Synthesis and catalytic properties of large ligand stabilized palladium clusters

Chemically modified polymer beads for sorption of gold from waste gold solution

A simple method to convert gold from waste gold solutions used in chemical laboratories and chemical industries into metallic gold nano particles using styrene maleic acid copolymer beads has been approached. The styrene maleic acid copolymer beads with an average bead diameter 400-600 microns, exhibiting exceptionally high rough surface was used as a polymer matrix for the reducing gold from aqueous solution to metallic nano gold. Uptake of gold ions from aqueous waste gold solution was attempted in a batch process. Conversion of gold to metallic nano gold was achieved without the use of any external reducing agents. The metallic nano gold particles could be embedded into polymer matrix within 2h. The beads exhibited high temperature resistance and could sustain upto 400°C.

Characterizations of Core-Shell Nanoparticle Catalysts for Methanol Electrooxidation

This paper describes the results of an investigation of the structure and composition of core-shell gold and alloy nanoparticles as catalytically active nanomaterials for potential fuel cell catalysis. Centered on the electrocatalytic methanol oxidation, we show three sets of results based on electrochemical, surface, and composition characterizations. First, electrochemical studies have revealed that the nanostructured catalysts are active towards the electrooxidation of methanol and carbon monoxide. Second, X-ray photoelectron spectroscopy (XPS) data have shown that the organic encapsulating shells can be effectively removed electrochemically or thermally, which involves the formation of oxides on the nanocrystals. Thirdly, direct current plasma - atomic emission spectrometry (DCP-AES) has revealed insights for the correlation of the composition of alloy nanoparticles with the catalytic activities. Implications of these results to the design of nanostructured catalysts will also be discussed.

A novel nanogold multilayer constructed by Langmuir–Blodgett and self-assembly techniques

A multilayer comprising nanogold particles and organic molecules was constructed by self-assembly of the small organic molecule 1-phenyl-5-mercaptotetrazole onto the octadecylamine-protected nanogold monolayer in the course of transferring the monolayer, layer by layer, from a Langmuir-Blodgett trough to solid substrates. The structure and properties of the constructed multilayer were characterized by TEM images and ATR-IR, XPS, and UV-vis spectra. It is evidenced for the first time that the combination of Langmuir-Blodgett and self-assembly techniques provides a new way to organize functional nanoparticles such as organic-nanogold complexes.

A new palladium nanoparticle catalyst on mesoporous silica prepared from a molecular cluster precursor

A promising approach to the controlled synthesis of supported nanoparticles involves the use of molecular carbonyl clusters as precursors. Molecular metal clusters consist of a defined number of structurally ordered atoms, and active monodisperse metal particles are formed after dispersing the molecules and removing the ligands. An octanuclear palladium cluster precursor with easily displaceable ligands was used to generate palladium nanoparticles on mesoporous MCM-41. The molecular cluster precursor, [Pd8(CO)8(PMe3)7], was directly adsorbed from solution onto MCM-41, followed by gentle thermolysis which yielded small metal nanoparticles. Compared to MCM-41-based catalysts prepared from palladium salts by conventional methods, this cluster-derived palladium catalyst has shown an efficient activity for liquid-phase hydrogenation of alkenes.

Spectroscopic characterizations of molecularly linked gold nanoparticle assemblies upon thermal treatment

The understanding of surface properties of core-shell type nanoparticles is important for exploiting the unique nanostructured catalytic properties. We report herein findings of a spectroscopic investigation of the thermal treatment of such nanoparticle assemblies. We have studied assemblies of gold nanocrystals of approximately 2 nm core sizes that are capped by alkanethiolate shells and are assembled by covalent or hydrogen-bonding linkages on a substrate as a model system. The structural evolution of the nanoparticle assemblies treated at different temperatures was probed by several spectroscopic techniques, including UV-visible, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The results show that the capping/linking shell molecules can be effectively removed to produce controllable surface and optical properties. The data further revealed that the thermally induced evolution of the surface plasmon resonance property of gold nanoparticles is dependent on the chemical nature of the linker molecule. The spectral evolution is discussed in terms of changes in particle size, interparticle distance, and dielectric medium properties, which has important implications for controlled preparation and thermal processing of core-shell nanostructured metal catalysts.

Thermal activation of molecularly-wired gold nanoparticles on a substrate as catalyst

The ability to prepare nanostructured metal catalysts requires the ability to control size and interparticle spatial and surface access properties. In this work, we report novel findings of an atomic force microscopic investigation of a controlled thermal activation strategy of gold catalysts nanostructured via molecular wiring or linking on a substrate surface. Gold nanocrystals of approximately 2 nm diameter capped by decanethiolate and wired by 1,9-nonanedithiolate on mica substrates were studied as a model system. By manipulating the activation temperature (200-250 degrees C), the capping/wiring molecules can be removed to produce controllable particle size and interparticle spatial morphology. The electrocatalytic activity of the activated nanostructures toward methanol oxidation, which is of fundamental importance to fuel cell catalysis, has been demonstrated. The novelty of the findings is the viability of a thermal activation strategy of core-shell nanostructured catalysts based on molecularly predefined interparticle spatial properties on a substrate, which upon further investigation may form the basis for spatially controllable nanostructured catalysts.

Derivatization of organometal(loid) species by sodium borohydride problems and solutions

Like other derivatization techniques, hydride generation is a chemical reaction that produces side-reactions leading to analytical problems. Demethylation of dimethylarsinic acid was observed to be dependent upon the pH level of the hydride generation reaction mixture. If the reaction mixture was acidic, then in addition to (CH3)2AsH, the monomethyl arsenic hydride [(CH3)AsH2] could be detected. Demethylation and also the formation of an unidentified arsenic species were noted when trimethyl arsonic oxide was used as derivatization educt. All of these effects depend on the pH level of the hydride generation mixture. We observed significant levels of organometal(loid) species of elements such as Ge, As, Sn, Sb, Hg and Bi in blank hydride generation mixtures. The organometal(loid) contamination was irreproducible even during I day using a single solution of sodium borohydride in deionized water. We concluded that the organometal(loid) contamination arises directly from the derivatization agent, sodium borohydride, itself. Use of helium purging and various adsorptive materials to decontaminate the sodium borohydride solution prior to analysis did not result in a significant decrease in organometal(loid) contamination levels. Use of a palladium-cluster stabilised with 1,10-phenanthrolin as alternative hydride generation derivatization agent was not found to be suitable, since reaction yields were poor and transmethylation reactions were noted.

Preparation and Characterization of Polymer-Stabilized Ruthenium-Platinum and Ruthenium-Palladium Bimetallic Colloids and Their Catalytic Properties for Hydrogenation of o-Chloronitrobenzene

Colloidal dispersions of poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium-platinum and ruthenium-palladium bimetallic colloids were prepared by NaBH4 reduction of the corresponding mixed-metal salts at room temperature and characterized by TEM, XPS, and XRD. The resulting bimetallic colloids were used as catalysts for the selective hydrogenation of o-chloronitrobenzene (o-CNB) in methanol at 303 K under 0.1 MPa of hydrogen. It was observed that the catalytic performance of PVP-stabilized ruthenium-platinum colloids (PVP-Ru/Pt) and ruthenium-palladium colloids (PVP-Ru/Pd) was dependent on their compositions and could be remarkably affected by some added metal cations. In the presence of cobalt ion, nearly 100% selectivity to o-chloroaniline (o-CAN) was achieved over PVP-Ru/Pt colloids at 100% conversion of o-CNB, with an activity two orders of magnitude higher than that of monometallic PVP-Ru colloid. Copyright 1999 Academic Press.