Synthesis and visible-light photochromism of a new composite based on magadiite containing polytungstate

Abstract

A new photochromic composite based on magadiite containing polytungstate has been synthesized by an exfoliation/self-assembly process. The composition, nature of polytungstate, photochromism, reversibility (irradiation–bleaching), and photochromic mechanism have been investigated by X-ray diffraction (XRD), an X-ray photoelectron spectrometer (XPS), a Scanning Electron Microscope equipped with Energy Dispersive X-ray (SEM-EDX), thermogravimetry (TG), Raman spectroscopy, a UV-vis spectrum, and Transmission Electron Microscopy (TEM). Results revealed the composite based on the H₂W₁₂O₄₀⁶⁻ species incorporated into the layered magadiite. Upon the irradiation of visible light (420–630 nm), the composite can change colour from pale yellow to blue. The color change can be reversed upon exposure to thermal bleaching. Moreover, the visible-light illumination and thermal bleaching can be repeated in excess of 20 times. The mechanism of photochromism has been studied, and the reversibility is attributed to the hydration property of the host magadiite.