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 potentio metric titration, laser Doppler electrophoresis, and conductometry are employed to measure the adsorption isotherms (pH) and (pH) of potential determining ions, as well as the dependences of surface charge density σ 0 , 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 ζ 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 elec troosmotic flows of solutions in pores of dispersed particles, yields more correct ζ potential values for DND agglomerates.

Colloidal properties and behaviors of 3 nm primary particles of detonation nanodiamonds in aqueous media

“…Note that high C 0 values, close to ours C, have been determined under similar conditions using an absolutely different experimental method, for larger ND species of another origin. 25 On the other hand, taking into account that the TEM images give no evidence of tight spherical shapes of the ND secondary aggregates, which are probably porous, the determined C values may reflect rather the local electrostatic potential in the region where the indicator dye is situated on the non-uniform ND interface. In turn, the local positive charges of the primary particles, as revealed via electrophoresis measurements, counteract in the tight association in the secondary aggregates.…”

“…14 Both positively and negatively charged ND species have been comparatively studied in water 4,5,15,16 and dimethyl sulfoxide. 17,18 The expressed dependence of the electrokinetic potential (zeta potential, z) on pH 4,15,16,[19][20][21][22][23] and on the addition of inorganic electrolytes [22][23][24][25] has been reported as well as the size dependence on pH. 12,19,26 These observations have been discussed in terms of ion adsorption, interfacial acid-base reactions, and screening of interfacial electrical charges.…”

“…These groups may be protonated alcohols or ethers, pyrones, ammonium groups or lyonium ions attached to some of the negatively charged [111] facets of the diamond exposed to the water phase. 12,15,16,25,36,70 Reasoning from the IR spectrum of our ND sample, we cannot exclude the presence of different functional groups, given below.…”

The Properties of 3 nm-Sized Detonation Diamond from the Point of View of Colloid Science

“…There are different explanations of the origin of the surface charge of colloid DND species obtained via various procedures [3,[10][11][12][13]17]. In the case of particles with > 0, the protonated amino and ether groups and pyrones seem to be the most likely.…”