Low Temperature Synthesis of Cu₂O Crystals: Shape Evolution and Growth Mechanism

An interesting shape evolution of Cu 2 O crystals, that is, from cubes, truncated octahedra, octahedra, and finally to nanospheres was first realized in high yield by reducing the copper−citrate complex solution with glucose. X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM) techniques were employed to characterize the samples. We elucidate the important parameters (including poly (vinyl pyrrolidone) (PVP) concentration, reaction time, and reaction temperature) responsible for the shape-controlled synthesis of Cu 2 O crystals. The possible formation mechanism for the products with various architectures is presented, which is mainly based on the variation of the ratio ( R ) of the growth rates along the ⟨100⟩ and ⟨111⟩ direction. In addition, the effect of the low supersaturation on the formation of star-shaped samples with six symmetric branches is also taken into account. This polymer-mediated method should be readily extended to the controlled synthesis of other metal oxides and the proposed growth model could also be used to explain and direct the growth of crystals with a cubic structure.