Nanoconfinement-Enhanced CO₂ Retention in Fenamate-Loaded Silica Aerogels

The interaction between carbon dioxide and molecularly confined pharmaceutical compounds can result in CO₂ retention that exceeds that achieved through conventional physical adsorption. This study investigates CO₂ retention following sorption in hydrophilic and hydrophobic silica aerogels containing the fenamates mefenamic acid and flufenamic acid. The Thermal stability of the retained CO₂ was characterized using temperature-programmed oxidation and temperature-programmed desorption measurements. Concurrently, single-point nitrogen adsorption measurements monitored relative changes in the apparent accessible surface area of the porous matrix. Untreated silica aerogels did not exhibit a significant CO₂ desorption peak at elevated temperatures. In contrast, all composites containing fenamates exhibited an additional high-temperature desorption step beginning at approximately 225 °C, indicating enhanced CO₂ retention after sorption once the external CO₂ layer was removed. This characteristic persisted following preliminary thermal treatment, suggesting it is not solely attributable to residual volatile substances. Surface-area measurements indicated minimal changes in the original aerogels after the CO₂ cycle, whereas composites with flufenamic acid demonstrated more pronounced alterations. Considering previous nuclear magnetic resonance, spectroscopic, and computational studies, these findings suggest a combined effect of nanoconfinement, surface-dependent interfacial phenomena, and specific interactions involving the fenamate-containing phase. Reversible chemical interactions may contribute to the observed retention, although the current measurements do not allow for quantitative separation of their effects from those of physical confinement.