Chromism of Bi2WO6 in single crystal and nanosheet forms

Nanosheets of Bi2WO6 with lateral dimensions of 1-2 mu m 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 similar to 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.