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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Nonaromatic core-shell structure of nanodiamond from solid-state NMR spectroscopy.
XiaoWen Fang1, JingDong Mao, E M Levin
1Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
Journal of the American Chemical Society
|January 13, 2009
Summary
Synthetic nanodiamonds feature a core-shell structure with sp(3)-hybridized carbons. Unpaired electrons are located in the disordered shell, not surface dangling bonds, revealing key structural insights.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Nanotechnology
Background:
- Synthetic nanodiamonds are advanced carbon nanomaterials with potential applications in various fields.
- Understanding their precise structure, especially surface chemistry and defect localization, is crucial for optimizing performance.
- Previous characterization methods have provided limited insights into the core-shell structure and defect distribution.
Purpose of the Study:
- To elucidate the detailed structure of synthetic nanodiamond particles.
- To determine the hybridization state and bonding of surface carbons.
- To localize the position of unpaired electrons and understand their influence on nanodiamond properties.
Main Methods:
- Characterization using carbon-13 nuclear magnetic resonance (NMR) spectral editing.
- Measurements of long-range proton-carbon (1H-13C) dipolar couplings.
- Analysis of carbon-13 relaxation times (T1,C) and simulations.
- Nitrogen-15 (15N) NMR spectroscopy.
Main Results:
- Nanodiamond surface (approx. 4.8 nm diameter) is primarily sp(3)-hybridized carbon, protonated or bonded to OH groups.
- Less than 1% of the material is sp(2)-hybridized carbon; surface protons resonate at 3.8 ppm.
- Unpaired electrons (approx. 40 per particle) are located in a disordered shell (0.4-1 nm from surface), not surface dangling bonds.
- Nitrogen is mostly non-protonated and contributes to carbon spectral shifts.
Conclusions:
- A nonaromatic core-shell structural model for synthetic nanodiamonds is proposed.
- The findings clarify the distribution of defects and surface functionalities.
- This structural understanding is vital for tailoring nanodiamonds for specific applications.
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