Carbon dioxide (CO2) emissions have been rising indiscriminately and are becoming a major contributor to Earth's greenhouse effect. One of the most promising means of separating the hazardous CO2 gas is to develop a cost effective and high-performance CO2 separation membrane. From the wide range of membrane materials available, mixed matrix membrane (MMM) technology has shown the most promising results. In this study, NIMMs were synthesized from cellulose acetate (CA) with multiwalled carbon nanotubes (MWCNTs) using the wet phase inversion technique. The results shown that MNIMs with functionalized MWCNTs (MWCNTs-F) demonstrated the enhance permeance and selectivity towards the separation of CO2/nitrogen (N-2). Thus, different loadings of MWCNTs-F into MMM were further investigated to interpret the physical morphologies and functionalities of MMMs, which enable the separation of CO2/N-2 in a specific manner. Gas permeation measurements showed excellent MMM performances in terms of permeance and selectivity at 0.1 wt% loadings of MWCNTs-f. This superior performance was due to the homogeneous dispersion between the MWCNTs-F and the CA matrix, which increased the sufficient free volumes between the polymer chains and enlarged the polymer/nanofiller interface, as confirmed by the X-ray diffraction results. (C) 2013 Elsevier B.V. All rights reserved