Interfacial microdroplets reshape the oxidation pathways of polycyclic aromatic hydrocarbons

Area of Science:

• Environmental Chemistry
• Physical Chemistry
• Materials Science

Background:

• Aromatic molecules, particularly polycyclic aromatic hydrocarbons (PAHs), are prevalent in various scientific domains.
• The reaction mechanisms of PAHs at air-water interfaces are not well understood.
• Understanding these reactions is crucial for environmental and materials science applications.

Purpose of the Study:

• To investigate the degradation pathways of PAHs at air-water interfaces.
• To explore the role of microdroplets and interfacial phenomena in PAH transformation.
• To elucidate novel reaction mechanisms and identify degradation products.

Main Methods:

• Ultrasonic atomization to generate microdroplets containing PAHs.
• Interfacial reaction monitoring and product analysis.
• Density Functional Theory (DFT) calculations for mechanistic insights.

Main Results:

• Achieved up to 95% degradation of tested PAHs (naphthalene, phenanthrene, pyrene, fluoranthene) within 20 minutes.
• Identified synergistic effects of interfacial enrichment and reactive oxygen species in driving PAH transformation.
• Discovered a carbocation-mediated SN1-type skeletal rearrangement pathway alongside conventional oxidation.

Conclusions:

• Microdroplet-based oxidation efficiently transforms PAHs but leads to intermediate accumulation rather than full mineralization.
• Revealed a previously unrecognized interfacial oxidation pathway for phenanthrene.
• Provides new insights into the interfacial reaction chemistry of aromatic molecules.