Structural and Surface Properties of Modified Sorbents Based on Mineral Raw Materials

We have demonstrated the feasibility of preparing xerogels with a large specific surface area and mesoporous structure from natural aluminosilicate raw materials. Their surface has been modified with organic radicals derived from fatty acids: stearic and oleic (18:0 and 18:1n-9cis, respectively). IR spectra of the synthesized xerogels contain characteristic peaks of silica and, after modification, those of organic molecules adsorbed on the xerogel surface. Analogous investigation has been carried out for silica aerogel. We have studied structural and surface properties of the xerogels and compared them to those of the aerogel. The results demonstrate that the specific surface area of all the materials studied is below 500 m²/g, but the aerogel has a larger pore diameter and its pore diameter distribution is shifted toward macroscopic pores, whereas a mesoporous structure prevails in the xerogels prepared from nepheline. In addition, the steric factor for the surface modifiers has been shown to play an important role in adsorption on the materials we obtained. In particular, the specific surface area of the sorbent prepared via surface modification of 18:1n-9cis is 30% smaller than that of the parent xerogel, and the one of the surface-modified 18:0 is 14% smaller, which suggests that, in the former case, the access to pores is spatially blocked for the adsorbate gas in larger measure.