Graphene oxide (GO) laminar membranes for concentrating pharmaceuticals and food additives in organic solvents

Abstract

An ultrathin graphene oxide (GO) laminar composite membrane has been fabricated in-house via pressure-assisted filtration. It has a relatively high pure water permeability (PWP) of 7.70 LMH/bar with a molecular weight cut-off (MWCO) of 1243 Da. When being treated with various solvents, the membrane exhibits good stability in both polar and nonpolar solvents. The GO laminar composite membrane has relatively high pure solvent fluxes of 24.89 Lm−2h−1, 7.95 Lm−2h−1 and 12.08 Lm−2h−1 for ethanol, isopropanol and hexane, respectively. Its rejections to orange II sodium salt, safranin O, solvent blue 35, rhodamine B and remazol brilliant blue are 56.60%, 86.52%, 4.39%, 66.95% and 97.11%, respectively. Experimental results suggest that the Donnan exclusion is less effective in organic solvent nanofiltration (OSN) than in aqueous systems, while the size exclusion and solute-membrane affinity are the dominant factors in determining separation performance. Some active pharmaceutical ingredients (APIs) and food additives, e.g. tetracycline, rifampicin, roxithromycin, spiramycin, vitamin B12 and lecithin, are used to demonstrate the separation capability of the newly developed membrane in real-life applications. It can effectively retain those compounds with rejections of 65.80%, 82.67%, 84.27%, 92.21%, 95.34% and 98.44%, respectively. Several 7-day tests of vitamin B12 in isopropanol also confirm the membrane integrity and separation performance for continuous OSN uses.