Abstract
Computer calculations were carried out to determine the reaction rates and the mean structure of bimetallic nanoparticles prepared via a microemulsion route. The rates of reaction of each metal were calculated for a particular microemulsion composition (fixed intermicellar exchange rate) and varying reduction rate ratios between both metal and metal salt concentration inside the micelles. Model predictions show that, even in the case of a very small difference in reduction potential of both metals, the formation of an external shell in a bimetallic nanoparticle is possible if a large reactant concentration is used. The modification of metal arrangement with concentration was analyzed from a mechanistic point of view, and proved to be due to the different impact of confinement on each metal: the reaction rate of the faster metal is only controlled by the intermicellar exchange rate but the slower metal is also affected by a cage-like effect.
Highlights
Bimetallic nanoparticles, in which two kinds of metals are assembled, are attractive because their properties often differ markedly from either of the constituent metals [1,2,3]
Our hypothesis is that the resulting nanostructure is due to the particular combination of three main factors: the reduction rate ratio between both metals, the amount of metal precursors inside micelles, and the intermicellar exchange rate
Monte Carlo simulations have been employed to determine the mean structure and the reaction rates of bimetallic nanoparticles prepared via a microemulsion route
Summary
Bimetallic nanoparticles, in which two kinds of metals are assembled, are attractive because their properties often differ markedly from either of the constituent metals [1,2,3]. Previous simulation studies [29,30] concluded that the nanoparticle structure is defined by the difference in the reduction rates only if both reductions occur at the same rate (an alloy is obtained) or if both reductions have very different rates (a core-shell structure is obtained) These two extreme cases reproduce the behavior obtained in homogeneous media, that is, compartmentalization of the reaction media cannot modify the metal arrangement. A vast majority of bimetallic systems belong to the large space between both extremes (1 < vA/vB < 100, where vA and vB are the reduction rates of fast and slow metal respectively), in which metal distribution depends on microemulsion composition. This study contributes to fundamental research concerning the understanding of microemulsion-based nanoparticle synthesis, and can open up a new way to synthesize bimetallic nanoparticles with ad-hoc controlled nanostructures
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