关键词: tungsten oxide, gas sensor, hierarchical structure, hydrothermal synthesis

Abstract: A novel three-dimensional (3D) hierarchical structure and a roughly oriented one-dimensional (1D) nanowire of WO₃ are selectively prepared on an alumina substrate by an induced hydrothermal growth method. Each hierarchical structure is constructed hydrothermally through bilateral inductive growth of WO₃ nanowire arrays from a nanosheet preformed on the substrate. Only roughly oriented 1D WO₃ nanowire can be obtained from a spherical induction layer. The analyses show that as-prepared 1D nanowire and 3D hierarchical structures exhibit monoclinic and hexagonal phases of WO₃, respectively. The gas-sensing properties of the nanowires and the hierarchical structure of WO₃, which include the variations of their resistances and response times when exposed to NO₂, are investigated at temperatures ranging from room temperature (20 ℃) to 250 ℃ over 0.015 ppm-5 ppm NO₂. The hierarchical WO₃ behaves as a p-type semiconductor at room temperature, and shows p-to-n response characteristic reversal with the increase of temperature. Meanwhile, unlike the 1D nanowire, the hierarchical WO₃ exhibits an excellent response characteristic and very good reversibility and selectivity to NO₂ gas at room temperature due to its unique microstructure. Especially, it is found that the hierarchical WO₃-based sensor is capable of detecting NO₂ at a ppb level with ultrashort response time shorter than 5 s, indicating the potential of this material in developing a highly sensitive gas sensor with a low power consumption.

Key words: tungsten oxide, gas sensor, hierarchical structure, hydrothermal synthesis