CO₂ Adsorption on the N- and P-Modified Mesoporous Silicas

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 CO₂ was measured in a dynamic CO₂ adsorption regime. The modified silicas displayed an enhanced adsorption capacity compared to the initial material. The ¹³C NMR spectra with high-power proton decoupling proved the presence of physically captured CO₂. A value of 4.60 mmol/g was achieved for the MCM-48 material grafted with the Schiff base residues. The total CO₂ desorption was achieved at 40 °C. A slight decrease of about 5% in CO₂ adsorption capacities was registered for the modified silicas in three adsorption/desorption cycles, indicating their performance stability.