High-flux polyamide reverse osmosis membranes by surface grafting 4-(2-hydroxyethyl)morpholine

Abstract

Surface modification is a common approach to improve the desalination performance of polyamide (PA) reverse osmosis (RO) membranes. Nevertheless, the water flux normally decreases due to the additional hydraulic resistance of the surface modification layer. Surface grafted PA RO membrane with 4-(2-hydroxyethyl)morpholine was first fabricated to improve water flux in this study. 4-(2-Hydroxyethyl)morpholine was in situ grafted onto the nascent PA membrane by the reaction between the –OH group of 4-(2-hydroxyethyl)morpholine and the unreacted –COCl groups of the nascent PA membrane and residual trimesoyl chloride. The surface grafted RO membranes were characterized by X-ray photoelectron spectrometry, field emission scanning electron microscopy, atomic force microscopy and contact angle measurement. The surface grafting conditions, including 4-(2-hydroxyethyl)morpholine dipping time, heat treatment time, and 4-(2-hydroxyethyl)morpholine concentration, were optimized by characterizing the desalination performance under brackish water desalination conditions. The resulting surface grafted membrane exhibited a water flux of 125.71 L m⁻² h⁻¹ and a salt rejection of 98.6%. The surface grafted membrane surpassed the control polyamide membrane with 41.9% increase in the water flux. Our results demonstrated that surface modification by in situ grafting 4-(2-hydroxyethyl)morpholine is a promising approach to fabricate high-flux RO membranes.