Honeycomb Texturing of Hierarchical Nanoflowers of WO3 as an Efficient Route to Improve Repeatability and Stability of Room Temperature Vapor Sensor

Hierarchical nanostructures of WO
₃
was synthesized by a hydrothermal method at 180°C using sodium tungstate dihydrate (Na
₂
WO
₄
.2H
₂
O), sodium bisulfate dihydrate (NaHSO
₄
.2H
₂
O) and ethylene glycol (having different molar concentrations) with Titanium as the substrate. Molar concentrations of ethylene glycol was taken to be 2.241 M, 8.274 M and 15.693 M, which eventually produced, (i) nanoneedles with sparsely distributed nanosphere clusters (S-I) (ii) nanospheres (S-II) (iii) honeycomb textured hierarchical nanoflowers (S-III), respectively. After detailed morphological and structural characterizations, like field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), these different nanostructures were employed as the gas sensing layer targeting the alcohol vapors in the concentration range of 10-400 ppm over a temperature range of 27°C (room temperature) to 200°C. Among the hierarchical nanoforms, S-III offered the best sensing performance in terms of response magnitude (~29.35%/~91.59%), response time (~31 s/~19 s) and recovery time (~42 s/~27 s), for 10/400 ppm ethanol at 27°C. Moreover, improved stability and repeatability were also achieved by the same structure. Such improvement in the sensing performance was duly correlated with the corresponding morphology of the nanostructure employing a semi-quantitative geometrical model.