WO 3 has emerged as an outstanding nanomaterial composite for gas sensing applications. In this paper, we report the synthesis of WO 3 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 WO 3 material was investigated and presented. The WO 3 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. WO 3 synthesized using oxalic acid exhibited orthorhombic phase with crystallite size of 10 nm, while WO 3 obtained using citric acid shows monoclinic phase with crystallite size of 20 nm. WO 3 obtained using both capping agents were used to study their gas sensing characteristics, particularly for NO x 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 WO 3 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 WO 3 material exhibits better response towards NO x sensing when compared with oxalic acid-assisted WO 3 . Moreover, the sensitivity of the WO 3 /graphene nanocomposite was better than that of the pristine WO 3 material towards NO x gas. The WO 3 composite prepared using citric acid as capping agent and graphene exhibits sensing response and recovery time of 29 and 24 s, respectively.

A novel, highly sensitive gold nanowire (AuNW) resistive sensor is reported here for humidity sensing in the relative humidity range of 11% to 92% RH as well as for breath sensing.

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