Toxic Gas and Vapour Detection by Polyaniline Gas Sensors

The response mechanism of polyaniline to a selection of gases and vapours was investigated by measuring its conductance and mass changes by using a fourprobe method, elemental analysis, and X-Ray fluorescence (XRF) technique. The prepared films were exposed to hydrogen halides, hydrogen cyanide, hydrogen sulphide, halogens, acetic acid, rnono-, di-, and trichloroacetic acid, formaldehyde, hexachloroacetone, 1,3,5-trichloromethyl benzene, methyl benzyl bromide, bromoacetone and cyanogen bromide. It is observed that the polyaniline conductance changes are partly due to two-stage sorption perhaps involving the swelling of the polymer and gas diffusion. All the films were exposed to dilute ammonia solution or vapours of organic solvents and swelled before doping, which could modify the mass and electrical measurements. It was demonstrated that slightly additional amounts of Hel gas in tested gases will significantly influence the conductivity. It is concluded that the response mechanism of polyaniline sensing of different gases and vapours is due to a mixed response involving electronic and physical effects.