Enhanced photocatalytic performance of tungsten oxide through tuning exposed facets and introducing oxygen vacancies

It is known that the exposed facet and defect state are crucial to the photocatalytic performance. Here, we report that the exposed facets of the building blocks in the tungsten oxide hierarchical nanostructures could be controlled by adjusting the amount of formamide in the hydrothermal precursor solution and the oxygen vacancies were successfully introduced through the post-air annealing. It is found that exposing high percentage (020) facet is unbeneficial for the photocatalytic performance and (200) and (002) facets should be the photocatalytic active facets of the hexagonal tungsten oxide. The hexagonal tungsten oxide with oxygen vacancies and maximum (200) and (002) facets archives highest photocatalytic performance in degrading rhodamine B under simulated solar light irradiation, which the rate constant per specific surface area (k/SBET) is 7.3 times as high as the sample without oxygen vacancies and minimum (200) and (002) facets. Both introducing oxygen vacancies and exposing (200) and (002) facets can enhance the separation efficiency of photo-generated charges, thus improving the photocatalytic performance.