(660g) Hierarchical, Flower-like Carbon Microspheres for CO2 Capture | AIChE

(660g) Hierarchical, Flower-like Carbon Microspheres for CO2 Capture


Snyder, M. - Presenter, Lehigh University
Sharma, M., Lehigh University
Among classes of porous sorbents with promise for use in mitigating carbon dioxide (CO2) emissions, carbons remain attractive due to their economical synthesis, high CO2 uptake/selectivity, and easy regeneration. Here, we report a facile and scalable imidization-induced precipitation route to intrinsically nitrogen-doped carbon microspheres (~6 µm) bearing a unique, hierarchically structured flower-like morphology. Simple tuning of solution precursor composition offers a handle for tailoring morphology and mesostructure among core (dense)/shell (petal) structures, petaled lobes, and extended petal structures, bearing a direct functional influence on molecular accessibility of the thin (ca. 10-20 nm) highly anisotropic microporous petals. The resulting carbons have tunable specific surface area spanning 750-2064 m2/g and total pore volumes ranging from 0.38-1 cm3/g, achieved through activation by CO2 at 800-900 °C. Detailed study of the textural properties and surface chemistry of these materials as a function of activation temperature and duration reveals that CO2 uptake is strongly correlated to the volume of the narrowest micropores (diameters < 1 nm) rather than to specific nitrogen content. Ultramicropore volume, and thus CO2 uptake, increases as a function of activation until devolving into larger micro- and meso-pores, with the optimal materials in this study yielding high CO2 uptake at 1 bar of 6.44 mmol/g at 0 °C and 4.5 mmol/g at 25 °C. These intrinsically nitrogen-doped carbons, derived from the simple processing of cheap precursors show competitive CO2/N2 selectivity as estimated by the Ideal Adsorbed Solution Theory (IAST), fast uptake kinetics, low isosteric heats of adsorption (20-30 kJ/mol), and, thereby, easy regeneration by both temperature and pressure-swing. Ultimately, these materials show promise as efficient and cost-effective CO2 sorbents and, given their tunable pore and morphological hierarchy, strong promise for efficient and selective processing of bulky molecules.