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

ABSTRACT 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.