Center for Nanoparticle Research , Institute for Basic Science (IBS) , Seoul 08826 , Republic of Korea.
School of Chemical and Biological Engineering, and Institute of Chemical Process , Seoul National University , Seoul 08826 , Republic of Korea.
J Am Chem Soc. 2019 May 1;141(17):7037-7045. doi: 10.1021/jacs.9b01670. Epub 2019 Apr 18.
The formation of inorganic nanoparticles has been understood based on the classical crystallization theory described by a burst of nucleation, where surface energy is known to play a critical role, and a diffusion-controlled growth process. However, this nucleation and growth model may not be universally applicable to the entire nanoparticle systems because different precursors and surface ligands are used during their synthesis. Their intrinsic chemical reactivity can lead to a formation pathway that deviates from a classical nucleation and growth model. The formation of metal oxide nanoparticles is one such case because of several distinct chemical aspects during their synthesis. Typical carboxylate surface ligands, which are often employed in the synthesis of oxide nanoparticles, tend to continuously remain on the surface of the nanoparticles throughout the growth process. They can also act as an oxygen source during the growth of metal oxide nanoparticles. Carboxylates are prone to chemical reactions with different chemical species in the synthesis such as alcohol or amine. Such reactions can frequently leave reactive hydroxyl groups on the surface. Herein, we track the entire growth process of iron oxide nanoparticles synthesized from conventional iron precursors, iron-oleate complexes, with strongly chelating carboxylate moieties. Mass spectrometry studies reveal that the iron-oleate precursor is a cluster comprising a tri-iron-oxo core and carboxylate ligands rather than a mononuclear complex. A combinatorial analysis shows that the entire growth, regulated by organic reactions of chelating ligands, is continuous without a discrete nucleation step.
基于经典的成核理论，我们已经了解了无机纳米粒子的形成过程，其中表面能起着至关重要的作用，同时还伴随着扩散控制的生长过程。然而，这种成核和生长模型可能并不适用于所有的纳米粒子体系，因为在合成过程中使用了不同的前体和表面配体。它们的内在化学反应性可能导致形成途径偏离经典的成核和生长模型。金属氧化物纳米粒子的形成就是一个这样的例子，因为在其合成过程中有几个明显的化学方面。在氧化物纳米粒子的合成中，通常使用的典型羧酸盐表面配体往往在整个生长过程中都留在纳米粒子的表面上。它们也可以作为金属氧化物纳米粒子生长过程中的氧源。羧酸盐容易与合成过程中不同的化学物质发生化学反应，如醇或胺。这种反应通常会在表面上留下反应性的羟基。在此，我们跟踪了由传统铁前体和具有强螯合羧基的铁油酸配合物合成的氧化铁纳米粒子的整个生长过程。质谱研究表明，铁油酸前体是一个包含三铁-氧核和羧基配体的团簇，而不是单核配合物。组合分析表明，整个生长过程是由螯合配体的有机反应调控的，是连续的，没有离散的成核步骤。
