Electrochemical Insight into the Brust-Schiffrin Synthesis of Au Nanoparticles

摘要

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 [AuCl_4]~- and thiol (RSH) in homogeneous toluene (TL) solution. Ion transfer calculations indicate the formation of [AnCl_2]~- 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. BH_4~- ion transfer reactions between water and DCE indicate that the reduction of [AuCl_4]~- or [AuCl_2]~- to Au nanoparticles by BH_4~- proceeds in the bulk organic phase. On the other hand, BH_4~- 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.