NH3 and HCl sensing characteristics of polyaniline nanofibers deposited on commercial ceramic substrates using interfacial polymerization

This paper reports the use of the interfacial polymerization method in a simple route for fabricating low-cost, highly sensitive NH3 and HCl gas sensors made of polyaniline (PANI) nanofiber coatings on commercially available ceramic substrates. The PANI coatings consisted of uniform nanofibers and formed emeraldine salt. NH3 gas-sensing properties of as-synthesized PANI nanofibers were also investigated in detail. The influence of PANI nanofiber acidification treatment at different HCl solutions (pH = 0, 1, 2, and 3) on NH3-sensing properties was discussed as well. As-synthesized PANI nanofibers exhibited very low detection limit (1 ppm) and high sensing response (response S) was above 2 when the sensor was exposed to 50 ppm NH3 gas, though a limited drift of the response appeared in the reproducibility test. For acid-treated PANI sensors, the response time increased and response S decreased with increasing pH value of HCl solutions. Response S, especially after acid-treatment, increased as testing proceeded. This is possibly due to the creation of reaction sites on the surface and/or the bulk of the sensors. When PANI was used to detect gaseous HCl, an irreversible process occurred and response S became saturated when the concentration of gaseous HCl reached 200 ppm.