Degradation of [D-Leu]-Microcystin-LR by solar heterogeneous photocatalysis (TiO2)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Obtenção e Caracterização Físico-Química do Sistema Compósito PEG-TiO2

Hybrid systems formed from polymers and transition metals have now their physical and chemical properties extensively investigated for use in electronic devices. In this work, Titanium Dioxide (TiO2) from the precursor of titanium tetrabutoxide and the composite system Poly(Ethylene Glycol)-Titanium Dioxide (TiO2-PEG) were synthesized by sol-gel method. The PEG as acquired and TiO2 and composites powders were analyzed by X-Ray Diffraction (XRD), Spectroscopy in the Infrared region with Fourier transform (IRFT), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and Electrochemical Impedance Spectroscopy (EIS). In the XRD analysis were observed in the TiO2 crystal faces of one of its polymorphs - anatase phase, crystal planes in Poly (Ethylene Glycol) with considerable intensity and in the composite systems the mixture of crystal faces of their precursors isolated and reduction of crystallinity. The TG / DTG suggested increasing the thermal instability of PEG in the composite powders as TiO2 is incorporated into the system. Spectral analysis presented in the infrared overlapping bands for the polymer and metal oxide, reducing the intensity of symmetric stretching of ligand groups in the main chain polymer and angular deformations; were observed using SEM micrographs of the morphological changes suffered by composite systems with the variation of the oxide concentration. Analyses by impedance spectroscopy indicated that the increased conductivity in composite occurs in line with the addition of the metal oxide concentration in the composite system

Confecção e caracterização físico-química de filmes compósitos autossustentáveis NaAlg-TiO2-WO3

A new self-sustainable film was prepared through the sol-gel modified method, previously employed in our research group; sodium alginate was used as the polymer matrix, along with plasticizer glycerol, doped with titanium dioxide (TiO2) and tungsten trioxide (WO3). By varying WO3 concentration (0,8, 1,6, 2,4 and 3,2 μmol) and keeping TiO2 concentration constant (059 mmol), it was possible to study the contribution of these oxides on the obtained films morphological and electrical properties. Self-sustainable films have analyzed by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XDR), Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and Electrochemical Impedance Spectroscopy (EIS). By the IR specters, it was possible identify the TiO2, and posteriorly WO3, addition has provided dislocation of alginate characteristics bands to smaller vibrations frequencies indicating an electrostatic interaction between the oxides and the polymer matrix. Diffractograms show predominance of the amorphous phase in the films. SEM, along with EDX, analysis revealed self-sustainable films showed surface with no cracks and relative dispersion of the oxides throughout the polymer matrix. From Impedance analysis, it was observe increasing WO3 concentration to 2,4 μmol provided a reduction of films resistive properties and consequent improvement of conductive properties

Obtenção e caracterização do sistema compósito alginato de sódio-dióxido de titânio em formas de pó e de membrana

The alginates are copolymers of 1→4-linked β-D-mannuronic acid (M) and α-Lguluronic acid (G) residues that are arranjed in a block structure along a linear chain. Titanium dioxide, TiO2, is a ceramic material and can exist in three distinct crystallography forms: anatase, brookite and rutile. composites of organic and inorganic materials have better properties than the components alone. Thus, this study aims to synthesize, characterize and analyze the composite NaAlg-TiO2 in the form of powder and film. The synthesis of composite powders was performed using the sol-gel process and obtain the composite film was performed using the slow evaporation process, then the composites were analyzed by infrared spectroscopy, fluorescence x ray, thermal analysis, attenuated total reflection (ATR), x ray diffraction and impedance spectroscopy. The X ray diffraction patterns of composite powders show that with increasing calcination temperature, there were no complete transition of rutile-anatase crystalline phase, since at all temperatures studied (300, 500, 700, 900 and 1100ºC) were observed peaks of anatase phase. Thermal analysis shows that at 400°C caused the decomposition of sodium alginate in sodium carbonate and above 600°C, we observe an exothermic peak related to the decomposition of sodium carbonate and in the presence of titanium dioxide becomes sodium titanate. The XRD results confirm the formation of sodium carbonate at 700ºC and the formation sodium titanate in the temperature range 900-1100ºC. The sodium titanate influenced the electrical properties of the material, because with increasing temperature there was a decrease in conductivity, probably due to the creation of Ti vacancies, since the sodium can induce the reduction of surface Ti4+ ions into Ti3+ species. The infrared spectra of the composites in the form of powder and film showed a small shift in the bands compared to the spectrum of pure alginate, indicating that these shifts, even small ones, have evidence of miscibility between the polymer and ceramic material

Activity and characterization by XPS, HR-TEM, Raman spectroscopy, and BET surface area of CuO/CeO2-TiO2 catalysts

Structural and textural studies of a CuO/TiO2 System modified by cerium oxide were conducted using Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N-2 absorption (BET specific surface area). The introduction of a minor amount of CeO2 (Ce0.09Ti0.82O1.91CU0.09 sample) resulted in a material with the maximum surface area value. The results of Raman spectroscopy revealed the presence of only two crystalline phases, TiO2 anatase and CeO2 cerianite, with well-dispersed copper species. TEM micrographs showed a trend toward smaller TiO2 crystallites when the cerium oxide content was increased. The XPS analysis indicated the rise of a second peak in Ti 2p spectra with the increasing amount of CeO2 located at higher binding energies than that due to the Till in a tetragonal symmetry. The CuO/TiO2 system modified by CeO2 displayed a superior performance for methanol dehydrogenation than the copper catalyst supported only on TiO2 or CeO2.

X-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and x-ray diffraction characterization of CuO-TiO2-CeO2 catalyst system

X-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and x-ray absorption spectroscopy (XAS) techniques have been applied to characterize the surface composition and structure of a series of CuO-TiO2-CeO2 catalysts. For a small loading of cerium, ceria was mainly dispersed on the titania surface and a minor amount of CeO2 crystallite appeared. At higher loading of cerium, the CeO2 phase increased and the atomic Ce/Ti ratio values were smaller than the nominal composition, as a consequence of cerium agglomeration. This result suggests that only a fraction of cerium can be spread on the titania surface. For titanium-based mixed oxide, we observed that cerium is found as Ce3+ uniquely on the surface. The atomic Cu/(Ce+Ti) ratio values showed no influence from cerium concentration on the dispersion of copper, although the copper on the surface was shown to be dependent on the cerium species. For samples with a high amount of cerium, XPS analysis indicated the raise of second titanium species due cerium with spin-orbit components at higher binding energies than those presented by Ti4+ in a tetragonal structure. The structural results obtained by XAS are consistent with those obtained by XRD and XPS. (C) 2001 American Vacuum Society.

Photoelectrocatalytic treatment of p-nitrophenol using Ti/TiO2 thin-film electrode

The photoelectrochemical degradation of p-nitrophenol (PNP) was investigated using titanium dioxide thin-film photoelectrode. The effects of different supporting electrolytes, pH, applied potential and PNP concentration were examined and discussed. Complete photodegradation was obtained in perchlorate medium at pH 2 when the photoanode was biased at +1.0 V (versus SCE) during a 3-h experiment. Under these conditions, carbon removal of approximately 60% was achieved. (C) 2005 Elsevier B.V. All rights reserved.

Studies on the adsorption and kinetics of photodegradation of a model compound for heterogeneous photocatalysis onto TiO2

An investigation was made on the adsorption and kinetics of photodegradation of potassium hydrogenphthalate in an aqueous suspension of TiO2. Two models, Langmuir and Freundlich, were used to describe the adsorption process and the model proposed by Langmuir-Hinshelwood (L-H) was employed to describe the kinetics of the photodecomposition reactions of hydrogenphthalate. The results of the adsorptions were fitted to the models proposed by Langmuir and Freundlich. Adsorption was found to be a function of the temperature, with adsorption capacity increasing from 2.4 to 4.5 mg/g when the temperature rose from 20 to 30 degrees C. The kinetic model indicates that the rate constant, k, of the first order reaction, is high in the 10.0 to 100 mg/l interval, which is coherent with the low value of the adsorption constant, K. The results fitted to the L-H model led to an equation that, within the range of concentrations studied here, theoretically allows one to evaluate the photodegradation rate. (c) 2005 Elsevier Ltd. All rights reserved.

Hidrogeneoftalato de potássio como molécula modelo para estudos de adsorção sobre TiO2

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Síntese e caracterização textural do catalisador CeO2/TiO2 obtido via sol-gel: fotocatálise do composto modelo hidrogenoftalato de potássio

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis and characterization of TiO2 chemically modified by Pd(II) 2-aminothiazole complex for the photocatalytic degradation of phenol

An investigation was made into the photocatalytic activity of in situ synthesized TiO2 chemically modified by Pd(II) 2-aminothiazole complex for phenol degradation at different pH values. At longer reaction times, the bare titania presented far poorer pbotoactivity than the modified catalysts in the entire range of pH studied. The catalyst complexed with Pd(II) was more efficient than the metal-free Pd, irrespective of pH and reaction time, suggesting that metal plays an important role. A cooperative mechanism is proposed, involving the possible photoactivation of both TiO2 and sensitizer. (C) 2007 Elsevier B.V. All rights reserved.

Photocatalytic Degradation of Phenol by Thermal Titanium Dioxide Thin Layer Electrodes

Electrochemical processes in industrial effluents have been studied as a means to obtain higher efficiency in wastewater treatment. Heterogeneous photocatalysis appears as a low-cost alternative through the use of lower wattage lamps and thermal TiO2 films. Photocatalysis became a clean process for water treatment due to hydroxyl radicals generated on semiconductor surface. Such radicals are able to degrade several organic compounds. This study used different electrodes and analytical methods for degradation of phenol molecules to reduce treatment costs, improve efficiency, and identify compounds formed during the decomposition of phenolic molecules. Thermal growth of TiO2 film was observed on the titanium electrode in rutile form. Application of an electrical potential on the Ti/TiO2 working electrode increases efficiency in reducing concentration of phenol after photocatalytic treatment. Still, high energy radiation (UVC) showed best degradation rates in photolytic process. Different compounds formed during the degradation of phenol were also identified in the UVC-PE treatment.

NMR study of styrene-butadiene rubber (SBR) and TiO2 nanocomposites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Obtenção de filmes finos de TiO2 nanoestruturado pelo método dos precursores poliméricos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Liquid crystalline formulations containing modified surface TiO2 nanoparticles obtained by sol-gel process

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)