High-temperature solid-state reaction induced structure modifications and associated photoactivity and gas-sensing performance of binary oxide one-dimensional composite system

Abstract

The effects of high-temperature solid-state reactions on the microstructures, optical properties, photoactivity, and low-concentration NO₂ gas-sensing sensitivity of ZnO–SnO₂ core–shell nanorods were investigated. In this study, the ZnO–SnO₂ core–shell nanorods were synthesized through a combination of the hydrothermal method and vacuum sputtering. According to X-ray diffraction and transmission electron microscopy analyses, high-temperature solid-state reactions between the SnO₂ shell and ZnO core materials at 900 °C engendered an ultrathin SnO₂ shell layer for transforming into the ternary Zn₂SnO₄ (ZTO) phase. Moreover, surface roughening was involved in the high-temperature solid-state reactions, as determined from electron microscopy images. Comparatively, the ZnO–ZTO nanorods have a higher oxygen vacancy density near the nanostructure surfaces than do the ZnO–SnO₂ nanorods. The photodegradation of rhodamine B dyes under simulated solar light irradiation in presence of the ZnO–SnO₂ and ZnO–ZTO nanorods revealed that the ZnO–ZTO nanorods have a higher photocatalytic activity than do the ZnO–SnO₂ nanorods. Furthermore, the ZnO–ZTO nanorods exhibited higher gas-sensing sensitivity than did the ZnO–SnO₂ nanorods on exposure to low-concentration NO₂ gases. The substantial differences in the microstructure and optical properties between the ZnO–SnO₂ and ZnO–ZTO nanorods accounted for the photocatalytic activity and NO₂ gas-sensing results obtained in this study.