title: Characterization of a Mixture of CO2 Adsorption Products in Hyperbranched Aminosilica Adsorbents by (13)C Solid-State NMR.
abstract: Hyperbranched amine polymers (HAS) grown from the mesoporous silica SBA-15 (hereafter "SBA-15-HAS") exhibit large capacities for CO2 adsorption. We have used static in situ and magic-angle spinning (MAS) ex situ (13)C nuclear magnetic resonance (NMR) to examine the adsorption of CO2 by SBA-15-HAS. (13)C NMR distinguishes the signal of gas-phase (13)CO2 from that of the chemisorbed species. HAS polymers possess primary, secondary, and tertiary amines, leading to multiple chemisorption reaction outcomes, including carbamate (RnNCOO(-)), carbamic acid (RnNCOOH), and bicarbonate (HCO3(-)) moieties. Carbamates and bicarbonate fall within a small (13)C chemical shift range (162-166 ppm), and a mixture was observed including carbamic acid and carbamate, the former disappearing upon evacuation of the sample. By examining the (13)C-(14)N dipolar coupling through low-field (B0 = 3 T) (13)C{(1)H} cross-polarization MAS NMR, carbamate is confirmed through splitting of the (13)C resonance. A third species that is either bicarbonate or a second carbamate is evident from bimodal T2 decay times of the ∼163 ppm peak, indicating the presence of two species comprising that single resonance. The mixture of products suggests that (1) the presence of amines and water leads to bicarbonate being present and/or (2) the multiple types of amine sites in HAS permit formation of chemically distinct carbamates.
authors.forename: Jeremy K
authors.initials: JK
authors.lastname: Moore
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology , 311 Ferst Drive, Atlanta, Georgia 30332, United States.
authors.forename: Miles A
authors.initials: MA
authors.lastname: Sakwa-Novak
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology , 311 Ferst Drive, Atlanta, Georgia 30332, United States.
authors.forename: Watcharop
authors.initials: W
authors.lastname: Chaikittisilp
authors.affiliation: Department of Chemistry, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States.
authors.forename: Anil K
authors.initials: AK
authors.lastname: Mehta
authors.forename: Mark S
authors.initials: MS
authors.lastname: Conradi
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology , 311 Ferst Drive, Atlanta, Georgia 30332, United States.
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Jones
authors.forename: Sophia E
authors.initials: SE
authors.lastname: Hayes
mesh_terms: D000327:Adsorption; D000588:Amines / Q000737:chemistry; D002219:Carbamates / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011108:Polymers / Q000737:chemistry*; D012822:Silicon Dioxide; D014867:Water / Q000737:chemistry
chemical_list: D000588:Amines; D002219:Carbamates; D002247:Carbon Isotopes; D011108:Polymers; C509969:SBA-15; D014867:Water; D002245:Carbon Dioxide; D012822:Silicon Dioxide