Nanoscale soldering of metal nanoparticles for construction of higher-order structures

We demonstrated that platinum nanoparticles dispersed in pure water were "soldered" by gold into higher-order structures such as "nanowebs". In practice, gold nanoparticles in water containing the platinum nanoparticles were melted by irradiation of a pulsed 532-nm laser, which excites selectively the surface plasmon band of the gold nanoparticles, and the melted gold nanoparticles solder the platinum nanoparticles together into the nanowebs. Optical absorption spectroscopy and electron microscopy together with electron probe microanalysis were employed to observe the structure of the nanowebs and to elucidate their formation dynamics.     

The Suitability of Various Electrode Materials for the Electrogeneration of Halogens in Constant-Current Coulometry

Abstract

During a voltammetric study of the suitability of platinum, gold, glassy carbon, tungsten, and tantalum as electrode materials for generating halogens in constant-current coulometry it was found that glassy carbon, tungsten, and tantalum are not suitable. Both platinum and gold electrodes can be used; with platinum the possibility of interference caused by formation of complexes of the electrode metal with halides is smaller than with gold.     

Stability of Gold and Platinum Nanowires on Graphite Edges

The stability of coinage and noble metal nanowires supported on graphite steps is examined by density functional theory. In particular, we study the stability of supported gold and platinum wires and compare their chemical properties with those of surfaces and bare wires. A substantially stronger bond with graphite was found for platinum wires due to unfilled antibonding states, which are occupied in the case of gold. This difference has direct consequences for the adsorption of hydrogen. This reaction can occur either on the wire or directly on graphite steps. In the case of gold, the reaction is favoured on steps, while on platinum wires, it has no thermodynamical preferences. Our results suggest that, in early stages of wire formation, hydrogen could desorb gold from graphite, but not platinum.     

Preparation of polymer-protected gold/platinum bimetallic clusters and their application to visible light-induced hydrogen evolution

The dispersions of polymer-protected gold/platinum bimetallic clusters were easily and reproducibly prepared by refluxing the mixed solutions of tetrachloroaureic(III) acid and hexachloroplatinic(IV) acid in ethanol/water (1/1) at 90 ∼ 95 °C for 2 h in the presence of a protective polymer such as poly(N-vinyl-2-pyrrolidone) (PVP). The gold/platinum bimetallic clusters thus obtained were very small, well dispersed and very stable. The UV-Vis spectra and the transmission electron micrographs have indicated that each bimetallic particle has an alloy structure consisting of both gold and platinum atoms, and that the surface of the cluster particle is rich in platinum atoms and the inner core in gold atoms. The gold/platinum bimetallic clusters were used as the multi-electron redox catalysts for visible light-induced hydrogen evolution from water. The rate of hydrogen evolution depended on the mole ratio of the gold/platinum bimetallic clusters. The bimetallic clusters at the mole ratio of Au/Pt = 2/3 were the most active catalyst. The in-situ UV-Vis spectra during the reaction have indicated that the order of the aggregation in the two kinds of metal atoms is very important for structure determination of the Au/Pt bimetallic clusters. The protective polymer PVP plays a role not only in protecting hydrophobic colloidal particles in an aqueous solution, but also in determining the metal composition of the cluster surface.     

The electrochemistry of gold–platinum alloys

The electrochemical properties of gold, platinum and gold–platinum alloy electrodes under different heat treatment conditions have been studied in 0.5 M H₂SO₄ and 0.5 M NaOH. The electro-oxidation of 0.1 M ethylene glycol in 0.5 M NaOH at these electrodes has also been studied. It was found that all the gold–platinum electrodes are more active for ethylene glycol electro-oxidation than both pure gold and platinum, and that the gold–platinum electrodes in the solid solution condition are more active than the two-phase electrodes. Poisoning of all the electrodes occurs during electrolysis of ethylene glycol at a fixed potential. Potential pulsing is successful in removing the poisoning species formed at the pure gold and pure platinum electrodes. High apparent current densities are found during the first few cycles at the Au–Pt alloy electrodes. These high current densities are also associated with more severe poisoning – than at both pure gold and platinum – and longer cleaning cycles are needed to remove the poisons at these electrodes.     

A distinct platinum growth mode on shaped gold nanocrystals

An ultralow amount of platinum can be deposited on the gold surface using copper underpotential deposition and galvanic exchange. The platinum tended to deposit as layers on the octahedral gold nanocrystals with an Au(111) surface, while it aggregated and formed small particles on the cubic gold nanocrystals with an Au(100) surface.     

Deposition of continuous platinum shells on gold nanoparticles by chemical precipitation

Continuous platinum shells consisting of ~5 atomic layers were deposited onto preformed gold seeds in aqueous medium by reducing hexachloroplatinic acid with ascorbic acid. By controlling the reduction kinetics of Pt(IV) species and the properties of the substrate, it was possible to ensure a slow and controlled deposition of platinum atoms onto the gold cores. Electrochemical evaluations revealed the presence of a compact platinum shell. The mass specific oxygen reduction activity of platinum in the AuPt core-shell nanoparticles was found to be four times higher than that of platinum black and comparable to that of polycrystalline bulk metal.     

Separations involving sulphides : Separation of bismuth,cadmium and indium from various other elements that form thiosalts

It has been shown that 2N sodium sulphide reagent can be successfully used in separating tellurium, molybdenum, antimony or rhenium from bismuth., platinum, gold, selenium, rhenium, arsenic, molybdenum or tellurium from cadmium; platinum, gold, selenium, rhenium, arsenic, molybdenum, tellurium or antimony from indium.It is not possible to separate quantitatively arsenic, platinum, gold or selenium from bismuth; antimony from cadmium; and tin from bismuth, cadmium or indium.     

A critical review of titrimetric methods for determination of the noble metals-II

Titrimetric methods for palladium, platinum, rhodium, iridium, ruthenium and gold are critically reviewed to the end of 1964. Previous reviews covered the literature to the end of 1957 for the five platinum metals and to mid-1960 for gold.     

Studies on the extraction of platinum metals with tri-iso-octylamine from hydrochloric and hydrobromic acid: separation and determination of gold, palladium and platinum

The extraction of Pd(II), Rh(III), Ir(III), Au(III) and Pt(IV) from hydrochloric and hydrobromic acid with 5% tri-iso-octylamine solution in carbon tetrachloride has been studied. The gold extract from hydrochloric acid is yellow and absorbs at 325 nm, the palladium compound is red and absorbs at 290 nm and 467 nm, and the platinum compound is blood-red and shows absorption at 268 nm. The gold, palladium and platinum extracts from hydrobromic acid are crimson. reddish brown and blood-red, with maximum absorption at 260, 345 and 300 nm respectively. Methods have been devised for the separation of gold from platinum and for its determination and also for the simultaneous determination of palladium and platinum.     

Aqueous-organic phase-transfer of highly stable gold, silver, and platinum nanoparticles and new route for fabrication of gold nanofilms at the oil/water interface and on solid supports

A simple but effective aqueous-organic phase-transfer method for gold, silver, and platinum nanoparticles was developed on the basis of the decrease of the PVP's solubility in water with the temperature increase. The present method is superior in the transfer efficiency of highly stable nanoparticles to the common phase-transfer methods. The gold, silver, and platinum nanoparticles transferred to the 1-butanol phase dispersed well, especially silver and platinum particles almost kept the previous particle size. Electrochemical synthesis of gold nanoparticles in an oil-water system was achieved by controlling the reaction temperature at 80 degrees C, which provides great conveniences for collecting metal particles at the oil/water interface and especially for fabricating dense metal nanoparticle films. A technique to fabricate gold nanofilms on solid supports was also established. The shapes and sizes of gold nanoparticles as the building blocks may be controllable through changing reaction conditions.     

Spectrophotometric determination of noble metals with tin(II) in bromide solutions

In presence of tin(II) bromide, noble metals give coloured products which are suitable for spcctrophotometric determinations. The colours are red (platinum), yellow-orange (rhodium), yellow-brown (palladium), yellow (iridium) and violet (gold) They are extracted, except for gold, with isoamyl alcohol Platinum, rhodium and palladium can be separated from irdium, and rhodium and platinum from palladium. Rhodium and platinum can be determined simultaneously.     

A fire-assay and wet chemical method for the determination of palladium, platinum, gold, and silver in ores and concentrates

A method is presented for the determination of palladium, platinum, gold and silver in ores and concentrates by a fire-assay and wet chemical technique. After parting of the lead assay button with dilute nitric acid, and separation of the solution from the residue, the palladium and platinum in the solution are precipitated by the addition of stannous chloride, with tellurium as collector. The resulting precipitate is combined with the gold residue and dissolved in aqua regia, then the solution is analysed for palladium, platinum and gold by atomic-absorption spectrophotometry (AAS). Silver is determined in the original solution by AAS before the reduction step.     

Gold Trace Separation from some Platinum Group Metals on Cationic Exchanger in the Presence of Amines

Abstract

The sorption behaviour of gold in the presence of amines on different kinds of cationic exchangers with phosphonic groups has bee investigated. The system Cellex P - amine has been found very useful for gold separation from platinum metals. The method was adopted for trace gold determination in PdC1₂ and platinum powder.     

Extraction of gold, palladium and platinum from chloride, bromide and iodide solution with di-n-octyl sulphide (DOS) in cyclohexane

The extraction of gold, palladium and platinum from hydrochloric acid, hydrobromic acid and iodide media by solutions of di-n-octyl sulphide in cyclohexane was examined. From distribution data it was concluded that the monosolvates AuX(3).DOS and disolvates PdX(2).2DOS are extracted. Extraction of platinum was efficient only from iodide solutions; a disolvate PtI(4).2DOS was formed. The possibility of separation of gold and palladium from platinum by extraction from bromide or chloride solutions and simultaneous extraction of palladium and platinum from an iodide medium was demonstrated.     

The application of thiosalts in analysis : Estimations based on decomposition of thiosalts Part C. Estimation of gold,platinum and antimony

The general method of forming and then decomposing the thiosalts has been applied to the gravimetric estimation of gold, platinum and antimony. In the case of gold and antimony the metals are weighed as Au₂S₃ and Sb₂S₃ respectively, while in the case of platinum, the precipitate of platinum sulphide is ignited and weighed as metal.     

碳酸丙烯酯萃取金、铂的机理及其反萃过程的研究

本文研究了PC-CHCl₃体系中,杂质金属离子对金、铂萃取的影响;金、铂反萃条件的选择.并用斜率法、饱和法、化学分析法、紫外光谱、红外光谱探讨了PC萃取金、铂的机理。     

Hydrogen chemisorption on supported platinum, gold, and platinum-gold-alloy catalysts

Alloyed catalysts receive considerable attention, because of their unique catalytic properties; they often show higher selectivity, activity, and stability compared to the pure metal particles. To provide insights in the origins of these features, we report the structure and the interaction of hydrogen with each of the metals in an intimately mixed platinum-gold catalyst and compare these characteristics to those in the single metal particles. X-Ray absorption spectroscopy (XAS) and electron microscopy analysis showed that the structure of the mixed particle differed from the single metal particles. The interaction of platinum with hydrogen is stronger than the H-Au interaction and the adsorption sites were different. EXAFS analysis showed that the structure of the platinum clusters changes with increasing hydrogen coverage, observed as a relaxation of the contracted Pt-Pt distance and an increase in the Pt-Pt coordination number. No such changes were observed for gold clusters. Well-mixed PtAu-alloy clusters, with a bulk Au-to-Pt ratio of two, supported on SiO(2), adsorb hydrogen on both platinum and gold atoms, which indicates that gold cannot be regarded as an inert metal. The heat of adsorption on the platinum ensembles does not decrease upon alloying; the weakening of the overall hydrogen adsorption strength when alloying platinum with gold is an ensemble-size effect.     

Electrocatalysis by ad-atoms: Part IV. Enhancement of the oxidation of formic acid on Pt-Au(subs) and Au-Pt(subs) electrodes by bismuth ad-atoms

The roles of surface and bulk for electrocatalysis have been investigated. Bi ad-atoms enhance a platinum electrode to a great extent for HCOOH oxidation. In order to examine whether bulk platinum atoms are necessary for the electrocatalysis, monolayer or submonolayer amounts of platinum atoms were made to deposit on a gold electrode which is quite inactive for the oxidation. The deposition of a complete monolayer of platinum atoms on a gold electrode makes the electrode as active as a platinum electrode itself. Bi ad-atoms enhance this electrode to the same extent as they do a platinum electrode for the oxidation. Thus surface atoms, Pt and Bi atoms, having no bulk atoms on a quite inactive electrode work effectively for the electrocatalysis, the platinum atoms for the adsorption of the main reactant and the Bi atoms for blocking of the sites against the formation of poison. It is the adsorptive property of the surface that controls the electrocatalytic activity.     

火试金减杂-电感耦合等离子体原子发射光谱法（ICP-AES）法测定高冰镍的金、银、铂、钯含量

建立了火试金减杂-电感耦合等离子体原子发射光谱法（ICP-AES）测定高冰镍中金、银、铂、钯含量的分析方法。实验采用火试金富集、熔融、灰吹得到合粒,通过减杂法得到银含量,通过ICP-AES法测定得到金、铂、钯含量。金、银、铂、钯的加标回收率在99.53%-101.83%之间,相对标准偏差小于3%。此方法快速、简洁,准确度高、精密度好,能够满足高冰镍的测定需求。