Electronic and Optical Properties of Polypyrrole as a Toxic Carbonyl Gas Sensor

Abstract

Chronic formaldehyde and acetaldehyde exposure is known to cause various health problems and the detection of these toxic carbonyl gases is very important and a subject of interest both experimentally and theoretically. In this study, the interaction of various oligomers (n = 1, 3, 5, 7, and 9) of polypyrrole towards toxic carbonyl species: acetaldehyde and formaldehyde, and less toxic carbonyl species: acetone and butanone were studied using density functional theory (DFT). The interactions of the carbonyl species with oligopyrrole lead to differences in interaction energies and changes in structural features: H-bond distances, bond angles, and dihedral angles. The changes resulted in variations in the electronic properties of the pyrrole-gas complexes: HOMO/LUMO energies, ionization potentials (IP), electron affinity (EA), and energy gap (EGap). The pyrrole-carbonyl complexes resulted in higher HOMO energies due to electron charge donation from the carbonyl gases and lower LUMO energies resulting in smaller EGap values compared to pyrrole. It was observed that the smallest carbonyl molecule, formaldehyde (For), had the lowest LUMO energy and lowest EGap value, while the largest carbonyl molecule, butanone (MEK), had the highest LUMO energy and highest EGap value. Furthermore, simulated UV–Vis absorption studies showed red-shifted first singlet excited state, λ1st, for the pyrrole-gas complexes. The results do not only demonstrate the potential of polypyrrole as a toxic carbonyl gas sensor but also its selectivity towards different carbonyl species.