Polypyrrole nanofiber surface acoustic wave gas sensors

We present for the first time, to the best of authors’ knowledge, surface acoustic wave (SAW) gas sensors featuring polypyrrole nanofibers as the active component for hydrogen (H2) and nitrogen dioxide (NO2) detection at room temperature. Polypyrrole nanofibers were synthesized through a template-free chemical route by introducing bipyrrole as an initiator to speed up the polymerization of pyrrole in the presence of iron (III) chloride (FeCl3) as the oxidizing agent. Polypyrrole nanofibers were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopic (FT-IR) techniques which indicated that the average diameter of the nanofibers was 18 nm with lengths in the order of several microns. The polypyrrole nanofibers were dispersed onto the surface of a ZnO/36°YX LiTaO3 SAW transducer. Gas testing towards H2 and NO2 was conducted in an enclosed environmental cell at room temperature. Measured frequency shifts due to sensor responses were 20 kHz towards 1% of H2 and 4.5 kHz towards 2.1 ppm NO2, respectively. The sensor performance was assessed during a five-day period and repeatable results were obtained.