Rational Design of Electron Transfer Kineties of CdS/Zn(impim) Dots-on-Rods for Efficient Visible-Light Reduced C-X Bond.

Halogenated organic compounds are a kind of common environmental pollutants. Photocatalytic dehalogenation of C-halogen (C-X) bonds to C-H bonds can not only control environmental pollution but also realize important organic conversion reactions. However, the electron transfer kinetics of photocatalytic reduction of the C-X bond for semiconductor/MOF composites has remained unexplored. Herein, we successfully synthesized CdS/Zn(impim) (MOF) dots-on-rods composite photocatalyst under mild conditions. Zn(impim) MOF consists of Zn(μ-N) clusters and imidazole derivative ligands. Zn(impim), as a carrier, is beneficial to the dispersion of CdS nanoparticles and avoiding the agglomeration of CdS nanoparticles. The photocatalytic performance of CdS/Zn(impim) composites for the reduction of the C-X bond is much higher than that of pure CdS or Zn(impim). This high activity is due to the high electron separation efficiency of CdS assisted by Zn(impim). Under visible light irradiation, Zn(impim) is not excited due to its wide band gap of 3.26 eV. Through metal-to-ligand charge transfer of Zn(μ-N) clusters, Zn(impim) accepts excited electrons from CdS because the Fermi energy level of CdS is more negative by Kelvin probe force microscopy. Moreover, fluorescence spectrum and femtosecond transient absorption spectroscopy reveal the related electron transfer kinetics in detail. In addition, the inherent porous structure of MOFs is beneficial to the adsorption of halogenated hydrocarbons, providing a suitable environment for the dehalogenation reaction, thus improving the activity. This work can further understand the electron transfer mechanism in semiconductor/MOF composites for photocatalytic halide dehalogenation.