Oxygen is present in the vast majority of inorganic materials and minerals, where it is found in a variety of different chemical bonds, including covalent, ionic and hydrogen bonds. The identification of oxygen bonding environments and their reactivity is thus an important target, in order to rationalize and optimize the properties of different systems. Oxygen-17 solid state NMR spectroscopy appears as ideally suited for this purpose, due to the wide range of variation of its chemical shift and quadrupolar parameters. However, it intrinsically suffers from a very poor sensitivity, the natural abundance of 17O being only 0.04%. This implies that 17O-labeling is most-often necessary to perform high resolution analyses, especially for the study of surfaces and interfaces in functional (nano)materials. Unfortunately, the 17O-enrichment of materials is rarely straightforward, and many labeling protocols suffer from various drawbacks, including high costs, long reaction times, and/or constraining chemical reactions or experimental set-ups. This has motivated several research groups to look into the development of alternative synthetic approaches. In recent years, we have focussed our research on implementing cost-effective and user-friendly 17O-labeling protocols based on mechanochemistry. We have shown that ball milling procedures are attractive for the 17O-labeling of a variety of organic and inorganic compounds, using microliter quantities of 17O-enriched water, and working under ambient temperature and pressure. In this presentation, some of our most recent advances in the development of mechanochemistry-based protocols for the 17O-enrichment of inorganic compounds will first be discussed. Particular emphasis will be made on the labeling of oxides, hydroxides and hydrates. The characterization of the structure and texture of the enriched phases will be described, including using high-resolution 17O solid state NMR (with ultra-high field measurements at 35.2 T and 1H-17O D-HMQC correlations) and Dynamic Nuclear Polarization analyses. Then, it will be shown how thanks to these enrichment protocols, new information on the reactivity of interfacial oxygen atoms can be reached.

Unraveling the structure and reactivity of interfacial oxygen sites thanks to oxygen-17 mechanochemical labeling and high resolution NMR

ACS Spring Meeting 2021

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