Unraveling Ammonia and Trimethylamine Uptake on Conductive Doped Polyaniline.

Polyaniline (PAni)-based sensors are a promising solution for ammonia (NH 3 ) detection at the ppb level. However, the nature of the NH 3 -PAni interaction and underlying drivers remain unclear. This paper proposes to characterize the interaction between doped PAni (dPAni) sensing material and NH 3 by using a Knudsen cell. First, to characterize the dPAni interface, the probe-gas method, i.e., titration of surface sites with a gas of specific properties, is deployed. The dPAni interface is found to be homogeneous with more than 96% of surface sites of acid nature or with hydroxyl functional groups. This result highlights that basic gases such as amines might act as interfering gases for NH 3 detection by polyaniline-based sensors. Second, the adsorption isotherms of NH 3 and trimethylamine (TMA) on dPAni are reported at ambient temperature conditions, 293 K. The uptake of NH 3 and TMA on dPAni follows a Langmuir-type behavior. This approach allows for the first time to quantify the uptake of NH 3 and TMA on gas-sensor materials and determine typical Langmuir adsorption parameters, i.e., the partitioning coefficient, K Lang , and the maximum surface coverage, N max . The corresponding values obtained for NH 3 and TMA are K lang (NH 3 ) = 19.7 × 10 -15 cm 3 molecules -1 N max (NH 3 ) = 11.6 × 10 14 molecules cm -2 , K Lang (TMA) = 7.0 × 10 -15 cm 3 molecules -1 N max (TMA) = 5.0 × 10 14 molecules cm -2 . K Lang and N max values of NH 3 are higher than those of TMA, suggesting that NH 3 is more efficiently taken up than TMA on dPAni. The results of this work suggest that strong hydrogen bonding drives the performance of a polyaniline-based gas sensor for NH 3 and amines. In conclusion, the Knudsen cell approach allows reconsidering the fundamentals of NH 3 interactions with dPAni and provides new insights on drivers to enhance sensing properties.