Laser synthesized TiO₂-based nanoparticles and their efficiency in the photocatalytic degradation of linear carboxylic acids

Abstract

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 NO2− 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.

X-ray Photoelectron Spectroscopy Analysis of Nitrogen-Doped TiO2 Films Prepared by Reactive-Ion-Beam Sputtering with Various NH3/O2 Gas Mixture Ratios

“…Generally, photocatalytic activity and chemical and electronic states were investigated by UV-visible absorption experiments and X-ray photoelectron spectroscopy (XPS) analysis, respectively. N-doped TiO 2 can be prepared by physical or chemical methods, such as the sol-gel method [6], microwave plasma synthesis [8], sputtering [9], laser pyrolysis [10], plasma-enhanced chemical vapor deposition [11], hydrothermal processing [12], or annealing of TiO 2 films in gaseous NH 3 [13]. In this study, N-doped TiO 2 films were fabricated using different NH 3 /O 2 gas mixture ratios with reactive ion-beam sputtering deposition (IBSD) to achieve nitridization or oxidation of the film at a high substrate temperature of 400 • C under high vacuum conditions of~10 −4 Torr.…”