Carbon dioxide solid sorbents produced from mesoporous functionalized silica microparticles (SBA-15) have been investigated (i) theoretically using density functional theory and (ii) evaluated empirically for assessing their CO2 adsorption capacity. Two different families of organosilyl groups have been tested possessing a common anchoring group (silanol), in one extreme, but bearing two different types of CO2 sensitive groups in the other extreme; (i) hyperbranched polymeric PAMAM moieties, carrying multiple −NH2 groups, and (ii) a collection of linear functional ending groups such as −SH, −SO3H, −guanidine (Gdn), −NH2, −NCO, and −N3. The adsorption isotherms revealed that SBA-15 bearing (3-aminopropyl)­triethoxysilane (APTES) showed an impressive 3.4-fold adsorption enhancement at 1 bar and 50 °C when compared to the pristine SBA-15, following a straightforward synthetic protocol. The maximum adsorption capacity was increased from 0.34 mmol/g (SBA-15) to 1.15 mmol/g (SBA-15@NH2) under conditions relevant to CO2 capture (1 bar and 50 °C). We also found intriguing certain discrepancies observed between the calculated CO2 isotherms and the theorized binding energy in two of the materials. This will be addressed in the present work.