Facile synthesis of AgAu alloy and core/shell nanocrystals by using Ag nanocrystals as seeds

A facile seed-growth method was developed to synthesize AgAu alloy and core/shell nanocrystals (NCs) using different-sized Ag NCs (6.1, 7.4, and 9.6 nm) as seeds and octadecylamine as the reducing agent, surface ligand, and solvent. Pre-synthesized Ag NCs acted as catalysts for the reduction of Au precursors at 130 °C. Transmission electron microscopy, energy-dispersive spectroscopy, and optical absorption spectroscopy were used to characterize as-synthesized NCs. Spherical AgAu alloy NCs were obtained when pre-synthesized 6.1 and 7.4 nm Ag NCs were used as seeds. While, if 9.6 nm Ag NCs were used as seeds, cubic Ag/Au core/shell NCs were finally obtained. The shapes and structures of AgAu NCs are related to the Ag seed sizes and the growth mechanism of alloy and core/shell NCs is discussed in detail. Different reaction temperatures were tested to optimize the synthesis of AgAu alloy NCs, and it was found that the optimum reaction temperature for the growth of AgAu alloy NCs is 130 °C.