Core-shell nanowire arrays based on ZnO and Cu_xO for water stable photocatalysts

Staggered gap radial heterojunctions based on ZnO-Cu_xO core-shell nanowires are used as water stable photocatalysts to harvest solar energy for pollutants removal. ZnO nanowires with a wurtzite crystalline structure and a band gap of approximately 3.3 eV are obtained by thermal oxidation in air. These are covered with an amorphous Cu_xO layer having a band gap of 1.74 eV and subsequently form core-shell heterojunctions. The electrical characterization of the ZnO pristine and ZnO-Cu_xO core-shell nanowires emphasizes the charge transfer phenomena at the junction and at the interface between the nanowires and water based solutions. The methylene blue degradation mechanism is discussed taking into consideration the dissolution of ZnO in water based solutions for ZnO nanowires and ZnO-Cu_xO core-shell nanowires with different shell thicknesses. An optimum thickness of the Cu_xO layer is used to obtain water stable photocatalysts, where the ZnO-Cu_xO radial heterojunction enhances the separation and transport of the photogenerated charge carriers when irradiating with UV-light, leading to swift pollutant degradation.