Pebax-based mixed matrix membranes loaded with graphene oxide/core shell ZIF-8@ZIF-67 nanocomposites improved CO2 permeability and selectivity

In order to facilitate CO2 transport in Pebax-based membranes, graphene oxide (GO)/core shell ZIF-8@ZIF-67 nanocomposites were loaded in Pebax copolymer to improve CO2 permeability and selectivity. The 0.5 wt% GO doped core shell ZIF-8@ZIF-67, which gave highest CO2 adsorption capacity of 1.12 mmol/g, was used as nanocomposite. The incorporated GO/core shell ZIF enhanced CO2 adsorption via unsaturated metal sites (Zn-O or Co-O), because O atoms in GO substituted for N atoms coordinated with Zn and Co single atoms in core shell ZIF-8@ZIF-67. Positron annihilation lifetime spectroscopy indicated that GO-templated core shell ZIF nanocomposites generated extra free volume and provided low-resistance channels to facilitate CO2 transport. Fourier transform infrared spectroscopy analysis revealed that hydrogen bonds were generated between Pebax polymer chains and GO-templated core shell ZIF which improved swelling resistance and reduced interface defects. Therefore, Pebax-based MMMs loaded with 5 wt% GO/core shell ZIF-8@ZIF-67 exhibited optimum CO2 permeability (173.2 barrers) and ideal selectivity of CO2/N-2 (61.9) and CO2/H-2 (11.6), which were 99.7%, 66.4%, and 20.8% higher than Pebax membranes and surpass Robeson 2008 upper bound. The tensile strength increased by 17.6% to 28.8 MPa and elongation at break increased by 7.61%-554.6% when pure Pebax membranes were incorporated with 2.5 wt% GO/core shell ZIF-8@ZIF-67.

Automated summary

Incorporating GO/core shell ZIF-8@ZIF-67 nanocomposites into Pebax membranes significantly improved CO2 permeability and selectivity, while also increasing tensile strength and elongation at break.