Manipulating Electron Transfer in Hybrid ZnO–Au Nanostructures: Size of Gold Matters

Hybrid semiconductor–plasmonic metal nanostructures (NSs) tailoring of zinc oxide–gold (ZnO–Au) have been synthesized by direct addition of an aliquot of ZnO quantum dots (QDs) to aqueous dispersions of gold nanoparticles (NPs) of five different sizes. Gold nanoparticles of variable sizes have been prepared by Frens’ citrate reduction procedure and ZnO QDs by alkaline hydrolysis of zinc acetate dihydrate in methanol. The optical properties of hybrid ZnO–Au nanostructures have been explored by absorption, photoluminescence, and Raman spectroscopy; the intrinsic changes in the optical characteristics of the individual components reflect strong interfacial interaction between ZnO and Au nanostructures. The binding of ZnO QDs to the colloidal gold particles has further been elucidated by Fourier transform infrared spectroscopy and cyclic voltammetry measurements. The morphology and crystallinity of the ZnO–Au NSs have been characterized by transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, and X-ray diffraction techniques. Absorption spectral studies have revealed that ZnO QDs attached on the size-specific Au NPs elicites the modification of band gap in hybrid semiconductor–metal nanostructures. The catalytic activities of the as-prepared ZnO–Au NSs consisting of gold nanoparticles of variable sizes have been probed by employing photochemical decomposition of Evans blue under visible light irradiation as the model reaction. Finally, the trends in the alteration of different interaction parameters in structuring hybrid semiconductor–metal nanostructures with the band gap have been correlated.