Organic-Mineral Interactions under Natural Conditions: A Computational Study of Flavone Adsorption on Smectite Clay

Interactions betweenorganic species and natural minerals are fundamentalto the processes around us. In this work, with the aid of moleculardynamics simulations, we investigate interactions of apigenin flavonoidwith montmorillonite clay mineral under a range of environmental conditions.The adsorption mechanisms are found to be sensitive to both the acidityand ionic composition of the surrounding brines. In particular, themechanism of adsorption changes from cocrystallization in acidic-to-neutralsolutions to ion-bridging in mild-alkaline. The ionic species playa significant role in alkaline environments: the deprotonated apigeninspecies chelate metals, which, in turn, leads to the formation ofa stable organic-metal-mineral complex and strongeradsorption in the presence of divalent cations. Smectite clays bufferthe solution to mildly alkaline; hence, the type of exchangeable cationsin the clay will be critical in determining the adsorption mechanismand organic retention capacity.