Article pubs.acs.org/cm
Generic Synthetic Route to Monodisperse Sub-10 nm Lanthanide Oxide Nanodisks: A Modified Digestive Ripening Process Jinhoo Jeong, Nayon Kim, Myeong-Geun Kim, and Woong Kim* Department of Materials Science and Engineering, Korea University, Seoul 136-713, Republic of Korea S Supporting Information *
ABSTRACT: The development of generic methods to synthesize monodisperse nanomaterials is one of the most critical issues in the current research field of nanomaterial synthesis. In this work, we demonstrate for the first time that a digestive ripening process can produce monodisperse sub-10 nm lanthanide oxide nanodisks. Moreover, we show that nanodisks of nine different lanthanide oxides can be synthesized under the same reaction conditions. The successful synthesis is realized by employing a hot injection step to induce a single nucleation event and by introducing transition metal ions to delicately define the size and shape of the nanodisks in the digestive ripening process. Among the various nanodisks, Gd2O3, Dy2O3, and Ho2O3 nanodisks show promising magnetic properties as magnetic resonance imaging contrast agents. We expect that this novel synthetic route can be extended to various nanomaterials, including metallic and semiconducting nanocrystals.
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anisotropic shape.15−17 Accordingly, sub-10 nm monodisperse lanthanide oxide that has anisotropic shape such as nanodisks is highly desirable for MRI applications. However, their synthesis is still very challenging, and a generic method has not been achieved yet. There are three main categories of synthetic methods for monodisperse nanocrystals: hot injection, heat-up, and digestive ripening method. First, although the hot injection method has been widely used to synthesize nanocrystals of various semiconductors and metals, reports on the synthesis of oxide nanocrystals are relatively rare; especially, there has been no report on the synthesis of lanthanide oxide nanomaterials.18−20 This is perhaps because appropriate precursors working as oxygen sources for lanthanide oxides are not readily available. Second, there are several reports on the synthesis of lanthanide oxide nanocrystals by using the heat-up method. However, it is still challenging to precisely control the size, shape, and distribution of nanocrystals.21−23 This is because choosing right precursors with the proper reactivity for sub-10 nm nanoparticles with narrow size distributions is an intricate process; moreover, the experimental conditions of the heat-up method are usually very material specific.1,21,22,24 Finally, a digestive ripening method has produced uniform metals, metal alloys, and recently semiconductor nanoparticles.24−26 However, the successful synthesis of monodisperse oxide nanomaterials has not been demonstrated, and the mechanism of the digestive ripening process is not completely understood yet.24
INTRODUCTION The development of generic synthetic methods for highly monodisperse nanomaterials is a critical issue.1−4 In general, as the reaction conditions are very specific to a target nanomaterial, considerable time and effort are required to find an optimal set of experimental parameters for each target nanomaterial. Furthermore, small variations in the experimental conditions often lead to large differences in the size and shape of the nanomaterials. A generic method may simplify significantly the synthetic process and greatly improve the reproducibility of the products. On the other hand, the size, shape, and dispersity of nanomaterials largely determine various important properties such as the electronic, magnetic, and optical properties as well their chemical activities.4−6 Especially, small size (
