title: Elucidation of Surface Species through in Situ FTIR Spectroscopy of Carbon Dioxide Adsorption on Amine-Grafted SBA-15.
abstract: The nature of the surface species formed through the adsorption of CO2on amine-grafted mesoporous silica is investigated through in situ FTIR spectroscopy with the aid of15N dynamic nuclear polarization (DNP) and13C NMR spectroscopy. Primary, secondary, and tertiary amines are functionalized onto a mesoporous SBA-15 silica. Both isotopically labeled13CO2and natural-abundance CO2are used for accurate FTIR peak assignments, which are compared with assignments reported previously. The results support the formation of monomeric and dimeric carbamic acid species on secondary amines that are stabilized differently to the monocarbamic acid species on primary amines. Furthermore, the results from isotopically labelled13CO2experiments suggest the existence of two carbamate species on primary amines, whereas only one species is observed predominantly on secondary amines. The analysis of the IR peak intensities and frequencies indicate that the second carbamate species on primary amines is probably more asymmetric in nature and forms in a relatively smaller amount. Only the formation of bicarbonate ions at a low concentration is observed on tertiary amines; therefore, physisorbed water on the surface plays a role in the hydrolysis of CO2even if water is not added intentionally and dry gases are used. This suggests that a small amount of bicarbonate ions could be expected to form on primary and secondary amines, which are more hydrophilic than tertiary amines, and these low concentration species are difficult to observe on such samples.
authors: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia, 30332, United States.
authors: Guo Shiou
authors: GS
authors: Foo
authors: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia, 30332, United States.
authors: Jason J
authors: JJ
authors: Lee
authors: Department of Chemistry, Washington University, One Brookings Drive, Saint Louis, Missouri, 63130, United States.
authors: Chia-Hsin
authors: CH
authors: Chen
authors: Department of Chemistry, Washington University, One Brookings Drive, Saint Louis, Missouri, 63130, United States.
authors: Sophia E
authors: SE
authors: Hayes
authors: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia, 30332, United States.
authors: Carsten
authors: C
authors: Sievers
authors: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia, 30332, United States.
authors: Christopher W
authors: http://orcid.org/0000-0003-3255-5791
authors: CW
authors: Jones
mesh_terms: D000327:Adsorption; D000588:Amines / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: D000588:Amines; C509969:SBA-15; D002245:Carbon Dioxide; D012822:Silicon Dioxide
keywords: adsorption; amines; mesoporous materials; nmr spectroscopy; surface chemistry