Comparative DFT study of inner-sphere As(III) complexes on hydrated α-Fe2O3(0001) surface models

Area of Science:

• Environmental Science
• Geochemistry
• Computational Chemistry

Background:

• Arsenic contamination in water poses significant human health risks, primarily due to its interaction with natural solid phases.
• Predicting arsenic surface complexation is hindered by a lack of molecular-level understanding of arsenic-solid interactions.
• Hematite (α-Fe(2)O(3)) is a common iron oxide mineral involved in arsenic sequestration.

Purpose of the Study:

• To model arsenic(III) (As(III)) surface complexation on hydrated hematite using density functional theory (DFT).
• To investigate the influence of different surface structures and oxygen functional groups on As(III) adsorption energetics.
• To elucidate fundamental principles of interface reactivity between arsenic and mineral surfaces.

Main Methods:

• Utilized density functional theory (DFT) to model As(III) adsorption on two distinct α-Fe(2)O(3)(0001)-water interfaces.
• Simulated mono-, bi-, and tri-dentate As(III) surface complexes.
• Analyzed adsorption energies, coordination, surface geometry, and electronic structure.

Main Results:

• DFT energetics favored monodentate As(III) surface complexation on both modeled hematite surfaces.
• The models did not fully replicate experimental observations of bidentate As(III) coordination.
• Ligand oxygen functional groups demonstrated a greater impact on interface reactivity than surface oxygen coordination with iron.

Conclusions:

• The distinction between surface and ligand oxygen functional groups is critical for understanding mineral-water reactivity.
• Findings challenge the equal treatment of all oxygen functional groups in bond-valence-based predictions.
• Results provide fundamental insights for future modeling efforts linking macroscopic arsenic behavior to molecular-level interactions.