(680b) CO2 Adsorption from Intra Versus Inter Molecular Interactions on Aminosilane Grafted SBA-15

Most of amine adsorbents studied for CO₂ capture have high amine loadings on the various supports, such that it may be presumed that CO₂ adsorption most often occurs via cooperative interactions of two amines in different molecules or chains. However, a fundamental molecular level understanding of CO₂ adsorption requires insight into the propensity or probability for intramolecular vs intermolecular cooperative adsorption when using amine molecules that contain multiple amine species. Very limited research to date has targeted intramolecular amineâ??amine interactions during CO₂ capture.

In this study, ultralow loadings (â?¼0.45 mmol silane/g) of four different organosilane molecules were grafted onto a mesoporous silica SBA-15 support so that CO₂ could be adsorbed by primarily or only intramolecular amine interactions.¹ The four grafted molecules studied contain four different functional moieties [propylamine, (MONO); propylethylenediamine, (DI); propyldiethylenetriamine, (TRI); propyltriethylenetetramine, (TREN)] including organosilanes that can only bind to form alkylammonium carbamates intermolecularly (MONO) as well as amines that can bind with inter- or intramolecular interactions (DI, TRI, TREN). For a series of these samples, hexamethyldisilazane (HMDS) was used to cap accessible surface silanols and exclude the potential for CO₂ capture by amine interactions with silanols on the surface, which is hypothesized to give carbamic acid species.² The CO₂ uptake over various CO₂ partial pressures was measured over these adsorbents, and simultaneously, the isosteric heats of adsorption of CO₂ were measured via calorimetry. Thus, the potential for intramolecular CO₂ adsorption has been explored and the effective distances between two amine molecules for CO₂ adsorption via intramolecular interactions was estimated for each silane.

The insights from this work may be utilized in the design of new amine molecules that might have improved sorption properties, while the collected data provide new understanding of the mechanism and kinetics of CO₂ adsorption at low amine loadings.

References

1) C.-J. Yoo, L.-C. Lee, C. W. Jones, â??Probing Intramolecular vs. Intermolecular CO₂ Adsorption On Amine-grafted SBA15.â?Â Langmuir (2015) 31, 9356-9365

2) A. Danon; P.C. Stair, E. Weitz, â??FTIR Study of CO2 Adsorption on Amine-Grafted SBA-15: Elucidation of Adsorbed Species.â? J. Phys. Chem. C (2011) 115, 11540â??11549