Fabrication of Sensitive and Selective Ammonia Gas Sensors Based on Pyrrole Interfacial Polymerization

In this work, we used polypyrrole (PPy) films prepared by chemical interfacial polymerization at the interface of hexane/water, as sensing layers in ammonia gas sensors. Anhydrous ferric chloride (FeCl3) was used as an oxidant and p-toluenesulfonic acid as a dopant. The polypyrrole films were grinded and dispersed in methanol and then deposited, via drop-casting, onto interdigitated electrodes screen printed on ceramic substrates. The prepared PPy was characterized by four-probe method, Fourier transform infrared spectroscopy, x-ray diffraction and scanning electron microscopy. Analyses confirmed the formation of PPy with quasi-spherical nanoparticles morphology, suitable for gas sensing applications. Design of experiments approach was used in order to investigate the effect of polymerization parameters (monomer and dopant concentration) on sensor sensitivity towards acetone, ethanol, chloroform, methanol, dichloromethane, toluene and ammonia vapors in the range of 100-4000ppm at room temperature and 20% relative humidity. All sensors showed high selectivity and good sensitivity towards ammonia. Under optimal conditions, the sensitivity reached 31% at 100ppm with a response time of 55s, and a recovery time of 640s, while the sensitivity towards all other analytes up to 4000ppm was negligible.