Suzanne Giorgio

The best current way to prepare Au/TiO2 catalysts is the method of deposition−precipitation with NaOH (DP NaOH) developed by Haruta and co-workers. With this method, it is possible to obtain small gold metal particles (2−3 nm), but the corresponding gold loading remains rather low (∼3 wt %). The main goal of this work is to investigate other methods of preparation of Au/TiO2 catalysts to obtain small gold metal particles (2−3 nm) and a higher Au loading. It is shown that anion adsorption with AuCl4- (AA) does not produce Au loading higher than 1.5 wt % and the average particle size is not very small (∼4 nm). Cation adsorption with Au(en)23+ (CA) leads to small particles (2 nm) when the solution/support contact time is moderate (1 h), but the Au loading does not exceed 2 wt %. The most promising method of preparation appears to be deposition−precipitation with urea (DP urea). Indeed, samples with gold particles as small as those obtained with DP NaOH (∼2 nm) can be prepared, and all gold in solution is deposited on TiO2 in contrast to DP NaOH. The DP urea samples reported in this paper can reach a Au loading as high as 8 wt % using a TiO2 support with a surface area of 45 m2 g-1. The possible mechanisms of deposition of gold on the TiO2 support by the different methods of preparation are discussed.

Flat silver nanocrystals have been synthesized by using a soft chemical procedure that involves mixing two reverse micellar solutions. The resulting “nanodisks” display highly anisotropic optical properties attributed to their shape anisotropy. A dark-field TEM image of such a nanodisk, illustrating its single crystal nature, is shown in the Figure.

This paper describes the first method for making nanodisks having similar aspect ratios and differing by their size. Flat, single-crystal silver nanodisks in equilibrium with spheres are produced using colloidal solutions. The nanodisk size is tuned by the relative amount of reducing agent involved in the synthesis whereas their aspect ratios remain the same order of magnitude. The 3D nanodisk shape is determined by transmission electronic microscopy using the weak-beam dark-field technique. These nanodisks characterized by such anisotropic shapes exhibit several plasmon resonance modes observed in the UV−visible range.

In this paper, copper nanocrystals are produced by using Cu(AOT)2−isooctane−water solution as a template. Even if the template does not change with various salt additions, the nanocrystal growth markedly depends on the salt used. It is demonstrated that chloride ions enable the growth of nanorods with an aspect ratio varying with chloride concentration. Conversely, only a slight amount of bromide ion is needed to increase the nanorod aspect ratio from 3 to 5 without any changes when increasing the bromide ion concentration. A rather large number of cubes are produced. Formations of nanorods and cubes are explained in terms of anion adsorption on (111) and (100) faces, respectively. By replacing chloride by other ions, the morphology of copper nanocrystals drastically changes. In all cases, the nanocrystals formed are fcc single crystals with a polyhedral shape or crystals composed of fcc tetrahedra (deformed or not) bounded by (111) faces. Some cylinders are formed by the connection of 2 different crystals with different 5-fold axes and/or with additional planes. This gives rise to various particle shapes.

We report a photoluminescence study of silicon nanoclusters produced by laser ablation. It was found that by varying the preparation parameters it was possible to change the mean cluster size in the range 1–5 nm. Within this size variation, the photoluminescence band shifts in a wide spectral region from near ultraviolet to near infrared. This size-dependent photoluminescence of Si nanoclusters is consistent with a quantum confinement effect. The observed influence of cluster oxidation on the luminescence properties also supports the quantum confinement interpretation. We proposed a discrete size model which supposes that the spectral position of the luminescence band is essentially determined by the volume of clusters with a complete outer atomic layer. In the framework of this model, we were able to deconvolute the observed luminescence bands into a set of fixed Gaussian bands. The model is supported by the observation of a size selective doping of Si nanoclusters whose effect was well explained by Auger recombination. Finally, our model allowed us to obtain a dependence of the optical gap on the cluster size which is in good agreement with existing calculations of Si nanocrystal electronic structure.