Tojo C, de Dios M, Buceta D, López-Quintela M A
Physical Chemistry Department, Faculty of Chemistry, University of Vigo, E-36310 Vigo, Spain.
Phys Chem Chem Phys. 2014 Sep 28;16(36):19720-31. doi: 10.1039/c4cp02936d.
The different distributions of metals in bimetallic nanoparticles synthesized in microemulsions were studied by computer simulation. The simulations demonstrated that if the difference between the reduction potentials of both metals is about 0.15-0.3 V, the compartmentalization of the reaction media causes the accumulation of slower reduction reactants in the microemulsions droplets, which favours the chemical reaction like a cage effect: increasing the local concentration of the slower reduction metal salt gives rise to a faster reduction, so the differences in reduction rates of both metals are attenuated. A more coincidental reduction of both metals deeply affects the nanoparticle structure, causing a better mixed alloy. This effect will be more pronounced when the concentration is higher and the intermicellar exchange rate is faster. This means that for any fixed microemulsion the nanoparticle structure can be modified by changing the reactant concentration: the core can be enriched in the faster reduction metal by lower concentrations, and the shell can be enriched in the slower metal by higher concentrations. Based on these observations, this study suggests a route to help experimentalists better create nanoparticles with a pre-defined structure.
通过计算机模拟研究了微乳液中合成的双金属纳米颗粒中金属的不同分布。模拟结果表明，如果两种金属的还原电位之差约为0.15 - 0.3 V，反应介质的分隔会导致还原较慢的反应物在微乳液滴中积累，这有利于类似笼效应的化学反应：增加还原较慢的金属盐的局部浓度会导致更快的还原，因此两种金属还原速率的差异会减弱。两种金属更同步的还原会深刻影响纳米颗粒的结构，形成混合更好的合金。当浓度较高且胶束间交换速率较快时，这种效应会更明显。这意味着对于任何固定的微乳液，通过改变反应物浓度可以改变纳米颗粒的结构：较低浓度时，纳米颗粒的核可以富集还原较快的金属，较高浓度时，壳可以富集还原较慢的金属。基于这些观察结果，本研究提出了一条帮助实验人员更好地创建具有预定义结构的纳米颗粒的途径。
