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.