Photochemistry Aspects of the Laser Pyrolysis Addressing the Preparation of Oxide Semiconductor Photocatalysts

The laser pyrolysis is a powerful and a versatile tool for the gas‐phase synthesis of nanoparticles. In this paper, some fundamental and applicative characteristics of this technique are outlined and recent results obtained in the preparation of gamma iron oxide (γ‐Fe2O3) and titania (TiO2) semiconductor nanostructures are illustrated. Nanosized iron oxide particles (4 to 9 nm diameter values) have been directly synthesized by the laser‐induced pyrolysis of a mixture containing iron pentacarbonyl/air (as oxidizer)/ethylene (as sensitizer). Temperature‐dependent Mossbauer spectroscopy shows that mainly maghemite is present in the sample obtained at higher laser power. The use of selected Fe2O3 samples for the preparation of water‐dispersed magnetic nanofluids is also discussed. TiO2 nanoparticles comprising a mixture of anatase and rutile phases were synthesized via the laser pyrolysis of TiCl4‐ (vapors) based gas‐phase mixtures. High precursor concentration of the oxidizer was found to favor the prevalent anatase phase (about 90%) in the titania nanopowders.