期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 119, 期 22, 页码 12408-12422出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.5b02171
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资金
- CNRS
- French ministry of research
- Region Nord/Pas de Calais
- European Union (FEDER)
- TGIR-RMN-THC Fr 3050 CNRS
- Universite de Lille
- Chinese Academy of Sciences President's international fellowship initiative
- National Natural Science Foundation of China [21450110412]
- Swiss National Science Foundation
- Swiss Commission for Technology and Innovation
- EPFL
- Bruker Biospin
- COST [TD 1103]
- ENSCL [ANR-2020-jcjc-0811-01]
- CEFIPRA [85208-E]
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 H-1, P-31, and C-13 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 N-0 defects, corresponding to the substitution of carbon atoms by nitrogen ones. Hyperfine sublevel correlation spectroscopy indicates that the N-0 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.
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