Materiais SiO2-TiO2 para a degradação fotocatalítica de diuron

SiO2-TiO2 materials prepared by sol-gel method were evaluated in the photocatalytic degradation of diuron. The materials were prepared with and without surfactant cetyltrimethylammonium chloride at different temperatures (25, 50 and 100 ºC). The samples were characterized by N2 adsorption-desorption measurements, scanning electron microscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy and infrared diffuse reflectance spectroscopy. The results showed that the materials synthesized with the surfactant had higher surface areas and band-gap values similar to anatase. All materials were more active than the commercial catalyst P-25 and better performance was achieved using the surfactant in the material synthesis.

Fotoeletrodegradação do corante AO7 utilizando filmes de nanocompósitos de ZnO-TiO2

The Zn-TiO2nanocomposite films were prepared by electrodeposition, using an acidic zinc sulphate solution with TiO2 nanoparticles in suspension. The as-deposited samples have been heated in air at 450 ºC for 6 h. The XRD and SEM analyses pointed out to the metal matrix conversion from Zn to ZnO and a rich morphology of needles-shaped grains. These materials were used on the photoelectrochemical degradation of AO7, which was efficiently degraded, with 40% of color removal, after 2 h period at 1.0 V, under white light irradiation. The apparent first order rate constant of the photoelectrodegradation reaction was 4.12 x 10-3 min-1.

Degradação fotoeletroquímica do herbicida bentazona sobre eletrodos de carbono modificados por TiO2

This work involved the study of degradation of the herbicide bentazone in aqueous solution by different routes, in order to search a method that generates safe products to the environment. It was tested electrochemical polarization methods involving positive and negative potential, irradiation with UV light and deposition of TiO2 on the electrode surface, seeking a catalytic effect. After different times of degradation, aliquots were removed and the scan of molecular absorption spectrum of UV-Vis was performed. From the spectra decay of bentazone, the kinetics of different processes was accompanied and the rate constants were determined.

Formation of TiO2 photoanodes by simultaneous electrophoretic deposition of anatase and rutile particles for photoassisted electrolytic copper ions removal

The influence of Anatasa/Rutile ratio on TiO2 films, grown by electrophoretic deposition was studied in the photoassisted electrolytic copper ions removal from cyanide solutions. The proper dispersant dosage allowing the simultaneous electrophoretic deposition of Anatase and Rutile was chosen based on electrokinetic measurements; evidenced by the XRD spectra of the formed films. The evaluation of films photoassisted electrolytic copper ion removal showeds that it is possible to enhance the activity of Anatase films by adding some Rutile exploiting the synergetic interaction between these two materials, achieve by its proper deposition.

Energia de superfície para nanossuperfícies de TiO2 na direção (001)

In this work was made an investigation about bulk and surface models (at maximum 20 layers) of the TiO2 material in the (001) direction. TiO2 commercial sample was feature using XDR technique to determine phase and crystallites average size. Bulk and (001) surface models were simulated for TiO2 material using DFT/B3LYP and its results were used for calculating energy surface, electronic levels, superficial atomic displacement and charge maps. Atoms of the first and second layers of the slab model showed electronic densities very well organized in the form of chains or wires.

Nanotubos de TiO2 dopados com nitrogênio: comparação das atividades fotocatalíticas de materiais obtidos através de diferentes técnicas

TiO2 nanotubes were synthesized by hydrothermal method and doped with three nitrogen compounds to enhance photocatalytic activity under visible light. Catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and specific surface area and pore volume determined by BET and BJH methods, respectively. Photocatalytic activity was evaluated by photodegradation of rhodamine B under visible and UV radiations. Results showed doped-nanotubes were more efficient under visible light. The best photocatalytic activity was for sample NTT-7-600/NH3I, being 30% higher than the non-doped sample.

Enhanced photocatalytic activity of TiO2 films by modification with polyethylene glycol

Titanium dioxide porous thin films on the Anatase phase were deposited onto glass slides by the sol-gel method assisted with polyethylene glycol (PEG). The dip-coated films were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA and DTG), UV-visible spectroscopy and X-ray diffraction (XRD). The photocatalytic activity of the films was determined by means of methyl-orange oxidation tests. The resultant PEG-modified films were crack-free and developed a porous structure after calcination at 500 °C. Photo-oxidation tests showed the dependency of catalytic activity of the films on the number of layers (thickness) and porosity, i.e. of the interfacial area.

Efeito da adição de TIO2 nas propriedades térmicas e na cristalinidade do copolímero de etileno/acetato de vinila

We investigated the effect of adding titanium dioxide nanoparticles (TiO2) to ethylene vinyl acetate (EVA) copolymer, containing 28% vinyl acetate groups, on the crystallinity and miscibility of the copolymer. Films of EVA/TiO2 containing 0.25%-1% TiO2, relative to the total weight of EVA, were prepared from their solution. The obtained films were characterized by X-ray diffraction, low-field nuclear magnetic resonance, and differential scanning calorimetry. The addition of TiO2 to the EVA copolymer was proved to cause changes in the crystallinity and mobility of the polymer chains of EVA, due to new intermolecular interactions and nanostructure organization.

Method for determining the photocatalytic potential of portland cement mortar containing TiO2 for decomposing the pollutant nitrogen monoxide

Photocatalytic materials can minimize atmospheric pollution by decomposing certain organic and inorganic pollutants using sunlight as an energy source. In this paper, the development of a methodology to measure the photocatalytic potential of mortar containing TiO2 nanoparticles is reported. The results indicate that up to 40% of NOx can be degraded by Portland cement mortar containing 30-50% of TiO2, which validates the method developed for evaluating the photocatalytic potential of materials.

Propriedades estruturais e eletrônicas de nanofilmes de TiO2 anatase: cálculos B3LYP-D* em sistemas periódicos bidimensionais

Structural and electronic properties of titanium dioxide (TiO2) thin films, in anatase phase, were investigated using periodic 2D calculations at density functional theory (DFT) level with B3LYP hybrid functional. The Grimme dispersion correction (DFT/B3LYP-D*) was included to better reproduce structural features. The electronic properties were discussed based on the band gap energy, and proved dependent on surface termination. Surface energies ranged from 0.80 to 2.07 J/m², with the stability orders: (101) > (100) > (112) > (110) ~ (103) > (001) >> (111), and crystal shape by Wulff construction in accordance with experimental data.

INFLUÊNCIA DO TRATAMENTO TÉRMICO NO NANOCOMPÓSITO FOTOCATALISADOR ZnO/TiO2

ZnO/TiO2 nanocomposites were prepared by impregnating zinc acetate dihydrate on the surface of titanium dioxide P25, followed by thermal treatment at 350, 600, 750, and 900 °C, in order to investigate the TiO2 phase and titanate formation and the role of the latter in the photocatalytic activity of the nanocomposite. In the nanocomposites, the anatase-to-rutile transition is favored due to the presence of Zn2+, and the conversion is nearly complete at 750 °C. The presence of zinc metatitanate in the sample heated at 600 °C had no significant effect on the nanocomposite photocatalytic activity.

UTILIZAÇÃO DO COMPÓSITO NANOESTRUTURADO SIO2/TIO2NA FOTODEGRADAÇÃO DE CORANTES TÊXTEIS COM LUZ SOLAR NATURAL

SiO2/TiO2 nanostructured composites with three different ratios of Si:Ti were prepared using the sol-gel method. These materials were characterized using energy dispersive X-ray fluorescence, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, Raman with Fourier transform infrared spectroscopy, and the specific surface area. The band gaps of materials were determined by diffuse reflectance spectra, and the values of 3.20 ± 0.01, 2.92 ± 0.02, and 2.85 ± 0.01 eV were obtained as a result of the proportional increases in the amount of Ti within the composite. The materials exhibit only the anatase (TiO2) crystalline phase and have crystalline domains ranging from 4 to 5 nm. The photodegradation process of methylene blue, royal blue GRL, and golden yellow GL dyes were studied with respect to their contact times, pH variations within the solution, and the variations in the dye concentration of the solution in response to only sunlight. The maximum amount of time for the mineralization of dyes was 90 min. The kinetics of the process follows an apparently first order model, in which the obtained rate constant values were 5.72 × 10-2 min-1 for methylene blue, 6.44 × 10-2min-1 for royal blue GRL, and 1.07 × 10-1min-1 for golden yellow.

A FTIR study of the metal-support interactions and hydrogen spillover on Pd/TiO2 and Ni/TiO2

Nickel and palladium dispersed on titania support were submitted to reductive treatment, under hydrogen, at 200 and 500 ºC. After the reductive thermal treatment the materials were exposed to carbon monoxide (10 Torr) and analyzed in the infrared region. The increasing of the electronic density in the metallic d subshell, produced by the reductive thermal treatment, was monitored by the infrared stretching band shift of carbon monoxide adsorbed and it was interpreted as a consequence of the metal-support interactions. The highest effect was observed for Pd/TiO2 system. From the FTIR spectra was also observed that the hydrogen spillover was stronger on Pd/TiO2 than Ni/TiO2 system.

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

Este trabalho teve por objetivo utilizar o hidrogenoftalato de potássio como molécula modelo para estudos de adsorção em TiO2. Os resultados de adsorção do hidrogeneoftalato sobre TiO2 se ajustaram aos modelos de adsorção propostos por Langmuir e Freundlich, sendo que o modelo de Freundlich descreveu melhor o fenômeno. A adsorção foi função da temperatura e a capacidade de adsorção aumentou de 2,4 para 4,5 mg.g-1 quando se elevou a temperatura de 20 para 30ºC.

The Li+, Na+ and K+ ion exchange reaction process on the surface of mixed oxide SiO2/TiO2/Sb2O5 surface prepared by the sol-gel processing method

The porous mixed oxide SiO2/TiO2/Sb2O5 obtained by the sol-gel processing method presented a good ion exchange property and a high exchange capacity towards the Li+, Na+ and K+ ions. In the H+/M+ ion exchange process, the H+ / Na+ could be described as presenting an ideal character. The ion exchange equilibria of Li+ and K+ were quantitatively described with the help of the model of fixed tetradentate centers. The results of simulation evidence that for the H+ / Li+ exchange the usual situation takes place: the affinity of the material to the Li+ ions is decreased with increasing the degree of ion exchange. On the contrary, for K+ the effects of positive cooperativity, that facilitate the H+ / K+ exchange, were revealed.