Preparation of POSS-derived robust RO membranes for water desalination

Abstract

POSS (polyhedral oligomeric silsesquioxane)-containing silica sols were prepared by hydrolysis/condensation of octakis(triethoxysilylethyl)-substituted POSS (TESE-POSS) and mixtures of 1,2-bis(triethoxysilyl)ethane (BTESE1) and TESE-POSS in HCl/H2O/EtOH. Nitrogen adsorption isotherms of bulk gels prepared by drying the sols indicated that the gels had porous properties with surface areas of 168–424m2/g, depending on the BTESE1/TESE-POSS molar ratio. The sols were coated on SiO2/ZrO2/TiO2 porous supports and calcinated at 350 or 400°C to produce the membranes. Water desalination performance of the membranes was evaluated by reverse osmosis (RO) experiments using 2000ppm NaCl aqueous solution. At 25°C, liquid permeance was approximately 1×10−13m/s·Pa and NaCl rejection was 90%. Interestingly, the membranes were robust to heat and chlorine. Membrane performance was not changed even after exposure of the membranes to as high as 1×104ppm·h aqueous NaOCl. When RO experiments were conducted at 90°C, liquid permeance was increased to approximately 1×10−12m/s·Pa whereas NaCl rejection remained nearly unchanged, indicating potential application of the membranes to high-temperature water separation. Lowering the operation temperature again to 25°C resulted in the recovery of the original data, indicating that the membranes were neither decomposed nor damaged upon contact with hot water.