L-cysteine and maleimide modified acid-resistant poly(amide-sulfonamide) nanofiltration membranes for tetracycline separation

Acidic pharmaceutical wastewater containing antibiotics and inorganic salts presents a challenging environmental issue. Conventional polyamide nanofiltration membranes suffer from acid-induced hydrolysis under strongly acidic conditions, resulting in severe performance degradation. Herein, a poly(amide-sulfonamide) nanofiltration membrane was developed via interfacial polymerization using trimesoyl chloride (TMC) as the organic-phase monomer and a mixed aqueous phase containing 3-aminobenzenesulfonamide (ABSA) and L-cysteine (L-Cys). The introduction of L-Cys provided thiol groups for subsequent thiol-maleimide click modification, and maleimide (MAL) post-treatment was employed to regulate the selective layer structure and improve acid stability. The effects of ABSA/L-Cys composition and MAL modification conditions on membrane structure and separation performance were systematically investigated. The optimized membrane achieved complete tetracycline (TC) rejection (100%) and maintained Na 2 SO 4 rejection above 82%. The TC permeance of the ABSA/L-Cys-MAL membrane increased from 7.0 to 14.6 L m −2 h −1 bar −1 while retaining excellent rejection performance. After exposure to 20 wt% H 2 SO 4 for 30 days, the membrane preserved 100% TC rejection, demonstrating superior acid stability and antifouling performance. This study provides a molecular design strategy for developing acid-resistant nanofiltration membranes for challenging acidic antibiotic wastewater treatment.