Morphology-dependent photocatalytic and gas-sensing functions of three-dimensional TiO2–ZnO nanoarchitectures

Abstract

Nanocomposites consisting of three-dimensional ZnO nanorods-decorated TiO₂ nanorod templates (TiO₂–ZnO) have been prepared by combining sputtering and hydrothermal growth strategies. The TiO₂–ZnO heterostructures (TiO₂–ZnO-1) were formed via an elevated temperature-grown ZnO seed layer-assisted crystal growth comprised of hexagonally structured ZnO nanorod branches on the top region and numerous ZnO nanoparticles on the sidewall region of the TiO₂ nanorod template. In contrast, ZnO nanorods were randomly oriented on the top region of the TiO₂ nanorod template by interweaving the neighboring segments via a room-temperature-grown ZnO seed layer-assisted crystal growth (TiO₂–ZnO-2). The as-synthesized three-dimensional TiO₂–ZnO nanoarchitectures exhibited significantly enhanced photocatalytic and photoelectrocatalytic performances towards the degradation of rhodamine B dyes under solar light irradiation as compared to the single-component counterparts. Moreover, the branched hexagonally structured ZnO nanorods in TiO₂–ZnO-1 contributed to higher degrees of charge transfer ability and charge separation efficiency than those of the TiO₂–ZnO-2 composite nanorods, explaining the superior photoactive performance of the TiO₂–ZnO-1 composite nanorods under irradiation. The unique three-dimensional branched morphology of the TiO₂–ZnO-1 composite nanorods also resulted in a greater number of potential barriers in the composite nanorod system, demonstrating their high gas-sensing performance towards ethanol vapor than that of the TiO₂–ZnO-2. The control of the three-dimensional crystal morphology of the hydrothermally derived ZnO nanorods on the surface of the TiO₂ nanorod template via changing the initial microstructures of the sputtering deposited ZnO seed layer is a promising approach to the design of three-dimensional TiO₂–ZnO nanoarchitectures with desirable photocatalytic and gas-sensing functions.