Effect of annealing on microstructure and NO2-sensing properties of tungsten oxide nanowires synthesized by solvothermal method

Quasi-orienting W18O49 nanowire bundles were synthesized by solvothermal method. The microstructures and the NO2-sensing properties of the as-synthesized nanowires annealed at different temperatures were studied. To characterize the morphology and crystalline structure of the annealed tungsten oxide, field emission scanning electron microscope, X-ray diffraction and transmission electron microscope were employed. It was found that with annealing temperature increasing, the nanowire bundles became straighter and slightly thicker, and eventually a nonobelt-like structure was formed via the nanowires coalescence at 450 degrees C. Meanwhile, the monoclinic W18O49 was transformed to monoclinic WO3 when annealing temperature rising from 350 to 450 degrees C. In comparison to the W18O49 nanowire bundles-based sensor, the sensor based on the 450 degrees C annealing-induced WO3 nanobelt-like structure exhibited markedly higher response value and gas selectivity, as well as much better response-recovery characteristics to NO2 gas due to its favorable microstructure feature to gas-sensing. (C) 2011 Elsevier B.V. All rights reserved.