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

A facile aqueous approach to the synthesis of metastable hexagonal tungsten oxide (h‐WO3) hierarchical nanostructures at low temperature was investigated. The spherelike h‐WO3 architectures are constructed from 1D nanorods. Polyvinyl pyrrolidone (PVP) in the reaction system facilitates the quick formation of h‐WO3 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 WO3 crystallites. Oriented growth of WO3 crystallites along the [001] direction resulted in the nanorod‐assembled h‐WO3 architectures. The h‐WO3‐rich samples all exhibited good recycled visible‐light photochromic performance. Metastable hexagonal tungsten oxide (h‐WO3) hierarchical nanostructures are prepared at low temperature. Growth of WO3 crystallites along the [001] direction results in the nanorod‐assembled h‐WO3 architectures. The h‐WO3‐rich samples all exhibit good recycled visible‐light photochromic performance.