Adsorption of nitrate on kaolinite surfaces: a theoretical study

Area of Science:

• Environmental Chemistry
• Surface Science
• Computational Chemistry

Background:

• Airborne clay minerals interact with atmospheric trace gases.
• Understanding these interactions is crucial for atmospheric chemistry.
• Nitric acid (HNO3) and nitrate (NO3-) are key atmospheric species.

Purpose of the Study:

• To investigate the interactions of HNO3 and NO3- with kaolinite surfaces.
• To theoretically model different surface complex structures of NO3- on kaolinite.
• To compare calculated vibrational frequencies with experimental data.

Main Methods:

• Density Functional Theory (DFT) calculations using the B3LYP/6-311++G(d,p) level.
• Modeling of HNO3 and NO3- on kaolinite surface clusters.
• Analysis of vibrational frequencies (symmetric and asymmetric stretches) for various surface complexes.

Main Results:

• Calculated vibrational frequencies for NO3- on kaolinite are consistent with literature values for symmetric and low-frequency asymmetric stretches.
• Calculations suggest higher frequencies for bridged NO3- complexes.
• The study assigns calculated higher-frequency asymmetric stretches to monodentate surface complexes, differing from previous assignments for bidentate and bridged complexes.

Conclusions:

• Theoretical calculations provide insights into HNO3 and NO3- adsorption on kaolinite.
• The findings refine the interpretation of vibrational spectroscopy data for mineral-surface nitrate interactions.
• This research contributes to understanding atmospheric trace gas reactions involving clay minerals.