DFT Study of Polyaniline NH3, CO2, and CO Gas Sensors: Comparison with Recent Experimental Data

Density functional theory studies (DFT) have been carried out to evaluate the ability of polyaniline emeraldine salt (PANT ES) from 2 to 8 phenyl rings as sensor for NH3, CO2, and CO. The sensitivity and selectivity of nPANI ES among NH3, CO2, and CO are studied at UB3LYP/6-31G(d) level of theory. Interaction of nPANI ES with CO is studied from both 0 (CO(1)) and C (CO(2)) sides of CO. Interaction energy, NBO, and Mulliken charge analysis were used to evaluate the sensing ability of PANT ES for different analytes. Interaction energies are calculated and corrected for BSSE. Large forces of attraction in nPANI ES-NH3 complexes are observed compared to nPANI ES-CO2, nPANI ES-CO(1), and nPANI ES-CO(2) complexes. The inertness of C+ O- in nPANI ES-CO(1) and nPANI ES-CO(2) complexes are also discussed. Frontier molecular orbitals and energies indicate that NH3 changes the orbital energy of nPANI ES to a greater extent compared to CO2, CO (1), and CO(2). Peaks in UV-vis and UV-vis-near-IR spectra of nPANI ES are blue-shifted upon doping with NH3, CO2, CO(1), and CO(2) which illustrates dedoping of PANI ES to PANT emeraldine base (PANI EB). Finally, it is concluded that PANI ES has greater response selectivity toward NH3 compared to CO2 and CO and it is consistent with the experimental observations.