Facile fabrication of hydroxyl-rich polyamide TFC RO membranes for enhanced boron removal performance

The insufficient boron removal performance is a conspicuous infirmity of reverse osmosis (RO) membranes for seawater desalination. Herein, RO membranes with high boron removal performance were prepared by adding 2-hydroxyethyl acrylate (HEA) and acrylamide (AA) into the m-phenylenediamine (MPD) solution and employing ultraviolet (UV) irradiation during the interfacial polymerization (IP) process. During the UV-imported IP process, the radical polymerization between HEA and AA was triggered to produce hydroxyl-containing HEA-co-AA copolymers, while polyamide polymers were simultaneously generated. Attributed to the interspersion of hydroxyl-containing copolymers in the polyamide chain segments, the superior dense and tight structure of the hybrid separation layer was achieved. Crucially, the high electron density hydroxyl groups enriched in the hybrid separation layer could specifically interact with the electron-deficient boric acid via electrostatic interaction and hydrogen bond. Therefore, in the modified membrane, the diffusion of boric acid was inhibited. Consequently, for the modified membrane, the boric acid retention rate was dramatically increased from 84.42% to 92.80%. Additionally, NaCl retention rate and water flux were also promoted. The UV-imported IP process was neither process-intensive nor time-consuming, exhibiting high compatibility with the continuous membrane production. It was expected that this work would guide the innovation of high boron removal RO membranes and other types of IP-made membranes.