This study presents a layer-by-layer interfacial polymerization approach to enhance the chlorine resistance and water permeability of thin-film composite (TFC) polyamide (PA) forward osmosis membranes . The PA film was prepared by self-polymerization using 3,5-Dihydroxybenzoic acid (DHBA) and trimesoyl chloride (TMC) with addition of 4-amino-benzene sulfonamide (4-ABSA), which is a sulfonamide monomer , on a polysulfone (PSF) support layer. The cross-linking structure and surface characterisation of the DHBA-ABSA membrane was studied systematically. FTIR results showed the successful grafting of the sulfonamide group on the membrane surface. Compared with the MPD-TMC membrane, the water flux of three modified membranes—DHBA, ABSA, and DHBA with ABSA—improved by 27.6%, 44.0%, and 67.6%, respectively, and reverse salt flux decreased by 9.9%, 12.3%, and 16.2%, respectively. Furthermore, the chlorine-stability test using 200 ppm NaClO indicated stable long-term performance under different pH values. The stable sulfonamide structure of ABSA with N-H group effectively prevented chlorine from directly attacking the active layer and improve the chlorine-stability of the membrane. In addition, the abundant hydrophilic groups on ABSA and DHBA monomers formed a hydration layer with water molecules on the membrane surface through hydrogen bonding , which enhanced the permeability of the TFC-PA membranes. The findings of this study demonstrate the DHBA-ABSA membrane's wider application potential in water and wastewater treatment processes .
Xinfei Dong,Qing-Wei Meng,Wenxiu Hu,Rongzhen Chen,Qingchun Ge
Wastewater containing trace organic contaminants (TrOCs) is usually poorly purified by unmodified polyamide (PA) membrane due to its poor selectivity and low water permeability. Herein we design a series of carboxylate-functionalized PA membranes via the chelation of Fe 3+ and carboxylate for efficient TrOCs removal through forward osmosis (FO). Citric acid, oxalic acid and their sodium salts are individually tethered to the PA membrane in water under ambient conditions. Factors influencing membrane performance are systematically investigated. The carboxylate based modification greatly improves the membrane properties that substantially enhance its separation performance. The sodium citrate (CA-Na) modified membrane produces water fluxes of up to 106% (PRO mode) and 144% (FO mode) higher than those of the PA membrane. This membrane also increases the TrOCs rejection from 75% to over 92%, irrespective of the TrOCs properties. Membrane fouling experiments reveal that the water flux of the CA-Na membrane declines by 26%, while that of the PA membrane decreases by 38% after 10-h tests. The flux recovery ratio of the CA-Na membrane achieves over 95% after physical cleaning. This study demonstrates an eco-friendly protocol to construct PA-based membrane for efficient TrOCs removal.
危险品化学品经营许可证（带存储）