A review on 2D transition metal di-chalcogenides and metal oxide nanostructures based NO2 gas sensors

NO2, having a reddish-brown color and biting odor, is the most prominent toxic waste present in the atmosphere. The major contributors to NO2 gas include emissions from industrial and transport sectors. There are many porous nanostructures which have shown enormous potential for NO2 gas sensing. Among these, the first group comprises metal oxides while the second group includes two-dimensional transition metal dichalcogenides (2D TMDs). Besides, these materials have also been modified or functionalized with different metals for improving various sensing parameters such as selectivity, sensitivity, affordability, stability and life span of the device. In this article, we discuss new developments in the fields of metal oxide nanostructures and 2D TMDs for NO2 sensing. Additionally, a comparative analysis of different modifications and their effects on sensing properties of both the materials is presented.