Functionalized chitosan derived novel positively charged organic–inorganic hybrid ultrafiltration membranes for protein separation

Novel positively charged organic-inorganic hybrid ultrafiltration membranes with adjustable charge density were fabricated from blends of water soluble poly vinyl alcohol (PVA) and methylated N-(4-N, N-dimethylaminobenzyl) chitosan (TMBC) in combination with tetraethyl orthosilicate (TEOS) silica precursor by the sol-gel method and precipitation in a mixture of methanol and water (80 wt% : 20 wt%). The porous hybrid membrane morphologies, structures, charge and surface properties were characterized comprehensively using scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, outer surface zeta potential and contact angle measurements. The results confirmed that the fabricated membranes were porous, hydrophilic and mildly charged in nature. The water flux and flux recovery ratio (i.e. protein fouling resistance) of the membranes were highly dependent on the fraction of TMBC. The protein transmission as a function of pH and the fraction of TMBC was studied for two model proteins (ovalbumin; OVA and lysozyme; LYZ) and found to be controlled by size exclusion and the membrane charge density (controlled by the fraction of TMBC). The highest transmission of proteins at their isoelectric points was obtained for the membrane with 40 wt% of TMBC. The best separation of LYZ from OVA in the model mixture solution was obtained at pH = 11 when membrane A-40 was used in ultrafiltration of protein solution at 2 bar applied transmembrane pressure.