Fabrication of Au-Ag Bimetallic Nanostructures Through the Galvanic Replacement Reaction of Block Copolymer-Stabilized Ag Nanoparticles with HAuCl4

Silver nanoparticles (AgNPs) with block copolymer shells were synthesized by UV irradiation of the solution of poly(2-vinyl pyridine)-b-poly(ethylene oxide) (P2VP-b-PEO)/AgNO3 complexes in tetrahydrofuran (THF), which were then used as sacrificial templates to fabricate Ag-Au bimetallic nanoparticles (NPs) through a galvanic replacement reaction. The obtained Ag-Au NPs were characterized by UV-vis spectroscopy and high resolution transmission electron microscopy (TEM). The results indicate that the morphology and structure of the Ag-Au NPs can be controlled by adjusting the molar ratio (MR) of HAuCl4 to Ag. When the MR is less than 0.16, Ag-Au alloys form. When the MR is greater or equal to 0.16, hollow Ag-Au nanostructures begin to appear and the system exhibits two surface plasmon resonance (SPR) peaks. This simple strategy can prepare Ag-Au NPs with different optical properties.