Study On Preparation And Gas-sensing Properties Of Tungsten Oxide Hierarchical Structure

Nitrogen dioxide?NO₂? is a highly harmful atmospheric pollutant. It contributes to photochemical smog and acid rain and it is also the main source of PM 2.5. The fast and reliable detection of toxic NO₂ gas is therefore important for both environmental protection and human health. In particular, tungsten oxide?WO₃?, a wide band-gap n-type semiconductor, has exhibited remarkable sensing performance to NO₂ gas. In this paper, novel WO₃ hierarchical structure film demonstrates to be a promising material for building highly sensitive and ultrafast responding gas sensors.Gas sensors based on WO₃ nanostructure are formed through a direct induction layer-induced hydrothermal growth of nanostructured WO₃ on the substrate attached a pair of patterned Pt electrodes. Novel three-dimensional?3D? hierarchical structure and roughly oriented one-dimensional?1D? nanowire of WO₃ are selectively prepared on the alumina substrate. 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 gas-sensing properties of the nanowires and hierarchical structure of WO₃,include the variation of resistance and response time when they are exposed to NO₂, are investigated at temperatures ranging from room temperature?20?? to 250 ? over 0.015-5ppm 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, 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 5s, indicating the potential of this material in developing high sensitive gas sensor with low power consumption.