Silylation of a crystalline silicic acid: an MAS NMR and porosity study

Abstract

Tailor-made adsorbents and supports are attracting increasing interest for a wide range of advanced applications in the field of separation techniques and biotechnology. Silica gel silylated with chlorosilanes or alkoxysilanes is a well-established material in chromatography, biotechnology, and affinity separation processes. The surface of the silica gels is disordered, and complete surface coverage with silanes is not always achieved. Crystalline silicic acids from layered potassium silicates, similar to the minerals kenyaite or magadiite, are microcrystalline and their surfaces show a higher degree of regularity. They were modified with different alkyl methoxysilanes to evaluate the possibility of surface silylation. Binding of the silane molecules on surface silanol groups of the crystalline silicic acids was investigated by 29Si MAS NMR spectroscopy. The total surface area was accessible to the silylating agents and almost all surface silanol groups reacted with these molecules. The derivatives contained micropores (between the layers and, possibly, within the layers) and mesopores.