Forward osmosis membrane developed from the chelation of Fe3+ and carboxylate for trace organic contaminants removal

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.