Facile Amine Termination of Nanodiamond Particles and Their Surface Reaction Dynamics

Nanodiamond synthesized by the detonation method is a composite of sp³/sp² carbon structures; amorphous and disordered-sp² carbons populate the surface of a sp³ diamond core lattice. Because of the production process, various elemental impurities such as N, O, H, and so forth are inherent in interstitial sites or the surface carbon (sp²/amorphous) network. Herein, the reaction dynamics on the surface of ultradisperse diamond (UDD) due to the surface transformation or reconstruction during annealing in vacuum with temperatures ranging from ambient to 800 °C is described. In situ measurement of Fourier transform infrared spectroscopic analysis shows that low-temperature (<500 °C) annealing of UDD in vacuum results in isonitrile/isocyanide (-N=C:) and nitrile functionalization (-C≡N) on the surface. At temperatures ∼500 °C, the surface hydrogenation of UDD is initiated. During annealing at 780-800 °C, the nitrile group (-C≡N) is reduced to the primary amine (NH₂), and isonitrile (-N=C:) turns it to be in the saturated () structure. On exposure to air, the obtained isonitrile is transformed to an N-formyl derivative (Aryl/R-NH-CHO) structure via hydrolysis. This study provides a fundamental insight into the surface reactive profile of UDD which could lead to facile surface functionalization properties and their applications in various fields such as biomedical, biosensing, drug delivery, epoxy materials process, tribology, and possibly in cyano (-C≡N/-N=C:) chemistry.