DFT Study of Polyaniline NH<sub>3</sub>, CO<sub>2</sub>, and CO Gas Sensors: Comparison with Recent Experimental Data

Abstract

Density functional theory studies (DFT) have been carried out to evaluate the ability of polyaniline emeraldine salt (PANI ES) from 2 to 8 phenyl rings as sensor for NH<sub>3</sub>, CO<sub>2</sub>, and CO. The sensitivity and selectivity of <i>n</i>PANI ES among NH<sub>3</sub>, CO<sub>2</sub>, and CO are studied at UB3LYP/6-31G­(d) level of theory. Interaction of <i>n</i>PANI ES with CO is studied from both O (CO(1)) and C (CO(2)) sides of CO. Interaction energy, NBO, and Mulliken charge analysis were used to evaluate the sensing ability of PANI ES for different analytes. Interaction energies are calculated and corrected for BSSE. Large forces of attraction in <i>n</i>PANI ES-NH<sub>3</sub> complexes are observed compared to <i>n</i>PANI ES–CO<sub>2</sub>, <i>n</i>PANI ES-CO(1), and <i>n</i>PANI ES-CO(2) complexes. The inertness of <sup>+</sup>CO<sup>–</sup> in <i>n</i>PANI ES-CO(1) and <i>n</i>PANI ES-CO(2) complexes are also discussed. Frontier molecular orbitals and energies indicate that NH<sub>3</sub> changes the orbital energy of <i>n</i>PANI ES to a greater extent compared to CO<sub>2</sub>, CO(1), and CO(2). Peaks in UV–vis and UV–vis–near-IR spectra of <i>n</i>PANI ES are blue-shifted upon doping with NH<sub>3</sub>, CO<sub>2</sub>, CO(1), and CO(2) which illustrates dedoping of PANI ES to PANI emeraldine base (PANI EB). Finally, it is concluded that PANI ES has greater response selectivity toward NH<sub>3</sub> compared to CO<sub>2</sub> and CO and it is consistent with the experimental observations

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