Nanostructured tungsten oxide as photochromic material for smart devices, energy conversion, and environmental remediation

The reversible photochromic response of tungsten oxide (WO 3 ) holds promise for solar-related applications as it is capable of photo charging during illumination (color-switching) and spontaneous discharging post-illumination (self-bleaching). Advances in WO 3 -based nanostructures synthesis via micro/nanofabrication techniques have created remarkable potential application opportunities. Smart windows represent a typical energy-saving technology; ultraviolet indicators can sense radiation safety limits, and the around-the-clock photocatalysts can be used for pollutant degradation and bacterial disinfection applications. These materials, their distinct properties, and the effects of their application must be comprehensively understood prior to commercialization. In this work, we first summarize the affiliation between the crystallographic properties-optical features-photochromic behavior of WO 3 . Several photochromic models and kinetic equations are then presented, accompanied by the related characterization techniques and evaluation methods. The factors affecting photochromic efficiency (e.g., light absorption, surface reaction, and carrier migration) are delineated to clarify the advantages of the specific nanostructured WO 3 and the most efficient available strategies for constructing WO 3 -based nanomaterials. The theory, technique, and performance associated with chromogenic applications in smart devices, energy conversion, and environmental remediation are deliberated in detail. Finally, we outline the challenges and emerging trends in this area calling for further innovation to fill various gaps. • Effects of WO 3 crystallographic and optical properties on color-switching features upon light irradiation are clarified. • Advances in photochromic mechanisms and the related spectroscopic techniques for analysis and evaluation are illustrated. • Typical features, synthesis, and modification strategies are summarized for nanosized WO 3 with specific dimensions. • Chromogenic applications available for creating smart devices and addressing energy and environmental crisis are outlined.