Deriving a CO2-Permselective Carbon Membrane from a Multilayered Matrix of Polyion Complexes

A multilayered assembly consisting of polyion complexes was developed over porous ceramic as a unique precursor for a carbon membrane (CM). This specific layer was attained through in situ polymerization of N-methylpyrrole (mPy) over a prime coating layer of poly(4-styrenesulfonic acid) (PSSA) with an embedded oxidant on the ceramic surface. Extensive ion-pair complexation between the sulfonic acid groups of PSSA and the tertiary amine groups of the resulting poly(N-methylpyrrole) (PmPy) sustains this assembly layer. Incorporating cetyltrimethylammonium bromide (CTAB) into the PSSA is critical in facilitating the infiltration of mPy into the PSSA layer and promoting interfacial contact between the two polymers. Upon pyrolysis, the precursor coating was collectively converted into a carbon composite matrix. Such copyrolysis restrains the grain sizes of the carbonized PmPy, thereby halting defects in the resultant carbonaceous matrix. The gas separation performances of the CMs obtained at various graphitization temperatures showed that the least graphitized carbon matrix exhibited the best selectivity of CO2/CH4 = 167 with a CO2 permeability of 7.19 Barrer. This specific feature is attributed to both imine and imide pendant groups that function as selective adsorption sites for CO2 in the carbon skeleton.