Studies of biosilicas; structural aspects, chemical principles, model studies and the future.

Abstract

Silica and silicates are extensively used in industry and medicine. The materials find use in paints, foods, medicines, adhesives, detergents, chromatography materials, catalysts and photonic materials (reviewed by Iler 1979). Silica may be produced at high temperature, via aqueous processing or by largely non-aqueous routes such as the low-temperature sol-gel process (reviewed in Brinker and Scherrer 1990; Hench and West 1990).Whatever the eventual use of the silica, it is its structure that determines its properties. By structure we mean order and organization on length scales from angstroms to the size of the final object, morphology, surface area, porosity and surface functionality. The essential building block is the SiO4 tetrahedron although other structural units such as the SiO6 octahedron are also used. These units can be put together in a wide range of patterns to yield both porous and non-porous crystalline materials including silica-based zeolite materials. As well as crystalline silica and silicates, an extremely diverse range of amorphous materials exist, such as disordered precipitates, gels, glasses and shaped objects (spheres, screws,hollow tubes etc.; Stöer et al. 1968; Yang et al. 1997; Miyaki et al. 1999), produced under a wide range of synthesis conditions. The amorphous materials, in contrast to their crystalline analogues, exhibit no long-range order and are built up from SiO4 tetrahedra with variable Si¡ªO¡ªSi bond angles and Si¡ªO bond distances.KeywordsSilicic AcidSilicon AtomBiogenic SilicaChemical PrincipleOrthosilicic AcidThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.