Desenvolvimento e otimização de reatores com eletrodos tridimensionais para eletrogeração de H2O2

Orientador : Rodnei BertazzoliTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Este trabalho apresenta o estudo de um processo para a eletrogeração de peróxido de hidrogênio. Foram usadas duas configurações de reatores eletroquímicos com eletrodos tridimensionais tipo esponja, e o processo de eletrossíntese do composto oxidante foi otimizado com relação ao potencial aplicado, vazão do eletrólito, e uso de promotores de turbulência. Inicialmente, foi feito um estudo da cinética de dissolução de oxigênio nas soluções usadas como eletrólito suporte. O eletrólito suporte selecionado foi Na2S04 0,5 M, pH 10, onde observou-se uma velocidade de transferência de massa para a fase líquida (kL ae) de 0,0037 m-1 s. 1, correspondente a uma constante de velocidade de dissolução do oxigênIo de 0,116 !lmol L-I S-I. Devido à baixa solubilidade do oxigênio, o processo de eletrogeração de peróxido mostrou-se um processo controlado por transporte de massa com baixos valores de corrente limite. Para viabilizar o processo de eletrossíntese, utilizou-se eletrodos tridimensionais de carbono vítreo reticulado, que apresentou a vantagem de separar os processos de produção da água e do peróxido de hidrogênio em I V. O potencial de -1,3 V vs. Agi AgI mostrou-se como o mais indicado para a realização dos experimentos a potencial constante. A comparação do processo de geração de peróxido de hidrogênio em reatores eletroquímicos de fluxo paralelo e transversal mostrou que o primeiro apresentou uma maior eficiência. Porém, a introdução de diferentes tipos de promotores de turbulência mostrou-se bastante eficiente no aumento do coeficiente de transporte de massa para o reator de fluxo transversal para toda a faixa de velocidade avaliada. Nesse caso, observou-se um aumento de aproximadamente 20% na velocidade de produção de H202 e o reator de fluxo transversal passa a superar o reator de fluxo paralelo. A melhor configuração obtida para o reator de fluxo paralelo para a geração de peróxido de hidrogênio foi: a) potencial aplicado de -1,3 V vs. Agi AgI, b) distância anodo/catodo de 1,5 cm, c) velocidade linear do fluido de 9,3.10-3 m S-I, correspondente a uma vazão de 750 L h-I, e d) o emprego do promotor de turbulência tipo C. Nesta condição, o coeficiente de transporte de massa foi de 3,4.10-5 m S-I, a constante de velocidade de eletrogeração de peróxido de hidrogênio foi de 26 Jlg L-I S-I, o consumo energético de aproximadamente 5,0 kWh kg-I e a eficiência de corrente foi de 80 %. Para o reator de fluxo transversal, a condição ideal de operação foi: a) potencial aplicado de -1,3 V vs. Agi AgI, b) distância entre o anodo e catodo de 0,5 cm, c) velocidade linear do fluido de 6,79.10-2 m S-I, e d) o emprego do promotor de turbulência tipo B. Nesta condição, o coeficiente de transporte de massa foi superior a 5,0.10-5 m S-I, a constante de velocidade de eletrogeração de peróxido de hidrogênio foi de 40 Jlg L-I S-I, o consumo energético foi de 4,5 kWh kg-I e a eficiência de corrente, de 82%. Como experimentos finais, procedeu-se um estudo da degradação do corante reativo preto remazol. A comparação entre os reatores, nas condições otimizadas acima descritas, demonstrou um desempenho melhor para o reator de fluxo transversal, comprovado também pelos resultados obtidos no tratamento do corante preto remazol. Nesse caso obteve-se üma remoção superior a 90% da coloração no reator de fluxo transversal após 240 minutos de tratamento, atingindo níveis de absorbância abaixo do padrão permitido para descarte. O processo de descoloração na presença de radiação UV mostrou ser consideravelmente melhor que na ausência desta. Reduções de quase 100% da coloração do corante preto remazol foram alcançadas com 45 minutos de tratamento, com níveis de absorbância abaixo do permitidoAbstract: This work reports a study on a process for the electrogeneration of hydrogen peroxide. Two types of electrochemical reactors. using three-dimensional porous electrodes. with a reticulated structure. were used. In both systems the performance the reactors. during the hydrogen peroxide production was investigated. as a function of applied potential. flow rate and the use of different types of turbulence promoters. Initially. a kinetic study of oxygen dissolution in some aqueous solutions. which can be used as support electrolyte. Was carried out. A solution of 0.5M Na2 804. pH 10, was chosen as electrolyte. In this case, the rate constant for mass transfer to liquid phase (kL ae) was 0,0037 m-I S-I, which corresponds to a oxygen dissolution rate of 0.116 J.Ullol L-I S.I. In view of the low solubility of oxygen, the hydrogen peroxide electrogeneration process showed to be a mass transport controlled process which exhibits low values of limiting cürrents. Then, a threedimensional reticulated vitreous carbon electrode was used to become viable the oxygen electroredution processo Results showed that the hydrogen peroxide formation and its decomposition to water are separated by 1 V on the vitreous carbon surface. The potential of 1,3V vS. Agi AgI was the more appropriated potential for constant potential experiments. Hydrogen peroxide electrogeneration process was carried out for two reactor configurations: flow-through and flow-by. Mass transfer coefficients were greater for the flow hrough configuration than for the flow-by configuration. However, with an introduction of turbulence promoters, an increasing of the mass transport coefficient, for flow-by mo de, was observed. In this case, 20% increasing was observed and then the flow-by mode became more efficient than the flow-through mode. The characteristics of the best configuration for flow-through mode for the generation of hydrogen peroxide were: a) applied potential of -1,3 V vs. A/AgI, b) anode/cathode distance of 1,5 cm, c) linear velocity of 9,3 10-3 m S-I, which corresponds to flow rate of 750 L h-I, and d) the use of turbulence promoter of type C. In this condition, the mass transport efficient was 3,4 10-5 m S.I, the constant of hydrogen peroxide electrogeneration rate was 26 J.Lg L-I S.I, the energetic consumption was approximately 5,0 kWh kg-I and the current efficient was 80%. For the flow-by mode, the best operation condition were: a) applied potential of -1,3 V vs. A/AgI, b) anode/cathode distance of 0,5 cm, c) linear velocity of 6,79 10-2 m S-I, which corresponds to flow rate of 550 L h-I, and d) the use of turbulence promoter of type B. In this condition, the mass transport efficient was 5,0 10-5 m S.I, the constant of hydrogen peroxide electrogeneration rate was 40 J.Lg L-I S-I, the energetic consumption was approximately 4,5 kyvh kg-I and the current efficient was 82%. In a series of final experiments the efficiency of the cell reactors was followed during textile dye solution degradation. During the experiments using remazol black, at the optimized conditions, the flow-by configuration showed better performance. A textile dye degradation greater than 90% was observed for 240 min of treatment time. The discoloration process, when UV irradiation was used, showed to be considerably faster. In this case 100% of dye degradation was observed in 45 minutes. During these experiments, hydrogen peroxide remaining in the solution was also followed.DoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânic

Synthesis of self-organized nanostructured oxide for photocatalysis and photoelectrocatalysis application

Photocatalytic processes using self-organized TiO2 nanotubes semiconductor are considered together with the factors that affect the growth mechanism and formation of the nanotubes during the anodization of titanium. The chapter analyses the morphology of the nanotubes when they are modified with metals, oxides and wall decoration. Illustrated examples of the applications of TiO2 nanotubes in photocatalysis, photoelectrocatalysis, solar cells, semiconductors and biomedical areas are presented and the main characteristics required for these applications are highlighted.</p

Effect of W concentration in the organized Ti-W alloy oxide nanotubes array on the photoelectrocatalytic properties and its application in the removal of endocrine disruptors using real water matrix

To evaluate the tungsten content on the photoelectrocatalytic properties of self-organized nanotubes grown by anodization on Ti-xW (wt%) alloys, where x is 0.5, 2.5 or 5.0, this work investigated the phase transformation of TiO2, the tungsten oxidation states in the oxide layers and their photoelectrocatalytic performance in the degradation of estrone (E1) and 17α-ethinylestradiol (EE2). These films were employed in photocatalytic and photoelectrocatalytic removals of hormones from synthetic and real water matrices. In synthetic water, E1 and EE2 removals, reached efficiencies of 92% and 71%, respectively, after 2 min under UV–Vis photoelectrocatalysis using NT/Ti-5.0W as catalyst. About 30 times longer was needed to degrade 77% of both hormones from the real water matrix due to the presence of other high organic charge. The high performance of the NT/Ti-5.0W was associated with the combination of doping (W-doped TiO2) and WO3 (W6+) heterojunction. However, this electrode had its stability compromised under long degradation times, mainly under visible light, due to a WO3 leaching process. As for NT/Ti-0.5W, the substitutional W-doped TiO2 contributed to its greater stability and efficiency for a long time. The low performance of NT/Ti-2.5W was justified by high density of oxygen vacancy and unfavorable position of its adsorption bands

Synthesis and characterization of self-organized oxide layer grown on ti-cu alloys system for CO 2 reduction

Ti-Cu alloys could be used as a substrate to produce photoelectrode pn-heterojunctions to increase copper stability and consequently to improve photoconversion of CO2. Cu–Ti–O films were grown by anodizing directly of Ti–x%at.Cu (x= 0.5, 5.5, 10 and 50) and after these alloys were submitted different kinds heat treatment (annealing or quenching) to compare a directly influence of presents phases in nanotubes alloy substrate after it preparation by voltaic arc melting following a annealed or rapid quenching as heat treatment. All films presented TiO2 and copper dioxides in its compositions. These electrodes showed higher absorbance in visible light, anodic current for less copper alloy cathodic current equiatomic composition and copper stability for all cases due cu atomic insertion inside TiO2 crystal lattice and sharing oxygen atomic. The cathodic current varied in function of Cu concentration in the alloy8974551COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES001The authors thank Coordenação de Aperfeiçoamento Pessoal de Nível Superior Brasil (CAPES) – Finance Code 001 for financial support. The authors acknowledge the support of LNNano - Brazilian Nanotechnology National Laboratory, CNPEM for SEM-FEG and XPS characterizatio

Array of electrodeposited Ru-decorated TiO2 nanotubes with enhanced photoresponse

Although TiO2 anatase phase has been widely chosen as the main photocatalyst, it presents high electron/hole recombination rate. However, today, what is sought is a semiconductor material with enhanced photocatalytic activity with higher photon to electron conversion efficiency by introduction of electrons trap dopants. In this paper, TiO2 nanotubes arrays obtained by anodization of Ti substrates were decorated with Ru via electrodeposition, and their photo-response was investigated. First, voltammetric experiments were performed to elucidate the route of Ru reduction on the TiO2 surface and to select the range of potentials for Ru deposition. The reduction potentials were used for controlling the amount of Ru distributed all over the surface. Although Ru was electrodeposited at potentials over the range from − 0.025 to − 0.188 V vs. Ag/AgCl, the deposition of 3.7 mC cm−2 at − 0.100 V for 30 min resulted in a tenfold greater photocurrent when compared to the recorded photocurrent for the undecorated TiO2 nanotubes array. Next, Ru-decorated TiO2 nanotubes with a length of 323 ± 18 nm and inner and outer diameters of 91 and 104 nm, respectively, were characterized using SEM-WDS, SEM-FEG, XRD, and XPS. UV-Vis-NIR diffuse reflectance spectroscopy and photoluminescence (PL) measurements, which revealed a maximum PL emission at 445 nm, showed that for the array of Ru-decorated TiO2 nanotubes, the electron-hole recombination may be effectively inhibited by the presence of ruthenium electrodeposited, which can make this photocatalyst even more attractive for environmental applications. The performances of the TiO2 and Ru-decorated TiO2 catalysts were compared in heterogeneous photocatalysis experiments for color removal of an azo-dye, which presented a pseudo-first-order rate constant more than twofold greater for the Ru-decorated TiO2 catalysts22824452455FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP06/61261-2The authors thank FAPESP - Fundação de Amparo à Pesquisa do Estado de São Paulo (Process Number 06/61261-2) for financial support. The authors acknowledge the support of LNNano - Brazilian Nanotechnology National Laboratory, CNPEM/MCTI for MEV-FEG and XPS characterization, IQ-Unesp/Araraquara for the UV-Vis diffuse reflectance spectroscopy (DRS) experiments and Prof. Máximo Siu Lic for the photoluminescence analyse

Photoelectrocatalytic oxidation of methyl orange on TiO2 nanotubular anode using a flow-cell

Methyl orange from water was removed by photocatalytic anodic oxidation method using a titanium dioxide array surface. The coating was prepared by anodising a titanium plate using NH4F as electrolyte followed by heat treatment to render a photocatalytic surface under UV light. SEM imaging showed that the array coating consisted of closely spaced 1 µm long, 0.1 µm internal diameter tubes perpendicular to the titanium plate. The aqueous solution of methyl orange was circulated through a rectangular channel flow cell containing the coated anode and the effect of electrolyte flow rate and applied potential on the oxidation rate and efficiency were evaluated. At higher mean linear flow rates, the efficiency of the oxidation process improved, indicating a mass transport controlled process. At more positive applied potentials the TiO2 structure deteriorated resulted in lower oxidation efficiency