Controllable Syntheses of Hierarchical WO3 Films Consisting of Orientation-Ordered Nanorod Bundles and Their Photocatalytic Properties

A series of hierarchical hexagonal WO3 (h-WO3) films consisting of orientation-ordered nanorod bundles paralleling the fluorine-doped tin oxide (FTO) glass substrate were synthesized through a hydrothermal reaction of Na2WO4 solution (pH 2.30). By varying the Na2WO4 concentration, the aspect ratios of the h-WO3 nanorods and the shapes of the orderly stacked nanorod bundles can be conveniently adjusted, which then influence the morphology of the resultant hierarchical h-WO3 films on the FTO substrate. With enhancing the Na2WO4 concentration, the nanorod bundles are changed from a flat shape into a fusiform one to form h-WO3 film with a relatively smaller porosity and smoother surface. Compared with the h-WO3 film with fusiform-shaped nanorod bundles, the h-WO3 film with flat-shaped ones exhibits better photocatalytic O2 generation activity as the direct consequences of its larger specific surface area, higher roughness, and better light absorption property.