Size-Selective Mixed Matrix Membrane for CO2 Separation Driven by Porous Nanosheets with Exceptionally High Surface Area

Abstract

In this study, a new concept of porous nanocomposite sheets,zeolitic imidazolate framework-8 (ZIF-8) grown on porous graphene oxide (PGO) termed as ZPGO, was developed. Within mixed matrix membranes (MMMs), ZPGO provides diffusion-selective paths for CO2 separation even at very low filler concentration (0.02wt.%). Porous graphene oxide, the template for ZIF-8 growth was prepared by hydrothermal treatment of graphene oxide (GO) solution with oxidant, hydrogen peroxide. This procedure generated active nanopores that maximizes growth seed sites and minimizes barrier effect of GO nanosheets. Densely grown ZIF-8 on PGO as desired was confirmed directly by transmission electron microscopy (TEM) images, the composition calculated from thermal gravimetric analysis (TGA) data and new chemical interaction peak shown from x-ray photoelectron spectroscopy (XPS) lines, and indirectly by crystallinity change of polyamide region of prepared MMMs calculated from the peak area of differential scanning calorimetry (DSC) data and anomalously high Brunauer-Emmett-Teller (BET) surface area (2170m2/g) calculated from nitrogen isotherms. In regards to gas transport properties, ZPGO not only doubled the CO2 permeability by quadrupling diffusivity but also showed great potential in real operations by showing higher mixed gas selectivity than single gas selectivity and preventing plasticization of MMM by CO2. Therefore, this new nanocomposite can contribute to practical membrane-based gas separation applications as well as other fields where high surface area is of high value.