Thin films able to sustain an efficient photoreduction of Ag+ ions with 350 nm photons in air were prepared by crosslinking poly(vinyl alcohol) with glutaraldehyde in the presence of poly(acrylic acid). Standard colloid techniques served as screening methods for the selection of polymer compositions yielding films with desired properties. When present at high concentrations, Ag+ ions were reduced at room temperature in the films by poly(vinyl alcohol) but poly(acrylic acid) inhibited the slow dark reaction. Optical signals with maxima above 400 nm resulted from both reduction processes. The available evidence confirmed that they originated from nanometer-sized metal particles and is inconsistent with results for other proposed chromophores. An additional absorption centered at 280 nm that formed only under illumination was assigned to Ag3 + clusters. Small Ag crystallites with similar size distributions and with an average diameter of 5 nm were the main product of the photoreduction in non-crosslinked or crosslinked films. Larger particles were detected less frequently, and in the former films they consisted predominantly of crystallite aggregates. These results along with the long-term stability of the photogenerated Ag3 + clusters are consistent with a particle nucleation process based on diffusion and coalescence of mobile metal atoms in the films.

The photogeneration of Ag particles and clusters with 350 nm photons was studied in thin films containing poly(vinyl alcohol) and poly(acrylic acid) that were crosslinked with glutaraldehyde. Product formation occurred through two consecutive processes that were linear functions of time. Kinetic determinations showed that all the processes followed rate laws that varied linearly with I 0 2 and the [Ag+] present in the films. These findings are consistent with the occurrence of biphotonic reactions in which the light excitation step is rate-determining. Two kinetically indistinguishable particle formation mechanisms are able to replicate the empirical rate law. In these mechanisms, particles form via addition of photogenerated mobile Ag atoms to either cationic or neutral metal clusters. Mechanisms based on growth of cationic metal clusters provide the most realistic representations of the processes taking place in the films, including the formation of stable Ag3 + clusters as byproducts of the metal crystallite generation.

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The obtained samples are characterized by acidity measurements, TEM, powder XRD, NMR, and FTIR spectroscopy. The materials exhibit a mesoporous framework and an acidic surface functionalized with silicon and titanium phosphate species. Tests on esterefication catalysis show future perspectives of these materials as solid acid catalysts. -(KOVALCHUK, T. V.; SFIHI, H.; KORCHEV, A. S.; KOVALENKO, A. S.; IL'IN, V. G.; ZAITSEV, V. N.; FRAISSARD*, J.; J. Phys.