Effect of 2-Mercapto-1-methylimidazole on the Electrodeposition of Nickel on an Ordered Au(111) Electrode.

A nickel film electroplated onto a metal substrate can be used as a catalyst for water splitting and a magnetic material for spin valves. Although the nucleation and growth of Ni on Au(111) have already been examined with in situ scanning tunneling microscopy (STM), the current study provides new insights of the structure of the first layer of Ni on an ordered Au(111) electrode in 0.1 M KSO4 + 1 mM H2SO4 + 10 mM NiSO4 (pH 3). Prolonged STM scanning of the Ni monolayer on a Au(111) electrode revealed interfacial mixing to produce a surface alloy, initially assuming segregated Ni domains and later transforming them to a homogeneous Ni/Au phase. The formation of the Ni/Au(111) surface alloy affected the structure of the subsequent bulk Ni deposition. The inclusion of 2-mercapto-1-methylimidazole (MMI) in the deposition bath incurred Ni deposition at a less negative potential and a faster rate, resulting in an overall 5.3 times more Ni deposited on the Au electrode in potentiodynamic experiments. MMI molecules were adsorbed on the Ni deposit to prevent Ni dissolution in the Au(111) electrode. MMI could catalyze the presumed rate-determining step from Ni2+ to Ni+ en route to the metallic Ni. The resultant Ni film with MMI had a 3D texture without a preferred crystal orientation on the Au electrode, as opposed to a layer type growth of Ni on Au(111) without MMI.

Shape Dependence of Silver-Nanoparticle-Mediated Synthesis of Gold Nanoclusters with Small Molecules as Capping Ligands.

In this study, differently shaped silver nanoparticles used for the synthesis of gold nanoclusters with small capping ligands were demonstrated. Silver nanoparticles provide a reaction platform that plays dual roles in the formation of Au NCs. One is to reduce gold ions and the other is to attract capping ligands to the surface of nanoparticles. The binding of capping ligands to the AgNP surface creates a restricted space on the surface while gold ions are being reduced by the particles. Four different shapes of AgNPs were prepared and used to examine whether or not this approach is dependent on the morphology of AgNPs. Quasi-spherical AgNPs and silver nanoplates showed excellent results when they were used to synthesize Au NCs. Spherical AgNPs and triangular nanoplates exhibited limited synthesis of Au NCs. TEM images demonstrated that Au NCs were transiently assembled on the surface of silver nanoparticles in the method. The formation of Au NCs was observed on the whole surface of the QS-AgNPs if the synthesis of Au NCs was mediated by QS-AgNPs. In contrast, formation of Au NCs was only observed on the edges and corners of AgNPts if the synthesis of Au NCs was mediated by AgNPts. All of the synthesized Au NCs emitted bright red fluorescence under UV-box irradiation. The synthesized Au NCs displayed similar fluorescent properties, including quantum yields and excitation and emission wavelengths.

Silver Nanoparticle-Mediated Synthesis of Fluorescent Thiolated Gold Nanoclusters.

A new strategy using silver nanoparticles (Ag NPs) to synthesize thiolated Au NCs is demonstrated. The quasi-spherical Ag NPs serve as a platform, functioning as a reducing agent for Au (III) and attracting capping ligands to the surface of the Ag NPs. Glutathione disulfide (GSSG) and dithiothreitol (DTT) were used as capping ligands to synthesize thiolated Au NCs (glutathione-Au NCs and DTT-Au NCs). The glutathione-Au NCs and DTT-Au NCs showed red color luminance with similar emission wavelengths (630 nm) at an excitation wavelength of 354 nm. The quantum yields of the glutathione-Au NCs and DTT-Au NCs were measured to be 7.3% and 7.0%, respectively. An electrophoretic mobility assay showed that the glutathione-Au NCs moved toward the anode, while the DTT-Au NCs were not mobile under the electric field, suggesting that the total net charge of the thiolated Au NCs is determined by the charges on the capping ligands. The detection of the KSV values, 26 M-1 and 0 M-1, respectively, revealed that glutathione-Au NCs are much more accessible to an aqueous environment than DTT-Au NCs.