Morphology of silica derived from various ammonium carboxylate templates

Synthesis of silica from tetraethyl orthosilicate (TEOS) in the presence of various ammonium carboxylate crystal templates was attempted and the effect of these templates on the shape and size of silica was investigated. The carboxylic acids examined immediately precipitated the crystals of their ammonium salts from ethanol and/or water by ammonia addition. The shape, size, and stability of thus formed crystal templates were varied depending on kinds of carboxylic acids and affected the morphology of TEOS-derived silica products. When the crystal templates formed were needle-like and less soluble, silica deposited not on the end faces but on the side faces of the crystals to form tubes with channels corresponding to the shape and size of the templates. On the other hand, when the crystal templates formed were particle-like with a few micron long and liable to re-dissolve into the solution, silica deposited on the whole surfaces of the templates. In this case, the morphology that silica particles with round edge were connected like twig was observed. It was also found that the size and its distribution of the silica tubes are variable to a certain extent by the reaction conditions such as acid and TEOS concentrations.