Formation and Self-Assembly of Cadmium Hydroxide Nanoplates in Molten Composite-Hydroxide Solution

In this article, we report a novel molten hydroxide strategy to prepare bulk-sized complexes of three-dimensional (3D) nanostructures at a large scale. Taking cadmium hydroxide as an example, we revealed that the bulk-sized architectures were composed by cross-linked nanoplates, which could be fabricated by a one-step hydrothermal route in the presence of molten composite-hydroxide (NaOH + KOH) at 200 °C. Powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis show that the growth of the well-defined nanostructures actually undergoes two stages. Initially, with the mixture of cadmium chloride and a large excess of composite-hydroxide, a prestructure of aggregating nanoparticles is formed. Afterward, the prestructure recrystallizes into nanoplates of 150 nm thickness and with the (001) plane as exposed surface. Meanwhile, these nanoplates are interweaved and organized into a globe-like structure and 3D aggregates. We speculate that the molten hydroxide plays a critical role not only in providing a strong surface effect to allow recrystallization and anisotropic growth but also in realizing the self-assembly of nanoparticles in inorganic solution. The molten composite-hydroxide solution strategy was further extended into a calcium hydroxide system and the same assembling nanoplate architectures were successfully achieved.