Adsorption of diclofenac on nanosheet graphene and type-graphene boron nitride: a DFT-ONIOM calculations

Recently, researchers have widely studied a new problem regarding water quality, specifically the presence of certain chemical substances in diverse bodies of water that had not been detected previously due to their low concentrations but now are beginning to impact marine fauna and human health. Due to their elimination requiring urgent attention, they have been named emerging contaminants (ECs). Since the conventional wastewater treatment plants (WWTPs) had not considered these ECs, at present, new methodologies have emerged for producing the degradation or mineralization of these substances; particularly, the inclusion of adsorbent materials in these methodologies has been proposed to complement the removal process of the ECs. The investigated adsorbent materials are graphene (G) and diverse types of graphene, like boron nitride and boron nitride doped with carbon atoms (G-NB and G-NBC). In this work, a theoretical study of the adsorption of diclofenac over these types of nanosheets has been carried out, using the density functional theory (DFT) with the combination of functional and base, M062X/6-31G**, and the “Our own N-layered Integrated Molecular Orbital and Molecular Mechanics (ONIOM)" methodology, all within the computational Gaussian package. In this context, the aim of the investigation was addressed to evaluate, through various adsorption descriptors, if the DFC molecule can be adsorbed by these nanosheets. For the adsorption complexes studied, using the three nanosheets considered, the adsorption distances were in the range of 2.6–3.5 Å, with adsorption energies (Eads) close to 20 kcal mol⁻1 and thermodynamic parameters that denoted a spontaneous but exothermic adsorption process; these indicators allowed us to establish the existence of physisorption processes. Noncovalent interactions between the DFC molecule and the nanosheets were found, mainly through hydrogen atoms belonging to the -OH, -NH, and -CH2 (in α to > C = O) groups of the molecule and, besides, π-type stacking interactions in the complex involving the G-P nanosheet.