Lv Baoliang, Xu Yao, Gao Qiang, Wu Dong, Sun Yuhan
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China.
J Nanosci Nanotechnol. 2010 Apr;10(4):2348-59. doi: 10.1166/jnn.2010.2161.
Hematite (alpha-Fe2O3) nanorings were prepared via a facile hydrothermal route without using any template. The products were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). On the basis of these characterizations and condition experiments, an "oriented dissolution and recrystallization" mechanism under the effect of H2PO4- ions was proposed to explain the formation process of nanoring structure. Magnetite (Fe3O4) nanorings were obtained by reducing alpha-Fe2O3 nanorings, and then maghemite (gamma-Fe2O3) nanorings were obtained by reoxidizing Fe3O4 nanorings. The magnetic properties of these nanorings were investigated, and it was found that these nanorings have higher coercivity and lower saturation magnetization than many other nanostructures of iron oxides. The adsorbed phosphate on the surface and the nanoring morphology might be responsible for this phenomenon. Furthermore, it is interesting to find that the coercivity of the nanorings increased with the increase of d(in)/d(out) (d(in) and d(out) are the inner and outer diameters of the rings, respectively), and a rapid increase was observed at the value of d(in)/d(out) around 0.5.
通过简便的水热法制备了赤铁矿（α-Fe₂O₃）纳米环，且未使用任何模板。通过X射线粉末衍射（XRD）、X射线光电子能谱（XPS）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）对产物进行了表征。基于这些表征和条件实验，提出了在H₂PO₄⁻离子作用下的“定向溶解和重结晶”机制来解释纳米环结构的形成过程。通过还原α-Fe₂O₃纳米环获得磁铁矿（Fe₃O₄）纳米环，然后通过再氧化Fe₃O₄纳米环获得磁赤铁矿（γ-Fe₂O₃）纳米环。研究了这些纳米环的磁性，发现这些纳米环比许多其他铁氧化物纳米结构具有更高的矫顽力和更低的饱和磁化强度。表面吸附的磷酸盐和纳米环形态可能是造成这种现象的原因。此外，有趣的是发现纳米环的矫顽力随着d(in)/d(out)（d(in)和d(out)分别是环的内径和外径）的增加而增加，并且在d(in)/d(out)约为0.5时观察到快速增加。
