Quantification of CC and CO Surface Carbons in Detonation Nanodiamond by NMR

• Published in: Journal of physical chemistry. C Vol. 118; no. 18; pp. 9621 - 9627
• Main Authors: Cui, J.-F, Fang, X.-W, Schmidt-Rohr, K
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08.05.2014
• Subjects: MATERIALS SCIENCE; Surface chemistry and colloids
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp503053r

The ability of solid-state 13C NMR to detect and quantify small amounts of sp2-hybridized carbon on the surface of ∼5 nm diameter nanodiamond particles is demonstrated. The CC carbon fraction is only 1.1 ± 0.4% in pristine purified detonation nanodiamond, while a full single-layer graphitic or “bucky diamond” shell would contain ca. 25% of all C in a 5 nm diameter particle. Instead of large aromatic patches repeatedly proposed in the recent literature, sp3-hybridized CH and COH carbons cover most of the nanodiamond particle surface, accounting for ∼5% each. CO and COO groups also seen in X-ray absorption near-edge structure spectroscopy (XANES) but not detected in previous NMR studies make up ca. 1.5% of all C. They are removed by heat treatment at 800 °C, which increases the aromatic fraction. 13C{1H} NMR demonstrates that the various sp2-hybridized carbons are mostly not protonated, but cross-polarization shows that they are separated from 1H by only a few bond lengths, which proves that they are near the protonated surface. Together, the observed C–H, C–OH, CO, and CC groups account for 12–14% of all C, which matches the surface fraction expected for bulk-terminated 5 nm diameter diamond particles.