Photochemical Strategies for the Facile Synthesis of Gold-Silver Alloy and Core-Shell Bimetallic Nanoparticles

The reduction of HAuCl4 and AgNO3 in aqueous surfactant solutions by 2-hydroxy-2-propyl radical generated by the photochemical cleavage of 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one, commercialized as Irgacure-2959 (I-2959), produces Au-Ag bimetallic nanoparticles with different composition, and architecture,, alloys, and core-shells. The nanoparticle architecture depends on the surfactant employed. The use of hexadecyltrimethylammonium chloride (CTAC) produces Au(core)-Ag(shell) nanoparticles, as expected on the basis of the redox properties of the two metals, whereas when the surfactant is sodium dodecyl sulfate (SDS), it promotes the formation of Au-Ag alloy nanoparticles; the effect is attributed to silver's Coulombic advantage that compensates for the fact that gold is a "more noble" metal. Both structures are characterized by UV-vis spectroscopy, transmission electron microscopy (TEM) and high-resolution transmission spectroscopy (HR-TEM).