Humidity sensors based on TiO2 nanoparticles/polypyrrole composite thin films

Resistive-type humidity sensors were fabricated through in situ photopolymerization of pure polypyrrole (PPy) and TiO2 nanoparticles/polypyrrole (TiO2 NPs/PPy) composite thin films on an alumina substrate. The characterizations of the thin films were analysed by scanning electron microscopy (SEM) coupled with an energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR). The electronic properties of PPy and TiO2 NPs/PPy composite thin films were investigated based on the components AgNO3 and TiO2 used as electron acceptor and photoinitiator, respectively. The humidity sensing mechanism of TiO2 NPs/PPy composite thin films was investigated via the results of activation energy and impedance spectroscopy. The sensor made of TiO2 NPs/PPy composite thin films, using the added amount of TiO2 NPs as 0.0012 g showed the highest sensitivity, smaller hysteresis and best linearity. Moreover, other sensing properties, such as effects of applied frequency, ambient temperature, response and recovery time and long-term stability were also investigated.