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Inhibition Effect of H2O on the Heterogeneous Reaction between Isoprene and Fe-Substituted Cryptomelane
Ruoyi Chen1, Fuding Tan2,3, Xiang Wang1
1School of Environment and Energy, South China University of Technology, Guangzhou 510006, People's Republic of China.
Langmuir : the ACS Journal of Surfaces and Colloids
|March 12, 2025
Summary
Fe-substituted cryptomelane mineral dust oxidizes biogenic isoprene into acids. Water vapor significantly inhibits this oxidation, but the mineral
Area of Science:
- Atmospheric Chemistry
- Environmental Science
- Mineralogy
Background:
- Biogenic isoprene is crucial for tropospheric organic carbon cycling.
- Mineral dusts, like Fe-substituted cryptomelane, can influence atmospheric chemistry.
- Understanding isoprene transformation pathways is vital for climate modeling.
Purpose of the Study:
- To investigate the role of Fe-substituted cryptomelane in isoprene oxidation.
- To determine the effect of water vapor on this oxidation process.
- To elucidate the adsorption mechanisms of isoprene and water on the mineral surface.
Main Methods:
- Experimental analysis of isoprene oxidation by Fe-substituted cryptomelane.
- Gas-phase flow experiments with varying humidity levels.
- Theoretical calculations (DFT) to model surface interactions.
Main Results:
- Fe-substituted cryptomelane oxidizes isoprene to formic and acetic acids, reducing Mn ions.
- Water vapor significantly inhibits isoprene adsorption and oxidation, even at 10% relative humidity.
- Adsorption and oxidation capacity are restored upon water removal.
- Theoretical calculations show preferential adsorption of isoprene at Fe3+ sites and hydrogen bonding by H2O.
- Fe-substituted cryptomelane favors H2O adsorption in humid isoprene flow due to decreased total adsorption energy.
Conclusions:
- Water vapor plays a critical role in modulating the oxidation of biogenic isoprene by Fe-substituted cryptomelane.
- The inhibitory effect of humidity suggests that direct mineral dust oxidation may not be a primary nighttime transformation pathway for isoprene under ambient conditions.
- Mineral dusts' catalytic activity in the atmosphere is highly dependent on environmental factors like humidity.
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