Synthesis and characterization of tungstite (WO3·H2O) nanoleaves and nanoribbons

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.