Influence of functionalization method on isomorphic substitution and formation of extra-framework oxides in silica for water vapor adsorption

Water vapor adsorption is a process of great importance for several industries. Because of that, new materials formed by mesoporous silica with metallic heteroatom functionalization have been studied for water adsorption. This functionalization process is still little studied in the literature, with many topics remaining to be evaluated. One of them is how each functionalization method (grafting and co-condensation) influences the generation of isomorphic substitution or extra-framework oxides. Another is which of these configurations is most interesting for water adsorption. This work aims to address both questions. For this, two groups of samples were synthesized using grafting and co-condensation for the insertion of Al, Ti, Zr and Li into mesoporous silica SBA-15. These samples were analyzed using nitrogen adsorption, high resolution scanning microscopy, energy dispersive X-ray spectroscopy, magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, pyridine adsorption and water adsorption. These techniques revealed that the co-condensation approach used in this work was most interesting for water adsorption at low partial pressures. This occurred because it generated a higher degree of isomorphic substitution, which was found to be the most active configuration of heteroatoms for this application.