Gas sensing properties of layer-by-layer self-assembled ultrathin film of polyaniline/titanium dioxide

Electrostatic layer-by-layer (LbL) self-assembly (SA) was realized with processable polyaniline prepared with polystyrene sulfonic acid as a template (PANI-PSSA) and titanium dioxide sol as the starting materials, resulting in an ultrathin film of PANI-PSSA/TiO2. The SA process was confirmed by UV–vis spectra and quartz crystal microbalance measurements. The composite ultrathin film was characterized by X-ray photoelectron spectroscopy, X-ray diffraction patterns, field-emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. It was revealed that the content of TiO2 in the composite film was much higher than that of PANI-PSSA, and the doping level of PANI-PSSA was as high as 19.1%. Gas sensors were fabricated by depositing self-assembled ultrathin film of PANI-PSSA/TiO2 on interdigital gold electrodes, then covering another layer of PANI-PSSA via dip-coating. Electrical response to NH3 of the sensor was investigated at room temperature. Gas sensitivity of the sensor was found to closely relate to the number of self-assembled bilayers. Under optimal conditions, the sensor displayed high sensitivity (26.5% and 81.2% towards NH3 of 10 and 100 ppm, respectively), fast response (response time ∼ 1 min; recovery time ∼ 2 min), good reversibility and repeatability.