Silver atoms and clusters

Pulse radiolysis studies of the reactivity of 25-nm Agl particles with eaq in the presence of alcohol have shown that, first, the semiconductor spectrum at 360 nm is bleached, then silver atoms and clusters at 450-600 nm are formed [164,165]. The electron... 

B) Silver Atoms and Clusters in Faujasite Zeolites It has been shown recently by diifierent techniques that small, charged silver clusters can be formed and stabilized in the cavities of zeolites A, X and Y. Uytterhoeven et al (3b) have shown that... 

Rather dramatic alterations in the electronic properties and relaxation dynamics of supported silver atoms and clusters have been traced to extremely subtle differences in ground and excited state guest-host interaction potentials. For Ag° and Ag2+ in faujasite zeolites, pronounced changes in their optical... 

The results of this study suggest that silver atom and cluster optical absorption and fluorescent probes offer a very sensitive method for assessing the strength of a metal support interaction and a way of monitoring subtle alterations in electronic charge density at the trapping site of a metal guest. 

Ozin and Huber 112) synthesized and characterized very small silver particles, Ag n = 2-5) by conventional deposition methods, as well as by a novel technique that they have termed "cryophotoaggrega-tion. This study will be discussed in detail in Section III. Of interest here is a study of silver atoms and small, silver clusters entrapped in ice and high-molecular-weight paraffin (n-C22H46, n-C32Hg8) matrices 146) (see Figs. 7 and 8, and Tables IV and V). Besides the intriguing, multiple-site (solvation) occupancy of atomic silver in ice matrices, and their thermal and photochemical interconvertibility, their extremely... 

In this chapter, we discuss first how the silver clusters relate to silver atoms and silver nanoparticles. Then we overview the formation of fluorescent silver clusters in aqueous solution, using silver salts as precursors and various scaffolds as stabilizers. Finally we discuss applications of silver clusters in fluorescent labeling of biological tissues, and their use as fluorescent probes for sensing of molecules. 

Intrazeolitic and Rare Gas Isolated Silver Atom and Silver Cluster Spectroscopy, Photoprocesses, and Support Interactions... 

In the past five years, the field of metal-zeolite chemistry has developed to the point where a number of metal atomic and small cluster guests have been synthesized and unequivocally characterized by spectroscopic and crystallographic techniques. The silver-zeolite A, X and Y systems in particular have yielded a wealth of valuable structural and site information pertaining to silver guests in the size range of one to six atoms (3). The spectroscopy of these silver-zeolites can therefore be probed in detail and compared with the corresponding data for silver atoms and silver clusters immobilized in weakly interacting rare gas solid supports (4). 

In this section we describe our diffuse optical reflectance and fluorescence emission/excitation spectra (14) related to the silver atoms and silver clusters AgJJ9+ and Ag.3P+ stabilized in... 

Coupling pulse radiolysis with time-resolved spectroscopy also allowed the determination of the transient absorption spectra of hydrated silver atom and of the first silver clusters showing that the absorption properties of silver atoms and metal aggregates in solution are different from that of bare clusters in gas phase. Silver atom presents an absorption maximum at 360 nm in water,while it absorbs at substantially shorter wavelengths in argon (292-310 nm) or in xenon (322-333 nm) atmosphere. ... 

Pulse radiolysis experiments also allowed the study of the reactivity and the redox properties of transient species such as silver atoms and silver clusters. Ag° reacts faster than Agj and both species act as strong electron donors since their respective redox potentials are... 

Baxendale et al. observed, by pulse radiolysis, that Ag° as well as Agj, produced by the scavenging of hydrated electrons e and H radicals, were easily oxidized by oxygen back to Ag". This observation demonstrated that the silver atom and the first oligomers deviate from the known noble character of bulk silver. In the case of Cu" irradiated in liquid ammonia, no stable copper clusters were formed. However, molecular hydrogen was instead produced, as a consequence of copper corrosion in its nascent state.Therefore it was... 

An increasing interest in studying silver particles and clusters adsorbed on titanium dioxide surface is provided by the efficiency of such systems as photocatalysts. Their catalytic properties are more evident than those of individual Ti02, both anatase and rutile-anatase mixture. There are few publications devoted to quantum chemical calculations of metal clusters adsorbed on TiOz surface at the modem level of theory. Besides, existing theoretical data describe adsorption of silver atom on mtile surface only. 

Dimerization of alkanes can be brought about by the irradiation of zeolite-Y with added silver atoms and silver clusters lead to dimerization on irradiation at 220-300 nm104. Selective fluorination of di- and triphenyl methane in acetonitrile as solvent and TiC>2 as catalyst can be effected using AgF. Di- and triphenylacetic acid as well as alkenes can be fluorinated in the same way. A single electron transfer reaction is thought to be involved, followed by attack of fluoride105. It could be that the reaction is one that arises on the TiC>2 surface and that the Ag+, to which the electron transfer could take place, is not involved106. 

Time > tc. Not only is tc longer at pH 3.9 than at pH 4.8, but the observed rate after tc is smaller (Figures 4 and 5). This rate would depend linearly on the supercritical cluster concentration. This confirms that, under conditions yielding identical initial amounts of silver atoms, larger clusters are required to accept electrons from a weaker donor and that the nuclei concentration is much lower at pH 3.9. 

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