Nanotubular clay minerals for simultaneous sorption of pesticides and PFCAs: a molecular simulation study

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) and herbicides are important persistent contaminants that require specific management. A variety of herbicides is stored in fluorinated containers in the form of aquatic solutions. In such environments, the simultaneous release of PFAS and herbicides takes place. Nature-based solutions, such as the use of clay materials as possible sorbents, are attractive for the immobilization of such contaminants and environmental protection. Nanotubular clay minerals, such as halloysite and imogolite, are sufficient sorbents for herbicides. Due to their structural morphology, such materials could be efficient sorbents for the simultaneous immobilization of PFAS and herbicides. In this study, the potential sorption of a short chain PFAS, perfluorobutanoic acid (PFBA), sorbent of PFBA, and herbicides (atrazine and diuron) were investigated. Forcefield calculations were used for the classical molecular simulation study. Different distributions, arrangements, and ratios of the investigated molecules were investigated for the complete structural and energy characterization of the systems. Both clay minerals created stable complexes with PFBA as well as with both PFBA and herbicide molecules. Halloysite mineral led to similar total energies of the system with sorbed PFBA molecules alone, herbicides alone, or both of the pollutants. In contrast, imogolite led to lower energies with sorbed herbicides and showed relatively higher energies when interacting with PFBA. The complexes with both of the pollutants presented moderate energies. Electrostatic interactions were dominant in all the investigated complexes.