Model study on sorption of polycyclic aromatic hydrocarbons to goethite

Area of Science:

• Environmental Chemistry
• Surface Science
• Computational Chemistry

Background:

• Polyaromatic hydrocarbons (PAHs) are persistent organic pollutants.
• Goethite (α-FeOOH) is a common iron oxide mineral in soils and sediments.
• Understanding PAH-goethite interactions is crucial for predicting contaminant fate and transport.

Purpose of the Study:

• To investigate the adsorption mechanisms of PAHs on the goethite (110) surface.
• To determine the influence of PAH molecular shape on adsorption strength.
• To elucidate the role of goethite surface hydroxyl groups in PAH binding.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Systematic study of interactions between various PAHs and the goethite (110) surface.
• Analysis of binding energies, interaction distances, and preferred adsorption configurations.

Main Results:

• PAHs form weak surface complexes with their molecular planes parallel to the goethite surface.
• Interactions involve π-system polarization by surface OH groups and weak hydrogen bonding.
• Linear PAHs (e.g., anthracene) exhibit stronger binding than non-linear PAHs (e.g., pyrene) due to favorable surface geometry.
• Linear PAHs can easily slide along surface hydroxyl group valleys.

Conclusions:

• The goethite (110) surface preferentially retains linear PAHs over non-linear ones.
• Surface hydroxyl group configuration dictates the differential binding of PAHs.
• This study provides insights into the environmental behavior of PAHs on iron oxide surfaces.