Bottom-up Approach for the Synthesis of a Three-Dimensional Nanoporous Graphene Nanoribbon Framework and Its Gas Sorption Properties

We present a new polymerization strategy, that is catalyst-free DielsAlder cycloaddition polymerization and subsequent FeCl3-catalyzed intramolecular cyclodehydrogenation reaction, to introduce graphene nanoribbons up to 2 nm in length and 1.1 nm in width into a graphene nanoribbon framework (GNF). The first graphene nanoribbon framework showed high thermal stability up to 400 degrees C in air with relatively narrow pore size distribution and exhibited BET surface area of 679 m(2) g(-1). GNF possesses high affinity for H-2 (Qst 7.7 kJ mol(-1), 1.03 wt % at 77 K, 1 bar), CO2 (Q(st) = 28.7 kJ mol(-1), 94.6 mg g(-1) at 273 K, 1 bar), and CH4 (Q(st) = 24.1 kJ mol(-1), 11.5 mg g1 at 273 K, 1 bar). The enhancement in gas affinities was attributed to the unique combination of large p-surface area arising from graphene nanoribbons and small pores (similar to 5.8 angstrom) in GNF. The application of GNF can also be extended to natural gas purification process with exceptional CO2/CH4 (5:95) selectivity of 62.7, which is the highest value reported to date at 298 K. Unlike previous studies that focus mostly on increasing the affinity of CO2 toward the sorbent in order to tune CO2/CH4 selectivity, our approach takes advantage of the kinetic diameter difference between CO2 (3.30 angstrom) and CH4 (3.80 angstrom), thus offering a low-cost efficient alternative for the natural gas purification process.