Exfoliated nanosheet crystallite of cesium tungstate with 2D pyrochlore structure: Synthesis, characterization, and photochromic properties
Exfoliated nanosheet crystallite of cesium tungstate with 2D pyrochlore structure: Synthesis, characterization, and photochromic properties
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DOI：
10.1021/nn800184w
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发表时间：
2008-08-01
期刊：
影响因子：
17.1
通讯作者：
Sasaki, Takayoshi
中科院分区：
文献类型：
--
作者：
Fukuda, Katsutoshi;Akatsuka, Kosho;Sasaki, Takayoshi
通过软化学过程将具有二维（2D）烧绿石结构的层状钨酸铯Cs6+xW11O36剥离成胶体单层片。通过酸交换，层间 Cs 离子被质子取代，随后在优化条件下插入季铵离子。通过离心从胶体悬浮液中回收的胶状沉积物的 X 射线衍射 (XRD) 测量结果显示出明显的波状轮廓的广泛图案，其与计算出的单个主体层的结构因子的平方密切匹配。这表明层状钨酸盐完全分层成 Cs4W11O362- 纳米片。透射电子显微镜和原子力显微镜的显微观察清楚地揭示了具有非常高的二维各向异性的单层微晶的形成，其厚度仅类似于 2 nm，而横向尺寸高达几微米。面内 XRD 分析证实保留了二维烧绿石结构。胶体钨酸铯纳米片表现出对紫外光的强烈吸收，且起始时间急剧，表明其具有半导体性质。吸收曲线的分析提供了 3.6 eV 的间接带隙能量，这比块状层状前驱体的能量大 0.8 eV，这可能是由于尺寸量子化所致。该纳米片表现出高效的光致变色特性，在紫外线照射下显示出可逆的颜色变化。
Layered cesium tungstate, Cs6+xW11O36, 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 Cs4W11O362-. 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 similar to 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.