Growth Mechanism and Surface Chemical Characteristics of Dicarboxylic Acid-Modified CeO₂ Nanocrystals Produced in Supercritical Water: Tailor-Made Water-Soluble CeO₂ Nanocrystals

Abstract

Tailor-made surface-modified metal oxide nanocrystals enable various applications including medical, electronic, magnetic, and photovoltaic devices. Both the synthesis and application of surface-modified metal oxide nanocrystals rely on the interaction between organic molecules and the surface of metal oxides. From this viewpoint, we have focused on the synthesis of metal oxide nanocrystals using supercritical water in the presence of organic molecules as a surface modifier. Here, we describe the use of dicarboxylic acids with various chain lengths as the modifiers of CeO2 nanocrystals. The morphology and displayed crystallite plane of CeO2 nanocrystals could be controlled by the length of dicarboxylic acids. Long dicarboxylic acids produced cuboctahedral or cubic CeO2 nanocrystals, possibly because of the decreased growth rate of the {200} plane. The growth mechanism of the CeO2 nanocrystals is discussed in detail. Furthermore, dicarboxylic acids on the surface of the CeO2 nanocrystals changed the isoelectric point of the nanocrystals by displaying carboxyl groups. As a result, we have succeeded in synthesizing water-soluble CeO2 nanocrystals with various morphologies using dicarboxylic acids.