Formation and characterization of silver nanoparticles in aqueous solution via ultrasonic irradiation

•The formation of Ag NPs is observed in pure aqueous solution without reductant and surfactant under ultrasonic condition.•In pure aqueous solution, the reactive route producing oxygen related to hydroxyl radicals (OH) is presented.•In alkaline aqueous solution, ultrafine Ag NPs with diameter of 8nm are achieved via ultrasonic irradiation.•In alkaline aqueous solution, the effects of hydroxyl ions (OH−) on formation of Ag NPs are discussed detailedly. In this study, a simple and green method to synthesize silver nanoparticles (Ag NPs) in aqueous solution via ultrasonic irradiation has been developed. Ultrafine Ag NPs with average diameter of 8nm were obtained through sonicating aqueous solution of sodium hydroxide (NaOH, 0.1mM) with adding silver nitrate solution (AgNO3, 5.88mM) drop by drop. In pure aqueous solution, the reactive route related to hydroxyl radicals (OH) is presented. Furthermore, in alkaline aqueous solution, the effects of hydroxyl ions (OH−) on formation of Ag NPs are discussed detailedly. The formation of Ag NPs was tracked by surface plasmon resonance (SPR) band of ultraviolet–visible (UV–Vis) spectrum; the morphology of the obtained Ag NPs was characterized through transmission electron microscopy (TEM); energy dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD) confirmed the formation of metallic Ag NPs.