Controlled synthesis and optical properties of doughnut-aggregated hollow sphere-like CuS

Three-dimensional (3D) doughnuts-like copper sulfide (CuS) particles were successfully synthesized by a facile microwave hydrothermal method employing polyvinylpyrrolidone (PVP) as the surfactant. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy and UV–vis diffuse reflectance spectra. Results show that the products are selectively fabricated by varying the S/Cu molar ratio from 3 to 7, exhibiting a morphology change from uniform aggregated spheres to single doughnuts-like structures. Comparison of the UV–vis absorption spectra of these particles reveals that an obvious red-shift of ∼70 nm is found from the single doughnuts to the assembled doughnuts. Moreover, these spectra were calculated to show the bandgap of the as-prepared CuS particles varies from 1.46 eV to 1.64 eV with the morphology change from the single doughnuts-like to the aggregated spheres-like structures, respectively, indicating that the optical properties of the product may be strongly related to the state of their morphologies.