Insight into properties and reutilization potential of spent polyaniline adsorbents containing transition metals through DFT calculations

Although adsorption technology is an efficient way for removing heavy metal pollutants from wastewater, its widespread application faces challenges related to the disposal and reutilization of hazardous spent adsorbents. Here, we employ density functional theory (DFT) calculations to investigate the properties and reutilization potential of spent PANI adsorbents containing transition metal ions. Bond strength analysis reveals the high stability of spent PANI adsorbents, which is crucial for their safe reutilization. The interaction region indicator (IRI), localized orbital locator (LOL), and decomposition analysis of Wiberg bond order were employed to understand the nature of the bonds between transition metals and imine N atoms. Fukui function analysis indicates that the presence of reducing groups and reductive metal ions in spent PANI adsorbents enhances their chemical stability. The atomic dipole moment corrected Hirshfeld (ADCH) charge and electron density difference (EDD) analysis reveals electron transfers between transition metals and PANI. Moreover, assessments of electrical conductivity, electronic density under electric fields, excited states, and surface charge demonstrate that spent PANI adsorbents hold significant potential for use in energy storage, electrocatalysis, photocatalysis, and environmental pollutant removal. This study provides a molecular-level understanding of the properties and reutilization potential of spent PANI adsorbents.