Surface Properties of Calcinated Titanium Dioxide Probed by Solvatochromic Indicators: Relevance to Catalytic Applications

Titanium dioxide was obtained by hydrolysis of the corresponding ethoxide, followed by washing, drying, and calcination at 80, 160, 240, 320, 400, and 700 C, respectively. The following surface properties of the solids obtained were determined as a function of the calcinations temperature: T(Calcn); area by the BET method; BrOnsted acidity by titration with sodium hydroxide; empirical polarity, ET(30); Lewis acidity, alpha(Surf); Lewis basicity, beta(Surf); and dipolarity/polarizability pi*(Sturf), by use of solvatochromic indicators. Except for le surf whose value increased slightly, heating the samples resulted in a decrease of all of the above-mentioned surface properties, due to the decrease of surface hydroxyl groups. This conclusion has been corroborated by FTIR. Values of E(T)(30), alpha(Surf), and pi*(Surf) are higher than those of water and alcohols; the BrOnsted and Lewis acidities of the samples correlate linearly. The advantages of using solvatochromic indicators to probe the surface properties and relevance of the results to the applications of TiO(2) are discussed.

Hybrid photocatalysts for the degradation of trichloroethylene in air

Hybrid photocatalysts based on an adsorbent SiMgOx and a photocatalyst TiO(2) were developed in a plate shape. The ceramic surface was coated with TiO(2) by the slip-casting technique. The effect of the support in the photocatalytic degradation of trichloroethylene (TCE) was analyzed by modifying TiO(2) loading and the layer thickness. Photocatalysts were characterised by N(2) adsorption-desorption, mercury intrusion porosimetry, SEM, UV-vis spectroscopy and XRD. A direct relationship between the TiO(2) content and the photocatalytic activity was observed up to three layers of TiO(2) (0.66 wt.%). Our results indicate that intermediate species generated on the TiO(2) layer can migrate through relatively long distances to react with the OH(-) surface groups of the support. By increasing the TiO(2) loading of the photocatalyst two effects were observed: trichloroethylene conversion is enhanced, while the efficiency of the oxidation process is decreased at expenses of increasing the selectivity to COCl(2) and dichloroacetylchloride (DCAC). The results are discussed in terms of the layer thickness, TiO(2) amount, TCE conversion and CO(2), and COCl(2) selectivity. (C) 2009 Elsevier B.V. All rights reserved.

Gelatin-based protonic electrolyte for electrochromic windows

Proton-conducting gel polymer electrolytes based on gelatin plasticized with glycerol and containing acetic acid were investigated, characterized, and applied to electrochromic window. For glycerol contents varying from 7% to 48%, the conductivity of the uniform and predominantly amorphous gel electrolyte was found to follow a Vogel-Tamman-Fulcher behavior with the temperature. Typically, for the electrolyte chosen to make 7 x 2 cm(2) electrochromic smart window with the configuration: glass/fluor-doped tin oxide (FTO)/WO(3)/gelatin electrolyte/CeO(2)-TiO(2)/FTO/glass and containing 28% of glycerol, the conductivities were found to be of the order of 5 x 10(-5) S/cm at room temperature and 3.6 x 10(-4) S/cm at 80 A degrees C. The device was characterized by spectroelectrochemical techniques and was tested up to 10,000 cycles showing a fast coloring/bleaching behavior, where the coloring process was achieved in 10 s and the bleaching in 2 s. The transmission variation at the wavelength of 550 nm was about 15%. The cyclic voltammograms showed a very good reversibility of the cathodic/anodic processes, and the charge density was about 3.5 mC/cm(2). The memory tests showed that the transmittance in the colored state increased by 8% in 90 min after removing the potential.

Photocatalytic Decolorization of Commercial Acid Dyes using Solar Irradiation

This work investigates the solar heterogeneous photocatalytic degradation of three commercial acid dyes: Blue 9 (C.I. 42090), Red 51 (C.I. 45430), and Yellow 23 (C.I. 19140). TiO(2) P25 from Degussa was used as the photocatalyst. The dyes were completely degraded within 120 min of treatment in the following increasing order of removal rate: Blue 9 < Yellow 23 < Red 51. The photocatalytic color removal process was well described by a two-first-order in-series reaction, followed by another first-order reaction. Photolytic experiments showed that this process is quite inefficient and highly selective towards Red 51 only. The dyes` solution was completely decolorized and organic matter removals up to 99% were achieved with photocatalysis. The lack of selectivity and the possibility of using solar light to excite the photocatalyst are promising results regarding the feasibility of this technology.

Digital Light Microscopy of Macroporous Ceramics Processed by Consolidation Casting with Mixtures of Native Starches

Porosity in starch consolidation casting technique is rightly related to original size and morphology of starch granules, leaving a pore structure after burning out. This work reports the results for the addition of different native potato and corn starch proportions in suspension,; with TiO(2) (rutile) powder. Gelling temperature have been defined after observation under light microscopy using a heating stage. Analysis of porous network and isolated pores have been clone from images of samples surfaces obtained by depth from focus reconstruction, revealing a qualitative correlation of pores characteristics and starches additions in suspensions, suggesting that the presence of isolated or interconnected pores can be handled by starches selection to control the amylopectin and amylose contents in slurries. Also, the analysis of porous fraction distribution shows no consistent pattern through specimens' volume according to starches in mixtures.

Analytical Methods in Photoelectrochemical Treatment of Phenol

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Photoeletrolytic system applied to remazol red brilliant degradation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Reaction pathway to the synthesis of anatase via the chemical modification of titanium isopropoxide with acetic acid

Anatase nanoparticles were obtained through a modified sol-gel route from titanium isopropoxide modified with acetic acid in order to control hydrolysis and condensation reactions. The modification of Ti(O(i)Pr)(4) with acetic acid reduces the availability of groups that hydrolyze and condense easily through the formation of a stable complex whose structure was determined to be Ti(OCOCH(3))(O(i)Pr)(2) by means of FTIR and (13)C NMR. The presence of this complex was confirmed with FTIR in the early stages of the process. A doublet in 1542 and 1440 cm(-1) stands for the asymmetric and symmetric stretching vibrations of the carboxylic group coordinated to Ti as a bidentate ligand. The gap of 102 cm(-1) between these signals suggests that acetate acts preferentially as a bidentate rather than as a bridging ligand between two titanium atoms. The use of acetic acid as modifier allows the control of both the degree of condensation and oligomerization of the precursor and leads to the preferential crystallization of TiO(2) in the anatase phase. A possible reaction pathway toward the formation of anatase is proposed on the basis of the intermediate species present in a 1:1 Ti(O(i)Pr)(4):CH(3)COOH molar system in which esterification reactions that introduce H(2)O into the reaction mixture were seen to be negligible. The Rietveld refinement and TEM analysis revealed that the powder is composed of isotropic anatase nanocrystallites.

Electron Transport in Dye-Sensitized Solar Cells Based on ZnO Nanotubes: Evidence for Highly Efficient Charge Collection and Exceptionally Rapid Dynamics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Piezoresponse behavior of niobium doped bismuth ferrite thin films grown by chemical method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Mutagenic activity removal of selected disperse dye by photoeletrocatalytic treatment

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

The photoelectrocatalytic oxidative treatment of textile wastewater containing disperse dyes

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

Evaluation of the photoelectrocatalytic method for oxidizing chloride and simultaneous removal of microcystin toxins in surface waters

The production of chlorine was investigated in the photoelectrocatalytic oxidation of a chloride-containing solution using a TiO(2) thin-film electrode biased at current density from 5 to 50 mA cm(-2) and illuminated by UV light. Such parameters as chloride concentrations from 0.001 to 0.10 mol L(-1), pH 2-12, and interfering salts were varied in this study in order to determine their effect on this oxidation process. At an optimum condition this photoelectrocatalytic method can produce active chlorine at levels compatible to water disinfections processes using a chloride concentration higher than 0.010 mol L(-1) at a pH of 4 and a current density of 30 mA cm(-2). The method was successfully applied to treat surface water collected from a Brazilian river. After 150 min of photoelectrocatalytic oxidation, we obtained a 90% reduction in total organic carbon removal, a 100% removal of turbidity, a 93% decrease in colour and a chemical oxygen demand (COD) removal of around 96% (N=3). The proposed technology based on photoelectrocatalytic oxidation was also tested in treating 250 mL of a solution containing 0.05 mol L(-1) NaCl and 50 mu g L(-1) of Microcystin aeruginosa. The bacteria is completely removed after 5 min of photoelectrocatalysis following an initial rate constant removal of -0.260 min(-1), suggesting that the present method could be considered as a promising alternative to chlorine-based disinfections. (C) 2008 Elsevier Ltd. All rights reserved.

Simultaneous removal of chromium and leather dye from simulated tannery effluent by photoelectrochemistry

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

Comparison of oxidation efficiency of disperse dyes by chemical and photoelectrocatalytic chlorination and removal of mutagenic activity

Degradation of Disperse Orange 1, Disperse Red 1 and Disperse Red 13 dyes has been performed using electrochemical oxidation on Pt electrode, chemical chlorination and photoelectrochemical oxidation on Ti/TiO(2) thin film electrodes in NaCl or Na(2)SO(4) medium. 100% discoloration was obtained for all tested methods after 1 h of treatment. Faster color removal was obtained by photoelectrocatalytic oxidation in 0.1 mol L(-1) NaCl pH 4.0 under UV light and an applied potential of +1.0V (vs SCE reference electrode), which indicates also values around 60% of TOC removal. The conventional chlorination method and electrochemical oxidation on Pt electrode resulted in negligible reduction of TOC removal. All dyes showed positive mutagenic activity in the Salmonella/microsome assay with the strain TA98 in the absence and presence of S9 (exogenous metabolic activation). Nevertheless, there is complete reduction of the mutagenic activity after 1 h of photoelectrocatalytic oxidation, suggesting that this process would be good option to remove disperse azo dyes from aqueous media. (C) 2008 Elsevier Ltd. All rights reserved.