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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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A non-enzymatic, duo-active sensor using nickel ferrite/PANI (NF–PANI) nanocomposite based on peroxidase mimic and electrochemical methods for sensitive and selective detection of ascorbic acid.

Chemiresistive gas sensing has attracted extensive research attention in recent years, and the facile low-cost synthesis of sensitive materials is important for realizing practical use. One feasible approach is to create a gas-sensing nanocomposite network by infusing an easily processable conducting polymer into a solution-grown interlinking metal oxide nanomaterial. In this work, a polyaniline (PANi) and ZnO nanorod (NR) composite is synthesized for selective UV-activated NO2 gas sensing at room temperature. The nanocomposite comprises interlinking ZnO NRs that are partially covered by PANi, thus forming a charge transport network with abundant gas adsorption sites. Uniform and interlinking ZnO NRs are grown on a prepatterned silicon substrate by using a hydrothermal method, and PANi is prepared by using an in situ oxidative polymerization method. A PANi/ZnO 0.5 nanocomposite with uniform morphology is obtained by drop-casting a PANi solution on the ZnO NRs. The nanocomposite exhibits selective NO2 gas toward various gases including CH2O, NO, and NH3. The responses are 130% and 20920% for 0.05 and 2.5 ppm NO2, respectively. The low-concentration linear sensitivity is 11.7% ppb–1. Based on the Langmuir adsorption model, the adsorption and the desorption constants are determined to be 7.65 × 10–3 ppm–1 s–1 and 1.07 × 10–2 s–1, respectively. The excellent gas-sensing performance of the PANi/ZnO 0.5 nanocomposite is attributed to the formation of abundant p–n heterojunction adsorption sites.