Single-step hydrothermally grown nanosheet-assembled tungsten oxide thin films for sensitive and selective NO2 gas detection

A well-organized tungsten oxide (WO3) nanosheet-assembled microbricks have been synthesized by the hydrothermal route at 180 °C with the help of peroxy-tungstic acid sol. The as-synthesized thin films have been characterized for structural, morphological and compositional studies by using X-ray diffraction, scanning electron microscopy and FT-Raman spectroscopy. The deposited WO3 thin films have been found to be polycrystalline in nature with the monoclinic crystal structure. The SEM micrographs revealed the formation of microbrick-like structure which was made up of two-dimensional (2D) nanosheets. The 2D nanosheets act as a nanobuilding blocks for the formation of microbricks. The gas-sensing performance of WO3 thin films was carried out for different gases, and it is observed that sensor exhibited maximum gas response towards Nitrogen dioxide (NO2) gas which is seven times higher than that of other gases at an operating temperature of 300 °C over the concentration range of 5–100 ppm. WO3 microbricks sensor showed higher response about 11.5 and fast response–recovery characteristics towards NO2 gas, especially a much quicker gas response time of 16 s and recovery time of 260 s at 100 ppm.