Mechanism of Metal Oxide Nanoparticle Loading in SBA-15 by the Double Solvent Technique

The interaction between SBA-15 mesoporous silica, alkane solvents, and water has been studied to understand the mechanism of the so-called double solvent technique. This method facilitates the loading of the pores of SBA-15 with a metal oxide precursor solution, by prewetting the SBA-15 with an alkane. In a previous study on cobalt oxide, it has been observed that differences in particle size, shape, and dispersion were obtained as a function of the solvent used (n-pentane, n-hexane, n-heptane, and cyclohexane). In order to understand this phenomenon and to explain the differences between the effects that the alkane solvents exert, a combined FT-IR spectroscopy, solid state NMR spectroscopy, and microcalorimetry study has been carried out. Though subtle, interactions between alkanes and the silica surface are different, indicating a more pronounced modification of the surface, i.e., rehydroxylation, in the presence of pentane. It is suggested that this leads to a better wettability and therefore increases the introduction of aqueous solutions into the pores. Moreover, the lower vapor pressure of this component, its lower interaction energy with the surface, and its lower interfacial tension toward water enhance the dispersion of the metal oxide precursor inside the pore network.