Capturing the Local Adsorption Structures of Carbon Dioxide in Polyamine-Impregnated Mesoporous Silica Adsorbents

Interactions between amines and carbon dioxide (CO₂) are essential to amine-functionalized solid adsorbents for carbon capture, and an in-depth knowledge of these interactions is crucial to adsorbent design and fabrication as well as adsorption/desorption processes. The local structures of CO₂ adsorbed on a tetraethylenepentamine-impregnated mesoporous silica SBA-15 were investigated by solid-state ¹³C­{¹⁴N} S-RESPDOR MAS NMR technique and theoretical DFT calculations. Two types of adsorption species, namely, secondary and tertiary carbamates as well as distant ammonium groups were identified together with their relative concentrations and relevant ¹⁴N quadrupolar parameters. Moreover, a dipolar coupling of 716 Hz was derived, corresponding to a ¹³C–¹⁴N internuclear distance of 1.45 Å. These experimental data are in excellent agreement with results obtained from DFT calculations, revealing that the distribution of surface primary and secondary amines readily dictates the CO₂ adsorption/desorption properties of the adsorbent