Synthesis of uniform WO3 square nanoplates via an organic acid-assisted hydrothermal process

Two kinds of tungsten oxide (WO3) square nanoplates have been prepared by a simple hydrothermal method using l(+)-tartaric acid or citric acid as assistant agents. The products are characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). XRD, SEM and TEM images of the products illustrate that WO3 square nanostructures prepared in the presence of l(+)-tartaric acid have a hexagonal phase, length of ∼ 200 nm and thickness of ∼ 100 nm, while WO3 nanostructures synthesized in the presence of citric acid have an orthorhombic phase, length of ∼ 500 nm and thickness of ∼ 100 nm. Selected area electron diffraction (SAED) suggests that both of the as-prepared WO3 square nanoplates are single crystalline. The plausible growth mechanism for the formation of WO3 square nanostructures is also proposed.