Influence of surface morphology and doping of PPy film simultaneously polymerized by vapour phase oxidation on gas sensing

In this work, polypyrrole (PPy) films were directly deposited on Al2O3 substrate by a facile template-free vapour phase polymerization route using ferric chloride (FeCl3) oxidant. Influence of the surface morphology and doping of the PPy structures on the gas sensing performance was investigated. The synthesized PPy films with different morphologies including nanoparticles-cluster, nanofibers-matrix and porous-structure were obtained by simply regulating the utilized FeCl3 solutions in concentration range from 0.01 to 0.06 M. The increase in the used FeCl3 concentration led to a monotonous increase in the doping/oxidant content of the PPy film. Sensing performances of the PPy films were examined by investigating their resistances responding to NH3, NO2, H-2, CO and CH4 gases, and relative humidity (11-95% RH) at room temperature (25 degrees C). All the PPy films presented to have high selectivity and reversibility to NH3 gas. The highest response to NH3 gas and the lowest humidity influence were found for the nanoparticles-cluster PPy film. The fast sensing response times of the PPy films were about 10, 7, 4 and 3 s in order of the used FeCl3 concentrations of 0.01, 0.02, 0.04 and 0.06 M, respectively. The sensing performances at room temperature of the PPy films were suggested to be attributed by both their surface morphology and doping content.