Unexpected SO₂ Photooxidation on Quantum-Sized Carbon

Area of Science:

• Environmental Chemistry
• Materials Science
• Astrochemistry

Background:

• Surface photochemistry of carbon quantum dots (CQDs) under atmospheric conditions is not well understood.
• The role of CQDs in atmospheric processes and their interactions with pollutants like sulfur dioxide (SO2) require further investigation.

Purpose of the Study:

• To systematically investigate the photoreactivity of CQDs in the presence of SO2 under atmospheric conditions.
• To elucidate the mechanisms behind CQD photoaging and SO2 interaction, particularly their dependence on oxygen.

Main Methods:

• A combined experimental and theoretical approach was employed.
• Identification of key reactive intermediates involved in CQD surface photooxidation.

Main Results:

• CQD photoaging and interaction with SO2 were found to be independent of oxygen (O2).
• Photoexcited CQDs induce unique energy transfer and photocatalytic processes driving these surface reactions.
• Key reactive intermediates including photogenerated holes, hydroxyl radicals, sulfite radicals, and carbon-centered radicals were identified.

Conclusions:

• This study provides novel insights into the atmospheric photochemistry of flame-formed soot.
• Advances the understanding of photocatalytic processes on synthetic nanosized carbon materials.
• Offers potential explanations for the origins of sulfated carbonaceous chondrites in interstellar media.