Effect of moisture and molecular weight of polyaniline on H 2 S sensing characteristics

Chemical behavior of some gases, such as H 2 S, changes with presence of moisture. Sensing of H 2 S by polyaniline (PANI) has been studied; the sensing characteristics depend upon the specific surface area, concentration of active surface sites, pore size, and surface heterogeneity controlled by the chain configuration, which is further governed by the molecular weight. However, effects of moisture in the environment and molecular weight of PANI on H 2 S sensing characteristics have not been studied, and this is the motivation of the present work. Here we have studied the H 2 S sensing by PANI of different molecular weights in the same environment (N 2 ) with different moisture (dry and humid) conditions, and in different environments (N 2 and compressed air) at the same humidity level. It was observed that regardless of the environment, (i) with increasing concentration of H 2 S gas, the resistance of the sensors increased in dry atmosphere and decreased in presence of moisture, and (ii) the response time was lower in moist conditions. The sensitivity and response were non-monotonous with respect to the molecular weight. However, response time decreased monotonically with increase in band gap of PANI. New correlations were developed to get surface site kinetics from the response data.