Development of Highly Water-Permeable Robust PSQ-Based RO Membranes by Introducing Hydroxyethylurea-Based Hydrophilic Water Channels

Abstract

Copolymerization of bis [3-(triethoxysilyl)propyl]amine (BTESPA) and N-(2-hydroxyethyl)-N′- [3-(triethoxysilyl)propyl]urea (HE-TESPU) provided highly permeable robust reverse osmosis (RO) membranes that have an organically bridged polysilsesquioxane (PSQ) structure. The RO experiments with NaCl aqueous solution (2000 ppm) indicated that the introduction of hydroxyethylurea groups markedly improved the permeability of water (1.86 × 10 −12 m 3 /m 2 sPa) to approximately 19 times higher than that of a membrane prepared via the BTESPA homopolymerization, with NaCl rejection remaining nearly unchanged (96%). This is the highest water permeability obtained so far for PSQ-based membranes that show higher than 90% NaCl rejection. The improvement of water permeability is likely due to aggregation through hydrogen bonding in the PSQ layer, which can be regarded as a hydrophilic water channel.