Optimal Surface Amino-Functionalization Following Thermo-Alkaline Treatment of Nanostructured Silica Adsorbents for Enhanced CO(2) Adsorption

Special preparation of Santa Barbara Amorphous (SBA)-15, mesoporous silica with highly hexagonal ordered, these materials have been carried out for creating adsorbents exhibiting an enhanced and partially selective adsorption toward CO(2). This creation starts from an adequate conditioning of the silica surface, via a thermo-alkaline treatment to increase the population of silanol species on it. CO(2) adsorption is only reasonably achieved when the SiO(2) surface becomes aminated after put in contact with a solution of an amino alkoxide compound in the right solvent. Unfunctionalized and amine-functionalized substrates were characterized through X-ray diffraction, N(2) sorption, Raman spectroscopy, electron microscopy, (29)Si solid-state Nuclear Magnetic Resonance (NMR), and NH(3) thermal programmed desorption. These analyses proved that the thermo-alkaline procedure desilicates the substrate and eliminates the micropores (without affecting the SBA-15 capillaries), present in the original solid. NMR analysis confirms that the hydroxylated solid anchors more amino functionalizing molecules than the unhydroxylated material. The SBA-15 sample subjected to hydroxylation and amino-functionalization displays a high enthalpy of interaction, a reason why this solid is suitable for a strong deposition of CO(2) but with the possibility of observing a low-pressure hysteresis phenomenon. Contrastingly, CH(4) adsorption on amino-functionalized, hydroxylated SBA-15 substrates becomes almost five times lower than the CO(2) one, thus giving proof of their selectivity toward CO(2). Although the amount of retained CO(2) is not yet similar to or higher than those determined in other investigations, the methodology herein described is still susceptible to optimization.