Effect of Ionized Amino Acid on the Water-selective Permeation through Graphene Oxide Membrane in Pervaporation Process

Abstract

The introduction of ionized groups into the channels of graphene oxide (GO) membrane can adsorb more water molecules through electrostatic interaction, which is expected to achieve more efficient water-selective permeation.In this work, a vacuum filtration method was adopted to introduce the ionized basic amino acid lysine (Lys) into the GO membrane, obtaining the Lys(Na + )-GO composite membrane through covalent crosslinking. The terminal amino groups in Lys covalently crosslink with GO through forming the C-N covalent bond, thus regulating the membrane structure to make it more orderly. Meanwhile, the ionized carboxylate groups are introduced into GO channels. Compared with unionized lysine, the negatively charged carboxylate in ionized lysine increases the interaction with water molecules, and improves the membrane hydrophilicity. Through the synergistic effect of tuning physical structure and chemical structure of GO channels, Lys(Na + )-GO composite membranes achieve the simultaneous enhancement of permeation flux and separation factor for the separation of different water/alcohol mixtures. For the pervaporation separation of ethanol/water, n-butanol/water and i-propanol/water mixtures at 40 o C with alcohol concentrations of 90%, the Lys(Na + )(10)-GO membrane(weight ratio of Lys(Na + ) to GO in the extract soultion is 10) shows permeation flux of 882, 2461 and 1127 g/m 2 h, with the water content in permeate reaching 95.38%, 99.11% and 99.42%, respectively.