Interactions of organic pollutants with soil components investigated by means of molecular modelling

摘要

The major objective of our work is to develop new tools based on theoretical methods for a quick first assessment of the potential behaviour of new compounds in soil interfaces based on a hypothesis that the behaviour of organic compounds on micro scale is driven by interactions of these compounds on the nano scale. Methods of computational chemistry can contribute to elucidate basic processes involved. These methods cover a large range of techniques (especially quantum chemical methods (DFT, DFTB),force-field methods, molecular dynamics (MD), and Monte Carlo(MC)). In this work an intensive study was conducted concerning sorption of polycyclic aromatic hydrocarbons (PAHs) on soil mineral goethite. Here, relatively large sorption energies were calculated. We found a relation between the surface structure/shape of the PAHs molecules and sorption energies. Linear PAHs, especially anthracene, showed the strongest sorption. The origin of adsorption is mostly in dispersion/polarization interactions between surface OH groups and pi-electrons of PAHs. Studies of interactions of humic moieties under different chemical environment showed a clear impact of the hydrophobicity of the environment on the observed Gibbs free energies. Owing to the structural complexity and flexibility of humic substances (HS) various "nano" pores and holes can be formed in their structure. These spaces can be filled by various small molecules, e.g. water. Water molecules can form in these spaces a stable network of hydrogen bonds, thus creating "wet spots" in HS.