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

TL;DR

This study uses molecular dynamics simulations to explore how organic molecules like apigenin adsorb onto smectite clay minerals, revealing pH-dependent mechanisms and the importance of ionic species in natural conditions.

Contribution

It introduces a computational approach to understand organic-mineral interactions, highlighting the influence of pH and ionic species on adsorption mechanisms.

Findings

Adsorption mechanism shifts from co-crystallisation to ion-bridging with pH change.

Deprotonated apigenin chelates metals, forming stable complexes.

Exchangeable cations in clay influence organic retention capacity.

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.