NMR and EPR characterization of functionalized nanodiamonds

C. Presti (1) , A.S.L. Thankamony (2, 3, 4) , J. Alauzun (1) , P. Hubert Mutin (1) , D. Carnevale (5) , C. Lion (4) , H. Vezin (3) , Danielle Laurencin (1) , O. Lafon (2)

1 ICGM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier
2 UCCS - Unité de Catalyse et Chimie du Solide - UMR 8181
3 LASIRE - Laboratoire Avancé de Spectroscopie pour les Intéractions la Réactivité et l'Environnement - UMR 8516
4 UGSF - Unité de Glycobiologie Structurale et Fonctionnelle - UMR 8576
5 Institut des Sciences et Ingénierie Chimiques

We investigated the potential of solid-state NMR using magic angle spinning (MAS) with and without dynamic nuclear polarization (DNP) and electron paramagnetic resonance (EPR) for the characterization of functionalized nanodiamonds (NDs). We showed that conventional ¹H, ³¹P, and ¹³C solid-state NMR spectra allow differentiating in a straightforward way NDs from commercial sources and custom-made NDs bearing aromatic or aliphatic phosphonate moieties at their surface. Besides, the short nuclear relaxation times prove the close proximity between the endogenous paramagnetic centers of NDs and the grafted organic moieties. EPR spectra confirmed the presence of these paramagnetic centers in functionalized NDs, which are centered on dangling bonds as well as a few N⁰ defects, corresponding to the substitution of carbon atoms by nitrogen ones. Hyperfine sublevel correlation spectroscopy indicates that the N⁰ paramagnetic centers are mostly located in the disordered shell of NDs. Preliminary DNP-enhanced NMR experiments at 9.4 T and 100 K under MAS have shown a lack of significant DNP enhancement, which can be attributed to the short relaxation times of the unpaired electrons and the nuclei in NDs. When using exogenous polarizing agents, the endogenous unpaired electrons contribute to a leakage of polarization. Furthermore, low temperatures lead to a broadening of NMR signals. It therefore appears that conventional direct excitation remains the NMR method of choice for the characterization of functionalized NDs.

Domaines: Chimie théorique et/ou physique

C. Presti, A.S.L. Thankamony, J. Alauzun, P. Hubert Mutin, D. Carnevale, et al.. NMR and EPR characterization of functionalized nanodiamonds. Journal of Physical Chemistry C, 2015, 119, pp.12408 - 12422. ⟨10.1021/acs.jpcc.5b02171⟩. ⟨hal-01164065⟩