Selective CO 2 Sequestration with Monolithic Bimodal Micro/Macroporous Carbon Aerogels Derived from Stepwise Pyrolytic Decomposition of Polyamide-Polyimide-Polyurea Random Copolymers

• Published in: ACS applied materials & interfaces Vol. 9; no. 15; pp. 13520 - 13536
• Main Authors: Saeed, Adnan M, Rewatkar, Parwani M, Majedi Far, Hojat, Taghvaee, Tahereh, Donthula, Suraj, Mandal, Chandana, Sotiriou-Leventis, Chariklia, Leventis, Nicholas
• Format: Journal Article
• Language: English
• Published: United States 19.04.2017
• Subjects: carboxylic acid; polyimide; copolymer; polyurea; CO2 sequestration; carbon aerogels; aerogels; polyamide; pryomellitic acid
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.7b01910

Polymeric aerogels (PA-xx) were synthesized via room-temperature reaction of an aromatic triisocyanate (tris(4-isocyanatophenyl) methane) with pyromellitic acid. Using solid-state CPMAS C and N 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 m g in PA-xx to 340 m g in the carbons. Next, reactive etching at 1,000 °C with CO opened access to the closed pores and the micropore area increased by almost 4× to 1150 m g (out of 1750 m g of a total BET surface area). At 0 °C, etched carbon aerogels demonstrated a good balance of adsorption capacity for CO (up to 4.9 mmol g ), and selectivity toward other gases (via Henry's law). The selectivity for CO versus H (up to 928:1) is suitable for precombustion fuel purification. Relevant to postcombustion CO capture and sequestration (CCS), the selectivity for CO versus N was 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 CO is preferentially engaged by surface pyridinic and pyridonic N on carbon (identified with XPS) in an energy-neutral surface reaction. Relatively high uptake of CH (2.16 mmol g at 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 CO selectivities, in combination with attractive CO adsorption capacities, low monomer cost, and the innate physicochemical stability of carbon render the materials of this study reasonable candidates for further practical consideration.