Selectivity Tailoring of Polyaniline-based Gas Sensors towards Amine Homologs by Adsorption Regulation

Abstract

Accurate detection of amines is crucial in various fields, but the coexistence of homologs severely hinders this accuracy. In this study, theoretical simulations and experiments were utilized to investigate the key factors influencing polyaniline adsorption behavior and gas-sensing selectivity towards amine homologs, which were identified as the charge and steric hindrance of the adsorption sites. Then, substituents such as chlorine, ethyl, amino, and methoxy groups were introduced at the ortho position of aniline monomers to modulate the adsorption driving force and resistance and thus regulate their selectivity towards amine homologs. Among them, poly(o-methoxyaniline) responded to only two primary amines, methylamine (MA) and ethylamine (EA), with MA/EA selectivity coefficient greater than 3, nearly achieving MA-specific detection. Poly(2-chloroaniline) exhibited high selectivity for dimethylamine (DMA), significantly enhanced the discrimination of DMA, EA, trimethylamine (TMA), and triethylamine (TEA), increasing the selectivity coefficients of DMA/EA, DMA/TMA, and DMA/TEA from 2.42, 1.05, and 1.03 for PANI to 3.49, 20.21, and 2.10. Furthermore, poly(2-chloroaniline) achieved an error of only 4% in detecting DMA in a mixture with TMA at the same concentration. The influence of the material's intrinsic conductivity and matching with the response polarity on the suitability and sensitivity was also discussed.