How herbicides like atrazine and diuron interact with the spiral halloysite structure

Abstract

The spiral tubular morphology of the halloysite mineral presents an interesting opportunity for pollutant remediation: a large specific surface area, porosity, high adsorption capacity, bivalent adsorbancy, and colloidal behaviour. Two worldwide used herbicides are atrazine and diuron, which have shown harmful impacts on the environment and fauna, including humans. Therefore, both herbicides were studied to test their interactions on the halloysite tubular structure. Force field methods using the COMPASS force field were applied to perform the geometry optimisation and molecular dynamics on the atrazine/diuron-halloysite models. The models were prepared with different herbicide loading ratios on the inner and outer parts of the halloysite structure to find the preferable interacting surface. The simulation showed that both halloysite surfaces could interact with atrazine and diuron molecules. Further, the herbicides’ arrangement on the surfaces depends on the herbicide’s concentration and subsequently on their mutual interactions. The inner surface of the halloysite showed stronger interactions with both herbicides than the outer surface, and especially with diuron (e.g., binding energies per herbicide molecule for atrazine and diuron were –115 ± 2 and –130 ± 3 kJ·mol−1, respectively). Increasing herbicide concentration on the inner surface is limited by free space, and the interaction capacity becomes gradually saturated both for atrazine and for diuron.