Preparation And Sensitive Properties Of Conductive Polymer / Inorganic Semiconductor Oxide Nanocomposite Gas Sensitive Materials

Gas sensors have been widely used in various fields in modern society, and their development has received great attention worldwide. Currently, one of the research focuses on gas sensors is the preparation of nanocomposite sensing materials to enhance the sensory properties. In this paper, nanosheets of tin dioxide (SnO2)、iron (Ⅲ) oxide (Fe2O3) and titanium dioxide (TiO2) were in-situ grown on the substrates at low temperatures (typically 135℃) by the hydrothermal treatment of electrospun nanofibers containing the corresponding metal oxide precursors, which avoids the calcination of nanofibers and the redispersion of nanomaterials. Composites of the metal oxide nanosheets with polyaniline (PANI) or polypyrrole (PPy) were prepared and employed to construct gas sensors featured with good contact between the sensing materials and substrates. The composition, structure and morphology of the nanocomposite sensing materials were characterized by FT-IR, XRD, SEM, HRTEM, XPS and EDAX. Room temperature NH3 sensing properties of the composite sensors were investigated, and optimized by manipulating the composition and morphology of the sensing materials. Meanwhile, the sensing mechanisms were explored.SnO2 nanosheets were in-situ grown on the substrate by hydrothermally treating the electrospun nanofibers containing SnCl2, and the growth mechanism of the nanosheets has been investigated. High performance gas sensors based on the nanocomposites of SnO2 with PANI or PPy were fabricated by depositing the conducting polymers onto the nanosheets via vapor phase polymerization of pyrrole or dip-coating of dispersible PANI. The composite sensors revealed much better sensing performance towards NH3 at room temperature than the sensors based on the single component. SnO2/PANI nanocomposite sensor demonstrated very high response magnitude toward NH3 (relative resistance change of ～3700% towards 10.7 ppm of NH3), ultra-low detection limit (-46 ppb), good sensing repeatability and excellent selectivity. By contrast, the sensing properties of SnO2/PPy nanocomposite sensor were affected by the types of doping acid and polymerization time, and the optimized composite sensor revealed good sensitivity of ～6.2%/ppm in the range of 1-10.7 ppm of NH3, detection limit as low as ～257 ppb, as well as highly selective and repeatable response to NH3. It is proposed that the formation of p/n junction between SnO2 and the conducting polymers of the composite played a crucial role in the improvement of its sensing performance, and the established nanostructure of the composite also contributed to the enhanced sensing properties.In-situ grown nanosheets of Fe2O3 and TiO2 have also been prepared on the substrates by means of hydrothermal synthesis of electrospun nanofibers containing the precursors of FeCl3 and tetrabutyl titanate (TBT), respectively. Gas sensors based on the nanocomposite of Fe2O3/PANI or TiO2/PANI were fabricated by dip-coating water-dispersible PANI on the interdigitated gold electrodes decorated with Fe2O3 or TiO2 nanosheets. Both composite sensors displayed high sensitivity (Fe2O3/PANI:relative resistance change of ～3000% towards 10.7 ppm of NH3; TiO2/PANI:relative resistance change of ～2800% towards 10 ppm NH3), excellent selectivity and good sensing repeatability in the detection of NH3 at room temperature. Moreover, the NH3 sensing performances of the composite sensors were better than that of the sensor based on the single component, suggesting an obvious synergetic effect between the inorganic metal oxides and PANI.