Ion-Exchange Synthesis and Enhanced Visible-Light Photoactivity of CuS/ZnS Nanocomposite Hollow Spheres

Monodisperse CuS/ZnS nanocomposite hollow spheres with diameters of about 255 nm and shells composed of nanoparticles have been successfully synthesized in high yield by an ion-exchange method using monodisperse ZnS solid spheres as a precursor. The prepared samples were characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, N-2 adsorption-desorption isotherms, and UV-visible absorption spectroscopy. The photocatalytic activity was evaluated by the photocatalytic decolorization of Rhodamine B (RhB) aqueous solution under visible-light irradiation. The results indicate that the difference of solubility products (K-sp) of ZnS and CuS is the main driving force for the formation of CuS/ZnS hollow spheres. A sequential evolution process involving surface deposition, mutual diffusion, interior dissolution, and interfacial reaction is proposed to account for the formation of CuS/ZnS nanocomposite hollow spheres. The reaction time greatly influences the physical properties and photocatalytic activity of hollow spheres. With increasing reaction time, the BET surface areas decrease and, contrarily, the average pore size and pore volume increase. The prepared CuS/ZnS composite hollow spheres exhibit a higher visible-light photocatalytic activity than single ZnS solid or CuS hollow spheres for the photocatalytic decolorization of RhB aqueous solution. The photogenerated holes are thought to be the main active species responsible for the photocatalytic degradation of RhB. The ion-exchange method will provide new insight into the fabrication of composite hollow spheres and other new photocatalytic materials. We believe that the prepared CuS/ZnS hollow spheres are also of great interest in solar cells, catalysis, separation technology, biomedical engineering, and nanotechnology.