Size Control of Gold Nanocrystals in Citrate Reduction: The Third Role of Citrate
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- 19 October 2007
- journal article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 129 (45), 13939-13948
- https://doi.org/10.1021/ja074447k
Abstract
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 (Na3Ct) 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 Na3Ct. 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 Na3Ct. 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/Na3Ct 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]-.Keywords
This publication has 20 references indexed in Scilit:
- Turkevich Method for Gold Nanoparticle Synthesis RevisitedThe Journal of Physical Chemistry B, 2006
- Formation of Nearly Monodisperse In2O3 Nanodots and Oriented-Attached Nanoflowers: Hydrolysis and Alcoholysis vs PyrolysisJournal of the American Chemical Society, 2006
- Manganese(II) Oxide Nanohexapods: Insight into Controlling the Form of NanocrystalsChemistry of Materials, 2006
- A Simple Large-Scale Synthesis of Nearly Monodisperse Gold and Silver Nanoparticles with Adjustable Sizes and with Exchangeable SurfactantsChemistry of Materials, 2004
- What Factors Control the Size and Shape of Silver Nanoparticles in the Citrate Ion Reduction Method?The Journal of Physical Chemistry B, 2003
- Preparation and Growth Mechanism of Gold Nanorods (NRs) Using Seed-Mediated Growth MethodChemistry of Materials, 2003
- Classical Approximation to Nonradiative Electronic Relaxation in Condensed Phase SystemsThe Journal of Physical Chemistry A, 1999
- Tetravalent Uranium in CalciteScience, 1998
- Kinetics of II-VI and III-V Colloidal Semiconductor Nanocrystal Growth: “Focusing” of Size DistributionsJournal of the American Chemical Society, 1998
- X. The Bakerian Lecture. —Experimental relations of gold (and other metals) to lightPhilosophical Transactions of the Royal Society of London, 1857