A cost-effective, facile method for simultaneously improving the CO2 permeance and CO2/N-2 selectivity of mixed matrix membranes (MMMs) was developed using commercially available MgCO3 microcrystals. The MgCO3 crystals were broken into small pieces and homogenously dispersed in polymer matrices via mechanical stirring to form MMMs. In particular, an amphiphilic comb polymer (CP) composed of poly(ethylene glycol) behenyl ether methacrylate (PEGBEM) and poly(oxyethylene methacrylate) (POEM), i.e., PEGBEM-POEM, was found to be an effective matrix due to the specific interactions between its carbonyl oxygen atoms and MgCO3. The detailed interactions, morphologies, and structures of MgCO3 and CP/MgCO3 hybrids were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), N-2 adsorption-desorption isotherm measurements, wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and Fourier transform infrared (FT-IR) and Raman spectroscopies. The CP/MgCO3 MMM with 45 wt% MgCO3 exhibited the highest CO2/N-2 selectivity of 93.8 and CO2 permeance of 30.9 GPU (1 GPU = 10(-6) cm(3) (STP)/(s center dot cm(2)center dot cmHg)). This performance surpasses other MgCO3 MMMs prepared using commercially available polymers such as PEBAX (R) (a polyether block amide) and poly(ethylene oxide) (PEO). The improved performance resulted from the enhanced CO2 solubility by MgCO3 crystals, as confirmed by the CO2 uptake measurements. (C) 2016 Elsevier B.V. All rights reserved.