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The use of MoS 2 nanosheets as a gas sensing material has been reported extensively in recent years. Sulfur vacancies (V S ) are known to play a significant role, but the detailed mechanism is still in dispute. In this work, we tried to investigate the relationship between the V S and the gas sensing response based on experimental and simulation results. Experimentally, we developed a NO 2 gas sensor based on liquid-exfoliated MoS 2 nanosheets with the response of 330% at 100 °C for 5 ppm NO 2 gas. The excellent performance is due to the creation of sulfur vacancies (undercoordinated Mo atoms) at room temperature. From density functional theory (DFT) calculations, a dominant MoS 2 −NO 2 adsorption complex is formed and higher adsorption energy (32.89 meV/Mo) of the NO 2 gas molecule on sulfur vacancy-induced MoS 2 is obtained. The V S acts as the singly ionized acceptor level (0.54 eV above the valence band). Finally, a detailed temperature-dependent sensing mechanism for p-type MoS 2 nanosheets has been proposed considering the V S as a single electron acceptor with the (0/−1) charged states. This level is responsible for enhanced NO 2 adsorption at low temperatures, and the observed behavior agrees well with the findings of DFT studies.

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