Study of the primary sensitivity of polypyrrole/r-Fe2O3 to toxic gases

Polypyrrole (PPy) was prepared by chemical oxidation using methoxy ethanol as solvent and Fe(NO3)3·9H2O as oxidant. PPy/r-Fe2O3 was prepared by simultaneously gelling and polymerization, using the same solvent and oxidant. The materials were characterized by FTIR, XRD, TG-DTA, SEM, and HRTEM, and studied for the gas sensitivity. From the TG-DTA curve of PPy/r-Fe2O3, we found that the degradation temperature of PPy was about 210 °C, so the annealing temperatures of PPy/r-Fe2O3 were selected at 110 °C, 150 °C, 180 °C, and 200 °C. The influence of the mole ratio of Fe(NO3)3·9H2O to py = 1:1, 2:1, 3:1, 4:1, and 5:1 on the gas sensitivities of PPy was investigated. It was found that PPy had the maximum sensitivity to NH3 and H2S at the mole ratio of Fe(NO3)3·9H2O:py = 3:1 at room temperature, and the sensitivities were 48.5 and 31.4, respectively. PPy/r-Fe2O3 materials had no gas sensitivity at room temperature. When the working temperature increased to 90 °C, PPy/r-Fe2O3 materials appeared gas sensitivity, PPy/r-Fe2O3 annealed at 150 °C had the maximum sensitivity to NH3 and H2S, and the sensitivities were 68 and 406.8, respectively, but PPy lost gas sensitivity at this temperature. The results suggested that PPy/r-Fe2O3 had higher sensitivity and more heat stability than PPy, and the working temperature was lower than the reported working temperature of r-Fe2O3 about 350 °C, it had better properties than both pure PPy and r-Fe2O3.