A porous, nitrogen-doped carbonaceous free-standing membrane (TFMT-550) is prepared by a facile template-free method using letrozole as an intermediate to a triazole-functionalized-triazine framework, followed by carbonization. Such adsorption/diffusion membranes exhibit good separation performance of CO2 over N2 and surpassing the most recent Robeson upper bound. An exceptional ideal CO2/N2 permselectivity of 47.5 was achieved with a good CO2 permeability of 2.40 x 1013 mol m m2 s1 Pa1. The latter results arise from the presence of micropores, narrow distribution of small mesopores and from the strong dipolequadrupole interactions between the large quadrupole moment of CO2 molecules and the polar sites associated with N groups (e.g., triazine units) within the framework.