Aqueous Synthesis and Visible‐Light Photochromism of Metastable h‐WO3 Hierarchical Nanostructures

Abstract A facile aqueous approach to the synthesis of metastable hexagonal tungsten oxide ( h ‐WO 3 ) hierarchical nanostructures at low temperature was investigated. The spherelike h ‐WO 3 architectures are constructed from 1D nanorods. Polyvinyl pyrrolidone (PVP) in the reaction system facilitates the quick formation of h ‐WO 3 nuclei of the metastable phase through electrostatic interactions between protonated PVP and tungstate anions, which is in accord with the rule of kinetics favoring the formation of the metastable form. PVP also acts as a soft template for the assembly of WO 3 crystallites. Oriented growth of WO 3 crystallites along the [001] direction resulted in the nanorod‐assembled h ‐WO 3 architectures. The h ‐WO 3 ‐rich samples all exhibited good recycled visible‐light photochromic performance.