Molecular modeling design of polyaniline as carbon dioxide sensor

Polyaniline (PANI) is a most promising material for sensing due to its straightforward preparation procedure, high chemical, environmental stabilities and low cost. The ability of PANI to interact with H2O and CO2 with concomitant changes in the electronic and geometric properties of PANI makes it as potential sensor for CO2. Detection and monitoring of CO2 by quantum mechanical studies have been devoted to examine the sensitivity and selectivity of PANI at the molecular level. From quantum mechanics to explain the CO2 adsorption is quite important because CO2 in the greenhouse can be detrimental for plant growth and consequently productivity. Compared with traditional industrial sensors, polymer-based sensors for the agricultural exhibit several advantages such as working under extreme temperatures, pressures, and complex environment. However, the poor solubility of PANI and low chemical reactivity restricts its widespread application to a great extent. Introducing functional groups in PANI backbone is an effective method to improve the solubility, chemical reactivity and sensitivity of PANI, this method can increase the sensing properties of PANI and do not strongly impact the conductivity. Therefore, measurements of the adsorption energy and charge transfer for H2O and CO2 in emeraldine base PANI (EB-PANI) and undoped sodium sulfonated PANI (Na-SPANI) using first principles methods were investigated. Doping could greatly changing the sensing mechanism of conducting polymer, so not only the adsorption sites but also the functional group affecting the gas sensitive performance were studied. The adsorption energy and Mulliken charge analysis were obtained for EB-PANI and Na-SPANI to evaluate the sensing ability of them for analytes. Besides, we also combined molecular dynamics to calculate mean square displacement of CO2 in EB-PANI and Na-SPANI. We concluded that Na-SPANI has greater response toward H2O and CO2 than EB-PANI. So Na-SPANI can be used as sensing material for CO2 detection. This study provides a rational way using first principle simulation to evaluate and design PANI for the application of carbon dioxide sensor.