Exposed facet and crystal phase tuning of hierarchical tungsten oxide nanostructures and their enhanced visible-light-driven photocatalytic performance

Hierarchical tungsten oxide nanostructures, controllably assembled with one-dimensional nanosized building blocks, which exhibit different exposed facets and crystal phases were synthesized via a facile hydrothermal reaction assisted by urea. Systematic and comprehensive investigations indicate that urea plays a significant role in tuning the exposed facets of the building blocks and controlling the crystal phase by effectively regulating the process of nucleation. By adjusting the amount of urea, a suitable crystal phase can be obtained and the exposed facets can be tuned to achieve the highest photocatalytic activity of tungsten oxide. It has been found that (020) is the active facet of orthorhombic WO3·0.33H2O but not of hexagonal WO3. The orthorhombic WO3·0.33H2O exposing the largest amount of (020) facets shows the highest photocatalytic activity for the degradation of rhodamine B under visible light illumination, which is 4.1 times as high as that of the sample exposing the least amount of (020) facets.