Structural controls on OH site availability and reactivity at iron oxyhydroxide particle surfaces

Area of Science:

• Mineralogy
• Surface Chemistry
• Spectroscopy

Background:

• Iron oxyhydroxides (FeOOH) are reactive minerals crucial in natural and industrial processes.
• Surface hydroxyl groups on FeOOH particles are key reaction sites for various compounds.
• Understanding these hydroxyl groups is vital for predicting mineral behavior and transformations.

Purpose of the Study:

• To develop methods for identifying hydroxyl groups on specific crystallographic planes of lepidocrocite (γ-FeOOH) and goethite (α-FeOOH).
• To provide molecular-scale resolution of gas-phase processes occurring on FeOOH mineral surfaces.

Main Methods:

• Fourier transform infrared (FTIR) spectroscopy to monitor O-H stretching vibrations.
• Analysis of spectral responses to proton loading and thermal gradients.
• Multivariate curve resolution for spectral component extraction.
• Molecular dynamics simulations to guide band assignment and identify hydrogen bonding.

Main Results:

• Successful identification of hydroxyl groups on distinct crystallographic planes of lepidocrocite and goethite.
• Correlation of spectral bands with specific hydroxyl group configurations (e.g., -OH, μ-OH, μ(3)-OH).
• Validation of band assignments through combined spectroscopic and simulation data.

Conclusions:

• The study provides novel tools for characterizing surface hydroxyl groups on FeOOH minerals.
• These findings enhance the understanding of mineral-surface interactions at a molecular level.
• This research opens new avenues for studying gas-phase reactions on important environmental minerals.