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

Camelia Florica,Nicoleta Apostol,Ionut Enculescu,Victor Diculescu,Nicoleta Preda,Andrei Kuncser,Gabriel Socol,Cristina Popa,Mihaela Beregoi,Andreea Costas

doi:10.1038/s41598-019-53873-0

Abstract

Staggered gap radial heterojunctions based on ZnO-CuxO 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 CuxO layer having a band gap of 1.74 eV and subsequently form core-shell heterojunctions. The electrical characterization of the ZnO pristine and ZnO-CuxO 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-CuxO core-shell nanowires with different shell thicknesses. An optimum thickness of the CuxO layer is used to obtain water stable photocatalysts, where the ZnO-CuxO radial heterojunction enhances the separation and transport of the photogenerated charge carriers when irradiating with UV-light, leading to swift pollutant degradation.

Highlights

Staggered gap radial heterojunctions based on ZnO-CuxO core-shell nanowires are used as water stable photocatalysts to harvest solar energy for pollutants removal
ZnO nanowires were obtained by thermal oxidation in air and covered with CuxO layers deposited by magnetron sputtering leading to water stable photocatalysts
Electrical charges transfer along the radial junction and between the ZnO-CuxO core-shell nanowires and an aqueous media are investigated for different thickness of the shell layer in order to explain the mechanism of the photocatalytic degradation of methylene blue

Summary

Introduction

Staggered gap radial heterojunctions based on ZnO-CuxO core-shell nanowires are used as water stable photocatalysts to harvest solar energy for pollutants removal. An optimum thickness of the CuxO layer is used to obtain water stable photocatalysts, where the ZnO-CuxO radial heterojunction enhances the separation and transport of the photogenerated charge carriers when irradiating with UV-light, leading to swift pollutant degradation. A major disadvantage to be overcome is the ZnO dissolution This process was observed previously for nanoparticles[25,26,27,28,29], thin films[30,31], porous nanosheets[32], and even nanowires[33,34,35], being enhanced under UV-light irradiation[32,36], but was not discussed, up to now, to our (c) obtaining ZnO – CuxO core-shell nanowire arrays by depositing a layer of CuxO by magnetron sputtering. When reaching an optimum thickness of CuxO, the staggered gap radial heterojunction based on ZnO-CuxO nanowires has a better photocatalytic response than the pristine ZnO nanowires, being in the same time water stable

Methods

Results

Conclusion