5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

Templating is one of the most important techniques for the controlled synthesis of nanostructured materials. This powerful tool uses a pre-existing guide with desired nanoscale features to direct the formation of nanomaterials into forms that are otherwise difficult to obtain. As a result, templated synthesis is capable of producing nanostructures with unique structures, morphologies and properties. In this review, we summarize the general principles of templated synthesis and cover recent developments in this area. As a wide variety of synthesis techniques are utilized to produce nanomaterials using template-based methods, the discussion is organized around the various types of common templates. We examine the use of both physical and chemical hard colloidal templates, soft templates, and other non-colloidal templates, followed by our perspective on the state of the field and potential future directions.

Templated synthesis of nanostructured materials

State of the art in gold nanoparticle synthesis

Pd–Au bimetallic catalysts often display enhanced catalytic activities and selectivities compared with Pd-alone catalysts. This enhancement is often caused by two alloy effects, i.e., ensemble and ligand effects. The ensemble effect is a dilution of surface Pd by Au. With increasing surface Au coverage, contiguous Pd ensembles disappear and isolated Pd ensembles form. For certain reactions, for example vinyl acetate synthesis, this effect is responsible for reaction rate enhancement via the formation of highly active surface sites, e.g., isolated Pd pairs. The disappearance of contiguous Pd ensembles also switches off side reactions catalyzed by these sites. This explains the selectivity increase of certain reactions, for example direct H2O2 synthesis. The ligand effects are electronic perturbation of Pd by Au. Via direct charge transfer or by affecting bond lengths, the ligand effects cause the Pd d band to be more filled, moving the d-band center away from the Fermi level. Both changes make Pd more “atomic like” therefore binding reactants and products more weakly. For certain reactions, this eliminates a so-called “self-poisoning” effect and enhances activity/selectivity.

Pd–Au bimetallic catalysts: understanding alloy effects from planar models and (supported) nanoparticles

Microemulsion method: A novel route to synthesize organic and inorganic nanomaterials

The synthesis of Au/Pd bimetallic nanoparticles at various molar ratios by the coreduction of HAuCl4 and H2PdCl4 with hydrazine in the reverse micelles of water/sodium bis(2-ethylhexyl) sulfosuccinate/isooctane at 25 °C was investigated. Transmission electron microscopy photographs showed that the Au/Pd bimetallic nanoparticles obtained at the feeding compositions of [HAuCl4]/[H2PdCl4] = 9/1 to 1/9 essentially had uniform sizes and mean diameters of about 3 nm. Both the UV−vis absorption spectra and X-ray diffraction patterns for the bimetallic systems and the physical mixtures of individual metallic nanoparticles suggested the formation of bimetallic nanoparticles. The energy dispersive X-ray analysis on the single particle showed that the composition for each particle was roughly consistent with that of feeding solution. The X-ray photoelectron spectroscopy measurement revealed that Pd atoms were significantly enriched in the outer part of Au/Pd bimetallic nanoparticles. The characterization and formati...

Synthesis of Au/Pd Bimetallic Nanoparticles in Reverse Micelles

Calcium and magnesium ions usually exist in natural water. When Cd2+ is removed from water by adsorption, it will be inhibited by these two ions. Titanate nanotubes (TNTs) have an effective adsorption capacity for Cd2+ due to extraordinary ion exchange property. However, TNTs also adsorb Ca2+ and Mg2+ in water. In this study, carbon-modified TNT (TNT/C) and TNT/C further treated with acid (TNT/HC) were synthesized by hydrothermal synthesis. The transmission electron microscope (TEM) images show that TNT/C or TNT/HC still keep nanotube morphology. The experimental results show the order of adsorption amount to Cd2+ is TNT (171.56 mg/g) > TNT/C (166 mg/g) > TNT/HC (159.88 mg/g) when there is no Ca2+ or Mg2+. But when there is 0.1 M Ca2+ or Mg2+ in the water, the order of Cd2+ adsorption capacity becomes TNT/HC (44.28, 49.04 mg/g) > TNT/C (58.84, 69.32 mg/g) > TNT (65.52, 70.6 mg/g). It indicates that the surface carbon modification can alleviate the hindrance of Ca2+ or Mg2+ to Cd2+ removal. This is because the carbon on the surface of TNT captured part of Ca2+ or Mg2+; it made more Cd2+ be successfully absorbed by TNT through ion exchange. This mechanism was confirmed by the X-ray photoelectron spectroscopy (XPS) spectra analysis. The results of this paper can provide ideas for the adsorption and removal of Cd2+ in water in the presence of Ca2+ or Mg2+. 

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Ming-Li Wu

Papers

Synthesis of Au/Pd Bimetallic Nanoparticles in Reverse Micelles

Removal of Cd2+ from water containing Ca2+ and Mg2+ using titanate nanotubes modified by carbon