Polymer-Silica Mixed Matrix Membranes for Solute Separation from Water

This study investigates the preparation of polymer-silica mixed matrix membranes, the effect of silica upon membrane water flux, permeability, and hydrodynamic pore diameter, and the ability of functionalized silica particles to separate a model polar organic compound (in this experiment benzyl alcohol) from water. Four membranes were synthesized using the polymer polysulfone (PSf): blank PSf, PSf with non-functionalized silica particles, PSf with functionalized silica particles, and PSf with non-functionalized ludox (TM-50) particles. Cellulose acetate (CA) was also used as a polymer for mixed matrix membranes containing silica, but it was found that they were too dense to conduct the chosen experiments. In future experiments, CA may provide additional benefits because the OH groups of CA can also be functionalized. The membranes containing PSf were characterized by flux, permeability, scanning electron microscopy (SEM), Dextran rejection, and benzyl alcohol rejection. When casting the membranes, room temperature, relative humidity, and evaporation time were held constant, as well as gelation bath temperature, which was held around 1.0 degree C. It was found that the incorporation of functionalized silica particles significantly increased the rejection of benzyl alcohol (47%) when compared to membranes that did not contain the functionalized particles (~10%), even though hydrodynamic pore diameters (as determined by Dextran rejection) were comparable (~37 nm). It was also found that the permeabilities of the mixed matrix membranes were significantly lower than that of the PSf membrane.