Size control of gold nanocrystals in citrate reduction: The third role of citrate
Size control of gold nanocrystals in citrate reduction: The third role of citrate
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金纳米晶体在柠檬酸盐还原中的尺寸控制：柠檬酸盐的第三个作用
DOI：
10.1021/ja074447k
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发表时间：
2007-11-14
影响因子：
15
通讯作者：
Peng, Xiaogang
中科院分区：
文献类型：
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作者：
Ji, Xiaohui;Song, Xiangning;Peng, Xiaogang
对沸水中柠檬酸盐还原法制备金纳米晶的生长动力学和尺寸/形状随时间的演变进行了系统定量的研究。结果表明，在传统的Frens合成法中，pH值的大小和反应机理主要取决于柠檬酸钠（Na（3）Ct）的浓度。这一结论进一步证实了与可变的pH值，但固定的两个反应物，HAuCl 4和Na（3）Ct的浓度的反应。鉴定了两种基本上不同的反应途径，切换点在pH = 6.2-6.5。第一种途径是低pH范围，由三个重叠的步骤组成：成核，随机附着到多晶纳米线，并通过粒子内成熟点的纳米线的平滑。在pH切换点以上发生的第二种途径与通常已知的成核-生长途径一致。使用第二种途径，我们展示了一种新的合成路线，通过简单地改变溶液的pH值与固定浓度的HAuCl 4和Na（3）Ct的大小范围从20到40 nm的近单分散的金纳米晶体的合成。反应途径的切换可能是由于水作为反应介质的整合性质。在柠檬酸盐还原中，通过改变初始HAuCl 4/Na（3）Ct比率来改变溶液pH。因此，当pH高于约6.2时，非常活性的[AuCl 3（OH）]（-）将转化为反应性较低的[AuCl 2（OH）（2）]（-）和[AuCl（OH）（3）]（-）。
Growth kinetics and temporal size/shape evolution of gold nanocrystals by citrate reduction in boiling water were studied systematically and quantitatively. Results reveal that the size variation and overall reaction mechanism were mostly determined by the solution pH that was in turn controlled by the concentration of sodium citrate (Na(3)Ct) in the traditional Frens's synthesis. This conclusion was further confirmed by the reactions with variable pH but fixed concentrations of the two reactants, HAuCl4 and Na(3)Ct. Two substantially different reaction pathways were identified, with the switching point at pH = 6.2-6.5. The first pathway is for the low pH range and consists of three overlapping steps: nucleation, random attachment to polycrystalline nanowires, and smoothing of the nanowires via intra-particle ripening to dots. The second pathway that occurred above the pH switching point is consistent with the commonly known nucleation-growth route. Using the second pathway, we demonstrated a new synthetic route for the synthesis of nearly monodisperse gold nanocrystals in the size range from 20 to 40 nm by simply varying the solution pH with fixed concentrations of HAuCl4 and Na(3)Ct. The switching of the reaction pathways is likely due to the integration nature of water as a reaction medium. In the citrate reduction, the solution pH was varied by changing the initial HAuCl4/Na(3)Ct ratio. Consequently, when pH was higher than about 6.2, the very reactive [AuCl3(OH)](-) would be converted to less reactive [AuCl2(OH)(2)](-) and [AuCl(OH)(3)](-).