Interactions of organic pollutants with soil components - elucidating mechanisms on a molecular level

Principle investigators: Prof. Dr. M.H. Gerzabek, Prof. Dr. H. Lischka, Doz. Dr. D. Tunega, Doz. Dr. G. Haberhauer, Dr. W. Friesl-Hanl

Co-workers: Dr. A. Aquino, Dr. G. Waldner, Dr. R. Solc

Aims:
a)Selection, improvement and development of simulation approaches.
b)To develop more realistic theoretical models for simulations of interactions
c)Prediction of thermodynamic and spectroscopic quantities and adsorption isotherms
d)Evaluation and linking of theoretical outcomes of the modelling to experimental results
e)The final objective is to develop new tools based on theoretical methods for a quick first assessment of the potential behaviour of new compounds in soil interfaces

Hypotheses:
The behaviour of organic compounds on the microscale is distinctly influenced by interactions of these compounds on the nanoscale. Theoretical chemical methods can contribute to elucidating basic processes involved.

Work planned:
• Modelling of minerals, mineral surfaces and organo-mineral complexes will be concentrated on typical soil minerals (kaolinite, montmorillonite, illite, phlogopite, goethite, lepidocrocite, ferrihydite, quartz, and boehmite).
• It is planned to build extended humic substances models (supramolecular, micelle-like and nanopore models) with varying content and distribution of typical functional groups such as -OH, -NH2 and -COOH aiming at investigation of interactions of SOMs with organic compounds selected from the set of species defined in the first SPP 1315 phase (phenanthrene, bentazone).
• elucidation of the chemical mechanism of the formation of humic-acid-like polycondensate structures
• Black carbon: A variety of defect models will be designed starting from the structural basis of PAHs (e.g. phenanthrene, coronene) and from graphene in case of periodic systems.
• Sorption experiments on kinetic and equilibrium conditions will be studied in batch experiments with artificial prepared soils. Bentazone and MCPA will be taken as probe sorbates. Effects like incubation, ionic strength and pH of solution will be investigated as well.

Cooperation within the SPP:
• Experimental techniques like XANES, NMR (TU München), AFM (FSU Jena) will be used for the complex characterization of the studied samples.
• TU Berlin: adsorption experiments and microcalorimetry
• University Koblenz: soil organic matter models and NMR and nanothermometry
• TU München: model experiments; complementary batch experiments
• Contact angle and XPS measurements by Univ. Hannover

Methods used in the project:
Quantum chemical methods:
- standard Density Functional Theory (DFT) based programs (VASP, Turbomole,
- new, efficient DFTB (approx. DF tight-binding) methods
Force-fields methods:
- standard FF intramolecular parameters will be used;
- interatomic potentials will be represented by the Lennard-Jones potential + atomic charges.
- potential of mean force method
Molecular dynamics:
- DFT, DFTB and FF will be combined with MD
- statistical methods for elucidation of MD results