High performance interlayer-free mesoporous cobalt oxide silica membranes for desalination applications

Abstract

Mesoporous cobalt oxide silica matrices and membranes were successfully prepared using a dual acid–base catalysed sol-gel and interlayer-free approach for desalination applications. The effects of cobalt addition (0–35mol%) on the structure–property relationship of the silica materials and membrane performance were systematically studied as a function of feed salt concentration (0.3–7.5wt.% NaCl) and temperature (22–60°C). As cobalt concentration increases beyond 5mol%, the concentration of tricobalt tetroxide and proportion of silica mesopores were found to increase within the matrices. Silica membranes with high amount of tricobalt tetroxide (35mol%) were found to be highly mesoporous with water fluxes of 20, 11.3 and 7.7kgm−2h−1 for the 0.3, 3.5 and 7.5wt.% solutions at 60°C, respectively, with >99.7% salt rejection at all times. This is attributed to the high pore volume (mesopores formation) and structural robustness of the silica network provided by the presence of tricobalt tetroxide. Even higher performance was achieved for low tricobalt tetroxide (1mol%) silica membranes with water fluxes of 47.6 (0.3wt.%) and 31.5 (3.5wt.%) kg m−2h−1 at 60°C, respectively, though with reduced salt rejections of 90%.