Nanosheets assembled hierarchical flower-like WO3 nanostructures: Synthesis, characterization, and their gas sensing properties

A three-dimensional hierarchical WO3 nanostructure with a novel nanosheet-assembled morphology was synthesized through acidification of Na2WO4·2H2O. Firstly, precipitate got from Na2WO4·2H2O and HCl was used as precursor. Secondly, the precursor was pretreated by concentrated acid for 24 h. Thirdly, deionized water was poured into the above solution directly to form the final products. The results revealed that the pretreatment by using high-concentration acid is the crucial factor in order to obtain the flower-like nanostructures. The WO3 samples were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET). The results revealed that the samples were flower-like structure. The subunits of the flower-like nanostructures are ultrathin nanosheets with a thickness of about 20 nm. Sensors based on the synthesized WO3 exhibited high response to NO2. The detection limit can be as low as ∼40 ppb level. Such novel WO3 nanostructures may be a promising material for sensor application in detecting NO2.