Thermally assisted NO$_{2}$ and NH$_{3}$ gas desorption process in a polyaniline thin film based optochemical sensor

Abstract

NO$_{2}$ gas is a strong electron acceptor that can oxidize the chemically deposited semiconductor polyaniline (PANI) at room temperature under atmospheric pressure. Since each redox state of this polymer is associated with a specific electronic structure, an oxidized PANI thin film undergoes a color change that can be detected in a sensitive optochemical sensor. But the strongly absorbed NO$_{2}$ molecules cannot be removed at room temperature from the polymer material during the purging process with a dried N$_{2}$ gas flux. We report in this work that a heating element can be integrated into the optochemical sensor to elevate the sensing sample temperature during the desorption process. At temperatures higher than 50$^{\circ}$C, the optical signal of the NO$_{2}$ absorbed PANI samples starts to return to its original value during the purging process, suggesting the desorption of the NO$_{2}$ species from the PANI samples. The higher the heating temperature, the greater the activation energy for desorption, and consequently the faster the desorption speed. Similar results are also obtained for the NH$_{3}$ desorption process occurring in the same polymer.