Degradação fotocatalítica do fungicida tebuconazole em solução aquosa

The tebuconazole photocatalytic degradation kinetics was studied in a batch reactor using TiO2 (P25-Degussa) as catalyst and a high pressure mercury lamp. The photolysis, adsorption and irradiation effects in the reaction rate were evaluated. Afterward, the suspension catalyst concentration and initial pH to the maximum reaction rate was determined. It was observed that the reaction rate can be approached by a pseudo-first order, with a maximum kinetics constant at 260 mg L-1catalyst concentration and pH 7.7.

Degradação fotocatalítica de sulfametoxazol, trimetoprima e diclofenaco em solução aquosa

In this work the photocatalytic degradation of sulfametoxazole, trimethoprim and potassium diclofenac was evaluated by using TiO2 and ZnO photocatalysts. In optimized experimental conditions (pH 4, TiO2: 50 mg) the TiO2-photocatalysis allowed an almost total degradation of the studied drugs with mineralization of about 80% at reaction times of 120 min. Some mechanistic differences were observed between TiO2 and ZnO in the degradation study involving potassium diclofenac. At the first reaction times the use of ZnO leads to generation of transient species that strongly absorb in the UV spectral region, a fact not observed in studies involving TiO2.

Incorporação de dióxido de titânio em zeólitas para emprego em fotocatálise heterogênea

This work proposes the study of heterogeneous photocatalysis using TiO2 impregnated in zeolites beta, ZSM-5, mordenite, NaXb, NaXp and NaY for the decomposition of methylene blue. The catalysts were characterized by XRD, IR, textural analyses by N2 adsorption, SEM, DRS and the reaction of decomposition was monitored by UV visible. The results indicated that didn't have structural changes in the catalysts after Ti impregnations, only in the case of NaY and NaX zeolites. The better photocatalyst to metylene blue decomposition was beta/Ti zeolite due had one structure more accessible (with bigger porous) helping in TiO2 dispersion and catalytic active.

Avaliação de metodologia eletroquímica no monitoramento da conversão de óleo de girassol em biodiesel

The development of analytical procedures to evaluate transesterification process is still a challenge in biodiesel production. Then, this paper shows an electroanalytical methodology to transesterification process assessment, proposing the application of nanostructured TiO2 electrodes. The results showed, for sunflower oil - methanol reaction catalyzed by KOH, a reduction peak in - 1050 mV and the gradual appearance of a second peak at - 1160 mV. This peak was observed as originated by the transesterification process and is probably related to intermediates. By measuring the intensity of this peak a kinetic profile was determined, showing that the conversion is almost finished in 2 h.

Preparação, caracterização e aplicação de fases estacionárias tipo C8 modificadas por óxidos metálicos para cromatografia líquida

This work describes three C8-stationary phases for high performance liquid chromatography based on silica metallized with ZrO2, TiO2 or Al2O3 layers, having poly(methyloctylsiloxane) immobilized onto their surfaces. The stationary phases were characterized using XRF, XAS, FTIR, SEM and elemental analysis to determine the physical characteristics of the oxide and polysiloxane layers formed on the surfaces and chromatographically to evaluate the separation parameters. The results show the changes on the silica surface and allowed proposing a structure for the oxide layer, being observed tetrahedral and octahedral structures, what is completely new in the literature. The formation of a homogeneous layer of metallic oxide (TiO2 and ZrO2) was observed on the silica. The C8-titanized and C8-aluminized stationary phases presented good chromatographic performances, with good values of asymmetry and efficiency. All stationary phase presented few loss of the polymeric layer after the HPLC, indicating that this layer is well attached on the metalized support.

Celdas solares fotoelectroquímicas basadas en Bi2WO6

In this study, photoelectrochemical solar cells based on bismuth tungstate electrodes were evaluated. Bi2WO6 was synthesized by a hydrothermal method and characterized by scanning electron microscopy, UV-Vis reflectance spectroscopy, and X-ray powder diffraction. For comparison, solar cells based on TiO2 semiconductor electrodes were evaluated. Photoelectrochemical response of Grätzel-type solar cells based on these semiconductors and their corresponding sensitization with two inexpensive phthalocyanines dyes were determined. Bi2WO6-based solar cells presented higher values of photocurrent and efficiency than those obtained with TiO2 electrodes, even without sensitization. These results portray solar cells based on Bi2WO6 as promising devices for solar energy conversion owing to lower cost of production and ease of acquisition.

Ocorrência e degradação de quinolonas por processos oxidativos avançados

In this review, the presence of quinolones in the environment, their risks and the available processes for water decontamination were addressed. Their occurrence in surface waters and also in soil raises concerns about the risk of the development of resistant bacteria and other potential chronic effects. AOPs (UV/H2O2, Fenton, photo-Fenton, and UV/TiO2) and ozonation proved effective for degrading these emerging contaminants due to hydroxyl radical formation, surpassing the efficacy of conventional methods. In addition, the main degradation mechanisms of these drugs as well as data on residual biological activity were analyzed.

TUNGSTOPHOSPHORIC ACID HETEROGENIZED ONTO NH4ZSM5 AS AN EFFICIENT AND RECYCLABLE CATALYST FOR THE PHOTOCATALYTIC DEGRADATION OF DYES

Materials based on tungstophosphoric acid (TPA) immobilized on NH4ZSM5 zeolite were prepared by wet impregnation of the zeolite matrix with TPA aqueous solutions. Their concentration was varied in order to obtain TPA contents of 5%, 10%, 20%, and 30% w/w in the solid. The materials were characterized by N2 adsorption-desorption isotherms, XRD, FT-IR, 31P MAS-NMR, TGA-DSC, DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (SBET) decreased when the TPA content was raised as a result of zeolite pore blocking. The X-ray diffraction patterns of the solids modified with TPA only presented the characteristic peaks of NH4ZSM5 zeolites, and an additional set of peaks assigned to the presence of (NH4)3PW12O40. According to the Fourier transform infrared and 31P magic angle spinning-nuclear magnetic resonance spectra, the main species present in the samples was the [PW12O40]3- anion, which was partially transformed into the [P2W21O71]6- anion during the synthesis and drying steps. The thermal stability of the NH4ZSM5TPA materials was similar to that of their parent zeolites. Moreover, the samples with the highest TPA content exhibited band gap energy values similar to those reported for TiO2. The immobilization of TPA on NH4ZSM5 zeolite allowed the obtention of catalysts with high photocatalytic activity in the degradation of methyl orange dye (MO) in water, at 25 ºC. These can be reused at least three times without any significant decrease in degree of degradation.

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.

CÉLULAS SOLARES SENSIBILIZADAS POR CORANTES NATURAIS: UM EXPERIMENTO INTRODUTÓRIO SOBRE ENERGIA RENOVÁVEL PARA ALUNOS DE GRADUAÇÃO

An interesting practical experiment about the preparation of dye–sensitized solar cells (DSSC) using natural dyes were carried out by the undergraduate students in the chemistry course at UNICAMP . Natural dyes were extracted from blueberries (Vaccinium myrtillus L.), jabuticabas (Myrciaria cauliflora), raw and cooked beets (Beta vulgaris L.), and annattos (Bixa orellana L.), which were used to sensitize TiO2 films that composed the photoanode in the DSSC. A polymer electrolyte containing an iodide/triiodide redox couple was used in lieu of the use of liquid solutions to prevent any leakage in the devices. A maximum solar-to-electric energy conversion of 0.26 ± 0.02% was obtained for the solar cell prepared with annatto extracts. This experiment was an effective way to illustrate to the undergraduate students how to apply some of the chemical concepts that they learned during their chemistry course to produce electric energy from a clean and renewable energy source. Teachers could also exploit the basics of the electronic transitions in inorganic and organic compounds (e.g., metal-to-ligand charge transfer and ϖ-ϖ* transitions), thermodynamics (e.g., Gibbs free energy), acid–base reactions in the oxide solid surface and electrolyte, and band theory (i.e., the importance of the Fermi level energy).

Identificação e quantificação de resinas, cargas e pigmentos em tintas latex branca

Resinas, pigmentos e cargas constituintes de tintas látex da linha branca foram identificados e quantificados após prévio tratamento à baixa temperatura e pressão para obtenção de amostras secas em forma de pó. TG/DTA permitiram, sob determinadas condições, distinguir e quantificar as resinas, cargas e pigmentos em tintas latex branca comerciais. Difratometria de raios X foi empregada para confirmar a presença do pigmento TiO2 de fase rutílo no resíduo final de termodecomposição.

Efeitos de oxidantes e sais inorgânicos na degradação fotocatalítica do herbicida imazetapir mediada por dióxido de titânio

A degradação fotocatalítica de imazetapir, um herbicida da família das imidazolinonas, em suspensão aquosa de dióxido titânio foi investigada na presença de dois receptores de elétrons como persulfato de potássio e periodato de sódio, assim como na presença de dois sais inorgânicos como sulfato de sódio e dihidrogenofosfato de sódio a 30ºC. O modelo cinético de pseudo-primeira ordem foi empregado para discutir os resultados. O desaparecimento de imazetapir em função do tempo de irradiação foi analisado por cromatografia líquida de alta eficiência. Entre os dois oxidantes estudados a degradação foi mais rápida quando se adicionou o periodato de sódio, enquanto a presença do sulfato de sódio retarda a degradação de imazetapir mais que o dihidrogenofosfato na suspensão de TiO2.

Adsorption of hidrogen peroxide on the surface of silica - titania mixed oxide obtained by the sol-gel processing method

This work describes the sol-gel mixed oxide SiO2/TiO2 property, ST, as prepared, and submitted to heat treatment a 773 K, STC. SEM and EDS images show, within magnification used, a uniform distribution of the TiO2 particles in SiO2/TiO2 matrix. Both, ST and STC adsorb hydrogen peroxide on the surface and through EPR and UV-Vis diffuse reflectance spectra, it was possible to conclude that the species on the surface is the peroxide molecule attached to the Lewis acid site of titanium particle surface, alphaTi(H2O2)+. As the material is very porous, presumably the hydrogen peroxide molecule is confined in the matrix pores on the surface, a reason why the adsorbed species presents an exceptional long lived stability.

Synthesis and characterization of Fe(III)-doped ceramic membranes of titanium dioxide and its application in photoelectrocatalysis of a textile dye

Pure and Fe(III)-doped TiO2 suspensions were prepared by the sol gel method with the use of titanium isopropoxide (Ti(OPri)4) as precursor material. The properties of doped materials were compared to TiO2 properties based on the characterization by thermal analysis (TG-DTA and DSC), X-ray powder diffractometry and spectroscopy measurements (FTIR). Both undoped and doped TiO2 suspensions were used to coat metallic substrate as a mean to make thin-film electrodes. Thermal treatment of the precursors at 400ºC for 2 h in air resulted in the formation of nanocrystalline anatase TiO2. The thin-film electrodes were tested with respect to their photocatalytic performance for degradation of a textile dye in aqueous solution. The plain TiO2 remains as the best catalyst at the conditions used in this report.

Fotodegradação heterogênea de efluente de polpa kraft branqueada com cloro

A polpa celulósica da madeira deve ser branqueada e alvejada para atingir elevado valor comercial. O cloro é muito eficiente no branqueamento da polpa obtida por processo químico, mas também produz subprodutos altamente poluentes e tóxicos. Outros produtos químicos de branqueamento têm sido propostos para reduzir a toxicidade, mas são mais caros e menos versáteis. A fotodegradação catalítica com o uso de radiação ultravioleta (UV) foi feita para avaliar o potencial de redução do teor de poluentes encontrados em um efluente de branqueamento de celulose com o uso de cloro. A polpa celulósica de Pinus taeda foi produzida e branqueada em laboratório. Três litros de efluente receberam 3 g de dióxido de titânio (TiO2) e foram submetidos à radiação UV. Essa radiação foi produzida com o uso da ampola de lâmpada de vapor de mercúrio de alta pressão de 250 W (12.500 Lm) durante 240 min. A fotodegradação a 25 ºC por 240 min com UV reduziu em cerca de 43% a cor, 40% a DBO5, 50% a DQO, 40% de material calcinável e 45% do carbono orgânico total, além de baixar a toxicidade LC50 para o efluente tratado. O bioindicador Artemia salina apresentou o tempo de sobrevida maior do que 1.000% para o efluente tratado. A distribuição dos pontos experimentais de 0 a 240 min sugere que a fotodegradação deveria ser estendida. Assim, a redução de poluentes observada sugere que esse processo oxidativo avançado (POA), com fotocatálise com o uso de UV e TiO2, pode ser conveniente para o tratamento de efluentes clorados de branqueamento. Isso pode viabilizar o uso seguro de branqueamento com cloro.