Morphology-controlled hydrothermal synthesis and growth mechanism of microcrystal Cu₂O

Cu₂O microcrystals with various shapes were obtained by reducing copper nitrate with formic acid, employing NH₃·H₂O as the morphology tailor. The volume of NH₃·H₂O plays a key role in controlling the final morphology, and hence Cu₂O with various shapes, such as sphere, hexapod, octahedron, truncated octahedron and rhombic dodecahedron can be obtained by varying the concentration of NH ₃·H₂O in the solution. Time-dependent experiments strongly showed that all the microcrystals originated from the intermediate octahedron microcrystal. We found that the intermediate octahedron microcrystal evolved directly from a microsphere. The growth of the microsphere could be divided into two steps: nanoparticles isokinetically aggregated quickly to produce a submicrometer-sphere, and then a microsphere formed by mass transportation. The shape evolution of the microcrystal in the present reaction system is quite meaningful to the growth process of the Cu₂O microcrystal.