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Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles
[Image: see text] Powder compaction-induced surface chemistry in metal oxide nanocrystal ensembles is important for very diverse fields such as triboelectrics, tribocatalysts, surface abrasion, and cold sintering of ceramics. Using a range of spectroscopic techniques, we show that MgO nanocube powde...
Autores principales: | , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
American Chemical Society
2021
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8521521/ https://www.ncbi.nlm.nih.gov/pubmed/34676020 http://dx.doi.org/10.1021/acs.jpcc.1c05898 |
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author | Schwab, Thomas Thomele, Daniel Aicher, Korbinian Dunlop, John W. C. McKenna, Keith Diwald, Oliver |
author_facet | Schwab, Thomas Thomele, Daniel Aicher, Korbinian Dunlop, John W. C. McKenna, Keith Diwald, Oliver |
author_sort | Schwab, Thomas |
collection | PubMed |
description | [Image: see text] Powder compaction-induced surface chemistry in metal oxide nanocrystal ensembles is important for very diverse fields such as triboelectrics, tribocatalysts, surface abrasion, and cold sintering of ceramics. Using a range of spectroscopic techniques, we show that MgO nanocube powder compaction with uniaxial pressures that can be achieved by gentle manual rubbing or pressing (p ≥ 5 MPa) excites energetic electron–hole pairs and generates oxygen radicals at interfacial defect structures. While the identification of paramagnetic O(–) radicals and their adsorption complexes with O(2) point to the emergence of hole centers, triboemitted electrons become scavenged by molecular oxygen to convert into adsorbed superoxide anions O(2)(–) as measured by electron paramagnetic resonance (EPR). By means of complementary UV-photoexcitation experiments, we found that photon energies in the range between 3 and 6 eV produce essentially the same EPR spectroscopic fingerprints and optical absorption features. To provide insights into this effect, we performed density functional theory calculations to explore the energetics of charge separation involving the ionization of low-coordinated anions and surface-adsorbed O(2)(–) radicals at points of contact. For all selected configurations, charge transfer is not spontaneous but requires an additional driving force. We propose that a plausible mechanism for oxygen radical formation is the generation of significant surface potential differences at points of contact under loading as a result of the highly inhomogeneous elastic deformations coupled with the flexoelectric effect. |
format | Online Article Text |
id | pubmed-8521521 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2021 |
publisher | American Chemical Society |
record_format | MEDLINE/PubMed |
spelling | pubmed-85215212021-10-19 Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles Schwab, Thomas Thomele, Daniel Aicher, Korbinian Dunlop, John W. C. McKenna, Keith Diwald, Oliver J Phys Chem C Nanomater Interfaces [Image: see text] Powder compaction-induced surface chemistry in metal oxide nanocrystal ensembles is important for very diverse fields such as triboelectrics, tribocatalysts, surface abrasion, and cold sintering of ceramics. Using a range of spectroscopic techniques, we show that MgO nanocube powder compaction with uniaxial pressures that can be achieved by gentle manual rubbing or pressing (p ≥ 5 MPa) excites energetic electron–hole pairs and generates oxygen radicals at interfacial defect structures. While the identification of paramagnetic O(–) radicals and their adsorption complexes with O(2) point to the emergence of hole centers, triboemitted electrons become scavenged by molecular oxygen to convert into adsorbed superoxide anions O(2)(–) as measured by electron paramagnetic resonance (EPR). By means of complementary UV-photoexcitation experiments, we found that photon energies in the range between 3 and 6 eV produce essentially the same EPR spectroscopic fingerprints and optical absorption features. To provide insights into this effect, we performed density functional theory calculations to explore the energetics of charge separation involving the ionization of low-coordinated anions and surface-adsorbed O(2)(–) radicals at points of contact. For all selected configurations, charge transfer is not spontaneous but requires an additional driving force. We propose that a plausible mechanism for oxygen radical formation is the generation of significant surface potential differences at points of contact under loading as a result of the highly inhomogeneous elastic deformations coupled with the flexoelectric effect. American Chemical Society 2021-09-29 2021-10-14 /pmc/articles/PMC8521521/ /pubmed/34676020 http://dx.doi.org/10.1021/acs.jpcc.1c05898 Text en © 2021 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by/4.0/Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/). |
spellingShingle | Schwab, Thomas Thomele, Daniel Aicher, Korbinian Dunlop, John W. C. McKenna, Keith Diwald, Oliver Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles |
title | Rubbing Powders: Direct Spectroscopic Observation
of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles |
title_full | Rubbing Powders: Direct Spectroscopic Observation
of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles |
title_fullStr | Rubbing Powders: Direct Spectroscopic Observation
of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles |
title_full_unstemmed | Rubbing Powders: Direct Spectroscopic Observation
of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles |
title_short | Rubbing Powders: Direct Spectroscopic Observation
of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles |
title_sort | rubbing powders: direct spectroscopic observation
of triboinduced oxygen radical formation in mgo nanocube ensembles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8521521/ https://www.ncbi.nlm.nih.gov/pubmed/34676020 http://dx.doi.org/10.1021/acs.jpcc.1c05898 |
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