Exploring an N-Type Conducting Polymer (BBL) as a Potential Gas Sensing Material for NH3 and H2S Detection: A Theoretical Study

Abstract

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, ammonia (NH3)and hydrogen sulfide (H2S), theoretically. Through molecular dynamics (MD) simulation and density functional theory (DFT)approach, we understand the adsorption behavior and selectivity of NH3 and H2S in the BBL film. Our results show that BBL displays remarkable adsorption for ammonia gas compared to hydrogen sulfide gas without compromising the π − π stacked crystallites within the polymer film. The DFT calculations show the adsorption energy of -0.32 eV and -0.21 eV for NH3 and H2S, respectively. MD simulations show that adsorption takes place in the free voids within the thin films, helping the polymer films to maintain their crystallinity, which indicates, upon detection of reducing gases, the generated free electrons will be able to be smoothly transported through the π − π stack network. The detailed theoretical insights obtained from this study indicate the suitability of the n-type conducting polymer, BBL, for the detection of reducing gases.