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Electrochemical Insight into the Brust–Schiffrin Synthesis of Au Nanoparticles

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journal contribution
posted on 09.12.2015, 00:00 by Akihiro Uehara, Samuel G. Booth, Sin Yuen Chang, Sven L. M. Schroeder, Takahito Imai, Teruo Hashimoto, J. Frederick W. Mosselmans, Robert A. W. Dryfe
The mechanism of the Brust–Schiffrin gold nanoparticle synthesis has been investigated through the use of ion transfer voltammetry at the water/1,2-dichloroethane (DCE) solution interface, combined with X-ray absorption fine structure (XAFS) of the reaction between [AuCl4] and thiol (RSH) in homogeneous toluene (TL) solution. Ion transfer calculations indicate the formation of [AuCl2] at RSH/Au ratios from 0.2–2 with a time-dependent variation observed over several days. At RSH/Au ratios above 2 and after time periods greater than 24 h, the formation of Au­(I)­SR is also observed. The relative concentrations of reaction products observed at the liquid/liquid interface are in excellent agreement with those observed by XAFS for the corresponding reaction in a single homogeneous phase. BH4 ion transfer reactions between water and DCE indicate that the reduction of [AuCl4] or [AuCl2] to Au nanoparticles by BH4 proceeds in the bulk organic phase. On the other hand, BH4 was unable to reduce the insoluble [Au­(I)­SR]n species to Au nanoparticles. The number and size of the nanoparticles formed was dependent on the concentration ratio of RSH/Au, as well as the experimental duration because of the competing formation of the [Au­(I)­SR]n precipitate. Higher concentrations of nanoparticles, with diameters of 1.0–1.5 nm, were formed at RSH/Au ratios from 1 to 2.