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

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 10 min. 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 0.7 mA/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.