  An environmentally benign method capable of producing large quantities of
materials was used to synthesize tungstite (WO3.H2O) leaf-shaped nanoplatelets
(LNPs) and nanoribbons (NRs). These materials were simply obtained by aging of
colloidal solutions prepared by adding hydrochloric acid (HCl) to dilute sodium
tungstate solutions (Na2WO4.2H2O) at a temperature of 5-10oC. The aging medium
and the pH of the precursor solutions were also investigated. Crystallization
and growth occurred by Ostwald ripening during the aging of the colloidal
solutions at ambient temperature for 24 to 48hrs. When dispersed in water, the
LNPs and NRs take many days to settle, which is a clear advantage for some
applications (e.g., photocatalysis). The materials were characterized using
scanning and transmission electron microscopy, Raman and UV/Vis spectroscopies.
The current versus voltage characteristics of the tungstite NRs showed that the
material behaved as a Schottky diode with a breakdown electric field of
3.0x105V.m-1. They can also be heat treated at relatively low temperatures
(300oC) to form tungsten oxide (WO3) NRs and be used as photoanodes for
photoelectrochemical water splitting.
