Synthesis of one-dimensional CdS@TiO₂ core-shell nanocomposites photocatalyst for selective redox: the dual role of TiO₂ shell.

One-dimensional (1D) CdS@TiO₂ core-shell nanocomposites (CSNs) have been successfully synthesized via a two-step solvothermal method. The structure and properties of 1D CdS@TiO₂ core-shell nanocomposites (CdS@TiO₂ CSNs) have been characterized by a series of techniques, including X-ray diffraction (XRD), ultraviolet-visible-light (UV-vis) diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FESEM), photoluminescence spectra (PL), and electron spin resonance (ESR) spectroscopy. The results demonstrate that 1D core-shell structure is formed by coating TiO₂ onto the substrate of CdS nanowires (NWs). The visible-light-driven photocatalytic activities of the as-prepared 1D CdS@TiO₂ CSNs are evaluated by selective oxidation of alcohols to aldehydes under mild conditions. Compared to bare CdS NWs, an obvious enhancement of both conversion and yield is achieved over 1D CdS@TiO₂ CSNs, which is ascribed to the prolonged lifetime of photogenerated charge carriers over 1D CdS@TiO₂ CSNs under visible-light irradiation. Furthermore, it is disclosed that the photogenerated holes from CdS core can be stuck by the TiO₂ shell, as evidenced by controlled radical scavenger experiments and efficiently selective reduction of heavy-metal ions, Cr(VI), over 1D CdS@TiO₂ CSNs, which consequently leads to the fact that the reaction mechanism of photocatalytic oxidation of alcohols over 1D CdS@TiO₂ CSNs is apparently different from that over 1D CdS NWs under visible-light irradiation. It is hoped that our work could not only offer useful information on the fabrication of various specific 1D core-shell nanostructures, but also open a new doorway of such 1D core-shell semiconductors as visible-light photocatalysts in the promising field of selective transformations.