Synthesis of different inorganic acids doped polyaniline materials and behavior of enhancing NH3 gas sensing properties

The rapid response gas sensor for detecting the NH3 gas in the environment at room temperature still stays many challenges, limited by the sensing material and their poor sensing characteristics. However, for conducting polymer polyaniline (PANI), researchers always bypass the most critical influence factor protonic acid to study the effect of oxide, graphene, and carbon nanotubes on it. Therefore, this paper focuses on the affecting of hydrochloric acid (HCl), phosphoric acid (H3PO4), and boric acid (H3BO3) as protonic acid on PANI as ammonia (NH3) sensitive material. In this work, a planar room temperature (RT) NH3 sensor was manufactured by coating X-PANI (HCl-PANI, H3PO4-PANI, H3BO3-PANI) organic semiconductor material on the gold interdigital electrode by air gun spraying. The micromorphology, element distribution, phase composition, and nanostructure of the sensing materials were obtained by FSEM, EDS, XRD, FTIR, and Raman. The results show that the HCl-PANI has excellent sensing response, low detection limit, good selectivity, and repeatability. Simultaneously, the process of X-PANI adsorbing NH3 or NH3 and H2O is calculated by density functional theory (DFT). The results further demonstrate that the synergistic effect of NH3 and H2O enhanced the adsorption of NH3 by X-PANI at higher relativity humidity (RH). This study provides a sufficient reference for the gas sensitivity of protonic acid-doped PANI and contributes to the understanding of the sensing mechanism.