Functionalized graphene oxide/polyimide nanocomposites as highly CO2-selective membranes

The design of highly CO2-selective membranes by incorporating low amounts (0.25-0.75 wt%) of functionalized graphene oxide (F-GO) nanosheets (polyethylene glycol functionalized and aminated GOs) into an Ultem (R) 1000 polyetherimide (PEI) is presented. Structural and morphological analysis of the membranes by infrared spectroscopy, Xray diffraction, differential scanning calorimetry and scanning electron microscopy revealed strong interfacial interactions between the F-GO nanosheets and PEI. The CO2/CH4 separation performance of the membranes was discussed in terms of filler-polymer interfacial interactions and free volume characteristics. The origins of free volume are proposed to be different for GO/PEI and F-GO/PEI membranes: free volume is mainly located at the GO-PEI interface of the GO/PEI membranes while distributed within interphase regions formed around the F-GO nanosheets in the F-GO/PEI ones. These different free volume localizations resulted in distinct gas separation properties of the membranes. The membranes containing aminated-GO showed outstanding CO2/CH4 selectivities up to 142, due to the activation of multi-permselectivity mechanism in the PEI membrane by addition of the aminated nanosheets. The promising potential of F-GOs in CO2 removal is highlighted by comparing the CO2/CH4 separation performance of the F-GO/PEI membranes with that of other nanocomposites of PEI.