Assessing CO₂ Capture in Porous Sorbents via Solid-State NMR-Assisted Adsorption Techniques

Adsorption isotherms obtained through volumetric measurements are widely used to estimate the gas adsorption performance of porous materials. Nonetheless, there is always ambiguity regarding the contributions of chemi- and physisorption processes to the overall retained gas volume. In this work, we propose, for the first time, the use of solid-state NMR (ssNMR) to generate isotherms of CO₂ adsorbed onto an amine-modified silica sorbent. This method enables the separation of six individual isotherms for chemi- and physisorbed CO₂ components, a feat only possible using the discrimination power of NMR spectroscopy. The adsorption mechanism for each adsorbed species was ascertained by tracking their adsorption profiles at various pressures. The proposed method was validated against conventional volumetric adsorption measurements. The isotherm curves obtained by the proposed ssNMR-assisted approach enable advanced analysis of the sorbents, revealing the potential of variable-pressure NMR experiments in gas adsorption applications.