Chromism of Bi2WO6 in single crystal and nanosheet forms

Abstract

Nanosheets of Bi₂WO₆ with lateral dimensions of 1–2 μm and thicknesses of 5–15 nm were prepared using Cs₄W₁₁O₃₆²⁻ nanosheets as the tungsten oxide precursor and lateral template. The formation of these nanosheets was followed by electron microscopy and powder X-ray diffraction techniques. The isolated Bi₂WO₆ nanosheet product was characterized with respect to structure, morphology, spectroscopic properties, and optical properties. The bandgap energy of Bi₂WO₆ nanosheets is relatively large at ∼3.1 eV. The chromism of these sheets with respect to UV irradiation and Li⁺ intercalation was examined in detail. The UV-induced photochromism of dispersed Bi₂WO₆ nanosheets is highly dependent on the solvent environment, and the initial color change from white to black is reversible. The photochromic properties of “flowerlike” and single crystal Bi₂WO₆ were evaluated as well. Another color change, pale yellow to brown-black, occurred when lithium ions were intercalated into the Bi₂WO₆ lattice using n-butyl lithium. Reaction of lithiated Bi₂WO₆ with water yielded nanofragments of Bi₂WO₆ rather than nanosheets.