Phase selective preparations and surface modifications of spherical hollow nanomagnets
Phase selective preparations and surface modifications of spherical hollow nanomagnets
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DOI：
10.1039/b605472b
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发表时间：
2006-08
影响因子：
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通讯作者：
Mototaka Ohnishi;Y. Kozuka;Q. Ye;Hirofumi Yoshikawa;K. Awaga;Ryosuke Matsuno;M. Kobayashi;A. Takahara;T. Yokoyama;S. Bandow;S. Iijima
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文献类型：
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作者：
Mototaka Ohnishi;Y. Kozuka;Q. Ye;Hirofumi Yoshikawa;K. Awaga;Ryosuke Matsuno;M. Kobayashi;A. Takahara;T. Yokoyama;S. Bandow;S. Iijima
以聚苯乙烯(PS)微珠为模板，制备了直径约600 nm、壳厚40 nm的CCP-Co、Co_3O_4、α-Fe、Fe_3O_4和α-Fe_2O_3空心球。采用均匀沉淀法在600 nm的PS微珠表面均匀包覆氢氧化钴或氢氧化铁。这些钴-盐/PS杂化粒子在400℃的空气中焙烧，并转化为Co3O4空心球。Co3O4空心球是由Co3O4粒子在氢气和氮气的1：1混合气体中于400℃下还原得到的，而CCP-Co空心球是通过母体钴盐/PS粒子在氢气中于400℃下焙烧得到的。α-Fe_2O_3空心球是通过铁盐/PS粒子在400~500℃的两种不同气氛下分别在氢气-氮气和空气中焙烧得到的。此外，α-Fe_2O_3颗粒在350°C的H2-N_2气氛中被还原为α-Fe，其形貌没有发生任何变化。用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和X射线衍射仪(XRD)对其进行了表征。磁性测量表明，Fe3O4(磁铁矿)颗粒的矫顽场与温度有显著的关系，而其他颗粒的磁性与相应的块体样品的磁性基本相似。对Fe3O4空心球进行了表面化学修饰，表面接枝了聚(4-N-甲基乙烯基吡啶)刷子。这种处理方法在水中具有良好的分散性。
We carried out the phase selective preparations of hollow spheres of ccp- and hcp-Co, Co3O4, α-Fe, Fe3O4 and α-Fe2O3 with a diameter of ca. 600 nm and a shell thickness of 40 nm, using polystyrene (PS)-bead templates. The 600 nm PS beads were uniformly coated with cobalt or iron hydroxides by means of a homogeneous precipitation method. These cobalt-salt/PS hybrid particles were calcined in air at 400 °C and were transformed into Co3O4 hollow spheres. The hcp-Co hollow spheres were obtained by a reduction reaction of the Co3O4 particles under a stream of a 1 ∶ 1 mixed gas of H2 and N2 at 400 °C; in contrast, the ccp-Co hollow spheres were obtained by the calcination of the parent cobalt-salt/PS particles under H2–N2 at 400 °C. Hollow spheres of Fe3O4 and α-Fe2O3 were selectively prepared by calcination of iron-salt/PS particles at 400–500 °C in two different atmospheres, namely under H2–N2 and in air, respectively. Furthermore, the α-Fe2O3 particles were reduced into α-Fe under H2–N2 at 350 °C without any changes in morphology. These spheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses. Magnetic measurements revealed a significant temperature dependence of the coercive field for the Fe3O4 (magnetite) particles, whereas the magnetic properties of the other particles were generally similar to those of the corresponding bulk samples. Surface chemical modifications were carried out on the Fe3O4 hollow spheres; the surfaces were grafted with poly(4-N-methylvinylpyridinium) brushes. This treatment was found to induce good dispersibility in water.