Electrooxidation of Silver in the Presence of Some Amino Acids

Data on the influence the solution's ionic composition and amino acids (histidine, methionine) have on the anodic dissolution of silver are presented. The dissolution is most effective in intensively agitated nitrate solutions containing methionine in excess of 0.05 M (current efficiency reaches 75%). By analogy with the gold dissolution, acceleration of the silver dissolution is attributed to oxidized methionine complexing with metals.     

Properties of conducting films of electrophoretic concentrates of silver and gold nanoparticles in AOT surfactant

Liquid concentrates of silver and gold nanoparticles with 1–2 M metal concentrations were isolated by electrophoresis in a capacitor-type cell from AOT reverse micellar solutions in n-decane. The electrophoretic concentrates and the starting micellar solutions were characterized by nonaqueous electrophoresis, transmission electron microscopy, photon correlation spectroscopy (dynamic light scattering), and spectrophotometry. The hydrodynamic diameter of silver and gold nanoparticles was 13.2 and 8.6 nm, respectively; the ζ-potential was 70 and 13 mV. The drying of the concentrates on glass and silicon substrates and subsequent treatment with a 30% solution of water in ethanol gave mirror conducting Ag, Au, Ag-Au, and Au/Ag films containing on the average 80% metal and 20 wt % AOT. The film structure, morphology, and composition were studied by scanning electron microscopy (SEM) and energy dispersion analysis (EDX).     

Manipulation of the growth of gold and silver nanomaterials on glass by seeding approach

This paper describes the growth of gold and silver nanomaterials from their corresponding colloidal seeds on glass substrates. The glass substrates were treated with 3-mercaptopropyltrimethoxysilane (MPTMS) and then with gold or silver nanoparticle seeds (AuNPSs or AgNPSs) at different concentrations. After separately immersing the thus-prepared MPTMS-AuNPS and MPTMS-AgNPS glass substrates in aqueous solutions containing cetyltrimethylammonium bromide, ascorbic acid, and gold or silver ions, we obtained Au and Ag nanomaterials of different sizes and shapes, which we characterized through scanning electron microscopy (SEM) and dark-field microscopy (DFM). At 0.001x concentrations AuNPSs and AgNPSs (i.e., 1000-fold-diluted solutions of the as-prepared samples), Au and Ag nanomaterials having 1.36 and 5.21 mum lengths and aspect ratios of 11 and 24 were prepared in yields of 27% and 54%, respectively. Scattering spectra of the thus-prepared single AuNRs and AgNRs revealed that the uniformity in the shape of the AuNRs was greater than that of the AgNRs. In addition, we demonstrate the preparation (using a laboratory-made synthesis system) and characterization (through DFM measurements) of Au nanomaterials, including AuNRs, from five AuNPS solutions of different concentrations on a single glass substrate.     

A simplified sampling technique for use with the Weisz ring oven: application to qualitative analysis of some gold and silver alloys

Up to 100 microg of sample can be collected from gold or silver alloys by rubbing the specimen with the ground hemispherical tip of a 4-mm Pyrex glass rod. Gold alloys are then dissolved in potassium cyanide solution containing hydrogen peroxide; silver alloys are exposed to vapours of nitric acid. Procedures for transfer, ring oven separation and identification of alloy constituents in the sample solutions are described.     

The potentiometric and amperometric determination of silver with mercaptophenylthiothiadiazolone and mercaptobenzthiazole

Summary The previously described gravimetric determinations of silver were used for the potentiometric and amperometric determinations of silver in the presence of interfering cations. The potentiometric titration of silver with MFTD (MBT) is a simple matter, if enough complexone is present, in both ammoniacal and neutral solutions. The amperometric determination of silver with MFTD (MBT) is carried out in neutral solution, containing complexone, with rotated platinum electrode and mercury-mercuric iodide half-cell, short-circuited through a microammeter. The only interfering elements are mercury, gold, and some of the platinum metals.     

Synthesis of tubular gold and silver nanoshells using silica nanowire core templates

We report the synthesis of tubular gold and silver nanoshells on silica nanowire core templates in solution. Silica nanowires were synthesized and characterized with optical and NMR methods. Gold nanoparticle seeds (2 to 3 nm) with weak repulsive surfactants such as tetrakis-hydroxymethyl-phosphonium chloride (THPC) were conjugated to the surface of these nanowires. A regrowth process was initiated from these nanoparticles on the surface of the silica nanowires dispersed in gold or silver stock solutions in the presence of reducing agents. Micrometers-long gold and silver tubular nanoshells (80-150 nm o.d.) were made, fully covering the silica nanowires.     

含硫氮螯合树脂对金、银及某些贱金属氰化物吸附性能的研究

用ＩＣＰ－ＡＥＳ研究了含硫氮螯合树脂对碱性氰化溶液中金、银、铜、铁、锌等金属离子的吸附行为。结果表明,该树脂除定量吸附金、银的氰化物外,也吸附铜、锌、铁的氰化物;吸附在树脂上的银及其它贱金属离子可以用２％ＮａＣＮ定量解吸,用硫脲－硫酸溶液可顺利地将金从树脂上洗脱下来,由此可实现金与银等元素的分离。树脂重复使用性能良好。对该树脂吸附金属氰化物的机理进行了初步探讨。     

Chelating ion-exchangers containing n-substituted hydroxylamine functional groups: Part 6. Sorption and separation of gold and silver by a polyhydroxamic acid

The sorption and desorption characteristics of gold and silver on a polyhydroxamic acid chelating resin are described. Gold is quantitatively sorbed from 0.5 M nitric acid or neutral solutions, and readily eluted with 0.5% ($\text{w}\text{v}$) potassium cyanide solution. Silver is removed from 0.05 M nitric acid or neutral solutions, and can be eluted with the cyanide solution or with 0.5 M nitric acid. Gold can be quantitatively separated from copper, iron and silver; gold and silver are sorbed from dilute cyanide solutions. Tests with river water and other eluting systems are reported.     

乙酸除铋火试金法测定粗铋中的金银含量

建立了用乙酸分离粗铋中铋-火试金重量法测定粗铋中金和银含量的方法。首先把粗铋焙烧氧化,然后用乙酸溶解粗铋的氧化物,过滤除去铋,消除铋对火试金法的干扰,将沉淀物灰化后,配料、高温熔融,熔态的金属铅捕集试样中的贵金属形成铅扣,将铅扣灰吹,得到金银合粒,用硝酸溶解分离金,用重量法测定金含量。方法准确度高,精密度好,金的加标回收率为99.2%～101%,银的加标回收率为98.2%～99.7%。能很好地满足粗铋中金、银的测定。     

Silver and gold nanoparticles in silica matrices: synthesis,properties, and application

Methods of synthesis, optical characteristics, morphology, and catalytic and bactericidal characteristics of composite materials based on silica (films and powders) containing nanoparticles of silver, gold, and their binary compounds with alloy or core–shell structure are examined. The photochemical reduction of Au³⁺ and Ag⁺ with a photocatalyst (a film of SiO₂ with adsorbed benzophenone) makes it possible to generate stable nanoparticles of gold and silver in solutions for subsequent introduction into adsorbents and catalysts. Examples of the use of nanosized composites in catalysis and in microbiological experiments are presented.     

A Sorbent Extraction Procedure for the Preconcentration of Gold,Silver and Palladium on an Activated Carbon Column

ABSTRACT

A preconcentration method based on the use of an activated carbon column has been established for flame atomic absorption spectrometric determinations of gold, silver and palladium. The analytes were sorbed on the column as a complex of dithiophosphoric acid O, O-diethyl ester (DDTP). The sorbed analytes were eluted through the column with 2M NH₃ in acetone. Quantitative recoveries (≥95 %) for gold, silver and palladium were obtained from acidic solutions. The developing method was successfully applied to the determination of trace amounts of gold, silver and palladium in some samples with satisfactory results (relative standard deviation < 7 %; relative error < 3 %).     

Gold and silver uptake and nanoprecipitation on calcium alginate beads

Calcium alginate beads were investigated for their biosorption performance in the removal of gold and silver from aqueous solutions. It was found that uptake capacities were significantly affected by the solution pH, with optimum pH values of 2 and 4 for gold and silver, respectively. Kinetic and isotherm experiments were carried out at the optimum pH. The maximum uptake capacities were 290 mg/g for Au and 52 mg/g for Ag. FTIR analysis indicated that both carboxylic and hydroxylic functional groups in alginate beads are involved in the metal binding and later reduction of gold (+3) and silver (+1) to gold (0) and silver (0). SEM and X-ray diffraction confirmed the formation of gold and silver nanoparticles.     

Dense aqueous colloidal gold nanoparticles prepared from highly concentrated precursor solution

Gold nanoparticles were fabricated by reduction of highly concentrated Au(III) ions (200 mM) with casein proteins from milk. The gold nanoparticles were converted to nanoparticle-powders after washing and subsequent vacuum drying without aggregation. The nanoparticle-powders completely re-dispersed in aqueous solution, and stable colloidal gold nanoparticles were obtained. UV-vis extinction spectra and dynamic light scattering (DLS) measurements revealed that large assemblies (size, ca. 3 μm) and subaggregates (size, <0.5 μm) composed of gold nanoparticle-casein protein chain-Au(III) ion were dynamically formed and disintegrated over the course of the growth of the gold nanoparticles. Fourier transform infrared (FT-IR) spectra indicated conformational changes of casein proteins induced by the interaction of casein protein-Au(III) ion and -gold nanoparticle. Finally, rapid, one-pot, and highly concentrated synthetic procedures of gold and silver nanoparticle powders protected by casein (mean diameters below 10 nm) were successfully developed using 3-amino-1-propanol aqueous solutions as reaction media. Dense colloidal gold (40 g L(-1)) and silver (22 g L(-1)) nanoparticle aqueous solutions were obtained by re-dispersing the metal nanoparticle powders.     

New pathway for sonoelectrochemical synthesis of gold–silver alloy nanoparticles from their bulk substrates

In this study, we report the first sonoelectrochemical methods to prepare gold–silver alloy nanoparticles with the mean diameter of 5 nm in 0.1 N HCl aqueous solutions without addition of any stabilizer. First, a silver substrate was roughened by a triangular-wave oxidation–reduction cycle (ORC) in an aqueous containing 0.1 N HCl. Silver-containing complexes were found in the solution after the ORC treatment. Then a gold substrate was subsequently roughened by the similar ORC treatment in the same solution containing the silver complexes. After this procedure Au- and Ag-containing complexes were left in the solution. Then the Au working electrode was immediately replaced by a Pt electrode and a cathodic overpotential of 0.6 V from the open circuit potential (OCP) of ca. 0.75 V vs Ag/AgCl was applied under sonification to synthesize Au–Ag alloy nanoparticles.     

Extraction of metals by neutral sulfur-containing extractants: Part I. o-isopropyl-n-ethylthiocarbamate

The formation of neutral mixed complexes of the MX_mS_p type (where M is a metal ion with m⁺ charge, X the inorganic anion, and S the sulfur-containing extractant) allows a selective extraction of various elements. The extraction of many metals from mineral acid solutions or from halide-sulfuric acid mixtures by 0.05 M O-isopropyl-N-ethylthiocarbamate(IPETC) solution in chloroform has been studied. (IPETC) possesses very high selectivity for silver and mercury ions in extractions from HNO₃, H_{2)SO4, HClO4 and HCl solutions. In addition to silver and mercury, Cu, Au, Tl and Se are readily extracted from solutions containing bromide. From iodide solutions, copper, gold and thallium ions may be selectively extracted because silver and mercury cannot be extracted at concentrations of iodide above 0.1 M.(IPETC} extracts metals as mixed complexes, containing the halide and apparently the extractant in the molecular form.     

Ion-selective electrodes for gold and silver determination

Some new ion-selective electrodes for silver and gold are described. They are based on the ion-associate species formed by the cyanide, chloride or thiourea complexes of the metals, with hydrophobic anions or cations, as appropriate. The electrodes have been applied to the determination of gold and silver in various technological process solutions in industry.     

Electrostatic-assembly metallized nanoparticles network by DNA template

Eighteen-nanometer gold and 3.5-nm silver colloidal particles closely packed by cetyltrimethylammonium bromide (CTAB) to form its positively charged shell. The DNA network was formed on a mica substrate firstly. Later, CTAB-capped gold or silver colloidal solutions were cast onto DNA network surface. It was found that the gold or silver nanoparticles metallized networks were formed owing to the electrostatic-driven template assembling of positive charge of CTAB-capped gold and silver particles on the negatively charged phosphate groups of DNA molecules by the characterizations of AFM, XPS and UV-vis. This method may provide a novel and simple way to studying nanoparticles assembly conjugating DNA molecules and offer some potential promising applications in nanocatalysis, nanoelectronics, and nanosensor on the basis of the fabricated metal nanoparticles network.     

Reactions of alkyl-radicals with gold and silver nanoparticles in aqueous solutions

Silver and gold nanoparticles are very efficient catalysts for the dimerization of methyl-radicals in aqueous solutions. The rate constants for the reaction of methyl-radicals with the gold and silver nanoparticles were measured and found to be 3.7 x 10(8) M(-1) s(-1) and 1.4 x 10(9) M(-1) s(-1), respectively. The results thus suggest that alkyl-radicals, also not reducing ones, are scavenged by these nanoparticles. This might explain the role, if such a role exists, of these nanoparticles in medical applications.     

Growth of gold nanorods and bipyramids using CTEAB surfactant

Gold nanorods and bipyramids have been synthesized using the seed-mediated approach in aqueous cetyltriethylammonium bromide (CTEAB) solutions in the presence of silver nitrate. Gold nanoparticle seeds that are stabilized with either CTEAB or sodium citrate have been used. The use of the CTEAB-stabilized seeds gives gold nanorods in high yield in one step with the longitudinal plasmon wavelength ranging from 750 to 1030 nm, depending on the amount of the seeds. The longitudinal plasmon wavelength can be extended to 1100 nm by the use of a two-step growth method. The growth of gold nanorods in CTEAB solutions takes 5-10 h, more than 5 times slower than that in cetyltrimethylammonium bromide solutions at the same concentration of surfactants. The use of the citrate-stabilized seeds gives both gold bipyramids and a small percentage of gold nanorods. The longitudinal plasmon wavelength of the bipyramids is tunable from 700 to 1100 nm by varying the amount of the citrate-stabilized seeds. The growth of gold bipyramids takes more than 1 day. Transmission electron microscopy characterizations reveal that the gold nanorods grown from both types of gold nanoparticle seeds are single-crystalline and that the gold bipyramids are penta-twinned.     

Direct determination of gold and silver in rat plasma by graphite furnace atomic absorption spectrometry with Zeeman effect background correction and its application to the pharmacological properties of a mixture of copper,gold and silver salts

Methods for determining gold and silver in rat plasma without prior mineralization are presented. They permit concentrations above 1 μg 1^?1 to be measured. They were applied to 96 rat plasma samples with gold and silver contents up to 3 μg 1^?1. In addition, the anti-inflammatory properties of a solution containing gold, silver and copper at the mg 1^?1 level were tested and demonstrated.