Surface charge of detonation nanodiamond particles in aqueous solutions of simple 1 : 1 Electrolytes

Abstract

Adsorption isotherms of potential-determining H+ and OH− ions and the pH dependences of the specific surface charge of detonation nanodiamond (DND) particles are obtained in a pH range of 3–10 by the acid-base titration of their hydrosols containing 0.001–1 M LiCl, NaCl, KCl, NaNO3, KNO3, and NaClO4 as background electrolytes. The data obtained attest to the chemical nonuniformity (heterogeneity) of a DND surface and different degrees of binding of background electrolyte cations and anions with ionized groups. It is revealed that the adsorption of OH-anions diminishes in the lyotropic series of cations Na+ > K+ > Li+ and increases with a decrease in the adsorbability of anions in the following series: NO 3 − ≊ ClO 4 − > Cl−. The adsorption of potential-determining H+ and OH− ions on a DND surface containing two types of functional groups, i.e., acidic carboxyl and amphoteric hydroxyl groups, is simulated by the Protofit software package. The optimal surface densities and ionization constants that correspond to minimal deviations of model adsorption isotherms from the experimental curves are found for these groups.