Novel three-dimensional (3D) hierarchical structure and roughly oriented one-dimensional (1D) nanowire of WO3 are selectively prepared on 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, re-spectively. The gas-sensing properties of the nanowires and 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 tempera-ture (20 ◦C) to 250 ◦C 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 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 high sensitive gas sensor with low power consumption.
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