Highly sensitive NH3 gas sensors based on novel polypyrrole-coated SnO2 nanosheet nanocomposites

•SnO2 nanosheets are prepared by hydrothermal synthesis assisted by electrospinning.•SnO2/polypyrrole nanocomposite is obtained by vapor phase polymerization.•Nanocomposite reveals high sensitivity, selectivity and repeatability to NH3.•High performance of nanocomposite relates to nanostructure and p/n junction. Nanocomposites of SnO2 nanosheets and polypyrrole (PPy) were facilely prepared and their gas sensing properties towards low concentration of NH3 have been investigated at room temperature. Vertically aligned SnO2 nanosheets were in situ grown on the substrates via hydrothermal treatment of electrospun nanofibers containing SnCl2 precursors at a low temperature (135°C), and coated with PPy by vapor phase polymerization of pyrrole. The SnO2 nanosheets and the nanocomposites were characterized by X-ray diffraction patterns, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and high resolution transmission microscopy. The nanocomposite sensors exhibited much higher response magnitude towards NH3 than the sensors based on PPy alone. The effect of the type of doping acids and polymerization time of pyrrole on the sensing properties of the nanocomposites was examined. The nanocomposite sensors revealed sensitive (sensitivity of ∼6.2%/ppm in the range of 1–10.7ppm of NH3, detection limit of ∼257ppb), selective and repeatable response to NH3, and the sensing mechanism has been explored. This work could provide references for the facile preparation of advanced gas sensors based on in situ grown nanostructured metal-oxide semiconductors and their composites.