The kinetics of the c-radiolytical or chemical reduction of AuIII or of the combination of both methods, is Cl 4~, followed as a function of the experimental conditions through the time evolution of the surface plasmon spectrum of the gold nanoparticles formed or of their sizes as observed by AFM imaging. It appears from the discussion on the mechanism that even with the strongly reducing radiolytic radicals, the low valency AuI ions are somewhat protected by the more concentrated AuIII ions from reduction, up to a ratio of AuI/AuIII \ 1, and are stabilized for hours, unless clusters or 2-propanol (or PVA, but more slowly) catalyze their disproportionation. The cluster concentration increases correlatively with the dose.

Radiolysis of mixed Au III /Ag I solutions at different dose rates is examined. The progressive evolution with dose of the UV-visible absorption spectra of radiation-induced metal clusters is discussed and compared with those calculated by Mie theory. The clusters have been also observed by transmission electron microscopy and analyzed by X-ray microanalysis and diffraction. At low dose rate, reduced silver atoms transfer an electron to gold ions (either free or at the surface of aggregates). Then, when Au III ions are totally reduced, reduction of the silver ions occurs in a second step at the surface of gold clusters, and silver-coated gold aggregates are obtained. At high dose rate, the shape of the absorption spectrum does not change with an increase in the absorbed dose and X-ray microdiffraction confirms that bimetallic alloyed Ag/Au clusters are synthesized. These results imply the preponderant influence of kinetics in the competition between the reduction-coalescence processes and intermetallic electron transfer. The segregation or the alloying of the metals is controlled by the reduction rate; a fast total reduction of both types of metal ions prevents the redox equilibrium through electron transfer from being established. A perfectly ordered nanocrystal, as observed by electron microdiffraction, also implies an intimate association of metal atoms from the early steps of reduction and aggregation. S1089-5647(98)01467-9 CCC: $15.00

This review is devoted to metal cluster synthesis in solution via radiolytic reduction of ionic precursors under the proper conditions. The size and structure of the Ðnal particles are described in relation to the nucleation and growth mechanism of the process with a special interest in oligomers and nanometric-sized particles. The inÑuence of either a polymeric surfactant or a ligand or a support is described. The role of a chemical electron donor in the development of cluster size is explained. Particular attention is paid to the formation of bimetallic clusters and to the synthesis conditions required to obtain either a core-shell or an alloyed structure in relation to a possible intermetal electron transfer.

TiO 2 (commercial-P25 and synthesized by sol-gel method) was surface modified with platinum ions or [Pt 3 (CO) 6 ] 6 2clusters to improve its photocatalytic activity. The physical properties of the synthesized photocatalysts were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer, Emmett and Teller adsorption (BET) methods. To characterize the absorption ability of visible light, the diffusion reflectance spectra (DRS) were recorded. The charge-carrier lifetimes in TiO 2 after UV illumination were determined by microwave absorption experiments using the time-resolved microwave conductivity (TRMC) method. The photocatalyst activity was examined by degradation of exemplary aqueous phase pollutants, such as Rhodamine B and phenol. The impact of the adsorbates on the photocatalytic activity depends strongly on the titania precursor (commercial or synthesized), the irradiation wavelength (UV or visible), and the model compound (dye or phenol). The results show that it is possible to enhance the P25 photocatalytic activity under UV-visible light by doping it with Pt clusters. Also, P25 doping with Pt(II) or Pt clusters results in enhancement of the activity under visible light. Pt(IV)/TiO 2 synthesized by sol-gel method exhibits better photoactivity under UV-visible and visible light compared to the unmodified titania. In all mentioned systems, a positive effect of modification with platinum clusters and, in particular, an important enhancement in photocatalytic activity under visible light were obtained. These results are explained by enhancement in visible light absorption and inhibition of charge-carrier recombination.

In a CO-saturated water/2-propanol mixed solvent, K 2 PtCl 4 salt can be radiolytically reduced either into molecular carbonyl clusters of the [Pt 3 (CO) 6 ] 2− n series or into colloidal metal particles by varying the CO : Pt ratio. The reduction occurs by a combined effect of CO and radicals produced by radiolysis, giving rise to unusually high reduction yields. The colloidal platinum and also the molecular clusters can easily be impregnated on carbon black. The particle size of the supported catalyst prepared in this way lies in the 2-3 nm range and is independent of the catalyst loading and support surface area, even for high loadings (3-nm particles have been deposited up to a 60 wt% loading on a Printex powder). These catalysts are found to be efficient for methanol or hydrogen electrooxidation and for oxygen electroreduction. The CO-stabilized colloids have been characterized by electron microscopy and UV-visible spectroscopy.

Recently, the use of gold nanoparticles as potential tumor selective radiosensitizers has been proposed as a breakthrough in radiotherapy. Experiments in living cells and in vivo have demonstrated the efficiency of the metal nanoparticles when combined with low energy x-ray radiations (below conventional 1 MeV Linac radiation). Further studies on DNA have been performed in order to better understand the fundamental processes of sensitization and to further improve the method.

Purpose: Metal-based nanoparticles (M-NPs) have attracted great attention in nanomedicine due to their capacity to amplify and improve the tumor targeting of medical beams. However, their simple, efficient, high-yield and reproducible production remains a challenge. Currently, M-NPs are mainly synthesized by chemical methods or radiolysis using toxic reactants. The waste of time, loss of material and potential environmental hazards are major limitations. Materials and Methods: This work proposes a simple, fast and green strategy to synthesize small, non-toxic and stable NPs in water with a 100% production rate. Ionizing radiation is used to simultaneously synthesize and sterilize the containing NPs solutions. The synthesis of platinum nanoparticles (Pt NPs) coated with biocompatible poly(ethylene glycol) ligands (PEG) is presented as proof of concept. The physicochemical properties of NPs were studied by complementary specialized techniques. Their toxicity and radio-enhancing properties were evaluated in a cancerous in vitro model. Using plasmid nanoprobes, we investigated the elementary mechanisms underpinning radio-enhancement. Results and Discussion: Pt NPs showed nearly spherical-like shapes and an average hydrodynamic diameter of 9 nm. NPs are zero-valent platinum successfully coated with PEG. They were found non-toxic and have the singular property of amplifying cell killing induced by γ-rays (14%) and even more, the effects of carbon ions (44%) used in particle therapy. They induce nanosized-molecular damage, which is a major finding to potentially implement this protocol in treatment planning simulations. Conclusion: This new eco-friendly, fast and simple proposed method opens a new era of engineering water-soluble biocompatible NPs and boosts the development of NP-aided radiation therapies.

We use hexagonal mesophases made of oil-swollen surfactant-stabilized tubes arranged on a triangular lattice in water and doped with metallic salts as templates for the radiolytic synthesis of nanostructures. The nanostructures formed in this type of soft matrix are bimetallic palladium-platinum porous nanoballs composed of 3D-connected nanowires, of typical thickness 2.5 nm, forming hexagonal cells. We demonstrate using electron microscopy and small-angle X-ray scattering that the pore size of the nanoballs is directly determined by the diameter of the oil tube of the doped mesophases, which we have varied in a controlled fashion from 10 to 55 nm. Bimetallic nanostructures comprising various proportions of palladium and platinum can be synthesized. Their alloy structure was evidenced by X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and high-angular dark field scanning transmission electron microscopy experiments. Our templating approach allows therefore the synthesis of bimetallic nanoballs of tunable porosity and composition.

Radiolytic synthesis of mixed Au III /Pd II solutions at different dose rates is examined. The evolution of the plasmon spectra and the local X-ray micro diffraction has been systematically studied as a function of irradiation dose and dose rate. At low dose rate, a bilayered cluster of Au core-Pd shell is characterized. Due to intermetal electron transfer from nascent Pd atoms to gold ions, the latter are reduced first and constitute mainly the core of the particle, Pd ions being finally reduced at the surface of gold clusters when all Au III ions have been reduced. In contrast, at high dose rate when the ion reduction is sudden and faster than a possible inter-metal electron transfer, it is shown by UV-vis spectroscopy, XPS, and EDAX results that genuine alloyed clusters are formed.

The reduction mechanism of Chini clusters [Pt 3 (CO) 6 ] n 2-(n) 6-9) has been studied by nanosecond pulse radiolysis in water/2-propanol solution. The monoelectronic reduction of all [Pt 3 (CO) 6 ] 6 2by the alcohol radicals produced by the solvent radiolysis is supposed to yield short-lived [Pt 3 (CO) 6 ] 6 3clusters that split immediately into [Pt 3 (CO) 6 ] 4 2and [Pt 3 (CO) 6 ] 2-. [Pt 3 (CO) 6 ] 2dimerizes to the stable tetramer [Pt 3 (CO) 6 ] 4 2with a diffusion-controlled rate constant. When only a fraction of the [Pt 3 (CO) 6 ] 6 2in solution is reduced, a slower addition reaction between excess [Pt 3 (CO) 6 ] 6 2and the newly formed [Pt 3 (CO) 6 ] 4 2gives then two [Pt 3 (CO) 6 ] 5 2-. Results concerning the early steps of the reduction of clusters of higher nuclearity [Pt 3 (CO) 6 ] n 2-(n) 7-9) are also presented. The general reduction mechanism of the platinum carbonyl compounds [Pt 3 (CO) 6 ] n 2displays some similarities with the reduction of n) 6; i.e., stable [Pt 3 (CO) 6 ] 4 2are formed together with the transient [Pt 3 (CO) 6 ] n-4- .

Avec le projet ELYSE, un groupe de physico-chimistes de l'Université d'Orsay Paris-Sud a proposé à la communauté scientifique française de se doter d'une nouvelle plate-forme permettant des études de cinétiques rapides au moyen des techniques complémentaires de radiolyse pulsée et de photolyse laser. L'accélérateur d'électrons, de type photodéclenché, est prévu pour délivrer des impulsions d'électrons de moins de 5 picosecondes avec une énergie comprise entre 5 et 9 MeV. Les photoelectrons sont générés au moyen d'un laser picoseconde synchronisé. On décrit les différentes performances de l'appareil, après l'obtention du premier faisceau d'électrons le 15 mars 2002, ainsi que les applications envisagées, plus particulièrement en radiolyse pulsée.

An important task of the scientific community is to provide non-specialized audience with explanations about what is nanoscience. Such explanations can be given during public conferences, seminars in high schools or lab work organized with teachers. And very often, the use of an experimental illustration greatly helps to raise the interest and the curiosity of the public. The present article will describe how the authors have used five simple and visual experiments in chemistry and physics to progressively introduce different audiences into the fascination of nanoscience. One experiment is the synthesis of gold nanoparticles with the Turkevich method and shows the progressive appearance of the rubyred colour of the nanometric gold particles. The second and third experiments describe the way for modulating their colour and how to include them into a polymer and form a ruby-red coloured plastic film. The fourth experiment shows that starting from these nanoparticles, it is possible to turn them back into a yellow golden film. The last experiment is based on the optical properties of ultra-thin gold films. Using the plasmon resonance, it is possible to demonstrate that gold change colours from yellow to orange and green when a white light beam is shone on the gold interface. These visual experiments cannot be fully interpreted in front of a large audience but serve for rising curiosity.

Noble metals deposited on TiO 2 act as electron traps facilitating electron-hole separation and promoting the interfacial electron transfer process. In particular, silver nanoparticles have the ability to absorb visible light due to localized surface plasmon resonance. Here we report a photochemical and photocatalytic method for depositing Ag nanoparticles (2-20 nm) on TiO 2 by using UV light at room temperature. UV-Vis diffuse reflectance spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and time-resolved microwave conductivity were used as characterization techniques. The photocatalytic activity was investigated by measuring the decomposition of rhodamine B under UV and visible light irradiation. The fastest bleaching of RhB under visible-light irradiation has been obtained by Ag/TiO 2 plasmonic photocatalyst prepared by the photocatalytic route. These results were explained in terms of the more efficient photon absorption due to the presence of the surface plasmon resonance.

The surface of four commercial TiO 2 compounds (Cristal Global PC-series) has been modified by Pd nanoparticles induced by gamma radiolysis. Their photocatalytic properties have been followed by phenol and rhodamine B photocatalytic degradation in aqueous suspensions under UV and visible light. Their electronic properties have been studied by time resolved microwave conductivity (TRMC) method to follow the charge-carrier dynamics. The experiments evidence a complex behavior of the surface-Pd. Its influence depends on the pollutant and on the irradiation. The modification may be strongly favorable to the photocatalytic activity. The results have been interpreted in terms of modification of charge-carrier dynamics with TRMC measurements. The surface-Pd plays a role in charge-carrier separations, increasing the photocatalytic activity under UV-light, but shows no effect on the absorption properties, preventing the creation of an activity under visible light.