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