinking water through in-situ modulation of macromolecular polyhydroxy monomers.