Hierarchical Titanate Nanostructures through Hydrothermal Treatment of Commercial Titania Powders

Hierarchical titanate nanostructures were hydrothermally synthesized in concentrated base solutions using commercial titania powders as starting materials. By varying the base concentration, nanowire arrays, flowers of nanosheets and nanotubes, and urchin-like nanostructures of nanowires and nanotubes were sequentially fabricated. If the NaOH concentration was higher than 6 M, hydrated Na2Ti6O13 nanowire arrays, with nanowire diameters of 20-90 nm and art aspect ratio of 1100-5000, were produced at suitable reaction temperatures over a large area. In 10 M KOH solutions, aligned nanowires with a diameter of 30 nm and a length of 80 mu m formed. In 4 M NaOH Solutions, micrometer-sized flowers of nanotubes and nanosheets formed. Reactions in 2 M NaOH solutions produced urchin-like materials with a size of ca. 10 mu m that were composed of nanotubes and nanowires. The adsorption behaviour of the urchin-like materials resembled macroporous materials with micropores. Since both base concentration and reaction temperature affected the reaction rate, the formation of various titanate nanostructures was proposed its it growth speed controlled process.