Interaction of CO₂ and CH₄ with Functionalized Periodic Mesoporous Phenylene–Silica: Periodic DFT Calculations and Gas Adsorption Measurements

Nonfunctionalized and functionalized periodic mesoporous phenylene–silicas (Ph–PMOs) with different kinds of amine groups were prepared and their capacity to uptake CO₂ and CH₄ molecules were experimentally evaluated considering biogas upgrading. It was found that aminopropyl groups grafted to the free silanols of the Ph–PMO displayed the highest selectivity for CO₂ gas, adsorbing 26.1 times more CO₂ than CH₄ at 25 °C. The interaction effect of the surface of these materials with the CO₂ or CH₄ molecules was obtained through the calculation of the Henry constants, and the adsorption mechanisms involved were elucidated from density functional theory calculations. The good synergy between experimental gas adsorption and computational studies suggests that the latter can be used to guide the experimental synthesis of more effective materials. Thus, our computational studies were extended to PMOs with other functional groups having different polarity for predicting interaction energies with CO₂ and thus identifying the most promising candidates for experimental synthesis.