Characterization of a Mixture of CO2 Adsorption Products in Hyperbranched Aminosilica Adsorbents by 13C Solid-State NMR

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• 作者：Jeremy K. Moore ; Miles A. Sakwa-Novak ; Watcharop Chaikittisilp ; Anil K. Mehta ; Mark S. Conradi ; Christopher W. Jones ; Sophia E. Hayes
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：November 17, 2015
• 年：2015
• 卷：49
• 期：22
• 页码：13684-13691
• 全文大小：354K
• ISSN：1520-5851

文摘

Hyperbranched amine polymers (HAS) grown from the mesoporous silica SBA-15 (hereafter 鈥淪BA-15鈥揌AS鈥? exhibit large capacities for CO₂ adsorption. We have used static in situ and magic-angle spinning (MAS) ex situ ¹³C nuclear magnetic resonance (NMR) to examine the adsorption of CO₂ by SBA-15鈥揌AS. ¹³C NMR distinguishes the signal of gas-phase ¹³CO₂ from that of the chemisorbed species. HAS polymers possess primary, secondary, and tertiary amines, leading to multiple chemisorption reaction outcomes, including carbamate (RnNCOO^{鈥?/sup>), carbamic acid (RnNCOOH), and bicarbonate (HCO₃鈥?/sup>) moieties. Carbamates and bicarbonate fall within a small 13C chemical shift range (162鈥?66 ppm), and a mixture was observed including carbamic acid and carbamate, the former disappearing upon evacuation of the sample. By examining the 13C鈥?sup>14N dipolar coupling through low-field (B₀ = 3 T) 13C{1H} cross-polarization MAS NMR, carbamate is confirmed through splitting of the 13C resonance. A third species that is either bicarbonate or a second carbamate is evident from bimodal T₂ decay times of the 鈭?63 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.}