Nanostructured WO₃/graphene composites for sensing NO at room temperature

WO₃ has emerged as an outstanding nanomaterial composite for gas sensing applications. In this paper, we report the synthesis of WO₃ using two different capping agents, namely, oxalic acid and citric acid, along with cetyltrimethyl ammonium bromide (CTAB). The effect of capping agent on the morphology of WO₃ material was investigated and presented. The WO₃ materials were characterized using X-ray diffraction analysis (XRD), field emission transmission electron microscopy (FETEM), field emission scanning electron microscopy (FESEM), particle size distribution (PSD) analysis, and UV-visible spectroscopic analysis. WO₃ synthesized using oxalic acid exhibited orthorhombic phase with crystallite size of 10 nm, while WO₃ obtained using citric acid shows monoclinic phase with crystallite size of 20 nm. WO₃ obtained using both capping agents were used to study their gas sensing characteristics, particularly for NO gas. The cross sensitivity towards interfering gases and organic vapors such as acetone, ethanol, methanol and triethylamine (TEA) was monitored and explained. Furthermore, the composites of WO₃ were prepared with graphene by physical mixing to improve the sensitivity, response and recovery time. The composites were tested for gas sensing at room temperature as well as at 50 °C and 100 °C. The results indicated that the citric acid-assisted WO₃ material exhibits better response towards NO sensing when compared with oxalic acid-assisted WO₃. Moreover, the sensitivity of the WO₃/graphene nanocomposite was better than that of the pristine WO₃ material towards NO gas. The WO₃ composite prepared using citric acid as capping agent and graphene exhibits sensing response and recovery time of 29 and 24 s, respectively.