Template-free Fabrication of Nano-sized Cu2O Hollow Spheres, Sheets and Octahedrons in Cu-citrate System and their Morphology-dependent Semiconductor Type

Nano-sized cuprous oxide (nano-Cu2O) materials with different morphologies such as hollow spheres, two-dimensional (2D) sheets and octahedrons were synthesized using a simple hydrothermal method in a Cu-citrate complex solution by making small adjustments to the solution’s pH value under alkaline conditions. The morphology of the Cu2O was observed using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The crystalline features of the materials were characterized by X-ray diffraction (XRD). The formation mechanism related to these materials was also discussed. The photoelectrochemical experiments showed that the hollow Cu2O structure synthesized under a pH range of 8-11 exhibited n-type semiconductor characteristics. Alternatively, solid octahedral Cu2O formed in the presence of strong alkaline conditions (i.e. pH greater than or equal to 12) and exhibited p-type behavior. The nanosheet Cu2O possesses the same n-type semiconductor properties as hollow spherical Cu2O and displays a larger photo-response. This indicated that nanosheet Cu2O is a promising material for photoelectric applications.