Adsorption methods for CO2capture are characterized by high selectivity and low energy consumption. Therefore, the engineering of solid supports for efficient CO2adsorption attracts research attention. Modification of mesoporous silica materials with tailor-made organic molecules can greatly improve silica’s performance in CO2capture and separation. In that context, a new derivative of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, possessing an electron-rich condensed aromatic structure and also known for its anti-oxidative properties, was synthesized and applied as a modifying agent of 2D SBA-15, 3D SBA-16, and KIT-6 silicates. The physicochemical properties of the initial and modified materials were studied using nitrogen physisorption and temperature-gravimetric analysis. The adsorption capacity of CO2was measured in a dynamic CO2adsorption regime. The three modified materials displayed a higher capacity for CO2adsorption than the initial ones. Among the studied sorbents, the modified mesoporous SBA-15 silica showed the highest adsorption capacity for CO2(3.9 mmol/g). In the presence of 1 vol.% water vapor, the adsorption capacities of the modified materials were enhanced. Total CO2desorption from the modified materials was achieved at 80 °C. The obtained silica materials displayed stable performance in five CO2adsorption/desorption cycles. The experimental data can be appropriately described by the Yoon–Nelson kinetic model.