Single-crystal dendritic micro-pines of magnetic α-Fe2O3:: Large-scale synthesis, formation mechanism, and properties
Single-crystal dendritic micro-pines of magnetic α-Fe2O3:: Large-scale synthesis, formation mechanism, and properties
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DOI：
10.1002/anie.200500448
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Wang, ZL
中科院分区：
文献类型：
--
作者：
Cao, MH;Liu, TF;Wang, ZL
纳米级构件（纳米团簇、纳米线、纳米带和纳米管）的分层自组装是一种构建功能性电子和光子纳米器件的技术。[1, 2] 分形结构在自然界中的所有长度尺度上都很常见，从自组装分子到海岸线的形状，到星系的分布，甚至到 3D 云的形状。在纳米尺度上，树枝状分形是一种超支化结构，通常是在非平衡条件下通过分层自组装形成的。 [3, 4] 对化学系统中分层自组装分形图案的研究表明，此类结构独特的尺寸、形状和化学功能使其成为设计和制造新型功能纳米材料的有希望的候选者，[5] 开发简单而新颖的合成方法来构建各种系统的分层自组装分形结构具有挑战性。磁性纳米材料由于其物理特性和技术应用而受到越来越多的关注。[6-8]在过去几年中，研究主要集中在零维和一维（1D）磁性纳米材料，如磁性金属、合金和金属氧化物，并导致了 重大进展包括从球形纳米颗粒或纳米棒组装2D或3D超晶格。[9-14]然而，据我们所知，磁性纳米材料的分层自组装尚未见报道。在这里，我们展示了磁性 Fe2O3 树枝状纳米结构（所谓的微松结构）的自发、大规模、分层自组装。通过K3[Fe(CN)6]在水溶液中在适当温度下的水热反应合成了a-Fe2O3微米松枝晶。该方法基于[Fe (CN) 6] 3¿离子在水热条件下的弱离解。由此产生的结构显示出精致的分形特征，其形态类似于一种松树。该结构是沿六个晶体学等效方向快速生长而形成的，该过程与报道的一般分形结构的形成机制不同。该纳米结构的磁性显示出较低的桑色素转变温度（216 K）。所报道的结构在生物医学和磁性方面具有重要的应用。微型松树是大规模且高纯度合成的。图1显示了a-Fe2O3的典型SEM图像
Hierarchical self-assembly of nanoscale building blocks (nanoclusters, nanowires, nanobelts, and nanotubes) is a technique for building functional electronic and photonic nanodevices.[1, 2] Fractal structures are common in nature across all length scales, from self-assembled molecules, to the shapes of coastlines, to the distribution of galaxies, and even to the 3D shapes of clouds. On the nanoscale, dendritic fractals are one type of hyperbranched structure which are generally formed by hierarchical self-assembly under nonequilibrium conditions.[3, 4] Investigation of hierarchically selfassembled fractal patterns in chemical systems has shown that the distinct size, shape, and chemical functionality of such structures make them promising candidates for the design and fabrication of new functional nanomaterials,[5] but it is challenging to develop simple and novel synthetic approaches for building hierarchically self-assembled fractal architectures of various systems.Magnetic nanomaterials have been the subject of increasing interest due to their physical properties and technological applications.[6–8] In the past few years, research has focused primarily on zero-and one-dimensional (1D) magnetic nanomaterials such as magnetic metals, alloys, and metal oxides and has led to substantial advances including the assembly of 2D or 3D superlattices from spherical nanoparticles or nanorods.[9–14] However, to the best of our knowledge, the hierarchical self-assembly of magnetic nanomaterials has not been reported. Here we present the spontaneous, large-scale, hierarchical self-assembly of dendritic nanostructures of magnetic Fe2O3 (so-called micro-pine structure). The a-Fe2O3 micron-pine dendrites were synthesized by hydrothermal reaction of K3 [Fe (CN) 6] in aqueous solution at suitable temperatures. The method is based on the weak dissociation of [Fe (CN) 6] 3¿ ions under hydrothermal conditions. The resulting structures display exquisite fractal features, which morphologically resemble a type of pine tree. The structure was formed as a result of fast growth along six crystallographically equivalent directions, and this process is different from the reported formation mechanism of general fractal structures. The magnetic properties of the nanostructure show a lower Morin transition temperature of 216 K. The reported structures could have important applications in biomedical science and magnetism. The micro-pines were synthesized on a large scale and in high purity. Figure 1 shows typical SEM images of a-Fe2O3