Fast and low-cost synthesis of 1D ZnO–TiO2 core–shell nanoarrays: Characterization and enhanced photo-electrochemical performance for water splitting

Abstract

We report on a simple, fast and low-cost synthesis procedure for the complete covering of zinc oxide (ZnO) 1D nanostructures with a protective shell of titania (TiO2) nanoparticles. ZnO nanowires (NWs) were grown on transparent F-doped Tin Oxide (FTO) conductive layer on glass by seed layer-assisted hydrothermal route in aqueous media, while the titania shell was deposited on the ZnO NWs through an in situ non-acid sol–gel synthesis. The nanowires impregnation time in the titania sol was varied from 3 to 10min. The resulting core–shell ZnO–TiO2 structures were characterized by different techniques, including Scanning and Transmission Electron Microscopy, X-ray diffraction and UV–Vis spectroscopy, confirming the uniform coverage of the wurzite ZnO NWs with anatase TiO2 nanoparticles (NPs), with a shell thickness dependent on the impregnation time in the titania synthesis bath. Photoelectrochemical (PEC) tests of the ZnO–TiO2 material, used as anode for the water splitting reaction, confirmed the formation of the heterojunction by the enhanced photocurrent densities, reaching values of about 0.7mA/cm2 under simulated solar light (AM1.5G, 100mW/cm2). The core–shell photo-anodes performance was about twice and forty- times better than the ones with a film of equivalent thickness of bare ZnO NWs and TiO2 NPs, respectively. Steady-state measures of the photocurrent over the time and FESEM analysis confirmed that this procedure could be effectively used to both protect the nanostructured ZnO from photo-corrosion into different electrolytic media and enhance its photocatalytic properties.