On the Trapping and Sensing Mechanism of Polyaniline with Heavy Metals (Cr, Cd, and Pb): Insights from Ab Initio Calculations

The bonding character of Polyaniline (PANI) and heavy metals (Cd, Cr, and Pb) is examined using density functional theory with Tkatchenko-Scheffler dispersion correction. Cr and Pb's interaction with PANI is generally described as chemisorption, while Cd bonds via physisorption. This claim is based on the calculated binding energy, interaction distance, hybridization of the frontier orbitals, and electron localization function. The calculations revealed that Cr adsorbed strongly with the highest magnitude of binding energy (-4.31eV), followed by Pb (-0.50eV) and Cd (-0.11eV). Significant deformation of the PANI upon adsorption of Cr and Pb, while Cd induces no significant bond deformation. The bandgap of the PANI is reduced upon the adsorption of Cr and Pb but minimal on the adsorption of Cd. Further, the optical response of PANI and heavy metals is examined using time-dependent density functional perturbation theory and independent particle approximation. The absorbance spectra of PANI compared with PANI-heavy metals (Cr and Pb) show a distinct feature. The adsorption of Cr and Pb allows the absorption of photons in the infrared region. The results indicate that PANI is a suitable sensing and adsorbent material for Cr and Pb. This work provides a fundamental understanding of the interaction of PANI with heavy metals and provides a basic trend on its optical response.