Primary detonation nanodiamond particles: Their core-shell structure and the behavior in organo-hydrosols

Detonation nanodiamond (DND) particles have promising applications ranging from lubrication and polishing to biotechnology and electronics. However, the physical and chemical properties of the surface of the nanodiamond are largely unknown due to a commonly assumed core-shell structure of the DND nanoparticles. The present paper is devoted to the examination of the one of most popular DND hydrosols with positively charged colloidal particles, manufactured in NanoCarbon Research Institute, Japan, and widely used by different researchers. We report the results of studies of structural and electronic properties of individual 4 nm-sized DND nanoparticle by means of advanced TEM techniques under contamination-free conditions. A 2 nm-size core of crystalline diamond is surrounded with ca. 1 nm thick diamond-like carbon that has been visualized by lowand core-loss EELS spectral imaging. The study of deposition of the secondary aggregates of the primary DND species via electrolytes in water-ethanol and water-acetonitrile solvents revealed three mechanisms of coagulation, namely, surface charge screening (NaCl), anionic adsorption (sodium n-dodecyl sulfate), and acid-base neutralization (NaOH). Both peptization of the coagulates by pure water and alteration of the electrical properties along with the changes of the composition of the binary solvents elucidate the role of H+ ions in the formation of the positive charge of species.