Fabrication and design of a toxic gas sensor based on polyaniline/titanium dioxide nanocomposite film by layer-by-layer self-assembly

A sensitive polyaniline (PANI)/titanium dioxide (TiO2) based toxic gas sensor deposited on a quartz crystal microbalance (QCM) chip was fabricated and developed through electrostatic layer-by-layer (LbL) self-assembly (SA) with polyaniline and titanium dioxide sol as original materials. The synthesis process and the obtained nanocomposite were confirmed through a home-made measurement set-up, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopic (FTIR) and X-ray diffraction (XRD), which demonstrates that a thin PANI/TiO2 nanocomposite sensing film was successfully achieved by LbL self-assembly. The sensor response was found to be greatly influenced by the number of deposited layers. The resulting PANI/TiO2 based gas sensor exhibited good sensitivity and smooth shift in terms of responses based on frequency data compared to responses based on resistance data. It exhibited high sensitivity toward 10 ppm of three different toxic gases (ammonia, hydrogen sulfide and trimethylamine) with an evident frequency shift and a fast response and recovery time. The sensor showed excellent reversibility and long-term stability as well as good selectivity towards NH3. In real-time application, the obtained PANI/TiO2 based gas sensor exhibited excellent performance and accurate evaluation of three typical foodstuffs. The PANI/TiO2 nanocomposite based gas sensor coated on QCM substrate via LbL self-assembly provides a promising efficient sensor to detect toxic gases in relatively low concentrations.