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2008


Optical properties of Zr and ZrO2 films deposited by laser ablation


Prieto-Lopez, LO; Yubero, F; Machorro, R; De La Cruz, W
Microelectronics Journal, 39 (2008) 1371-1373
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

Optical properties of Zr and ZrO2 films in the energy range from 1.5 to 100eV were obtained by quantitative analysis of reflection electron energy loss spectroscopy (REELS) and ellipsometry. The films were prepared oil (I 1 1) silicon substrates by reactive laser ablation using a zirconium target. For the growth of ZrO2 films a pressure of 5 m Torr of oxygen in the growth chamber was used. The substrate temperature during deposition was 400 degrees C. The deposits were Studied ex situ by X-ray diffraction (XRD) and in situ by X-ray photoelectron spectroscopy (XPS) and REELS. The ZrO2 films were found to be polycrystalline With monoclinic structure. The XPS results showed that the oxygen pressure used is the optimal control to produce ZrO2 films by laser ablation. A gap of 5eV for the ZrO2 film W IS measured by REELS.


Noviembre, 2008 | DOI: 10.1016/j.mejo.2008.01.048

Pt/TiO2 brain biocompatible nanoparticles: GBM treatment using the C6 model in Wistar rats


Lopez, T; Recillas, S; Guevara, P; Sotelo, J; Alvarez, M; Odriozola, JA
Acta Biomaterialia, 4 (2008) 2037-2044
Química de Superficies y Catálisis

ABSTRACT ▼

In the present work we synthesized inorganic oxide nanoparticle carriers of platinum compounds and tested their therapeutic effect on animal models in which C6 glioma cells have been inoculated. TiO2-containing Pt(NH3)(4)Cl-2 complexes were synthesized using sol-gel methods. The platinum species are chemically bonded to the TiO2 carrier, as shown by Fourier transform infrared spectroscopy of probe molecules. Treatment with TiO2-Pt nanoparticles reduces tumour growth rate by up to 56%, showing that a synergistic effect exists between the TiO2 carrier and the platinum drug.


Noviembre, 2008 | DOI: 10.1016/j.actbio.2008.05.027

Influence of the Capping Molecule on the Magnetic Behavior of Thiol-Capped Gold Nanoparticles


Crespo, Patricia; Guerrero, Estefania; Angel Munoz-Marquez, Miguel; Hernando, Antonio; Fernandez, Asuncion
IEEE Transactions on Magnetics, 44 (2008) 2768-2771
Materiales Nanoestructurados y Microestructura

ABSTRACT ▼

Gold nanoparticles with an average particle size below 3 nm have been synthesized and stabilized with different thiol-derivatized molecules for studying the influence of the capping molecule on the magnetic behavior. Thiolated-alkane chains with different lengths as well as a thiol-containing biomolecule (tiopronin) have been selected as protecting shells for the synthesized NPs. Magnetic characterization indicates that the appearance of a ferromagnetic-like behavior is related not only with the formation of Au-S bonds linking the protective molecules to the nanoparticle surface but also with the formation of the nanoparticle itself as well as with the geometry of the capping molecule. The later seems to determine whether the protective monolayer shell is ordered or not. The simultaneous presence of Au-Au and Au-S bonds together with a reduced particle diameter, and the formation of an ordered monolayer protective shell, have been proved to be key parameters for the ferromagnetic-like behavior exhibited by thiol-functionalized gold NPs.


Noviembre, 2008 | DOI: 10.1109/TMAG.2008.2001990

New production of TiCxN1-x-based cermets by one step mechanically induced self-sustaining reaction: Powder synthesis and pressureless sintering


Cordoba, JM; Alcala, MD; Aviles, MA; Sayagues, MJ; Gotor, FJ
Journal of The European Ceramic Society, 28 (2008) 2085-2098
Reactividad de Sólidos

ABSTRACT ▼

TiCxN1-x-based powdered cermets were synthesized by a one step mechanically induced self-sustaining reaction (MSR) process from mixtures of elemental powders, and subsequently sintered by a pressureless method. The composition and microstructure of the ceramic and binder phases before and after the sintering process were studied by X-ray diffraction, scanning and transmission electron microscopy, and electron diffraction. The powdered cermets showed excellent binder dispersion and a nanometer character for the ceramic and binder particles. The TiCxN1-x stoichiometry was consistently richer in carbon than expected from the raw powder composition. An important amount of titanium was present in the binder after MSR synthesis, and intermetallic Ti-Ni or Ti-Co phases were obtained in some cases. After sintering, the binder phase was always constituted by intermetallic compounds. The morphology of the ceramic phase in the final bodies was dependent on the C/N ratio of TiCxN1-x and its growth primarily occurred through a coalescence process. The presence of titanium in the binder reduced hard particle solubility in the melted binder and its grain growth. 


Octubre, 2008 | DOI: 10.1016/j.jeurceramsoc.2008.02.007

Synthesis, characterization, and photodegradation behavior of single-phase anatase TiO2 materials synthesized from Ti-oxychloride precursors


Colon, Gerardo; Sampedro, Patricia; Fernandez-Garcia, Marcos; Chen, Haiyan; Hanson, Jonathan C.; Rodriguez, Jose A.
Langmuir, 24 (2008) 11111-11118
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT ▼

Single-phase anatase-TiO2 nanomaterials with a size of ca. 10 nm and variable quantities of anion impurities were prepared using a novel pathway based on the use of amorphous ammonium Ti-oxychloride precursors synthesized using Ti/Cl initial ratios between 1 and 6. The precursor nature and evolution under thermal treatment were studied using chemical analysis, XRD, XPS, DRIFTS, and mass spectrometry. The nature and concentration of anatase-TiO2 materials anion impurities were analyzed by XPS and DRIFTS. It is shown that negatively charged impurities located in substitutional positions of the anatase network are maximized for a sample synthesized using a Ti/Cl 1:1 atomic ratio and are responsible for the elimination of liquid-phase (phenol) and gas-phase (isopropanol or methylcyclohexane) pollutants under sunlight excitation. A link is established among the initial chemical characterization of the precursors, the final morphological, structural, and chemical composition of the oxide materials, and their photochemical properties.


Octubre, 2008 | DOI: 10.1021/la8014018

Crystallographic texture in Al2O3-ZrO2 (Y2O3) directionally solidified eutectics


Ramirez-Rico, J; de Arellano-Lopez, AR; Martinez-Fernandez, J; Pena, JI; Larrea, A
Journal of The European Ceramic Society, 28 (2008) 2681-2686
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

Directionally solidified Al2O3-based eutectics are in situ composites grown from the melt. The directional nature of the solidification process makes these materials highly anisotropic and therefore the measurement and quantification of their crystallographic texture is necessary to understand their physical properties. We studied the texture of Al2O3-ZrO2 (12 mol% Y2O3) eutectic rods by means of X-ray and electron backscattering diffraction. The phases grow according to the relationship (10 (1) over bar2}(Al2O3) //{110}(ZrO2) and Al2O3 is oriented with its c-axis approximately parallel to the growth direction. We observed that the c-axis orientation is not constant throughout the sample, but instead changes according to the distance from the growth axis. The c-axis orientation spread was found to be 10 degrees. This spread is a consequence of the curvature of the liquid-solid interface during solidification, whose shape we reconstructed using EBSD data.


Octubre, 2008 | DOI: 10.1016/j.jeurceramsoc.2008.04.015

The Role of Hydroxyl Groups in the Self-Assembly of Long Chain Alkylhydroxyl Carboxylic Acids on Mica


Benitez, JJ; Heredia-Guerrero, JA; Serrano, FM; Heredia, A
Journal of Physical Chemistry C, 124 (2008) 16391-16401
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

The adsorption and self-assembly of hydroxylated long chain fatty acids on mica has been studied by AFM. The presence of secondary midchain hydroxyl groups is found to strongly affect the self-assembly process via the reinforcement of lateral interactions between molecules by -OH center dot center dot center dot HO- hydrogen bonding. On the other side, the availability of an exposed terminal hydroxyl group in the acid molecule triggers the formation of a second layer due to the strength of tile -OH center dot center dot center dot HOOC- tail-to-head interaction. Surface coverage (theta) data follow a Langmuir-type relationship vs solution concentration (c). The analysis of the slope of 1/theta vs 1/c plots provides a relative estimation of the adsorption enthalpy for the formation of the first and second monolayers. Based on that, both the contribution of molecule-substrate and lateral molecule-molecule energy terms are found to be relevant in the self-assembly of this type of molecule oil mica.


Octubre, 2008 | DOI: 10.1021/jp805445z

Synthesis of Spherical Down- and Up-Conversion NaYF4-Based Nanophosphors with Tunable Size in Ethylene Glycol without Surfactants or Capping Additives


Nunez, NO; Miguez, H; Quintanilla, M; Cantelar, E; Cusso, F; Ocana, M
European Journal of Inorganic Chemistry, 29 (2008) 4517-4524
Materiales Coloidales

ABSTRACT ▼

A very simple route for the synthesis of spherical down-conversion (DC) and up-conversion (UC) NaYF4-based nanophosphors is described which consists of a precipitation reaction at rather low temperature (max. 120 degrees C) from solutions containing sodium fluoride and appropriate Ln precursors in a common solvent (ethylene glycol/water mixtures), without the use of any other additive (complexing agent or surfactant). The role played by the nature of the yttrium precursor and the solvent on the morphological characteristics of the nanoparticles is discussed. The size of the nanospheres, which crystallized in the cubic alpha-NaYF4 phase, could be tuned within the 45-155 nm range by adjusting the reaction parameters (temperature and ethylene glycol/water ratio). The applicability of this method is illustrated for the synthesis of Eu-III-doped (DC), Tb-III-doped (DC) and Yb-III/Er-III codoped (UC) NaYF4 nanophosphors, whose luminescent properties were also analysed.


Octubre, 2008 | DOI: 10.1002/ejic.200800363

Nanostructural control in solution-derived epitaxial Ce1-xGdxO2-y films


Coll, M; Gazquez, J; Sandiumenge, F; Puig, T; Obradors, X; Espinos, JP; Huhne, R
Nanotechnology, 19 (2008) 395601
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

A novel mechanism based on aliovalent doping, allowing fine tuning of the nanostructure and surface topography of solution-derived ceria films, is reported. While under reducing atmospheric conditions, non-doped ceria films are inherently polycrystalline due to an interstitial amorphous Ce2C3 phase that inhibits grain growth, a high quality epitaxial film can be achieved simply by doping with Gd3+ cations. Gd3+ <-> Ce4+ substitutions within the lattice are accompanied by charge-compensating oxygen vacancies throughout the volume of the crystallites acting as an efficient vehicle to reduce the barrier for grain boundary motion caused by interstitial Ce2C3. In this way, the original nanostructure is self-purified by pushing the amorphous Ce2C3 phase towards the free surface of the film. Once a full epitaxial cube-on-cube oriented ceria film is obtained, its surface morphology is dictated by the interplay between faceting on low energy {110} and/or {111} pyramidal planes and truncation of those pyramids by (001) ones. The development of the latter requires the suppression of their polar character which is thought to be achieved by charge compensation between the dopand and oxygen along < 100 > directions.


Octubre, 2008 | DOI: 10.1088/0957-4484/19/39/395601

Role of water in the CO oxidation reaction on Au/CeO2: Modification of the surface properties


Romero-Sarria, F; Penkova, A; Martinez, LM; Centeno, MA; Hadjiivanov, K; Odriozola, JA
Applied Catalysis B-Environmental, 84 (2008) 119-124
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

A metallic monolith coated with 1% Au/CeO2 Catalyst has been calcined at 300 degrees C and tested in the CO oxidation reaction both in "dry" and "wet" conditions. The light-off curves show a positive effect of the presence of water in the reactive feed on the catalytic activity. With the aim to explain these observations, a FTIR CO adsorption study at liquid nitrogen temperature was performed over a similar powder catalyst. At this low temperature the oxygen mobility from the bulk to the surface is minimized and then surface phenomena are evidenced. Both, the effect of different pre-treatments of the catalysts and the presence of pre-adsorbed water on the surface have been examined. The studies reveal that the previous treatment of the sample deeply affects the surface species and the gold particle size. The water addition provokes oxidation of the surface and improves the CO oxidation activity.


Octubre, 2008 | DOI: 10.1016/j.apcatb.2008.03.010

Influence of particle size on electrochemical and gas-phase hydrogen storage in nanocrystalline Mg


Friedrichs, O; Kolodziejczyk, L; Sanchez-Lopez, JC; Fernandez, A; Lyubenova, L; Zander, D; Koster, U; Aguey-Zinsou, KF; Klassen, T; Bormann, R
Journal of Alloys and Compounds, 463 (2008) 539-545
Materiales Nanoestructurados y Microestructura - Tribología y Protección de Superficies

ABSTRACT ▼

Nanocrystalline Mg powders of different particle size were obtained by inert gas evaporation and studied during electrochemical and gas-phase hydrogen cycling processes. The samples were compared to dehydrided samples obtained by mechanical milling of MgH2 with and without 2 mol% Nb2O5 as catalyst. The hydrogen overpotential of the pure Mg, which is a measure of the hydrogen evolution at the electrode surface, was observed to be reduced with smaller particle sizes reaching values comparable to samples with Nb2O5 additive. On the other hand gas-phase charging experiments showed the capacity loss with smaller particle sizes due to oxidation effects. These oxidation effects are different depending on the synthesis method used and showed a major influence on the hydrogen sorption kinetics.


Septiembre, 2008 | DOI: 10.1016/j.jallcom.2007.09.085

Photoconducting Bragg Mirrors based on TiO2 Nanoparticle Multilayers


Calvo, ME; Colodrero, S; Rojas, TC; Anta, JA; Ocana, M; Miguez, H
Advanced Functional Materials, 18 (2008) 2708-2715
Materiales Coloidales - Materiales Ópticos Multifuncionales

ABSTRACT ▼

A synthetic route to building photoconducting films of TiO2 nanoparticles that display bright structural color is presented. The color arises as a result of the periodic modulation of the refractive index, which is achieved by controlling the degree of porosity of each alternate layer through the particle size distribution of the precursor suspensions. The suspensions are cast in the shape of a film by spin-coating, which allows tailoring of the lattice parameter of the periodic multilayer, thus tuning the Bragg peak spectral position (i.e., its color) over the entire visible region. Photoelectrochemical measurements show that the Bragg mirrors are conductive and distort the photocurrent response as a result of the interplay between photon and electron transport.


Septiembre, 2008 | DOI: 10.1002/adfm.200800039

Highly photoactive ZnO by amine capping-assisted hydrothermal treatment


Colon, G; Hidalgo, MC; Navio, JA; Melian, EP; Diaz, OG; Rodriguez, JMD
Applied Catalysis B-Environmental, 83 (2020) 30-38
Fotocatálisis Heterogénea: Aplicaciones - Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT ▼

ZnO nanoparticles have been prepared by amine template assisted sol-gel precipitation and further hydrothermal treatment. We have investigated the effect of different pH values achieved by means of triethylamine (TEA) addition in the final surface and structural properties. Two sets of samples were obtained after thermal treatment, one with no hydrothermal pre-treatment and a second hydrothermally pre-treated. Surprisingly the precipitate obtained after the amine addition also exhibits good photocatalytic properties. It has been stated that calcination treatment leads in both sets of samples to a significant improvement in the photocatalytic properties of the studied systems. Therefore, interesting comparison has been performed between hydrothermal pre-treated and direct thermal treated samples. Surface and morphological features notably differ from ZnO prepared using different synthetic route. Wide Surface and structural characterization of the samples have been carried out, and correlations with precipitation pH are pointed out from this characterization. In all cases. the amine templated ZnO obtained exhibit high conversion values for phenol photo-oxidation reaction. Further calcination treatment in all of the studied samples clearly leads to photocatalytic conversions higher than that exhibited by TiO2 Degussa P25. This fact is even more significant if we consider that hydrothermally and calcined ZnO exhibit almost null surface area values. leading to a startling intrinsic photoactivity. The structural excellence (crystallinity, lack of defects, crystallite size, etc.) of such systems is clearly responsible for their high photoactivity values.


Septiembre, 2008 | DOI: 10.1016/j.apcatb.2008.01.033

Preillumination of TiO2 and Ta2O5 photoactive thin films as a tool to tailor the synthesis of composite materials


Sanchez-Valencia, JR; Borras, A; Barranco, A; Rico, VJ; Espinos, JP; Gonzalez-Elipe, AR
Langmuir, 24 (2008) 9460–9469
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

Illumination of TiO2 thin films with UV light is known to induce the transformation of the surface of this material from partially hydrophobic into fully hydrophilic. The present work shows that this transformation is accompanied by other effects that may be used to control the synthesis of composite materials. For this purpose, TiO2 and Ta2O5 transparent thin films with a columnar structure and open pores were prepared by electron evaporation at glancing angles. Transparent TiO2 thin films with micropores (i.e., pores smaller than 2 nm) prepared by plasma enhanced chemical vapor deposition (PECVD) were also used. All these films became hydrophilic upon UV illumination. Rhodamine 6G and Rhodamine 800 dyes were irreversibly adsorbed within the columns of the TiO2 and Ta2O5 thin films by immersion into a water solution of these molecules. Isolated and aggregated molecules of these two dyes were detected by visible absorption spectroscopy. The infiltration adsorption efficiency was directly correlated with the acidity of the medium, increasing at basic pHs as expected from simple considerations based on the concepts of the point of zero charge (PZC) in colloidal oxides. The infiltration experiments were repeated with columnar TiO2 and Ta2O5 thin films that were subjected to preillumination with UV light. It was found that this treatment produced a modification in the type (isolated or aggregated) and amount of dye molecules incorporated into the pores. Moreover, the selective adsorption of a given dye in preilluminated areas of the films permitted the lithographic coloring of the films. Preillumination also controls the UV induced deposition of silver on the Surface of the microporous TiO2 thin films. It was found that the size distribution of the formed silver nanoparticles was dependent on the preillumination treatment and that a well-resolved surface plasmon resonance at around 500 nm was only monitored in the preilluminated films. A model is proposed to account for the effects induced by UV preillumination on the TiO2 and Ta2O5 oxide surfaces. The possibilities of this type of light treatment for the tailored synthesis of nanocomposite thin films (i.e., dye-oxide, metal nanoparticles-oxide) are highlighted.


Septiembre, 2008 | DOI: 10.1021/la800773v

Visible-light driven TiO2 photocatalysts from Ti-oxychloride precursors


Sampedro, R; Colon, G; Fernandez-Garcia, M
Journal of Photochemistry & Photobiology, A-Chemistry, 199 (2008) 136-143
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT ▼

Series of nanosized anion-containing TiO2-base materials with anatase-type structure were synthesized from N, Cl-containing precursors using two preparation methods, calcination and hydrotreatment. Samples were conditioned by a final calcination step in order to get free of surface anion impurities and their structural properties characterized by a combined X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) microscopy, X-ray energy dispersive (XEDS), X-ray photoelectron (XPS), and diffuse reflectance infrared Fourier transform (DRIFFS) Study. The structural characterization was used to interpret the UV-vis spectra. The resulting joint information allowed the rationalization of the photocatalytic activity observed for the visible-light-assisted liquid-phase degradation of phenol. We founded that maximization of photoactivity is not related with the net absorption power of our systems in the visible range but mostly driven by a combination of two characteristics; the adequate morphological properties and the presence of negatively charged N-containing species. 


Septiembre, 2008 | DOI: 10.1016/j.jphotochem.2008.05.008

Thermal characterization of montmorillonite clays saturated with various cations


Balek, V; Benes, M; Subrt, J; Perez-Rodriguez, JL; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Pascual-Cosp, J
Journal of Thermal Analysis and Calorimetry, 92 (2008) 191-197
Reactividad de Sólidos

ABSTRACT ▼

Emanation thermal analysis (ETA), thermogravimetry and high temperature XRD were used to characterize the thermal behavior during dehydration of natural Na montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite (MMT) samples saturated with different cations, i.e. Li+, Cs+, NH4+, Mg2+ and Al3+. ETA results characterized radon mobility and microstructure changes that accompanied the mass loss of the samples due to dehydration on heating in air. A collapse of interlayer space between the silicate sheets after water release from the MMT samples was characterized by a decrease of the radon release rate, Delta E. Decreases in c-axis basal spacing (d(001)) values determined from XRD patterns for the different montmorillonite samples follow the sequence:

Mg-MMT>AI-MMT>Li-MMT>Na-MMT>NH4-MMT>Cs-MMT

The decrease of the radon release rate (Delta E) determined by ETA that characterized microstructure changes due to collapse of interlayer space corresponded well to differences in the c-axis basal spacing (Delta d(001)) values determined from the XRD patterns before and after samples dehydration.


Septiembre, 2008 | DOI: 10.1007/s10973-007-8761-9

Comment on "Observation of higher-order diffraction features in self-assembled photonic crystals"


Dorado, LA; Depine, RA; Miguez, H
Physical Review A, 78 (2008) 037801
Materiales Ópticos Multifuncionales

ABSTRACT ▼

The purpose of this Comment is to show that we find that the conclusions presented in a paper by Nair and Vijaya [Phys. Rev. A 76, 053805 (2007)], concerning the perfect periodic ordering of self-assembled photonic crystals, are not supported and contradict previous studies of this matter.


Septiembre, 2008 | DOI: 10.1103/PhysRevA.78.037801

High-temperature mechanical properties of porous NaMgF3 derived from directionally solidified NaMgF3-NaF eutectics


Ramirez-Rico, J; de Arellano-Lopez, AR; Martinez-Fernandez, J; Larrea, A; Orera, VM
Journal of The European Ceramic Society, 28 (2008) 2451-2457
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

Porous NaMgF3 ceramics have been fabricated by leaching a NaF-NaMgF3 eutectic in distilled water, producing NaMgF3 with 53% of connected porosity. The eutectic was fabricated using the Bridgman technique at growth rates of 8, 10 and 15 mm/h. The microstructure and composition of the resulting material has been studied by means of X-ray diffraction and SEM. Compression mechanical tests have been performed at different temperatures up to 750 degrees C, both in constant strain rate and constant stress loading. The microstructure consists of plate-like grains with cylindrical pores in approximately hexagonal packing. Pores are perpendicular in adjacent grains. The compressive strength is found to be rather independent of growth rate, in the range studied. Small differences can be explained using a minimum solid area (MSA) model and differences in the microstructure. In creep experiments, no steady-state regime was observed. Instead, the strain exhibited a series of accelerations that could be associated with damage propagation. 


Septiembre, 2008 | DOI: 10.1016/j.jeurceramsoc.2008.04.002

Experimental and theoretical analysis of the intensity of beams diffracted by three-dimensional photonic crystals


Dorado, LA; Depine, RA; Schinca, D; Lozano, G; Miguez, H
Physical Review B, 78 (2008) 075102
Materiales Ópticos Multifuncionales

ABSTRACT ▼

An analysis of the diffracted beams emerging from three-dimensional photonic crystals is herein presented. The wave vectors of nonspecular beams are calculated for a triangular two-dimensional lattice and the change in their directions as a function of the wavelength is confirmed experimentally for the case of face-centered-cubic colloidal crystals illuminated under normal incidence. A fluctuating behavior of beam intensity as a function of the wavelength of the incident light is predicted for perfectly ordered lattices. As it is the case for specularly reflected and ballistically transmitted beams, this modulation arises from multipole resonances of the sphere ensemble that are smoothed out via the diffuse light scattering produced by imperfections in the crystalline structure. When optical extinction is introduced in order to model the effect of imperfections, it is possible to accurately reproduce experimental observations.


Agosto, 2008 | DOI: 10.1103/PhysRevB.78.075102

Functionalisation versus mineralisation of some N-heterocyclic compounds upon UV-illumination in the presence of un-doped and iron-doped TiO2 photocatalysts


Navio, J. A.; Macias, M.; Garcia-Gomez, M.; Pradera, M. A.
Applied Catalysis B-Environmental, 82 (2018) 225-232
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT ▼

Heterogeneous photocatalytic oxidation of some N-heterocyclic compounds (4-picoline, and 6- and 8-methylquinoline) in oxygenated solvents (water or acetonitrile), containing dispersed photocatalyst (un-doped or iron-doped titanium dioxide), was investigated under UV-illumination in a photochemical reactor. This work aimed to correlate experimental parameters such as structural aspects of the substrates, photocatalyst chemical and surface properties. illumination times, and the nature of the solvent with the extent of mineralisation of the substrates and, also, possible selective methyl group functionalisation.
Analysis of the products resulting from heterogeneous photocatalytic oxidation of 6- and 8-methylquinoline suspensions in oxygenated acetonitrile with illumination periods of <24 h detected, in both cases, the corresponding formyl derivatives quinoline-6- and -8-carbaldehyde, though at low levels. The presence of water appeared to inhibit heterogeneous photocatalytic functionalisation. However, the heterogeneous photocatalytic degradation of such compounds in water proceeds via polyhydroxylated intermediates which consequently undergo mineralisation, which, from a pollution control perspective is beneficial.
The physicochemical properties of the photocatalyst were also shown to be influential. Particularly, differences in the affinity to, and mode of adsorption of the substrate compounds studied gave rise to differences in the extent of oxidation.
Analysis of photogenerated oxidation products enabled some mechanistic insight into the course of the semiconductor-mediated reaction.
The results obtained allow a useful comparison of the functionalisation of N-Heterocyclic compounds via heterogeneous photocatalytic processes in the absence of water, to those carried out in the presence of water, which gave complete tnineralisation.


Agosto, 2008 | DOI: 10.1016/j.apcatb.2008.01.028

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