Visible-Light-Responsive Photoreversible Color Switching of Oxygen-Deficient WO_3–x Hierarchical Nanostructures for Long-Legible Rewritable Paper

Abstract

The development of visible-light-responsive inorganic photoreversible color switching materials (PCSMs) for constructing long-legible rewritable papers is fascinating owing to resource sustainability. This work reports the colloidal synthesis of WO 3−x hierarchical nanostructures constructed by 2D thin nanostructures with crystalline/amorphous homojunctions that show excellent visible-lightresponsive color switching properties. The surface-bound hydroxyl ligands, oxygen vacancies, and homojunctions could enhance absorption in the visible region, improve charge separation and transfer efficiencies, and act as internal sacrificial electron donors for scavenging photogenerated holes, endowing WO 3−x hierarchical nanostructures with high visible-light-responsive photoreductive activity. The protons localized in WO 3−x hierarchical nanostructures promote photoreduction for the coloration process and stabilize metastable W 5+ species for the discoloration process, enabling rapid coloration in 30 s upon 437 nm light illumination and excellent color stability under ambient air conditions (∼51 days). A light-printable rewritable paper (LPRP) fabricated by the WO 3−x hierarchical nanostructures exhibits a grayish white background, high reusability (>100 times), long legible time (>30 days), negligible interference by office light, and high color contrast. Moreover, the LPRP can be used for direct visible-light-responsive laser printing, which is fully compatible with current printing technology. This work opens an avenue for designing visible-light-responsive inorganic PCSMs for LPRP and utilizing visible light for practical applications.