Search results for "SPECTROSCOPY"
showing 10 items of 10293 documents
Influence of fluorine on the synthesis of anatase TiO2for photocatalytic partial oxidation: Are exposed facets the main actors?
2018
Anatase TiO2 samples were synthesized in the presence of different amounts of HF acid with the aim of understanding the effect of the presence of fluorine on the photocatalytic activity. It is well known that the presence of fluoride ions influences the photocatalytic performance by adsorption on the surface of TiO2 and that they are capping agents in the control of specific exposed facets. The samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption–desorption measurements, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectrophotometry, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity was eva…
Turning lipophilic phthalocyanines/TiO2 composites into efficient photocatalysts for the conversion of CO2 into formic acid under UV–vis light irradi…
2014
Metal-free, Cu(II)- or Zn(II) tetrakis [4-(2,4-bis-(1,1-dimethylpropyl)phenoxy)]phthalocyanines loaded over TiO2 (anatase) proved to be active in the photoreduction of CO2 to formic acid (HCO2H) in water under UV-vis light. CuPc/TiO2 is catalyst of choice, allowing to reach a maximum yield of HCO2H, unequalled by any other similar catalytic systems. Because of their low environmental impact, low potential cost, and efficient power conversion, these multipurpose materials show promise in the setup of sustainable methods for CO2 valorization. (C) 2014 Elsevier B.V. All rights reserved.
Clean analytical method for the determination of propoxur
1995
Abstract A method has been developed for the determination of propoxur, a carbamate pesticide, by means of its reaction with p-aminophenol (PAP). The method involves the reaction, in the presence of KIO4, between the quinoneimine form of PAP and the deprotonated form of 2-isopropoxyphenol, obtained by the alkaline hydrolysis of propoxur, to provide an indophenol dye which absorbs at 600 nm. The analysis is carried out in a flow system and, after the measurement step, the waste, the reaction product and the unreacted derivatising agent is detoxified in a UV-irradiated coil placed after the measurement flow-cell and after mixing the waste with a TiO2(anatase) catalyst slurry, which can be reu…
Fourier Transform Infrared Study of the Performance of Nanostructured TiO2 Particles for the Photocatalytic Oxidation of Gaseous Toluene
2001
Thermal and hydrothermal treatments have been applied to an amorphous TiO2 precursor for obtaining nanosized TiO2 particles (P11t and P11h, respectively) of different photocatalytic properties. The activity of these catalysts has been tested by performing the toluene oxidation in gas phase in a continuous photoreactor. A Fourier transform infrared (FTIR) investigation of the catalysts under conditions prevailing during the test photoreaction has also been carried out. The photoreactivity results showed that CO2 was the main oxidation product and benzaldehyde a stable intermediate. Anatase P11t photoactivity was similar to that observed for commercial photocatalysts, while anatase P11h prese…
Multichannel multiple scattering calculation ofL2,3-edge spectra ofTiO2andSrTiO3: Importance of multiplet coupling and band structure
2010
We report a theoretical study on x-ray absorption spectroscopy at the Ti-${L}_{2,3}$-edge of rutile and anatase ${\text{TiO}}_{2}$ as well as ${\text{SrTiO}}_{3}$. Using the first-principles multichannel multiple-scattering method, we obtain good agreement with experiment in all cases. We show that both multiplet-type electron correlation effects and the long-range band structure strongly influence the spectra. The differences in line shape between the three compounds are essentially a long-range effect which reflects the different crystal structures on a length scale of 1 nm.
Reactive direct current magnetron sputtered TiO2 thin films with amorphous to crystalline structures.
2008
International audience; TiO2 thin films were deposited on soda–lime glass substrates by reactive direct current magnetron sputtering in a mixture of pure argon and oxygen. The influence of both the deposition time, td, and the post-annealing treatments on the films morphology, composition and structure was analyzed by scanning electron microscopy, ellipsometry, X-ray photoelectrons spectroscopy, X-ray diffraction (XRD) and Raman spectroscopy. Amorphous TiO2 was obtained for the shortest deposition time, td=15 min. Increasing td up to 30 min, poorly crystallized anatase and rutile phases were formed together with amorphous TiO2, as was revealed by complementary XRD patterns and Raman spectra…
Study of surface layers and ejected powder formed by oxidation of titanium substrates with a pulsed Nd:YAG laser beam.
2009
Laser treatment of a titanium surface at certain conditions initiates the formation of titanium oxide layers as well as micro (nano) scale powder ejected from the surface of the substrate. The resultant morphology of the surface as well as the size and the structure of the particles are all strongly dependent on the treatment parameters (laser fluence, pulse frequency, overlap parameter, etc.). In this study, titanium substrates were treated with an industrial pulsed Nd:YAG laser in air, with varying parameters. Surface layers and ejected materials were compared using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The rutile phase of TiO(2) dominate…
Pulsed laser growth and characterization of thin films on titanium substrates
2007
Abstract Colored layers were obtained by laser surface treatment of Ti substrates with a pulsed Nd:YAG Q-switched laser. The changes in the morphology, structure and chemical composition of the layers were studied by SEM, EDS, XPS, SIMS and Raman spectroscopy as a function of the laser fluence in the 4–60 J cm −2 . For laser fluences lower than 25 J cm −2 , the layers are colorless or yellow. Their surface is smooth, but they display cracks which increase when the fluence increases. The O/Ti ratio, determined by XPS analysis, varies from 0.7 (colorless layers) to 1.3 (yellow layer). Moreover, XPS spectra evidence non-negligible amounts of nitrogen and carbon in these layers. Raman spectra s…
One-Dimensional TiO2-B Crystals Synthesised by Hydrothermal Process and Their Antibacterial Behaviour on Escherichia coli
2016
We have successfully synthesised one-dimensional single crystals of monoclinic phase titanium dioxide nanostructures (TiO2-B), prepared by a hydrothermal process. Morphological characterization was carried out by atomic force and scanning and transmission electron microscopy techniques. In order to study the crystalline structure, samples were calcined at 500°C in an air-filled chamber. X-ray diffraction results indicated that as-prepared samples presented diffraction patterns of hydrate hydrogen titanate and those calcined at 500°C exhibited the TiO2-B and anatase phases, confirmed by Raman spectroscopy. Scanning electron microscopy results showed that the one-dimensional nanostructures ha…
Optical and Acoustic Vibrations Confined in Anatase TiO2 Nanoparticles under High-Pressure
2014
International audience; The effect of an applied high pressure on the optical and acoustic vibrations of small anatase TiO2 nanoparticles is studied using Raman scattering. All the Raman peaks show a significant variation of their frequency with pressure, except for the low-frequency peak which is due to acoustic vibrations confined in the nanoparticles. These variations (or lack thereof) are compared to first-principles calculations of the stiffness tensor and phonons of bulk anatase TiO2 as a function of pressure. In particular, the variation of the shape of the low-frequency peak is explained by the increase of the elastic anisotropy of anatase TiO2 as pressure is increased.