Nanowire (nanorod) arrays-constructed tungsten oxide hierarchical structure and its unique NO2-sensing performances

Novel WO3 hierarchical structure film demonstrates to be a promising material for building highly sensitive and ultrafast responding gas sensors. The individual hierarchical WO3 structure was constructed hydrothermally through double-sided inductive growth of WO3 nanowire (or nanorod) arrays from the central nanosheet. The nanosheet was performed on the substrate via spin-coating and thermal annealing. Composed of well-aligned ultrathin nanowires (nanorods) as building blocks, the as-synthesized hierarchical WO3 shows high active surface area and loose microstructure favorable for gas adsorption and rapid gas diffusion. The NO2-sensing properties of the hierarchical WO3 film-based sensors were evaluated at room temperature over NO2 concentration ranging from 15 ppb to 5 ppm. At room temperature, the WO3 hierarchical structure behaves as an abnormal p-type semiconductor and exhibits unique gas-sensing performances including excellent sensitivity and excellent response characteristics towards NO2 gas. It is found that the sensors based on hierarchical WO3 responses to NO2 gas as low as 15 ppb with an ultrashort response time of short than 5 s at room temperature, highlighting the capability of the material for rapid detection of dilute NO2 at ppb level.