Imaging and Manipulating the Conversion from Single Cuprous Oxide Microparticles to Single Metal Hydroxide Microstructures.

The template-assisted route is an effective avenue for the preparation of core-shell and hollow micromaterials. However, the conversion process is usually characterized by ex situ transmission electron microscopy, limiting the comprehensive understanding of the structure evolution. Here, we use dark-field microscopy (DFM) to visually image the chemical conversion process of Cu2O concave microcubes into metal hydroxide (MHs, M = Co, Ni, and Mn) microstructures at the single-particle level. The details of the conversion process such as early steps in the conversion reaction, intermediate states, and final states are successfully tracked in real time. The in situ DFM experiments clarify that the etching of Cu2O predates the generation of MHs, and the conversion reaction shows significant particle-to-particle variation. Meanwhile, the results also show that experimental parameters dominate the conversion of Cu2O concave microcubes, allowing for the precise manipulation of the reaction degree to obtain Cu2O@Co(OH)2 core-shell microstructures with different shell thicknesses and hollow Co(OH)2 microstructures. The present work offers a direct observation and manipulation of the conversion process of Cu2O microparticles, paving the way for rational design and preparation of various core-shell and hollow micromaterials.