Exploring an n-type conducting polymer (BBL) as a potential gas sensing material for NH3 and H2S detection

Conducting polymers (CPs) have garnered significant interest in being used as an active material in gas sensors mainly because of their structural flexibility, ease of synthesis, and enhanced performance at room temperature. The p-type CPs and their composites are mostly studied in gas sensing, which, unfortunately, exhibit limitations in terms of selectivity, stability, and sensitivity toward reducing gases. This study focuses on one of the widely studied n-type polymers, BBL(benzimidazobenzophenanthroline), as an active material for the detection of two reducing gases, namely, hydrogen sulfide (H[Formula: see text]S) and ammonia (NH[Formula: see text]), theoretically. Through molecular dynamics (MD) simulation and density functional theory (DFT) approach, we understand the adsorption behavior and selectivity of H[Formula: see text]S and NH[Formula: see text] in the BBL film. The DFT calculated adsorption energy of the preferential site at the top of a [Formula: see text] stack for H[Formula: see text]S and NH[Formula: see text] are - 0.22 eV and - 0.33 eV, respectively, and at the sides of a [Formula: see text] stack for H[Formula: see text]S and NH[Formula: see text] are - 0.42 eV and - 0.47 eV, respectively. MD simulations show that adsorption takes place in the free voids within the thin films, and the overall structure of the polymer film remained almost unaltered upon gas adsorption without any apparent swelling or significant morphological changes in the film. Our results show that BBL displays remarkable adsorption along with a higher magnitude of charge transfer for ammonia over hydrogen sulfide gas and other common gases present in the air. Moreover, both H[Formula: see text]S and NH[Formula: see text] gas adsorption happen without compromising the size of the [Formula: see text] stacked crystallites within the polymer film, which indicates, upon detection of reducing gases, the generated free electrons via the redox reactions between the gas molecules and polymer, will be able to be smoothly transported through the [Formula: see text] stack network present in the film. The detailed theoretical insights obtained from this study indicate the suitability of the n-type conducting polymer, BBL, for detecting reducing gases, NH[Formula: see text] and H[Formula: see text]S.