Electrical conductivity and ammonia sensing studies on polythiophene/MWCNTs nanocomposites

Over the years, conducting polymer nanocomposites have been successfully utilized for the fabrication of ammonia sensors. But, fabrication of a sensor for selective detection of ammonia below 01 ppm is still a challenging task. Herein, we prepared polythiophene (PTh) and a series of PTh nanocomposites with multiwalled carbon nanotubes (MWCNTs) by in-situ chemical oxidation technique. The as-prepared samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). PTh/MWCNTs nanocomposites showed significantly enhanced electrical conductivity as well as ammonia sensing performance as compared to PTh. The sensor-based on PTh/MWCNTs-3 (PTh/MWCNTs nanocomposite containing 15% MWCNTs to the weight of monomers) was found to be an ultra-sensitive (detection limit of 0.1 ppm), completely reversible, highly selective and stable ammonia sensor at room temperature. The sensing response of PTh/MWCNTs-3 at 2000, 1500, 1000, 500, 400, 200, 100, 50, 1 and 0.1 ppm of ammonia was found to be 88.70%, 73.27%, 62.04%, 51.65%, 46.96%, 42.97%, 38.86%, 35.18%, 32.93% and 27.66%, respectively. The result showed that the relative humidity had only a small effect on ammonia sensing properties of PTh/MWCNTs-3. We demonstrated the sensing mechanism by electronic interaction of polarons (i.e. charge carriers) of PTh with the lone pairs of electrons of the ammonia molecule.