Highly sensitive and ultralow detection limit of room-temperature NO2 sensors using in-situ growth of PPy on mesoporous NiO nanosheets

Recently, inorganic-organic nanocomposites-based gas sensors have attracted great attention because they usually exhibit enhanced sensing properties compared to single component due to the formation of hetero-junction and the existing organic functional groups. Here, to improve the sensing properties of NiO and further detail the sensing mechanism of inorganic-organic nanocomposites-based sensors, polypyrrole (PPy)-functionalized NiO nanosheets were prepared for room-temperature NO2 sensing. The gas-sensing studies revealed that the response of PPy-NiO nanocomposites (45) to 60 ppm NO2 at room temperature is 30 times larger than that of the bare NiO (1.5). According to the fitting curves of the relationship between the sensitivity and NO2 concentration, the detection limit was calculated to be 49 ppb, indicating its potential application. On the basis of the energy band diagram, the significantly enhanced sensitivity of nanocomposites was attributed to the increased number of nickel vacancies induced by the effective charge transferring from PPy to NiO. Moreover, based on the different sensitivity of nanocomposites with different molar ratios, the relative importance of heterojunction resistance and bulk resistance was also clarified by constructing equivalent circuit model. We hope this work could guide us to explore more inorganic-organic nanocomposites-based sensors with the even higher sensing performances.