Electrokinetic properties of detonation nanodiamond aggregates in aqueous KCl solutions

Electrophoretic mobility of porous aggregates of detonation nanodiamond (DND) particles was measured using the laser Doppler electrophoresis technique in aqueous KCl solutions. Corresponding values of ζ-potential were calculated as functions of pH and KCl concentration using different equations of the theory of electrophoresis. It is suggested that use of the Miller formula, which takes into account the electromigration fluxes of ions and electroosmotic flows of solutions in pores of dispersed particles, should provide the most accurate ζ-potential values for DND aggregates. The hydrosols of DND purified from non-diamond carbon with nitric acid were additionally characterized by acid–base potentiometric titrations and conductometric measurements. The dependences of surface charge density and conductivity of the aggregates on the pH = 3.5–10.5 of aqueous 0.0001–0.1 M KCl solutions were obtained. The optimal values were determined for the reaction constants of ionization of acidic carboxyl (COOH) and amphoteric hydroxyl (COH) groups, predominant on the DND surface. It is revealed that the effective conductivity of the porous aggregates is one or two orders of magnitude higher than the conductivity of the equilibrium solutions.