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Oxygen Radicals Entrapped between MgO Nanocrystals: Formation, Spectroscopic Fingerprints, and Reactivity toward
Thomas Schwab1, Eva Muchová2, Korbinian Aicher1
1Department of Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Straße 2a, Salzburg A-5020, Austria.
The Journal of Physical Chemistry. C, Nanomaterials and Interfaces
|December 13, 2023
Summary
Compaction of dehydroxylated MgO nanocrystal powders generates adsorbed oxygen radicals, specifically superoxide and ozonide. Their UV-vis spectroscopic detection enables in situ monitoring of these transient species in metal oxides.
Area of Science:
- Materials Science
- Spectroscopy
- Surface Chemistry
Background:
- Dehydroxylated magnesium oxide (MgO) nanocrystal powders are crucial in various chemical processes.
- Understanding the surface chemistry of MgO is vital for applications in catalysis and sensing.
- Adsorbed oxygen species can significantly influence material properties and reactivity.
Purpose of the Study:
- To investigate the formation and spectroscopic identification of adsorbed oxygen radicals on dehydroxylated MgO nanocrystal powders.
- To correlate UV-vis absorption bands with specific oxygen radical species.
- To establish a method for in situ monitoring of these transient species.
Main Methods:
- Compaction of dehydroxylated MgO nanocrystal powders.
- UV-vis spectroscopy for detecting absorption bands.
- Photophysical calculations on MgO gas-phase clusters.
- Electron paramagnetic resonance (EPR) spectroscopy for corroboration.
- Study of reactions with interfacial water.
Main Results:
- Compaction induced adsorbed oxygen radicals with characteristic UV-vis fingerprints.
- UV excitation in oxygen atmosphere also produced identical absorption bands.
- Calculations identified 4.4 eV and 3.0 eV transitions with superoxide (O2·−) and ozonide (O3·−) species.
- EPR spectroscopy confirmed the presence of these oxygen radicals.
- Reaction with water converted radicals to diamagnetic products.
Conclusions:
- UV-vis spectroscopy can identify adsorbed superoxide and ozonide species on MgO.
- These oxygen radicals are transient and react with water.
- The developed spectroscopic method allows for in situ monitoring of oxygen radicals in metal oxide powders.
- This has implications for heterogeneous catalysis, sensing, and understanding cold sintering.
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