Ionic liquids as dynamic templating agents for sol-gel silica systems: synergistic anion and cation effect on the silica structured growth

Abstract: This work presents a detailed investigation about the influence of a complementary set of imidazolium ionic liquids (IL: [C<inf>4</inf>MIm][BF<inf>4</inf>]-[C<inf>10</inf>MIm][BF<inf>4</inf>]-[C<inf>7</inf>O<inf>3</inf>MIm][BF<inf>4</inf>]-[C<inf>4</inf>MIm][NTf<inf>2</inf>]-[C<inf>10</inf>MIm][NTf<inf>2</inf>]-[C<inf>7</inf>O<inf>3</inf>MIm][NTf<inf>2</inf>]) in the preparation of hydrolytic sol-gel silica wet gels and xerogels, providing insights into their hierarchical structures, morphologies of primary particles and aggregation domains. The reported IL decreased dramatically the gelation time (up to ~500 times), evolving the systems to transparent or opalescent wet gels with distinct consistencies, or silica powders. Characterization of the obtained silica xerogels was performed by transmission and scanning electron microscopy, atomic force microscopy, X-ray diffraction, small-angle X-ray scattering and thermogravimetric analysis. In general, the IL allowed controlling the silica particle size, color, compactness, structures and morphology. The xerogels showed homogenous and ordered structures (spherical or triangular) of different sizes and with distinct microporosities, depending on the IL applied. These results highlight the key role of IL in the sol-gel silica synthesis with controlled properties, which can be further tuned for specific applications by changing small process parameters. Graphical Abstract: [Figure not available: see fulltext.]