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We report a room-temperature ammonia sensor with extra high response values and ideal flexibility, including polyaniline (PANI)-coated titanium dioxide-silicon dioxide (TiO-SiO) or copper oxide-titanium dioxide-silicon dioxide (CuO-TiO-SiO) composite nanofibers. Such flexible inorganic TiO-SiO and CuO-TiO-SiO composite nanofibers were prepared by electrospinning, followed by calcination. Then, in situ polymerization of aniline monomers was carried out with inorganic TiO-SiO and CuO-TiO-SiO composite nanofibers as templates. Gas sensing tests at room temperature indicated that the obtained CuO-TiO-SiO/PANI composite nanofibers had much higher response values to ammonia gas (ca. 45.67-100 ppm) than most of those reported before as well as the prepared TiO-SiO/PANI composite nanofibers here. These excellent sensing properties may be due to the P-N, P-P heterojunctions and a structure similar to field-effect transistors formed on the interfaces between PANI, TiO, and CuO, which is p-type, n-type, and p-type semiconductor, respectively. In addition, the prepared free-standing CuO-TiO-SiO/PANI composite nanofiber membrane was easy to handle and possessed ideal flexibility, which is promising for potential applications in wearable sensors in the future.

SummaryIndium nitrate/polyvinyl pyrrolidone (In(NO3)3/PVP) composite nanofibers were synthesized via electrospinning, and then hollow structure indium oxide (In2O3) nanofibers were obtained through calcination with PVP as template material. In situ polymerization was used to prepare indium oxide/polyaniline (In2O3/PANI) composite nanofibers with different mass ratios of In2O3 to aniline. The structure and morphology of In(NO3)3/PVP, In2O3/PANI composite nanofibers and pure PANI were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and current–voltage (I–V) measurements. The gas sensing properties of these materials towards NH3 vapor (100 to 1000 ppm) were measured at room temperature. The results revealed that the gas sensing abilities of In2O3/PANI composite nanofibers were better than pure PANI. In addition, the mass ratio of In2O3 to aniline and the p–n heterostructure between In2O3 and PANI influences the sensing performance of the In2O3/PANI composite nanofibers. In this paper, In2O3/PANI composite nanofibers with a mass ratio of 1:2 exhibited the highest response values, excellent selectivity, good repeatability and reversibility.

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