Size, stability, and aggregation of citrates-coated silver nanoparticles: contribution of background electrolytes

The role of background electrolyte and ionic strength that control the behavior of silver nanoparticles (AgNPs) suspension were examined herein. Colloidal suspensions of AgNPs were prepared according to the chemical reduction method. Environment of these AgNPs was adjusted by 0.1 M solutions of NaCl, MgSO 4 , and AlCl 3 as background electrolytes. Several techniques were employed to characterize their behavior including UV–Vis spectra, Zeta potential, Zeta sizer, and scanning electron microscope (SEM) imaging. The spectrum for control suspension was typical, upon mixing AgNPs with electrolytes’ solutions, a consequent damping and broadening of absorption peaks was observed, while they kept centered almost at 420 nm. The absolute Zeta potential values decreased as the ionic strength and volume of background electrolyte increased which was accompanied by charge reversal as solutions passed though isoelectric point. The average particle size was found to be 25.58 nm and increased upon increasing the electrolyte’s dosage and ionic strength. AlCl 3 was effective at low dosage, while a restabilization process occurred accompanied by different aggregation mechanisms at higher dosages. Scanning electron microscope (SEM) images showed that the AgNPs were initially spherical then clustered and dramatically aggregated while reacting with electrolytes. AgNPs tend to form increasingly large aggregates with increasing both the electrolyte volume and valence.