Controlled solvent activation by iron (III) acetylacetonate for improving polyamide reverse osmosis membrane performance

Reverse osmosis (RO) membrane technology based on interfacial polymerization (IP) -synthesized polyamide (PA) RO membrane is a leading water treatment technology. PA RO membrane with both high permeability and selectivity is highly desirable. Solvent activation is a simple and effective method to improve PA RO membrane performance. However, developing a facile, effective and easy-to-enlarge approach to control solvent activation (that is, maximizing the positive role of activation and meanwhile avoiding the excessive activation) still faces challenges. Aiming at this, herein we propose to introduce iron (III) acetylacetonate (soluble in the organic phase), an organometallic compound, into the IP process for controlling solvent activation since iron (III) acetylacetonate could promote the cross-linking during the IP process. The characterization and performance testing results showed that the solvent activation was indeed well controlled by iron (III) acetylacetonate. In addition to promoting the cross-linking of PA layer (separation layer of membrane), iron (III) acetylacetonate made the separation layer become thinner, and then a RO membrane (non-activated) with performance at a high level was obtained. The flux and the rejection were 64.25 L·m−2·h−1 and 99.12%, respectively, and the water/salt selectivity coefficient was 10535. These values were higher than those of the pure membrane (membrane prepared without iron (III) acetylacetonate). Importantly, the well-controlled solvent activation improved the membrane performance further. The N, N-methylformamide (DMF)/ethanol solvent activation resulted in an increase of flux to 89.18 L·m−2·h−1 (increased by 83.23% compared to the non-activated pure membrane). Besides, after DMF/ethanol activation, the membranes prepared with iron (III) acetylacetonate exhibited a higher selectivity compared to the pure membrane (higher by 18.75%). This work may pave a novel avenue to develop high performance PA separation membranes.