Molecular dynamics simulations of the adsorption of bisphenol A on graphene oxide

The elimination of bisphenol A (BPA) from water solution is of great importance, since BPA can cause the functional abnormalities of human endocrine system. One feasible removal method is the adsorption by graphene oxide (GO). However, the interactions between BPA and GO at an atomic level are still unclear. In this study, molecular dynamics simulations are performed to investigate the adsorption of BPA on the GO surface. The results show that all BPA molecules are attached to both sides of GO. The adsorption conformations of BPA in the closest layer to GO surface mainly exhibit two patterns. One is that the benzene rings of BPA are parallel to the basal plane of GO to form pi-pi structures, and the other is the two hydroxyl groups of BPAs interacting with the oxygen-contained groups on GO to form hydrogen bonds. Exploration of the detailed interactions between BPA and GO indicates that the hydrophobic pi-pi stacking interaction is the dominant force in the adsorption of BPA on GO, while hydrogen bonding enhances the binding of BPA on GO surface. Eventually, potential of mean forces (PMF) of BPA and water molecules on GO are calculated by umbrella sampling. The binding energy of BPA on GO reaches 30 kJ/mol, six times as large as that of water on GO, which is only about 5 kJ/mol. Our simulations further confirm that GO owns strong adsorption capacity and GO can be used as sorbent to eliminate BPA in water solution.