Effects of gas bubbling for shape, size, and composition changes in Au–Ag bimetallic nanoparticles including polygonal Au seeds under oil-bath heating at 150 °C

Abstract

Effects of Ar or O2 gas bubbling for shape, size, and composition changes in Au–Ag bimetallic nanoparticles were studied under oil-bath heating at 150 °C for 10–60 min in ethylene glycol (EG). When a mixture of polygonal Au seeds, AgNO3, and polyvinylpyrrolidone (PVP) in EG solution was heated from room temperature to 150 °C and it was kept at that temperature for 10–60 min under Ar or O2 gas bubbling, different shape, size, and composition changes were observed. Under Ar gas bubbling, major products after heating for 10 min were polygonal Au core Ag-rich Ag/Au alloy shell particles, denoted as Au@Ag/Au, and spherical Ag-rich Ag/Au alloy particles. They were transformed to larger excentered Au@Ag/Au particles with an average diameter of 340 ± 106 nm after further heating for 20–50 min. Under O2 gas bubbling, major products after heating for 10 min were Au@Ag core–shell particles having a thin Ag shell, large Au-rich Au/Ag alloy particles, and many small spherical Ag particles with 4 ± 2 nm average diameter. After further heating for 20–50 min, the Au@Ag particles fuse and aggregate to form spherical Au-rich Au/Ag alloy particles with an average diameter of 259 ± 37 nm. Results show that Ag-rich or Au-rich Au–Ag bimetallic particles can be prepared easily under bubbling Ar or O2 gas, respectively. The different structure and composition changes in Au–Ag bimetallic particles under Ar or O2 bubbling are discussed in terms of fusion, aggregation, and oxidative etching of Au and Ag particles.