title: Exfoliated nanosheet crystallite of cesium tungstate with 2D pyrochlore structure: synthesis, characterization, and photochromic properties.
abstract: Layered cesium tungstate, Cs(6+x)W(11)O(36), with two-dimensional (2D) pyrochlore structure was exfoliated into colloidal unilamellar sheets through a soft-chemical process. Interlayer Cs ions were replaced with protons by acid exchange, and quaternary ammonium ions were subsequently intercalated under optimized conditions. X-ray diffraction (XRD) measurements on gluelike sediment recovered from the colloidal suspension by centrifugation showed a broad pattern of a pronounced wavy profile, which closely matched the square of calculated structure factor for the single host layer. This indicates the total delamination of the layered tungstate into nanosheets of Cs(4)W(11)O(36)(2-). Microscopic observations by transmission electron microscopy and atomic force microscopy clearly revealed the formation of unilamellar crystallites with a very high 2D anisotropy, a thickness of only approximately 2 nm versus lateral size up to several micrometers. In-plane XRD analysis confirmed that the 2D pyrochlore structure was retained. The colloidal cesium tungstate nanosheet showed strong absorption of UV light with sharp onset, suggesting a semiconducting nature. Analysis of the absorption profile provided 3.6 eV as indirect band gap energy, which is 0.8 eV larger than that of the bulk layered precursor, probably due to size quantization. The nanosheet exhibited highly efficient photochromic properties, showing reversible color change upon UV irradiation.
authors.affiliation: International Center for Materials Nanoarchitectonics and Nanoscale Materials Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Fukuda
authors.forename: Kosho
authors.initials: K
authors.lastname: Akatsuka
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ebina
authors.forename: Renzhi
authors.initials: R
authors.lastname: Ma
authors.forename: Kazunori
authors.initials: K
authors.lastname: Takada
authors.forename: Izumi
authors.initials: I
authors.lastname: Nakai
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Sasaki
mesh_terms: D002586:Cesium / Q000737:chemistry* / Q000528:radiation effects; D003116:Color; D003460:Crystallization / Q000379:methods*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008567:Membranes, Artificial; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000528:radiation effects / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods; D009556:Niobium / Q000737:chemistry* / Q000528:radiation effects; D010316:Particle Size; D010777:Photochemistry / Q000379:methods*; D012666:Semiconductors; D013499:Surface Properties; D017973:Tungsten Compounds / Q000737:chemistry* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D046911:Macromolecular Substances; D008567:Membranes, Artificial; D017973:Tungsten Compounds; D009556:Niobium; C016709:pyrochlore; D002586:Cesium