Two-step surface functionalization/alignment strategy to improve CO2/N2 separation from mixed matrix membranes based on PEBAX and graphene oxide

Abstract

In this study, a simple method to prepare mixed matrix membranes (MMM) based on Pebax with functionalized/oriented graphene oxide (GO) nanosheets is presented to improve CO2/N2 separation. First, the GO nanosheets were surface modified with different amounts of m-phenylenediamine (mPD) to maximize the CO2 adsorption affinity and minimize GO agglomeration within the matrix. Then, an external electric field was applied to organize/orient the GO nanosheets (modified and unmodified) during membrane preparation. The separation performance results showed that the CO2 permeability of unmodified and amine-functionalized GO-filled MMM respectively increased by 1.7 and 2.1 times compared to the neat matrix. This improvement is attributed to the high affinity of amino groups for CO2 uptake. Furthermore, applying a vertical electric field increased the CO2 permeability compared to a random GO orientation state by 1.3 and 2.8 times for the unmodified and modified GO-filled MMM, respectively. This significant improvement is related to a lower tortuosity in the membrane, improving the passage of gas molecules. Overall, the combination of surface treatment (amino group) and orientation (electric field) on GO nanosheets leads to better CO2 permselectivity for the membranes studied.