Plasticizer-assisted interfacial polymerization for fabricating advanced reverse osmosis membranes

Abstract

High-performance semi-permeable membranes play a vital role in the membrane-based separation technology for seawater and brackish water desalination. Herein, plasticizer-assisted interfacial polymerization (PAIP) was implemented to fabricate aromatic polyamide layers with improved water flux and comparable salt rejection for the first time. Specifically, plasticizer (i.e., diethyl phthalate, DEP) was introduced into the organic phase to perform interfacial polymerization. Effective regulation of the desalination performance was achieved via meticulously adjusting plasticizer concentration. With the addition of 0.5 wt% DEP, water flux promoted from 1.06 L m−2 h−1 bar−1 of the pristine membrane to 2.85 L m−2 h−1 bar−1, with NaCl rejection decreasing from 98.3% to 98.2%. With the addition of 1.5 wt% and 2.0 wt% DEP, water flux improved to 4.82 L m−2 h−1 bar−1 and 5.95 L m−2 h−1 bar−1, respectively, more than 4.5 and 5.5 times that of the pristine membrane. Nevertheless, NaCl rejection decreased to 96.6% and 95.9%, respectively. The infrared detection revealed that the introduction of DEP disrupted the original intermolecular hydrogen bonding between polyamide chains, thereby enhancing the softness of the polyamide layer, which was demonstrated by the decreased Young's modulus. As a result, the water diffusion efficiency through the polyamide layer was promoted, leading to the significant enhancement of water flux. These findings pave a new route for the synthesis of the aromatic polyamide layer with excellent desalination performance to expand the application of membrane technology.