Combining multi-scale simulations and experiments to unveil the adsorption of methylene blue in graphene tridimensional-based materials

Abstract

This work aimed to combine different experiments and multi-scale theoretical approaches to understand the adsorption process of methylene blue in three-dimensional graphene-based materials. For this, experiments were carried out on the adsorption of methylene blue dye onto three-dimensional graphene containing different amounts of reducing agent and, consequently, different pore sizes and degrees of oxidation. Kinetic studies and equilibrium isotherms were obtained, and kinetic and isothermal models were applied. Furthermore, we employ density functional theory (DFT) simulations to cover quantum details to unveil how methylene blue will interact with GO flakes. In addition, large-scale coarse-grained simulations based on the Martini force field were used to analyze the system at the micrometer scale. Our experimental results showed that the more oxidized the material, the greater the dye removal efficiency, with adsorptive capacities up to 1034.70 mg g⁻¹. Theoretical studies showed how the dye interacts with the graphene surface and the oxygenated groups and how the grouping of dye molecules is relevant for adsorption, mainly as a function of pore sizes. Also, according to theoretical studies, binding energies, binding distances, and charge transfer between oxidized graphene and MB dye are compatible with physical adsorption, dependent on functional groups on the graphene surface. Thus, the combination of different theoretical approaches allowed an unprecedented understanding of the adsorption process of methylene blue dye in graphene materials with different characteristics obtained during their synthesis.