Effect of Conditions for Obtaining Detonation Nanodiamond on Surface Composition and Stability of Its Aqueous Sols

Abstract

This work is devoted to studying the effect of an additional treatment of detonation nanodiamond (DND) powder of basic purification on the surface composition of DND particles, as well as their electrokinetic properties and aggregate stability in solutions of an indifferent electrolyte (NaCl) within a wide pH range. It has been found that an increase in the degree of purification and the number of protonated carboxyl groups on the surface of DND particles due to additional acidic and thermoammonia treatments leads to a shift in the position of the isoelectric point (IEP) from pH 7.0 for an initial sample to pH 6.3 and pH 6.0, respectively. It has been shown that the coagulation thresholds of the hydrosols at natural pH and the positions of stability zones in a 10^–3 M sodium chloride solution are in complete compliance with the IEP values. The highest thresholds values at pH 5.8 are observed for the initial DND, while, for the dispersion of DND particles subjected to the thermoammonia treatment, the fast coagulation occurs already at a concentration of 10^–4 M. It has also been found that the aggregate stability zones for additionally treated DND samples almost coincide with each other. For DND of basic purification, the stability zone expands in the region of positive zeta-potentials, while, in the region of negative values, no stability is observed, probably, due to the partial dissolution of surface impurities at high pH values and the transfer of their ionic forms to the solution, which causes coagulation of the DND particles.