Edge-Functionalized Graphene Nanoribbon Frameworks for the Capture and Separation of Greenhouse Gases

We
demonstrate a bottom-up synthetic approach for the synthesis
of graphene nanoribbon frameworks (GNFs) incorporating edge-functionalized
graphene nanoribbons via the Diels–Alder cycloaddition polymerization
and a subsequent FeCl3-catalyzed cyclo-dehydrogenation
reactions. This approach not only allowed us to precisely position
substituents, namely, −OMe (GNF-0), −H (GNF-1), −CF3 (GNF-2), and −F (GNF-3), but also enabled to tune
textural properties and gas affinity of resulting frameworks. GNFs
exhibited promising physical properties such as high surface areas
(up to 755 m2 g–1) and excellent physicochemical
and thermal stabilities (up to 400 °C). Narrow pore size distribution
and the presence of large aromatic units led to high affinity toward
gases such as CO2 (27.4–30.9 kJ mol–1 at 1 bar), CH4 (21.3–26.0 kJ mol–1 at 1 bar), and H2 (6.5–8.2 kJ mol–1 at 1 bar). Notably, GNFs also showed promising CO2/CH4 breakthrough separation performance for natural gas sweetening
and landfill gas separations at 298 K. The edge-functionalization
of GNFs with −CF3 and −F significantly improved
their affinity toward perfluorocarbons and CFCs, which are classified
as potent greenhouse gases. Compared to GNF-3, GNF-2 containing −CF3 moieties showed much higher uptake capacity toward CFC-113
(67 wt % at 298 K).