Chemically-reduced graphene-oxide-supported gold nanoparticles with a diameter, of 40-60 nm are considered here as catalytic materials for the reduction of oxygen in alkaline medium in comparison to analogous systems based on conventional Vulcan carbon carriers. Gold nanoparticles are prepared by the chemical reduction method, in which the NaBH4-prereduced Keggin-type phosphomolybdate heteropolyblue acts as the reducing agent for the precursor (HAuCl4). Polyoxometallate (PMo12O403) capping ligands stabilize gold nanoparticle deposits, facilitate their dispersion and attachment to carbon supports. Indeed, it is apparent from the independent diagnostic voltammetric experiments (in 0.5 mol dm (H2SO4)-H-3) that heteropolymolybdates form readily stable adsorbates on nanostructures of both gold and carbon (reduced graphene oxide and Vulcan). It is reasonable to expect that the polyoxometallate-assisted nucleation of gold has occurred in the proximity of oxygenated defects existing on carbon substrates. Under conditions of electrochemical diagnostic experiments (performed in 0.1 mol dm (3) KOH): (i) the phosphomolybdate adsorbates are removed from the interface as they undergo dissolution in alkaline medium; and (ii) the Au nanoparticles (Au loading, 30 mu g cm (2)) remain well-dispersed on the carbon as evident from transmission electron microscopy. High electrocatalytic activity of the reduced-graphene oxide-supported Au nanoparticles toward reduction of oxygen in alkaline medium is demonstrated using cyclic and rotating ring-disk voltammetric experiments. The latter system could also act as the active support for Pt nanoparticles during the reduction of oxygen. Among important issues are possible activating interactions between gold and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide (as evident from Raman spectroscopy)
Three-dimensional multi-layered films (on glassy carbon) composed of networks of polyoxometallate (PMo 12 O 40 3− )-modified gold nanoparticles linked together through the alternately deposited ultra-thin layers of polypyrrole have served as active supports for Co-porphyrin catalytic centers. The hybrid organic-inorganic films (supports) have been prepared by using the layer-by-layer approach. The fact that polyanionic (phosphomolybdate) adsorbates on gold nanoparticles are attracted by positively charged sites of conducting polymer (polypyrrole) structures leads to the stabilizing effect and facilitates distribution of Au nanostructures. The systems have been characterized using scanning electron microscopy, as well as with chronoamperometric and voltammetric techniques. By supporting Co-porphyrin centers o n t o t h e h y b r i d f i l m o f t h e p o l y m e r -l i n k e d phosphomolybdate-stabilized gold nanoparticles, significant electrocatalytic enhancement effects (namely voltammetric current increases) have been observed during the electroreduction of oxygen in acid medium relative to a standard response of the simple porphyrin deposit on glassy carbon measured under analogous conditions. Among important issues is the high activity of the hybrid film (support) itself toward the reductive decomposition of hydrogen peroxide to water. When it comes to performance of the Co-porphyrincontaining system, it is reasonable to expect that the O 2 reduction process is initiated at Co-porphyrin catalytic sites (twoelectron reduction to H 2 O 2 ) and continued (two-electron reduction to H 2 O) at the hybrid film containing gold nanoparticles dispersed within the highly porous cauliflower-like structures of polypyrrole multi-layers. While the gold networks facilitate charge distribution within the hybrid electrocatalytic film, non-covalent π-π interactions of porphyrin rings with polypyrrole interlayers and charge transfers between negatively charged (PMo 12 O 40 3− modified) gold nanoparticles and positively charged nitrogen sites of polypyrrole could also cause synergism.
An effective and simple process for the isolation of 106Ru from high-level liquid wastes was developed. Radioactive ruthenium was oxidized by H5IO6 in HNO3 solution and was extracted to CCl4 phase in the form of RuO4. In order to obtain ruthenium in the suitable form for production of brachytherapy sources, RuO4 in organic phase was reduced and re-extracted to aqueous phase. The efficiency of extraction of 103Ru to organic phase was 86 %, re-extraction to aqueous solution was near 100 %, so the overall recovery of 103Ru is estimated at more than 80 %.
Herein, we report on our investigation on the use of the aqueous solution of the phosphotungstate heteropolyblue as a reducing agent and stabilizer for the synthesis of gold nanoparticles deposited on multi-walled carbon nanotubes and functionalized with CO-type surface groups. Chemical reduction method allowed producing multi-walled carbon nanotube-supported gold (Au/MWCNTs) catalysts with high dispersion and loading of Au up to 5 wt%. The average diameter of Au nanoparticles on MWCNTs was 2.0-4.5 nm. The resulting gold nanoparticles were subsequently cleaned from their inorganic capping agents (PW 12 O 40 3-) by converting to alkaline medium (NaOH aq ). The high dispersion of gold nanoparticles at MWCNTs (pretreated with HCl, HNO 3 and H 3 PW 12 O 40 ) was attributed to the presence of a high density of active sites for nucleation created during the functionalization procedure. The nanocomposite system based on multi-walled carbon nanotubes decorated with gold nanoparticles was probed towards electrocatalytic oxidation of methanol in alkaline medium under voltammetric conditions. The existence of mesopores created at the surfaces of multi-walled carbon nanotubes originated from an easy accessibility of the OH -groups and methanol molecules at the electrocatalytic interface. The chemical functionalization of the open ends and the side walls of MWCNTs played a vital role in tailoring their electrochemical properties. Electrochemical studies demonstrated the promotional effect of quick pseudofaradaic reactions of surface polar groups created on carbon nanotubes during the methanol electrooxidation process.
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