First-principles study of the interaction between NO and large carbonaceous clusters modeling the soot surface

Area of Science:

• Environmental Chemistry
• Materials Science
• Computational Chemistry

Background:

• Nitrogen oxides (NO) are significant air pollutants.
• Soot, a carbonaceous material, is prevalent in the troposphere.
• Understanding NO interactions with soot is crucial for atmospheric chemistry.

Purpose of the Study:

• To investigate the adsorption mechanisms of NO on soot-like carbonaceous clusters.
• To determine the binding sites and types (physisorption vs. chemisorption) of NO on soot.
• To assess the potential of soot as a sink for atmospheric NO.

Main Methods:

• First-principles calculations were employed.
• Modeling of perfect and defective carbonaceous clusters representing soot surfaces.
• Consideration of adsorption on cluster faces and edges.
• Analysis of physisorption and chemisorption pathways.

Main Results:

• Physisorption occurs on the faces of soot clusters, requiring dispersion interactions.
• Chemisorption, forming C-N bonds, is favored at the unsaturated edges of defective clusters.
• Soot's efficiency as an NO sink depends on the concentration of unsaturated carbon atoms.

Conclusions:

• Defective soot edges with unsaturated carbons are key sites for NO removal.
• Accurate quantum chemical calculations for radical-surface interactions necessitate careful consideration of functionals, basis sets, and spin properties.
• Soot's role in tropospheric NO cycling is contingent on its structural defects.