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 center dot H2O) leaf-shaped nanoplatelets (LNPs) and nanoribbons (NRs). These materials were simply obtained by the aging of colloidal solutions prepared by adding hydrochloric acid (HCl) to dilute sodium tungstate solutions (Na2WO4 center dot 2H(2)0) at a temperature of 5-10 degrees C. 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 24-48 h. 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 ultraviolet/visible spectroscopies. The current vs. voltage characteristics of the tungstite NRs showed that the material behaved as a Schottky diode with a breakdown electric field of 3.0 x 10(5) V m(-1). They can also be heat-treated at relatively low temperatures (300 degrees C) to form tungsten oxide (WO3) NRs and can be used as photoanodes for photoelectrochemical water splitting. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.