Nanostructured WO3/graphene composites for sensing NOx 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 NOx 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 NOx 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 NOx 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.