Computational study of bisphenol A adsorption on reduced graphene oxide: interactions, energies, pH effects, and adsorption mechanisms

Abstract

Nanomaterials have numerous applications. One material that deserves to be highlighted is reduced graphite oxide (rGO) due to its excellent adsorption capacity. Among the emerging contaminants, bisphenol A (BPA) generates numerous problems for human health, such as hormonal changes, immune dysfunction, and type 2 diabetes mellitus. In this context, the adsorption of BPA and its form with an anionic oxygen and a protonated oxygen were studied to simulate the effect of pH on the adsorption process, elucidated through computational simulations using density functional theory. The binding energies (ΔE_Bind) and enthalpy variation (ΔH) for all complexes were less than zero, ΔE_Bind and ΔH < 0.00 kcal mol⁻¹, showing that interactions can occur and that they are exothermic. The Gibbs energy values showed that only the interactions of anionic and protonated oxygen with the matrix were spontaneous. The structural parameters were identified, and the protonation or deprotonation of the BPA hydroxyl forms stronger bonds/interactions with the rGO matrix, showing a positive effect of pH on adsorption. From the analysis of the topological parameters of the quantum theory of atoms in molecules and the non-covalent interaction, it was possible to demonstrate that the interactions are electrostatic, with the exception of those that occur between the protonation or deprotonation of the BPA hydroxyl with the matrix that forms bonds. Finally, based on the theoretical results, it can be concluded that the rGO matrix can interact with BPA and that the effect of pH improves the adsorption process. Therefore, this study could support new experimental tests for removing this emerging contaminant from effluents.