Supported and confined nanoclusters

The radiolytic synthesis consists in i) either preparing first nanometric metal clusters in solution which are then put in contact with the support (possibly by filtration), or ii) irradiating in situ the ionic precursors after their adsorption onto the supporting material. 

Colloidal support such as small Si02 particles restrict interparticle diffusion of silver atoms when formed by radiolysis of the ions at their surface. The silver oligomers absorbing at 290 and 330 nm are observed by pulse radiolysis. They are stable with respect to coalescence but they are oxidized by MV, O, Cu and RufNHj)/. Alumino-silica gels with silver ions give after irradiation optically clear xerogels containing silver clusters from 2.5 to 4.5 nm. 

Irradiation by ionizing radiation able to penetrate into a zeolite material exchanged by metal ions allows to generate metal atoms and clusters in situ in the cavities.The observation of irradiated faujasite (Na-Y zeolite) by optical absorption spectroscopy at increasing doses and at low silver content demonstrates the formation of two bands at 265 and 305 nm which have been assigned to the charged trimer Agj . Then, the ESR observation after a dehydration step indicates the reduction of this species into Agj . Irradiation of HjPtClg solution included in mesoporous channels of molecular sieves induces nanowires of platinum.  

Pulse radiolysis studies of the reactivity of 25 nm Agl particles with e3, 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.The electron transfer between the couple MV /MV and Ag clusters formed on an AgCl crystallite was studied by pulse radiolysis. The coalescence of Ag atoms at the AgCl surface is slow so that, as in the presence of CN, an electron transfer from subcritical clusters to precedes the 

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