Interlayer-free hybrid carbon-silica membranes for processing brackish to brine salt solutions by pervaporation

Mesoporous, interlayer-free, hybrid carbon-silica matrices and membranes based on tetraethoxysilane (TEOS), organosilica of triethoxyvinylsilane (TEVS) and pluronic triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P123) were successfully prepared using an acid-base catalysed sol-gel method for desalination applications. These membranes were carbonized to form the hybrid carbon-silica structures under inert conditions in vacuum and nitrogen. The effects of calcination conditions on the structure-property relationship of the carbon-silica xerogels were elucidated, and the membrane performances were systematically studied using brackish (1 wt%) to brine (15 wt%) feed concentrations of sodium chloride solution and feed temperatures (25-60 degrees C) under pervaporation process. Vacuum calcined (CS-Vc) membrane produced a slightly more mesoporous matrix and higher carbon yield than the nitrogen calcined (CS-N-2) membrane, and hence, led to comparatively superior desalination performance. CS-Vc membranes produced high water fluxes of 26.5 (1 wt%, 60 degrees C) and 9.2 (15 wt%, 60 degrees C) L m(-2) h(-1) with salt rejections of 99.5% and 98.6%, respectively. This study demonstrates that the combined strategy of hybrid organosilica with polymeric template and vacuum calcination offered the carbonized silica mesostructure membranes with excellent separation of water from the hydrated salt ions, and importantly, high water fluxes particularly for processing brine salt solutions.