Spontaneous formation of a tungsten trioxide sphere-in-shell superstructure by chemically induced self-transformation.-猫眼课题宝

DOI：

10.1002/smll.200700738

发表时间：

2008-01

期刊：

Small

影响因子：

13.3

通讯作者：

中科院分区：

材料科学1区

文献类型：

作者：

Jiaguo Yu;Huogen Yu;Hongtao Guo;Mei Li;S. Mann

基于碳、聚合物、金属和无机固体的中空纳米球和微球由于其在催化、控制输送、人工细胞、轻质填料、低介电常数材料、隔音和光子晶体等方面的潜在应用而受到广泛关注。[1]已经开发了各种制造程序，涉及模板，如乳液液滴，[2]喷雾干燥液滴，[3]聚合物/表面活性剂胶束，[4]和聚合物微球，[5]以及基于微分扩散（柯肯德尔效应）的化学过程，[6]奥斯特瓦尔德熟化，[7]或化学诱导的自转化。[8]尽管模板导向的化学方法已经很好地建立，但是构建具有复杂内部纹理的中空微球的能力通常是有限的，并且这可以在一定程度上通过使用经历局部转化的亚稳态固体微粒来规避，例如，经由无定形到结晶相转变，而没有总体形态学变化。[7，8]三氧化钨（WO 3）和水合氧化钨（WO 3·nH 2 O，n= 1/3，1或2）因其电致变色，[9]气体传感，[10]和催化性能而备受关注，其中许多取决于形态特征，如颗粒/孔径，形状和结构。在这里，我们演示了如何顺序的自转换过程中可以用来在一个单一的步骤中制备高产量的结晶WO 3· 1/3 H2O空心微球与无定形的内部核心，从封闭的结晶壳分离。壳层球型纳米微粒具有高度有序的多孔结构，并表现出显著的光催化活性。尽管最近已经描述了具有内部微粒的空心球，[12]但很少有关于使用一步工艺制造具有分离内核的空心无机球的报道。此外，以高产率生产这种结构的能力表明，这些材料可能具有广泛的技术兴趣。我们的方法基于在温和的水热条件下在pH= 0的含有硝酸锶、钨酸钠、聚（4-苯乙烯磺酸）钠（PSS）和HNO 3的溶液中发生的一系列颗粒自转化（详见方案1和实验部分）。在808 ℃下老化20 h后获得的产物由高收率的尺寸为2-15 μm的中空微球组成（图1a）。单个微球由厚度约为500 nm的完整球形壳组成，并包含从壳壁内表面分离的单个固体核（图1b）。壳壁的外表面是由长、宽约1.5 μ m的无规聚集的棒状颗粒组成。分别为80和350 nm，是广泛粗糙和多孔的（图1c）。相反，壳壁的内表面是光滑的。透射电子显微镜（TEM）图像证实，每个中空微球的内部核颗粒完全分离，并且在包封体积内自由移动（图1d）.单个空心微球壳碎片的电子衍射分析（图1d，插图）显示具有与三氧化钨水合物的WO 3· 1/3 H2O多晶型状态一致的d间距的多晶粉末图案（观察到的d间距和{hkl}值; 0.627（020），0.489（111），0.385（002），0.328（131），0.315（220），0.244

Hollow nanospheres and microspheres based on carbon, polymers, metals, and inorganic solids have received considerable attention recently because of their potential applications in catalysis, controlled delivery, artificial cells, lightweight fillers, low-dielectric-constant materials, acoustic insulation, and photonic crystals.[1] Various fabrication procedures have been developed that involve templates such as emulsion droplets,[2] spray-dried droplets,[3] polymer/surfactant micelles,[4] and polymer microspheres,[5] as well as chemical processes based on differential diffusion (Kirkendall effect),[6] Ostwald ripening,[7] or chemically induced self-transformation.[8] Although template-directed chemical approaches are well established, the ability to construct hollow microspheres with complex internal textures is often limited, and this can be circumvented to some extent by the use of metastable solid microparticles that undergo localized transformations, for example, via amorphous to crystalline phase transitions, without gross morphological changes.[7, 8] Tungsten trioxide (WO3) and hydrated tungsten oxide (WO3· nH2O, n= 1/3, 1, or 2) are of great interest because of their electrochromic,[9] gas sensing,[10] and catalytic properties,[11] many of which depend on morphological characteristics such as particle/pore size, shape, and structure. Here we demonstrate how a process of sequential self-transformation can be used to prepare in a single step high yields of crystalline WO3· 1/3H2O hollow microspheres with amorphous internal cores that are detached from the enclosing crystalline shell. The sphere-in-shell microparticles exhibit a hierarchically ordered porous superstructure and show significant photocatalytic activity. Although hollow spheres with internal microparticles have been recently described,[12] there are few reports concerning the fabrication of hollow inorganic spheres with detached internal cores using a single-step process. Moreover, the ability to produce such architectures in high yield suggests that these materials could be of wide-ranging technological interest. Our method is based on a series of particle self-transformations that occur under mild hydrothermal conditions in a solution containing strontium nitrate, sodium tungstate, sodium poly (4-styrenesulfonate)(PSS), and HNO3 at pH= 0 (see Scheme 1 and Experimental Section for details). The product obtained after aging at 808C for 20 h consisted of a high yield of hollow microspheres 2–15 μm in size (Figure1a). Individual microspheres consisted of an intact spheroidal shell that was approximately 500 nm in uniform thickness, and that enclosed a single solid core that was detached from the internal surface of the shell wall (Figure 1b). The external surface of the shell wall, which consisted of randomly aggregated rod-like particles with widths and lengths of ca. 80 and 350 nm, respectively, was extensively roughened and porous (Figure1c). In contrast, the inner surface of the shell wall was smooth. Transmission electron microscopy (TEM) images confirmed that the internal core particle of each hollow microsphere was completely detached and free to move within the encapsulated volume (Figure 1d).Electron-diffraction analysis of shell fragments from individual hollow microspheres (Figure1d, inset) showed polycrystalline powder patterns with d spacings consistent with the WO3· 1/3H2O polymorph state of tungsten trioxide hydrate (observed d spacings and {hkl} values; 0.627 (020), 0.489 (111), 0.385 (002), 0.328 (131), 0.315 (220), 0.244

Spontaneous formation of a tungsten trioxide sphere-in-shell superstructure by chemically induced self-transformation.

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