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SBA-15 and MCM-48 mesoporous silicas were modified with functionalized (3-aminopropyl)triethoxysilane (APTES) by using the post-synthesis method, thus introducing N- and P-containing groups to the pore surface. The structure of the newly synthesized modifiers (aldimine and aminophosphonate derivatives of (3-aminopropyl)triethoxysilane and their grafting onto the porous matrix were proved by applying multinuclear NMR and FTIR spectroscopies. The content of the grafted functional groups was determined via thermogravimetric analysis. The physicochemical properties of the adsorbent samples were studied by nitrogen physisorption and UV-Vis spectroscopy. The adsorption capacity of CO 2 was measured in a dynamic CO 2 adsorption regime. The modified silicas displayed an enhanced adsorption capacity compared to the initial material. The 13 C NMR spectra with high-power proton decoupling proved the presence of physically captured CO 2 . A value of 4.60 mmol/g was achieved for the MCM-48 material grafted with the Schiff base residues. The total CO 2 desorption was achieved at 40 °C. A slight decrease of about 5% in CO 2 adsorption capacities was registered for the modified silicas in three adsorption/desorption cycles, indicating their performance stability.

The post-synthesis procedure for cyclic amine (morpholine and 1-methylpiperazine) modified mesoporous MCM-48 and SBA-15 silicas was developed. The procedure for preparation of the modified mesoporous materials does not affect the structural characteristics of the initial mesoporous silicas strongly. The initial and modified materials were characterized by XRD, N 2 physisorption, thermal analysis, and solid-state NMR. The CO 2 adsorption of the obtained materials was tested under dynamic and equilibrium conditions. The NMR data revealed the formation of different CO 2 adsorbed forms. The materials exhibited high CO 2 absorption capacity lying above the benchmark value of 2 mmol/g and stretching out to the outstanding 4.4 mmol/g in the case of 1-methylpiperazin modified MCM-48. The materials are reusable, and their CO 2 adsorption capacities are slightly lower in three adsorption/desorption cycles.