Article pubs.acs.org/cm
Anisotropic Shaped Iron Oxide Nanostructures: Controlled Synthesis and Proton Relaxation Shortening Effects Zijian Zhou, Xianglong Zhu, Dongjun Wu, Qiaoli Chen, Dengtong Huang, Chengjie Sun, Jingyu Xin, Kaiyuan Ni, and Jinhao Gao* State Key Laboratory of Physical Chemistry of Solid Surfaces, The Key Laboratory for Chemical Biology of Fujian Province, and Department of Chemical Biology, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China S Supporting Information *
ABSTRACT: Controlled synthesis of monodisperse iron oxide (IO) nanostructures with diverse morphology remains a major challenge. In this work, IO nanostructures with various shapes and surface structures were synthesized by thermal decomposition of iron oleate (FeOL) in the presence of sodium oleate (NaOL). In a mild condition using 1octadecene (ODE) as solvent, NaOL may preferentially bind to Fe3O4{111} facets and lead to the formation of Fe3O4{111} facet exposed IO plates, truncated octahedrons, and tetrahedrons. While in a high-boiling temperature tri-noctylamine (TOA) solvent, we obtained Fe3O4{100} facet exposed IO cubes, concaves, multibranches, and assembled structures by varying the molar ratios of NaOL/FeOL. Moreover, we demonstrated that IO nanoparticles (NPs) with metalexposed surface structures have enhanced T1 relaxation time shortening effects to protons, and IO NPs with anisotropic shapes are superior in protons T2 relaxation shortening due to the larger effective radii compared to that of spherical IO NPs. This study can provide rational design considerations for the syntheses and applications of IO nanostructures for a broad community of material research fields.
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INTRODUCTION Over the past decades, magnetic nanomaterials have attracted tremendous interests in magnetic storage, biosensing, catalysis, and biomedical applications.1−5 Among various kinds of magnetic nanomaterials, superparamagnetic iron oxide nanoparticles (IO NPs, e.g., magnetite) are one of the most promising platforms owing to their excellent magnetic properties, ready availability, and environmental friendly merits.6 Synthesis of IO NPs with a monodispersed size (σ ≤ 5%) and shape is of scientific importance. For example, size determines either paramagnetism or superparamagnetism of IO NPs due to size-dependent spin exchange effect in magnetic NPs, while shape is related to switching property of IO NPs due to shape-induced magnetocrystalline anisotropy.7−10 In particular, it has been recently recognized that the irregular shape of IO NPs may govern their performance in T2-weighted magnetic resonance imaging (MRI) due to the influence on effective radii.11−13 Moreover, the unique shape can exhibit invaluable functions and be building-blocks in developing sophisticated superstructures and devices.14−17 Appreciable progress has been made in controlling the shape of noble metal (e.g., Au, Pd, Pt, and their alloys) NPs due to the relatively simplicity in processing the weak and nondirectional metallic bonding.18−22 However, it is still a persistent challenge to address metal oxides because of the strong metal−oxygen © 2015 American Chemical Society
covalent bonding and the diverse crystal packing structure of metal oxide compounds.23,24 For IO NPs with inverse spinel structure, controlling the shape at a nanometer range (e.g.,
