Molecular insights through computational modeling of methylene blue adsorption onto low-cost adsorbents derived from natural materials: A multi-model's approach

The fundamental phenomena involved in methylene blue adsorption onto three different activated car- bons (a raw adsorbent and two samples derived from either chemical or thermal treatment of the raw sample) are elucidated by coupling different multi-physics modeling approaches. Statistical physics ap- proach leads to understand that methylene blue adsorption is mainly affected by the porosity of sorbents rather than their functional groups. Electrostatic interactions, Van der Waals forces or hydrogen bonding might occur between dye cations and carboxylate anions on adsorbent surface. The quantum chemical calculations suggest that dispersive interactions and pore characteristics of the activated carbon derived from thermal treatment predominantly contribute. The investigated reactive sites show that the same preferable sites for both electrophilic and nucleophilic attacks are detected for the sample derived from thermal treatment, allowing explaining the best performances of this adsorbent. Finally, the most sta- ble energy configuration of methylene blue adsorption on activated carbon is obtained by Monte Carlo simulations.