Surface modification of nanofiltration membrane using quaternary diethanolamine for efficient antibiotics/salt separation

Nanofiltration plays a crucial role in antibiotic desalination from high salinity water, but the membranes often have low water permeability and insufficient selectivity between antibiotics and salts. In this study, a Gemini-type quaternary diethanolamine monomer (QTDEA) containing quaternary ammonium and hydroxyl groups was synthesized. This monomer had a hybrid spatial structure combining both rigid and flexible components, allowing it to covalently graft to the acyl chloride groups on the nascent polyamide (PA) film. The resulting modified PA-QTDEA membrane exhibited enhanced hydrophilicity, reduced negative charge, and a looser structure. It demonstrated a high water permeance of 18.2 L m−2 h−1·bar−1 for chlortetracycline hydrochloride (CTC) desalination from a NaCl solution of 10 g L−1, and the NaCl/CTC selectivity was 21.2. This research presents an efficient method for improving the performance of antibiotic desalination through surface modification using the novel QTDEA monomer.