title: Selective CO2Sequestration with Monolithic Bimodal Micro/Macroporous Carbon Aerogels Derived from Stepwise Pyrolytic Decomposition of Polyamide-Polyimide-Polyurea Random Copolymers.
abstract: Polymeric aerogels (PA-xx) were synthesized via room-temperature reaction of an aromatic triisocyanate (tris(4-isocyanatophenyl) methane) with pyromellitic acid. Using solid-state CPMAS13C and15N NMR, it was found that the skeletal framework of PA-xx was a statistical copolymer of polyamide, polyurea, polyimide, and of the primary condensation product of the two reactants, a carbamic-anhydride adduct. Stepwise pyrolytic decomposition of those components yielded carbon aerogels with both open and closed microporosity. The open micropore surface area increased from <15 m2g-1in PA-xx to 340 m2g-1in the carbons. Next, reactive etching at 1,000 °C with CO2opened access to the closed pores and the micropore area increased by almost 4× to 1150 m2g-1(out of 1750 m2g-1of a total BET surface area). At 0 °C, etched carbon aerogels demonstrated a good balance of adsorption capacity for CO2(up to 4.9 mmol g-1), and selectivity toward other gases (via Henry's law). The selectivity for CO2versus H2(up to 928:1) is suitable for precombustion fuel purification. Relevant to postcombustion CO2capture and sequestration (CCS), the selectivity for CO2versus N2was in the 17:1 to 31:1 range. In addition to typical factors involved in gas sorption (kinetic diameters, quadrupole moments and polarizabilities of the adsorbates), it is also suggested that CO2is preferentially engaged by surface pyridinic and pyridonic N on carbon (identified with XPS) in an energy-neutral surface reaction. Relatively high uptake of CH4(2.16 mmol g-1at 0 °C/1 bar) was attributed to its low polarizability, and that finding paves the way for further studies on adsorption of higher (i.e., more polarizable) hydrocarbons. Overall, high CO2selectivities, in combination with attractive CO2adsorption capacities, low monomer cost, and the innate physicochemical stability of carbon render the materials of this study reasonable candidates for further practical consideration.
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology , Rolla, Missouri 65409, United States.
authors.forename: Adnan M
authors.initials: AM
authors.lastname: Saeed
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology , Rolla, Missouri 65409, United States.
authors.forename: Parwani M
authors.initials: PM
authors.lastname: Rewatkar
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology , Rolla, Missouri 65409, United States.
authors.forename: Hojat
authors.initials: H
authors.lastname: Majedi Far
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology , Rolla, Missouri 65409, United States.
authors.forename: Tahereh
authors.initials: T
authors.lastname: Taghvaee
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology , Rolla, Missouri 65409, United States.
authors.forename: Suraj
authors.initials: S
authors.lastname: Donthula
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology , Rolla, Missouri 65409, United States.
authors.forename: Chandana
authors.initials: C
authors.lastname: Mandal
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology , Rolla, Missouri 65409, United States.
authors.forename: Chariklia
authors.initials: C
authors.lastname: Sotiriou-Leventis
authors.affiliation: Department of Chemistry, Missouri University of Science and Technology , Rolla, Missouri 65409, United States.
authors.forename: Nicholas
authors.identifier: http://orcid.org/0000-0002-7575-9498
authors.initials: N
authors.lastname: Leventis
keywords: CO2 sequestration; aerogels; carbon aerogels; carboxylic acid; copolymer; polyamide; polyimide; polyurea; pryomellitic acid