Transfer of nanodiamonds from the aqueous phase to the organic phase in the presence of oleylamine

Abstract

A radiotracer technique with tritium-labeled nanodiamonds (NDs) has been used to study the distribution of NDs in water/octane system. The surface of NDs has been modified by heat treatment (oxidation) in air and functionalization using oleylamine (OLA) as surfactant. It has been shown that oxidized NDs are concentrated in the aqueous phase, the distribution ratio (D = CO/CW) being 0.016 (CO and CW are the concentrations of the NDs in octane and water, respectively). The addition of OLA to the NDs hydrosol/octane system leads to increase in the distribution ratio and the concentration of NDs near the water/octane interface by a factor of three. The dispersion of NDs directly in a solution of OLA in octane followed by addition of water leads to more pronounced increase in the distribution ratio (by two orders of magnitude), and the major fraction of the nanoparticles (about 70%) is concentrated near the water/octane interface. Adsorption isotherm of OLA on NDs has been obtained; it has been found that the adsorption is irreversible due to the formation of ion pairs between surface carboxylic groups of NDs and amino groups of OLA. The nanoparticles and their dispersions have been investigated by Fourier transform infrared spectroscopy, dynamic light scattering, Boehm titration, interfacial tensiometry, optical microscopy, ζ-potential and pH measurements.