Incorporating amino acids functionalized graphene oxide nanosheets into Pebax membranes for CO2 separation

Abstract

Graphene oxide (GO) nanosheets, as versatile nanofillers, can create two-dimensional passageways in mixed matrixed membranes (MMMs), yet the flexible manipulation of GO nanosheets is hampered by the lack of appropriate chemical functional groups. In this study, we chose amino acids（arginine, histidine and cysteine）to modify GO nanosheets by direct crosslinking and the loading content of amino acids on GO nanosheets was more than 20%. The modified GO nanosheets were then filled into the Pebax matrix to prepare MMMs. The CO2 separation performance of MMMs with different nanofillers was compared and different amino acids modified GO nanosheets could fortify the solution mechanism for CO2 in the order of arginine@GO ＞ histidine@GO ＞ cysteine@GO. Density functional theory (DFT) calculations were conducted to further elucidate the interaction mechanism between gases molecules and amino acids. Under dry state, the complexation energy (Ec) between CO2 and amine groups was similar to the Ec between CO2 and carboxylic groups in amino acids. In particular, 0.4 wt% arg@GO nanosheets rendered the membranes with promising CO2 permeance of 169 Barrer and CO2/N2 selectivity of 70, and surpassed the 2008 upper bound. The amino acids modified GO nanosheets may enlighten an alternative way to explore CO2 transfer mechanism within MMMs and fabricate high separation performance membranes.