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 NH3·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.