Preparation of novel hollow fiber silica using an organic gel as a template

A novel hollow fiber silica was created by the use of the fibrous structures of an organic gel as a template. Its inner diameter ranged from 10 to 200 nm and the outer diameter ranged from 50 to 300 nm. A dichloromethane solution of an organic gelator was mixed with the silicate solution, TEOS/water/catalyst (acetic acid or benzylamine)/solvent (acetic acid or alcohol), which was gelated by the organic gelator. Subsequently, the resultant solution was evaporated in vacuo until the dichloromethane was removed to give a turbid gel. The SEM images of the product showed well-grown fibrous structures. After calcination, it was clearly found by TEM images that these fibers have a tubular structure. The most favorable gelator to form hollow fiber silica is one that has a cationic charge within the molecule, for example, a quaternary ammonium halide salt or a crown ether including a metal cation. In this study, the gel-forming segment of the gelator was a cholesterol derivative. Since the propagation species of silicate in the solution of acetic acid or benzylamine are considered to be anionic, the electrostatic interactions may be important for adsorption of silica onto the template fibers.