Hollow spheres to nanocups: tuning the morphology and magnetic properties of single-crystalline alpha-Fe2O3 nanostructures.
Hollow spheres to nanocups: tuning the morphology and magnetic properties of single-crystalline alpha-Fe2O3 nanostructures.
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DOI：
10.1002/anie.200802626
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发表时间：
2008-09
影响因子：
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通讯作者：
D. Jagadeesan;Uzma Mansoori;P. Mandal;A. Sundaresan;M. Eswaramoorthy
中科院分区：
文献类型：
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作者：
D. Jagadeesan;Uzma Mansoori;P. Mandal;A. Sundaresan;M. Eswaramoorthy
处理和操纵极少量试剂的未来技术肯定会对化学和生物研究产生巨大影响。它有望在酶动力学研究、[1] 免疫测定、[2] PCR 分析、[3] 以及分析物含量极低或对环境具有高毒性的所有其他领域得到应用。因此，合成具有纳米或泽升体积的容器已成为开发此类技术的重要步骤。介孔材料[4]中空胶囊[5]和纳米管[6]也被认为可以达到预期目的，但大量合成更复杂的形态（例如碗/杯子）非常具有挑战性。近年来人们在获得微米碗和纳米碗方面进行了一些尝试。[7-10] Xia等人的报告[11] Gracias 等人关于可控孔聚合物空心颗粒合成的研究[12]在获得自折叠金属亚微米容器方面值得注意。我们的研究小组最近报道了温度诱导形成 ZnO zeptoliter 碗。 [13]获得金属氧化物纳米杯的传统方法是基于将金属前体沉积在自组装单层胶体球上，然后将其去除。然而，用这种方法获得的杯子是多晶的或无定形的，并且产量仅限于球体的单层排列。因此，尚待寻求一种不限于胶体球单层组装的简单的自下而上的方法。在此，我们报告了一种新的化学策略，通过使用碳质球作为模板，将单晶 α-Fe2O3 的形貌从空心球调整为纳米杯。据我们所知，这是获得金属氧化物单晶纳米杯的第一种方法。有趣的是，我们的观察似乎与从此类球形模板中单独获得空心球的有据可查的方法相反。 [14]所获得的纳米结构还表现出与形状相关的磁性。在典型的过程中，将碳球悬浮在 Fe(NO3)3·9H2O 的乙醇溶液中，在 35 至 388℃ 下连续搅拌，直至获得触变凝胶（参见支持信息的 S1）。凝胶的形成与硝酸铁水解成羟基氧化铁聚合物有关。[15]发现在煅烧前获得触变凝胶对于获得空心球和纳米杯是必须的。在达到凝胶阶段之前对样品进行煅烧，形成多孔 α-Fe2O3 网络。将样品（胶凝时间为 12 小时，参见实验部分）在 4008℃ 下煅烧 5 小时获得的 α-Fe2O3 空心球的场发射扫描电子显微镜 (FESEM) 图像显示，尺寸变化范围为 100 至 400 nm（图 1 a），这比用作模板的碳球 (300-800 nm) 的尺寸要小得多。这种收缩可归因于金属氧化物的烧结和缩合。透射电子
Futuristic technology to handle and manipulate reagents in very low volumes would certainly have immense impact on chemical and biological research. It is expected to find applications in enzyme kinetics studies,[1] immunoassays,[2] PCR analysis,[3] and all other fields where the quantity of the analyte is either extremely low or highly toxic to the environment. The synthesis of containers with nano-or zeptoliter volume has therefore become a cardinal step in developing such a technology. Mesoporous materials,[4] hollow capsules,[5] and nanotubes [6] are also envisaged to serve the intended purpose, but the synthesis of more complex morphologies, such as a bowl/cup, in large quantities is very challenging. Some attempts have been made in recent times to obtain micro-and nanobowls.[7–10] The reports by Xia et al.[11] on the synthesis of polymer hollow particles with controllable holes and by Gracias et al.[12] on obtaining selffolding metal submicrometer containers are noteworthy. Our research group recently reported the temperature-induced formation of ZnO zeptoliter bowls.[13] The conventional approach to obtaining metal-oxide nanocups is based on the deposition of metal precursors on a self-assembled monolayer of colloidal spheres followed by their removal. However, the cups obtained in this method are polycrystalline or amorphous and the yield is limited to only the monolayer arrangement of spheres. Thus, a simple bottom-up approach, not restricted to monolayer assembly of colloidal spheres, is yet to be pursued. Herein, we report a new chemical strategy to tune the morphology of singlecrystalline α-Fe2O3 from hollow spheres to nanocups by using carbonaceous spheres as templates. To our knowledge, this is the first method to obtain single-crystalline nanocups of a metal oxide. Interestingly, our observation seems to be against the well-documented approach of obtaining hollow spheres alone from such spherical templates.[14] The obtained nanostructures also show shape-dependent magnetic properties.In a typical procedure, a suspension of carbon spheres in a solution of Fe (NO3) 3· 9 H2O in ethanol was stirred continuously at 35 to 388C until a thixotropic gel was obtained (see S1 of the Supporting Information). The formation of a gel is associated with the hydrolysis of ferric nitrate to iron oxohydroxide polymer.[15] Attaining the thixotropic gel before calcination was found to be mandatory to obtain hollow spheres and nanocups. Samples calcined before reaching the gel stage resulted in a porous α-Fe2O3 network. The field-emission scanning electron microscopy (FESEM) image of α-Fe2O3 hollow spheres obtained by calcining the sample (with a gelation time of 12 h—see the Experimental Section) at 4008C for 5 h shows a size variation from 100 to 400 nm (Figure 1 a), which is considerably smaller than the size of the carbon spheres (300–800 nm) used as the template. This shrinkage can be attributed to sintering and condensation of the metal oxide. The transmission electron