A novel acid resistant thin-film composite nanofiltration membrane with polyurea enhanced dually charged separation layer

Fabricating acid resistant nanofiltration (NF) membranes with precise solute separation performance is highly demanded for acidic wastewater treatment but remains a challenge. Herein, we propose a facile strategy for preparing dually charged acid resistant NF membranes with both high cations and anions rejections via a two-layer reverse interfacial polymerization (r-IP) process. Organic monomers of trimesoyl chloride (TMC) and 1,4-phenylene diisocyanate (PPDI) are firstly applied to react with 3-aminobenzenesulfonamide (ABSA) to construct a negatively charged loose intermediate layer, followed by the r-IP of TMC/PPDI and polyethyleneimine (PEI) to engineer a dense positively charged top layer. The highly cross-linked polyurea (PU) formed by isocyanate and amine leads to an enhanced size sieving effect, and the well-arranged dually charged layer endows the membrane stronger electrostatic exclusion. The resultant membrane has 97.7% rejection of Na₂SO₄ and 93.0% of MgCl₂, and it exhibits fairly high rejections to various heavy metals, as well as impressive long-term stability after exposure to strong acid (10 wt% of H₂SO₄ for 400 h).