Laser synthesized TiO$_2$ -based nanoparticles and their efficiency in the photocatalytic degradation of linear carboxylic acids
Résumé
Titanium dioxide nanoparticles were synthesized by laser pyrolysis, their surface and electronic
properties were modified by gold and/or nitrogen. These materials were characterized by
different techniques like X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and
electron paramagnetic resonance (EPR). Time resolved conductivity (TRMC) was used to study
the charge separation of electron/hole pairs. Altogether (XPS, EPR, TRMC), the physicochemical
characterizations are well correlated with chemical photoactivity of the different samples. Their
photocatalytic activity was evaluated for the degradation of linear carboxylic acids (C2-C3) under
UV and visible illumination. The decomposition rate of acids was measured, it shows that the
modification with gold increases the photoactivity while the presence of nitrogen slows down the
process. Such observations are in good agreement with evolution of TRMC signals. A degradation
pathway has been determined by identification of intermediate products by chromatography
and EPR, results show different intermediate species. In particular EPR confirms the presence of
NO$^{2−}$ paramagnetic centers and shows two novel N centered paramagnetic centers. A decrease
of the degradation rate is observed with increase of carboxylic acid chain length.
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