Stability study of ZnO nanoparticles in aqueous solutions of carboxylate anions

The paper is devoted to the use of carboxylic acids and salts for the elaboration of stable suspensions of ZnO engineered nanoparticles (40 and 200 nm) in physiological media at pH 6–8. It was shown that the aggregation degree of ZnO-200 particles increases with the growth of carboxylic anion activity, e.g., at pH 7 in the row «Acetate−–Citrate3−–Oxalate2−» the average size of ZnO-200 particles in suspensions amounts to «169–523–770» nm, zeta potential–«35.9–−19.9–+5.42 mV», respectively. The aggregation degree of ZnO-40 particles increases in the row «Citrate3−–Acetate−–Oxalate2−», at pH 7, the average size of ZnO-40 particles in suspension amounts to «50–121–430» nm, zeta potential–«−28.3–−14.5–+2.3» mV, respectively. pH-impact was found to be size-dependent: there was a significantly less effect of pH on adsorption, dispersion, and electrokinetic properties of ZnO-40 particles when compared to ZnO-200 particles. The main reason for the difference between micro- and nanosized particles behavior is a change of the ratio of acidic, basic, and neutral Bronsted centers for particles of nanosized scale.