TiO₂ nanoparticles have been intensely investigated as photocatalysts for environmental remediation processes, including the degradation of organic pollutants in waters. In this context, a critical factor to consider in using TiO₂ is that due to its wide band-gap (bulk anatase, Eg = 3.2 eV ), only a small portion of the solar spectrum is absorbed by the photocatalyst. Therefore, several attempts have been made to conjugate TiO₂ nanoparticles with light sensitizers, such as dyes or other semiconducting phases.

Here we present a first example of a TiO₂ based photocatalyst containing Ag₂S nanophases grown from a single-source. We will show, that silver (I) alkyldithiocarbamato complexes, in the presence of aliphatic amines yield the respective metal sulphide when subjected to moderate heating; in the presence of inorganic substrates, such as TiO₂ particles, the metal sulphide phase grows over the particles surfaces. This method provides control over nanoparticle growth and substrate coverage in a one-step process, which is clearly advantageous to design new catalysts.

The TiO₂/Ag₂S nanocomposites are composed of a Ag₂S nanophase evenly dispersed as islands that do not completely cover the TiO₂ surface. For nanocomposites prepared for longer reaction times, the Ag₂S islands spreads over the substrate and a less surface area of TiO₂ is available in contact with the solution. As expected, a dramatic decrease of the photocatalytic activity of the TiO₂/Ag₂S nanocomposite was observed for such cases. Our results concerning the photodegradation of phenol using such nanocomposites, under distinct reacting conditions, will be presented and discussed in detail.

Acknowledgments

O.C. Monteiro thanks Fundação para a Ciência e Tecnologia (FCT) for a pos-doc grant (SFRH/BPD/ 14554/2003). This work is supported by FCT, POCI and co-financed by FEDER (POCI/QUI/59615/2004)

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