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

Highlights: • Simple, fast and low-cost synthesis of 1-D ZnO–TiO₂ core–shell heterostructures. • ZnO NWs completely covered with a shell of anatase TiO₂ nanocrystals in only 3 min. • The TiO₂ shell thickness depends on the impregnation time in the titania synthesis bath. • 2-fold enhancement of photo-electrochemical activity and better stability of ZnONWs. • Forty- times higher photocurrent densities than TiO₂ nanoparticles film. - 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 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