E. Popovici

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 () and titania () 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 samples for the preparation of water-dispersed magnetic nanofluids is also discussed. nanoparticles comprising a mixture of anatase and rutile phases were synthesized via the laser pyrolysis of - (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.

Carbon nanostructures by gas-phase laser pyrolysis

Carbon-made materials have been the field of major discoveries with the identification of new phases, which have stimulated a huge effort to understand their properties. Laser pyrolysis of hydrocarbons is based on a high temperature C/H/O/... system of well-established composition and allows obtaining carbon nanostructures from the almost amorphous carbon and particles with a turbostratic structure up to those characterized by a high degree of curvature. The variation of the gas composition and experimental parameters controls the final particle morphology providing useful functional properties. Gas-phase hydrocarbons were used either in resonant or non-resonant laser pyrolysis processes. The formation of different nanostructures is related to the presence of heteroatom in the reactants. Focusing, in the context of necessary presence of this heteroatom in the gas composition, on the present questions concerning the rational synthesis of nanostructures with controlled dimensionality, size and potentially properties, the work presents some significant changes in soot morphology produced by the variation of the experimental parameters and these, sometimes unavoidable, heterogeneous atoms.