Comprehensive study of electrosurface properties of detonation nanodiamond particle agglomerates in aqueous KCl solutions

Abstract

The electrosurface properties of nanoporous agglomerates of detonation nanodiamond (DND) particles purified from acidic impurities by dialysis are comprehensively investigated. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry are employed to measure the adsorption isotherms $$\Gamma _{H^ + } (pH)$$ and $$\Gamma _{OH^ - } (pH)$$ of potential-determining ions, as well as the dependences of surface charge density σ0, electrophoretic mobility u e, and specific conductivity K p of the agglomerates on the pH = 3.5–10.5 of aqueous 0.0001–0.1 M KCl solutions. The obtained adsorption isotherms indicate heterogeneity of the DND surface, i.e., the presence of different proton-donor and proton-acceptor surface functional groups. Computer simulation of the adsorption isotherms is carried out for a DND surface containing two types of functional groups, namely, acidic carboxyl (-COOH) and amphoteric hydroxyl (-COH) groups, the predominant content of which is confirmed by FTIR spectroscopy data. The optimal values are determined for the reaction constants of ionization of these groups. It is revealed that the effective conductivity of the porous agglomerates is one or two orders of magnitude higher than the conductivity of equilibrium solutions. Corresponding values of electrokinetic potential ξ are calculated as functions of pH and KCl concentration from the electrophoretic mobility of the agglomerates using different equations of electrophoresis theory. It is shown 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, yields more correct ξ potential values for DND agglomerates.