Molecular aggregation effect on the antagonistic adsorption of pharmaceuticals from aqueous solution using bone char: DFT calculations and multicomponent experimental studies

Abstract

This study reports theoretical calculations and experimental results to understand the impact of molecular aggregation on the multicomponent adsorption of three non-steroidal anti-inflammatory drugs (i.e., acetaminophen, diclofenac and naproxen) on bone char from aqueous solutions. DFT calculations were performed to estimate the main molecular properties of monomers, dimers and trimers of these pharmaceuticals. The molecular properties of single compounds and their aggregates were used to explain the steric factors involved in the antagonistic and endothermic adsorption of these pharmaceuticals in binary and ternary systems. It was established that the molecular properties of homogeneous and heterogeneous dimers and trimers of these adsorbates played a relevant role in the multicomponent adsorption mechanism using bone char. Results showed that a transition from a multilayer to monolayer adsorption process could occur depending on the adsorption temperature and the presence of pharmaceutical co-adsorbate(s). Overall, the multicomponent adsorption of naproxen was not significantly affected by the competition effect generated by other pharmaceuticals present in the aqueous solution but its removal mechanism was essentially via the formation of a monolayer. In contrast, the acetaminophen adsorption implied a multilayer mechanism mainly due to the molecular dimensions of its aggregates. Adsorbent characterization results suggested that the phosphate group from hydroxyapatite contained in bone char played a relevant role in the multicomponent adsorption of these organic compounds. These new findings are useful to comprehend the role of molecular aggregation of organic pollutants on the adsorbent performance for water depollution.