Synthesis of Polypyrrole Using Ferric Chloride (FeCl3) as Oxidant Together with Some Dopants for Use in Gas Sensors

Polypyrrole (Ppy) was synthesized using Ferric Chloride (FeCl3) as oxidant. The ratio of monomer to oxidant was 1:2.4. The polymerization was carried out at 5 ̊C. Attempts were made to increase the electrical conductivity by using various dopants viz. Lithium per Chlorate (LiClO4), para-Toluene Sulfonate (p-TS) and Napthalene Sulfonic acid (NSA). The materials were characterized using FTIR, X-Ray diffraction and SEM. The electrical conductivity was measured by two probe method and was found to be in the range of 10 to 10 S/cm. Thin films of these preparations were casted on the interdigited electrodes to study the detection of gases such as ammonia and LPG. It was found that for the pure Ppy and one doped with LiClO4, when ammonia gas was allowed to flow in, there was a sudden increase in the current, which decreased rapidly when gas was stopped. This behavior is in contradiction to that observed in earlier investigations where Ppy was prepared by electrochemical method. However when Ppy doped with p-TS and NSA were used, the trend was reversed. Similarly it was noted that for pure Ppy and one doped with LiClO4, p-TS and NSA there was an increase in the current when LPG gas was brought in. However the response to LPG was somewhat low as compared ammonia gas.