Polyurea-Amide Based Thin-Film Composite Nanofiltration Membrane With Improved Acid Resistance

Polyurea emerges as a promising material for acid nanofiltration membranes due to its high hydrogen-bonding capacity and low electron density from carbonyl groups. However, conventional polyurea-based composite membranes suffer from limited separation performance and acid stability due to insufficient hydrophilicity and conjugated structures. In this study, a novel monomer, 3,5-diisocyanate benzoyl chloride, was synthesized and employed as the organic-phase precursor in interfacial polymerization to fabricate thin-film composite (TFC) membranes with polyurea-amide active layers. During polymerization, the acyl chloride groups undergo partial hydrolysis, introducing carboxylate anions into the active layer. The NF membrane shows over 98.6% rejection of MgSO 4 at pH 7, and membrane water permeability can reach 3.41 L m −2 h −1 bar −1 . Additionally, the aqueous phase monomer 2,4-diaminobenzenesulfonic acid was incorporated to construct a fully aromatic active layer, which strengthens intermolecular conjugation and acid resistance. Comparative analysis demonstrated that the synthesized membranes outperform traditional polyurea-based membranes (prepared via toluene diisocyanate and fatty amines) in acid stability: after soaking in 20 wt% H 2 SO 4 for 100 days, the MgSO 4 rejection remained nearly unchanged. This study establishes a molecular design strategy integrating hydrophilic functionalization and conjugated aromatic structures to address critical limitations in polyurea membranes, offering a pathway toward robust nanofiltration systems for acid-resistant applications.