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 Diels–Alder cycloaddition polymerization and subsequent FeCl 3 -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 °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 ( Q st 7.7 kJ mol –1, 1.03 wt % at 77 K, 1 bar), CO 2 ( Q st = 28.7 kJ mol –1, 94.6 mg g –1 at 273 K, 1 bar), and CH 4 ( Q st = 24.1 kJ mol –1, 11.5 mg g –1 at 273 K, 1 bar). The enhancement in gas affinities was attributed to the unique combination of large π-surface area arising from graphene nanoribbons and small pores (∼5.8 Å) in GNF. The application of GNF can also be extended to natural gas purification process with exceptional CO 2 /CH 4 (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 CO 2 toward the sorbent in order to tune CO 2 /CH 4 selectivity, our approach takes advantage of the kinetic diameter difference between CO 2 (3.30 Å) and CH 4 (3.80 Å), thus offering a low-cost efficient alternative for the natural gas purification process.