Development of PSQ-RO membranes with high water permeability by copolymerization of bis[3-(triethoxysilyl)propyl]amine and triethoxy(3-glycidyloxypropyl)silane

Epoxy-based reverse osmosis (RO) membranes with an organically bridged polysilsesquioxane (PSQ) skeleton were prepared by a sol-gel process that involved the copolymerization of bis[3-(triethoxysilyl)propyl]amine (BTESPA) and triethoxy(3-glycidyloxypropyl)silane (TEGPS). RO experiments using 2000 ppm NaCl aqueous solution indicated that the use of epoxy-containing monomer TEGPS significantly improved performance, yielding water permeability of 1 × 10−12 m3/m2sPa and salt rejection of 98%, approximately. This is likely because of the ring opening of the epoxy units, which leads to the formation of hydroxy (C–OH) groups during sol formation. Some C–OH groups underwent condensation with silanol to generate C–O–Si bonds in the gelation process. Immersion of the resultant membrane in water resulted in the hydrolysis of C–O–Si bonds to re-generate C–OH units. This increased membrane hydrophilicity and further improved permeability, although salt rejection slightly decreased. It was also found that membranes derived from TEGPS showed high resistance to chlorine and thermal stability.