Organic-mineral interactions under natural conditions -- a computational study of flavone adsorption on smectite clay

Abstract: Interactions between organic species and natural minerals are fundamental to the processes around us. With the aid of molecular dynamics simulations, we identify key adsorption mechanisms of apigenin on smectite clay minerals. The mechanism is highly sensitive to the pH -- changing from co-crystallisation in acidic-to-neutral solutions to the ion-bridging in mild-alkaline. The ionic species play a significant role in alkaline environments: the deprotonated apigenin species chelate metals, which, in turn, leads to the formation of a stable organic-metal-mineral complex and stronger adsorption in the presence of divalent cations.Smectite clays buffer the solution to mildly alkaline; hence, the type of exchangeable cations in the clay will be critical in determining the adsorption mechanism and organic retention capacity. Overall, our study showcases a computational strategy that can be transferred to a wide variety of organic-mineral systems in the natural environment.