Gold Bulletin最新文献

Tris(hydroxymethyl)phosphine oxide (THPO) and triphenyl phosphine oxide (PPh₃O) were introduced onto the surface of colloidal gold nanoparticles (Au NPs), and the effect of capping ligands on the catalytic electrooxidation of formaldehyde was studied voltammetrically by using colloidal Au-NP-modified glassy carbon electrodes (GCEs). This was compared with polycrystalline Au and another Au-NP-modified GCE without a capping molecule. We found that PPh₃O causes a larger decrease in the catalytic activity of the Au NPs in liquid than THPO does, indicating that the catalytic activity of the Au NPs is closely associated with the capping ligands. The effect of capping ligands is discussed based on the available surface ratio (ASR), which is defined as the ratio of the total surface area measured electrochemically to the calculated value based on the number and geometry of the Au NPs. These were determined to be 70.6?% for THPO and 0.23?% for PPh₃O, respectively. The significant blocking of formaldehyde is probably due to the structure and hydrophobicity of the benzene rings in the PPh₃O molecule, which is responsible for the decrease in catalytic activity of the Au NPs.

Electron transfer processes play an important role in surface chemistry. This paper presents results of a study of changes in resonant electron transfer processes, as a function of gold cluster sizes, on the example of electron transfer between Li⁺ ions scattered on Au clusters on highly oriented pyrolytic graphite (HOPG). The gold nanoclusters were grown on lightly sputtered HOPG surface in order to obtain a wide coverage distribution of clusters. The growth of clusters was monitored by scanning tunneling microscopy. We found that electron transfer is much more probable on small clusters, whose lateral size is of the order of 2 to 3?nm and height in the 1-nm range, than on bulk Au or thin Au films. A comparison with Au clusters grown on the semiconducting titania did not reveal significant differences with HOPG.

Novel pathways of the synthesis of photoluminescent gold quantum clusters (AuQCs) using biomolecules as reactants provide biocompatible products for biological imaging techniques. In order to rationalize the rules for the preparation of red-emitting AuQCs in aqueous phase using proteins or peptides, the role of different organic structural units was investigated. Three systems were studied: proteins, peptides, and amino acid mixtures, respectively. We have found that cysteine and tyrosine are indispensable residues. The SH/S-S ratio in a single molecule is not a critical factor in the synthesis, but on the other hand, the stoichiometry of cysteine residues and the gold precursor is crucial. These observations indicate the importance of proper chemical behavior of all species in a wide size range extending from the atomic distances (in the Au^I-S semi ring) to nanometer distances covering the larger sizes of proteins assuring the hierarchical structure of the whole self-assembled system.

The absence of unpaired d-electrons of gold leads to its lack of reactivity and paucity of catalytic activity. Synergistic activity of bimetallic PtAu has been proved, and its structure greatly influences on the electrocatalytic activity toward formic acid and carbon monoxide oxidation. Here, a comparison between Pt-modified Au (designated as Pt-on-Au) and PtAu alloy catalysts has been studied. The Pt-on-Au catalyst was prepared by electrodeposition of Pt on the pre-prepared Au, while PtAu alloy was obtained by co-electrodeposition. As a whole, both types of PtAu catalysts were found to be more active toward formic acid electrooxidation compared to pure Pt, exhibiting maximum activity on Pt-on-Au catalyst with Pt to Au atomic ratio of 1:10.22. Moreover, the Pt/Au atomic ratio directly relates to the oxidation pathway of formic acid and carbon monoxide oxidation. The results may be ascribed to much less CO_ads on the surface than single Pt catalyst due to the effect of Au nanoparticles. CO stripping voltammograms present the obvious variation between Pt-on-Au and PtAu alloy catalysts. Meanwhile, the electrocatalytic activities of bimetallic PtAu are evaluated by electrochemical impedance spectroscopy and Tafel analysis.

In this preliminary study, we demonstrate an environmentally friendly process for the green synthesis of gold nanometre scale particles using the leaf extract from an indigenous Australian plant Eucalyptus macrocarpa as both the stabilising agent and the reducing agent. The synthesis process is straightforward, clean and non-toxic. It also has the advantages of being performed at room temperature and does not need complex processing equipment. Formation of the gold nanometre sized particles was confirmed and characterised by UV-visible spectroscopy, X-ray diffraction, transmission electron microscopy and field emission scanning electron microscopy. The antibacterial activity of the synthesised gold particles was also quantified using the sensitivity method of Kirby–Bauer.

A novel layer-by-layer assembly of graphene sheets and gold nanoparticles modified carbon fiber electrode (GE/Au/GE/CFE) was successfully fabricated and applied to simultaneous determination of dopamine (DA) and uric acid (UA). The structure of GE/Au/GE/CFE was characterized by scanning electron microscopy (SEM). It was observed that the gold nanoparticles were homogeneously assembled between the two layers of GE sheets. Cyclic voltammetry (CV) measurements elucidate that GE/Au/GE/CFE has higher electrocatalytic activity for the oxidation of DA and UA when compared with graphene modified carbon fiber electrode (GE/CFE), and graphene and gold nanoparticles modified carbon fiber electrode (Au/GE/CFE). Simultaneous determination of UA and DA on GE/Au/GE/CFE was conducted with a differential pulse voltammetry technique, and two well-defined and fully resolved anodic oxidation peaks were observed. Anodic oxidation currents of DA and UA are linear with their concentration in the range of 0.59–43.96?μM and 12.6–413.62?μM, respectively. Moreover, the composite electrode displays high reproducibility and selectivity for the determination of UA and DA.