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Direct 17O Isotopic Labeling of Oxides Using Mechanochemistry
journal contribution
posted on 2020-03-13, 15:04 authored by Chia-Hsin Chen, Emeline Gaillard, Frédéric Mentink-Vigier, Kuizhi Chen, Zhehong Gan, Philippe Gaveau, Bertrand Rebière, Romain Berthelot, Pierre Florian, Christian Bonhomme, Mark E. Smith, Thomas-Xavier Métro, Bruno Alonso, Danielle LaurencinWhile 17O NMR is increasingly being used for elucidating
the structure and reactivity of complex molecular and materials systems,
much effort is still required for it to become a routine analytical
technique. One of the main difficulties for its development comes
from the very low natural abundance of 17O (0.04%), which
implies that isotopic labeling is generally needed prior to NMR analyses.
However, 17O-enrichment protocols are often unattractive
in terms of cost, safety, and/or practicality, even for compounds
as simple as metal oxides. Here, we demonstrate how mechanochemistry
can be used in a highly efficient way for the direct 17O isotopic labeling of a variety of s-, p-, and d-block oxides, which
are of major interest for the preparation of functional ceramics and
glasses: Li2O, CaO, Al2O3, SiO2, TiO2, and ZrO2. For each oxide, the
enrichment step was performed under ambient conditions in less than
1 h and at low cost, which makes these synthetic approaches highly
appealing in comparison to the existing literature. Using high-resolution
solid-state 17O NMR and dynamic nuclear polarization, atomic-level
insight into the enrichment process is achieved, especially for titania
and alumina. Indeed, it was possible to demonstrate that enriched
oxygen sites are present not only at the surface but also within the
oxide particles. Moreover, information on the actual reactions occurring
during the milling step could be obtained by 17O NMR, in
terms of both their kinetics and the nature of the reactive species.
Finally, it was demonstrated how high-resolution 17O NMR
can be used for studying the reactivity at the interfaces between
different oxide particles during ball-milling, especially in cases
when X-ray diffraction techniques are uninformative. More generally,
such investigations will be useful not only for producing 17O-enriched precursors efficiently but also for understanding better
mechanisms of mechanochemical processes themselves.