Clay minerals as sorbents for Hydrophobic Organic Chemicals (ClayHOC)

• Applicant: Dr. Leonard Böhm
• Subject Area: Soil Sciences
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 443637168

Hydrophobic organic chemicals (HOCs), such as halogenated aromatic hydrocarbons, may be highly persistent in the environment and cause harmful effects on humans and biota. They can be adsorbed in relevant amounts by clay minerals (CMs), but the structure-dependent mutual interactions between CMs (excess layer charge, specific surface, porosity, and cation type and distribution) and HOCs (molecular size, electronic structure, and hydrophobicity) are poorly understood. The aim of the DFG-FWF bilateral project is to elucidate the mechanisms underlying HOC–CM interactions with respect to the specific characteristics of both components. This aim will be achieved by combining adsorption experiments and molecular modeling methods. The major objectives are, experimentally, (i) to quantify the adsorption of HOCs with different hydrophobicities to CMs of varying layer charge; (ii) to determine the impact of the exchangeable cation type on the adsorption of model HOCs to CMs; (iii) to determine sorption hysteresis for HOC–CM interactions in terms of the specific surface and porosity of CMs; and, by using molecular simulations, (iv) to reveal the molecular mechanisms underlying the formation of surface complexes and intercalates of HOCs with CMs; and (v) to quantify HOC–CM interactions with respect to cation type and layer charge as well as to determine the impact of the solvent on the stability of HOC–CM complexes. HOC–CM interactions will be investigated in batch adsorption experiments accompanied by advanced experimental techniques (e.g., X-ray diffraction, XRD; transmission electron microscopy, TEM; atomic force microscopy, AFM) to obtain a complex characterization of the samples. The experiments will be conducted using 5 halogenated HOCs and 20 CMs (mostly smectites) with a defined layer charge and chemical composition, including the type of exchangeable cation. For selected HOCs and CMs, adsorption/desorption experiments will be performed to investigate sorption hysteresis. The HOCs will be extracted by solventless, miniaturized solid-phase microextraction (SPME). Molecular simulations will represent a combination of quantum chemical (QM) methods and classical (force field) molecular dynamics (FF-MD) using models determined on the basis of the experimental characterization. Molecular simulations will focus on elucidating the mechanisms of HOC–CM interactions at the molecular scale and determining the impacts of layer charge, cation type, and solvent effects on the stability of HOC–CM complexes. In specific cases, Grand Canonical Monte Carlo (GCMC) is planned for the prediction of adsorption isotherms. The collaboration between the German group (experiments) and the Austrian group (molecular modeling) will yield positive synergistic effects regarding new insights into HOC–CM interactions. The results will contribute to a better understanding of the environmental fate of HOC pollutants and improve assessments of the risk posed by these compounds.

• DFG Programme: Research Grants
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Cooperation Partner: Professor Dr. Martin H. Gerzabek