ZnO nanorods on reduced graphene sheets with excellent field emission, gas sensor and photocatalytic properties

In the flexible devices' fabrication, highly ordered nanoscale texturing such as semiconductor metal oxide nanorod arrays on the flexible substrates is critical for optimal performance. Herein, a simple and general hydrothermal route has been developed to result in a large-scale growth of ZnO nanorod arrays on double sides of the flexible reduced graphene sheets (rGss) forming sandwichlike heterostructures of ZnO/G/ZnO, and on a single side of the flexible rGss forming two-layered heterostructures of ZnO/G. The diameter and density of the ZnO nanorods grown on the rGss can be easily tuned as required by varying the seed-solution concentration. Due to the outstanding mechanical and electrical properties of the rGss, two-layered ZnO/G heterostructures were demonstrated to possess excellent field emission properties (turn-on field as low as 2.1 V μm^-1, the emitting current ∼470 μA cm ^-2 at 3 V μm^-1) and gas sensing (three times the ZnO nanorods); the sandwichlike ZnO/G/ZnO heterostructures have much higher photocatalytic activity under UV irradiation than those of ZnO nanorods and ZnO/G heterostructures, suggesting a promising candidate for photocatalytic decontamination. This would open up possibilities for the extensive study of the physical and chemical properties from these most promising nanostructures and extend their practical applications. © 2013 The Royal Society of Chemistry.