Analyzing the Azorubine (E122) Adsorption Mechanism on Alumina Using Molecular Dynamics Simulation and the Density...

This study investigates the adsorption mechanisms of the organic azo dye azorubine (E122) on the surface of alumina (γ-Al₂O₃), using molecular dynamics simulations, density functional theory (DFT), noncovalent interaction, and reduced density gradient analyses. The chemical reactivity of E122 was evaluated using DFT with the B3PW91 hybrid exchange-correlation functional and the LANL2DZ relativistic pseudopotential basis set. Speciation analysis showed that pH strongly influences the distribution of E122's ionic forms according to their pKa values, with forms 1, 2, and 3 predominating across the studied pH range, and the dye exhibiting strong affinity for the adsorbent surface in aqueous medium. DFT analysis identified key active sites and electronic properties governing dye-surface interactions and adsorbent affinity. Form 2 showed the highest adsorption energy (-917.107 kcal/mol), followed by forms 1 and 3 (-861.553 and -806.286 kcal/mol, respectively). These adsorption properties were further confirmed through density field and energy distribution analyses, while radial distribution function profiles, with all interatomic distances within 3.5 Å, confirmed a chemisorption-driven mechanism. Overall, γ-Al₂O₃ is an effective, low-cost, recyclable, and eco-friendly adsorbent for dye removal.