One-Step Controllable Synthesis of Silica Nanotubes and Hollow Spheres

A simple and facile sol-gel method was used to fabricate novel uniform silica nanotubes and hollow spheres controllably in the same reaction system. The different reaction conditions were investigated, such as reaction time, addition and stirring rate of tetraethyl orthosilicate (TEOS) and the ratio of water and ethanol, which had important influence on the formation of the silica nanotubes with uniform morphologies. The formation process investigation of silica nanotubes discloses that ammonium citrate (AC) crystals have the thin pillar-like morphologies in the mixed solution including ethanol and water, which acts as an important template for the gradual aggradation of silica colloids on their surface to form the tubular structure. The silica hollow spheres have the similar formation mechanism to that of silica nanotubes with a little difference of using citric acid (CA) as a starting structure-directing agent.