A facile preparation of ZnO/Au nano-needles: Optical, morphological and structural properties

Abstract Gold-doped ZnO (ZnO/Au) nano-needles were successfully synthesized in the shape of nano-needles through an aqueous medium using Pennisetum purpureum leaf extract. The Pennisetum purpureum acts as the natural bioreduction of Au3+ ions to Au0. Zinc nitrate hexahydrate (Zn(NO3)2·6H2O), hexamethylenetetramine (C6H12N4), and tetrachloroauric III acid (HAuCl4) solutions were employed as precursors. ZnO/Au nano-needles was characterized by Scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX), Particle size analyzer (PSA), UV–Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). SEM images show that the morphology change of ZnO to ZnO/Au was observed from hexagonal nano-tubes to nano-needles with the composition Zn, O, and Au confirmed by EDS characterization. The average particle size distribution of ZnO and ZnO/Au were 9.23 and 51.30 nm, respectively. The bandgap value of ZnO decreased from 3.3 to 2.5 eV after modification with Au. XRD analysis showed the crystallite size average of ZnO and ZnO/Au nano-needles which were found to be 12.30 and 30.25 nm, respectively. Raman spectra showed the existence of strong Au vibration in ZnO/Au nano-needles at 643 cm−1. FTIR spectra showed the presence of strong vibration of ZnO/Au nano-needles at 321 cm−1. Importantly, this research offers a feasible and low-cost method for the synthesis of ZnO/Au with a specified shape of nano-needles.