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. In this work, with the aid of molecular dynamics simulations, we investigate interactions of apigenin flavonoid with montmorillonite clay mineral under a range of environmental conditions. The adsorption mechanisms are found to be sensitive to both the acidity and ionic composition of the surrounding brines. In particular, the mechanism of adsorption changes from cocrystallization in acidic-to-neutral solutions to 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.