Facile synthesis of WO3•H2O square nanoplates via a mild aging of ion-exchanged precursor

A facile method to synthesize WO3·H2O square nanoplates via a mild aging (50°C) of ion-exchanged precursor was developed. The ion-exchanged precursor was prepared by passing the sodium tungstate solution (Na2WO4) through a protonated cation-exchange resin, and used as impurity-free acidified solution (H2WO4) for synthesizing WO3·H2O nanoplates. No shape-directing additive was employed. It was observed that the yellow particles were precipitated under aging at 50°C. After aging for 8 h, the precipitated particles were characterized as the WO3·H2O nanoplates, and their morphological evolution to square platelet proceeded with an increase of aging time. After aging for 24 h, the WO3·H2O square nanoplates were predominantly synthesized. The square nanoplates consisted of a few or several stacked thin layers (thickness, ~10 nm/layer), and provided the well-defined {010} facet for two dominantly exposed surfaces and {101} side facets. Their lateral dimension reached several hundreds of nanometers. It is thus demonstrated that the mild aging (50°C) of the ion-exchanged precursor is a simple and impurity-free synthetic route for WO3·H2O square nanoplates. In addition, the monoclinic WO3 nanoplates were successfully obtained by dehydration-induced topochemical transformation of the WO3·H2O nanoplates