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2D transition metal dichalcogenides have performed exceptionally as the active layer for chemiresistive gas sensors. Combining these materials with semiconductor oxides of tunable properties has proved to improve gas sensing and overall device performance due to the synergizing effect of the hybrid nanostructures. In this manuscript, we report the synthesis of a Co3O4/MoS2 nanostructure-based highly sensitive chemiresistive gas sensor selective toward NO x gases. An increase in air pollution has caused an equal increase in the concentrations of toxic NO x gases in the atmosphere. Exposure to these gases leads to grave health hazards such as pulmonary diseases and cardiovascular diseases. Furthermore, recent studies prove that NO x gases are also a contributor to COVID-19 fatality. We investigated the effect of the change in precursor concentration of cobalt nitrate (CoN2O6) and temperature on the gas sensor response. The precursor concentration was varied over an increasing range of molarities (1, 5, 10, and 25 mM), and it was observed that the gas sensor with a precursor concentration of 25 mM and an operating temperature of 200 °C exhibited the highest response of 145.7% toward NO2 gas (4.3 ppm) and then 105.37% toward NO (2.75 ppm). It was also noted that the device responded to NO2 gas of concentration as low as 300 ppb. This device was then subjected to an increasing range of temperatures (50, 100, 150, 200, 250, and 300 °C). A clear increase in the device performance was observed with an increase in temperature. It was found that the gas sensor was the most sensitive toward NO2 gas (4.3 ppm) and exhibited a response of 186.2% at 250 °C followed by NO (2.75 ppm) with a response of 141.6%. A stable and excellent response toward a low concentration of 50 ppb of NO2 was observed. Two activation energies (E a) were calculated from the Arrhenius plotE a1 (0.846 eV) between 150 and 200 °C and E a2 (1.316 eV) between 200 and 250 °C, indicating multiple energy trapping. These results pave a way for a plausible application of Co3O4/MoS2 hybrid nanostructures for the detection and monitoring of NO x gases in the air.

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