Robust silica-graphene oxide nanocomposite membrane for separating NaCl salt from seawater under atmospheric pressure

Abstract

When graphene oxide (GO) based membranes are used to filter high concentration salt ion solutions at atmosphere pressure, flow of water molecules is easily blocked by the narrow spaces of graphene oxide membrane (GM), thus causing severely reduced permeability. To solve this problem, in this study, multilayer and composite framework membranes with multiple scale porous channels of sub-nanometer to tens of nanometers was designed and synthesized to promote effective flow of water molecules. These nanocomposite membranes were fabricated by crosslinking, condensation and self-assembly of polyacrylic acid (PAA), nanosized silica (SiO2) and GO onto nylon membrane substrates using a vacuum filtration method. Their permeance obtained using 35 g·L−1 NaCl solution at a pressure of 0.98 bar was 38.6 L∙m−2∙h−1∙bar−1, about 1400 times of that using GM only, and their average retention rate was 27 %. The mechanisms of effective salt removal using these nanocomposite membranes were identified. Firstly the nanoscale SiO2 increased the permeated flux of water by increasing the spacings and defects of GO sheets. The barrier structures and nanochannels formed by adding nanoscale SiO2 effectively block the salt ions. Finally electrostatic adsorption of GO sheets and PAA provided more ion adsorption and rejection rates using the GO sheets.