Detecção e quantificação eletroquímica de substâncias de interesse clínico, ambiental e forense utilizando eletrodo de pasta de grafite modificado com trisilanol poss ligado a suportes porosos e eletrodos impressos obtidos via screen-printed

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Determinação de açucares em bagaço de palha de cana-de-açúcar por cromatografia líquida de alta eficiência com detecção eletroquímica utilizando eletrodos de nanotubos modificados com óxidos metálicos

Pós-graduação em Química - IQ

INVESTIGAÇÃO ELETROQUÍMICA E CALORIMÉTRICA DA INTERAÇÃO DE NOVOS AGENTES ANTITUMORAIS BISCATIÔNICOS COM DNA

ELECTROCHEMICAL AND CALORIMETRIC INVESTIGATION OF INTERACTION OF NOVEL BISCATIONIC ANTICANCER AGENTS WITH DNA. Biscationic amidines bind in the DNA minor groove and present biological activity against a range of infectious diseases. Two new biscationic compounds (bis-alpha,omega-S-thioureido, amino and sulfide analogues) were synthesized in good yields and fully characterized, and their interaction with DNA was also investigated. Isothermal titration calorimetry (ITC) was used to measure the thermodynamic properties of binding interactions between DNA and these ligands. A double stranded calf thymus DNA immobilized on an electrode surface was used to study the possible DNA-interacting abilities of these compounds towards dsDNA in situ. A remarkable interaction of these compounds with DNA was demonstrated and their potential application as anticancer agents was furthered.

Investigação eletroquímica e calorimétrica da interação de novos agentes antitumorais biscatiônicos com DNA

Biscationic amidines bind in the DNA minor groove and present biological activity against a range of infectious diseases. Two new biscationic compounds (bis-α,ω-S-thioureido, amino and sulfide analogues) were synthesized in good yields and fully characterized, and their interaction with DNA was also investigated. Isothermal titration calorimetry (ITC) was used to measure the thermodynamic properties of binding interactions between DNA and these ligands. A double stranded calf thymus DNA immobilized on an electrode surface was used to study the possible DNA-interacting abilities of these compounds towards dsDNA in situ. A remarkable interaction of these compounds with DNA was demonstrated and their potential application as anticancer agents was furthered.

Oxidação eletroquímica do herbicida tebutiuron utilizando eletrodo do tipo DSA

Tebuthiuron (TBH) is a herbicide widely used in different cultures and known for its toxic effects. Electrochemical methods are promising for removing pollutants such as pesticides. This study showed the degradation of TBH using a DSA® anode operated at current densities of 50 to 200 mA cm-2. Removal presented pseudo-first order kinetics while high-pressure liquid chromatography (UV detection) showed two peaks, ascribed to degradation intermediates. The maximum percentage of total organic carbon removed was 12.9%. Ion chromatography revealed that higher concentrations of nitrate and nitrite ions formed with increasing current density.

Desenvolvimento de microssensores eletroquímicos e aplicações no estudo de processos dinâmicos interfaciais utilizando microscopia eletroquímica de varredura

O trabalho descrito nesta tese mostra de forma detalhada a fabricação e caracterização de diferentes microssensores eletroquímicos os quais têm sido recentemente utilizados como sondas em grupo de técnicas conhecida como Scanning Electrochemical Probe Microscopy (SEPM). Desta forma, a caracterização de superfícies pode ser feita explorando diferentes fenômenos interfaciais relevantes à Ciência. Neste sentido, as interfaces de materiais cristalinos como hidroxiapatita (materiais dentários) e calcita foram o foco de estudo neste trabalho. Assim, diferentes técnicas SEPM foram exploradas no sentido de se obter informações relevantes relacionadas aos processos dentários, como a erosão ácida e hipersensibilidade. Inicialmente, microeletrodos de platina foram desenvolvidos empregando uma metodologia convencional na qual são utilizados microfibras encapsuladas em capilares de vidro. Scanning Electrochemical Microscopy (SECM) no modo amperométrico foi utilizada para obtenção de informações com relação às alterações de topografia do esmalte dentário causadas pelo contato com substâncias ácidas. Adicionalmente, SECM foi empregada no estudo do transporte de espécies eletroativas em amostras de dentina e investigações relacionadas ao bloqueio dos túbulos empregando-se cremes dentais comerciais foram realizadas. A permeação de peróxido de hidrogênio pela dentina também foi estudada. Os resultados de SECM foram comparados com imagens SEM obtidas nas mesmas condições experimentais. Microeletrodos de membrana ionófora íon-seletiva (Ion Selective Microelectrodes-ISMEs) sensíveis a íons cálcio também foram desenvolvidos e caracterizados, com subsequente aplicação em SECM no modo potenciométrico. A dissolução ácida de esmalte bovino (erosão dentária) foi investigada em diferentes valores de pH (2,5; 4,5; 6,8). Além disso, o transporte de íons cálcio através de membranas porosas sintéticas foi avaliado a uma distância tip/substrato de 300µm. Alterações no fluxo de íons cálcio foram correlacionadas em experimentos realizados na presença e ausência de campos magnéticos gerados por nanopartículas de magnetita incorporadas à membrana porosa. Microcristais de calcita facilmente sintetizados pelo método de precipitação foram utilizados como superfície modelo para investigações interfaciais, cujos resultados podem ser correlacionados aos materiais dentários. Desta forma, nanopipetas de vidro preenchidas com eletrólito suporte foram fabricadas e utilizadas como sonda em Scanning Ion Conductance Microscopy (SICM). O mapeamento topográfico de alta resolução espacial da superfície de um microcristal de calcita foi obtido utilizando o modo de varredura hopping mode. Adicionalmente, sondas multifuncionais ISME-SICM também foram desenvolvidas e caracterizadas para investigações simultâneas com relação às alterações topográficas e quantificação de íons cálcio sobre a superfície de um microcristal de calcita. A adição de reagentes ácidos no canal SICM promoveu a dissolução da superfície do microcristal, sendo obtidos dados cinéticos de dissolução. Investigações em meio neutro também foram realizadas utilizando a sonda ISME-SICM. Os resultados experimentais obtidos também foram comparados com aqueles oriundos de simulação computacional.

Síntese de óxidos metálicos binários suportados em carbono amorfo (printex 6L) para a produção eletroquímica de peróxido de hidrogênio (H2O2)

O presente trabalho visa o estudo da eletrossíntese de H2O2 a partir da reação de redução de oxigênio (RRO) utilizando carbono Printex 6L modificado com óxidos binários compostos de nióbio, molibdênio e paládio, síntetizados pelo método dos precursores poliméricos. A análise dos materiais preparados foi feita a partir de experimentos de análise termogravimétrica (do inglês, TGA), fluorescência de raios X (FRX) e também de difração de raios X (DRX). As temperaturas de síntese foram escolhidas a partir dos resultados de TGA e tendo como temperatura máxima de 400 °C. As análises dos espectros de emissão de FRX mostraram a eficiência na incorporação dos materiais na matriz de carbono. Experimentos de DRX mostraram a presença de fases cristalinas de MoO2 e Nb2 O5 e PdO, e em comparação aos resultados da técnica de voltametria cíclica, existem pares redox que podem ser associados as transições dos metais nos estados de oxidação de +4 e +5, para molibdênio e nióbio, respectivamente e do estado +2 para o paládio. Nos experimentos de voltametria de varredura linear pode-se observar a tendência de maior geração de H2O2 pelo material com teor de 1% NbMo quando comparado com o carbono Printex 6L, de modo que foram calculadas as eficiências de geração de H2O2 , obtendo um resultado de 55,5% para o modificador de 1% NbMo comparado com 47,4% para o Printex 6L, e também de número de elétrons envolvidos na reação com um valor de 2,9 para o material de 1% e 3,1 para o carbono Printex. As análises das curvas de Koutechy-Levich confirmam os resultados anteriores. Análises em condições reduzidas na síntese orgânica corroboraram a melhor eficiência do material de 1% para o material com nióbio e molibdênio e revelaram a também a melhora eletrocatalítica do carbono quando incorporado com óxidos mistos de nióbio e paládio, sendo o melhor resultado expresso no material contendo 5% de nióbio e paládio, na proporção molar de 95 para 5% de cada elemento, respectivamente.

Oxidação eletroquímica de etanol em temperatura ambiente e intermediária: estudo quantitativo das vias reacionais por espectrometria de massas on-line

Na primeira parte do trabalho, foram investigados materiais ativos para eletro-oxidar etanol e acetaldeído seletivos para a rota C2 (Carbono 2) e, também, ativos para eletro-oxidar hidrogênio molecular, visando a aplicação em células a combustível de hidrogênio indireto. Neste tipo de célula, um processador de combustível externo desidrogena o etanol e os produtos desta reação, contendo H2, acetaldeído e, possivelmente, etanol residual, são direcionados para alimentar o ânodo. Neste sentido, o eletrocatalisador anódico pode ser ativo para a eletro-oxidação de etanol residual, bem como acetaldeído, mas este deve catalisar a reação via C2 com o objetivo de evitar a formação de espécies que envenenam a superfície catalítica (CO ou CHx), ou seja, a ligação C-C deve permanecer intacta. Os eletrocatalisadores bimetálicos foram formados por M/Pt/C (onde M = W, Ru ou Sn) e os produtos reacionais foram analisados por DEMS On-line. Os resultados mostraram que Ru/Pt/C e Sn/Pt/C apresentaram maiores taxas de reação global, no entanto, eles não foram seletivos. Por outro lado, W2/Pt3/C foi mais seletivo para a rota C2, dada a não formação de CH4 e CO2. Além disso, este material também foi ativo e estável para a eletro-oxidação de H2, mesmo na presença de acetaldeído, o que o torna um potencial catalisador para aplicação no ânodo de células a combustível de hidrogênio indireto. Na segunda parte do trabalho, o objetivo foi relacionado com o estudo de eletrocatalisadores seletivos para a rota C1 (Carbono 1). A oxidação eletroquímica do etanol e de seus produtos reacionais foram investigados por DEMS on-line em temperatura ambiente e intermediária (245oC). Para temperatura ambiente, utilizou-se solução aquosa de ácido sulfúrico (H2SO4) e, para temperatura intermediária, utilizou-se ácido sólido (CsH2PO4) como eletrólito. Os eletrocatalisadores investigados foram formados por SnOxRuOx-Pt/C e Pt/C. Em temperatura ambiente, os resultados de polarização potenciodinâmica mostraram uma maior atividade eletrocatalítica para o material SnOxRuOx-Pt/C, com eficiência de corrente para formação de CO2 de 15,6% contra 15,2% para Pt/C, sob condições estagnantes, sem controle por transporte de massa. O stripping de resíduos reacionais, após a eletro-oxidação de etanol bulk, sob condições de fluxo, mostraram o acúmulo de espécies com 1 átomo de carbono (CO e CHx) que causam o bloqueio dos sítios ativos e são oxidadas eletroquimicamente somente em mais altos potenciais (ca. 1,0 V). Por outro lado, as curvas de polarização a 245oC mostraram maiores valores de eficiências de correntes para formação de CO2 (45% para Pt/C em ambos potenciais 0,5 V e 0,8 V contra 36% e 50% para SnOxRuOx-Pt/C em 0,5 V e 0,8 V respectivamente) quando comparado com os valores obtidos em temperatura ambiente, mas com atividades similares para SnOxRuOx-Pt/C e Pt/C. Para ambos os eletrocatalisadores, os estudos de espectrometria de massas a 245oC evidenciaram que as rotas eletroquímicas ocorrem em paralelo com rotas puramente químicas, envolvendo catálise heterogênea, de decomposição do etanol, produzindo H2 e CO2 como produtos majoritários.

Estudo da participação das espécies fortemente oxidantes produzidas durante a oxidação eletroquímica de corantes usando eletrodo de diamante dopado com boro: função das propriedades eletroquímicas do eletrodo e condições experimentais

The textile industry is one of the most polluting in the world (AHMEDCHEKKAT et al. 2011), generating wastewater with high organic loading. Among the pollutants present in these effluents are dyes, substances with complex structures, toxic and carcinogenic characteristics, besides having a strong staining. Improper disposal of these substances to the environment, without performing a pre-treatment can cause major environmental impacts. The objective this thesis to use a technique of electrochemical oxidation of boron doped diamond anode, BDD, for the treatment of a synthetic dye and a textile real effluent. In addition to studying the behavior of different electrolytes (HClO4, H3PO4, NaCl and Na2SO4) and current densities (15, 60, 90 and 120 mA.cm-2 ), and compare the methods with Rhodamine B (RhB) photolysis, electrolysis and photoelectrocatalytic using H3PO4 and Na2SO4. Electrochemical oxidation studies were performed in different ratio sp3 /sp2 of BDD with solution of RhB. To achieve these objectives, analysis of pH, conductivity, UV-visible, TOC, HPLC and GC-MS were developed. Based on the results with the Rhodamine B, it was observed that in all cases occurred at mineralization, independent of electrolyte and current density, but these parameters affect the speed and efficiency of mineralization. The radiation of light was favorable during the electrolysis of RhB with phosphate and sulfate. Regarding the oxidation in BDD anode with different ratio sp3 /sp2 (165, 176, 206, 220, 262 e 329), with lower carbon-sp3 had a longer favoring the electrochemical conversion of RhB, instead of combustion. The greater the carbon content on the anodes BDD took the biggest favor of direct electrochemical oxidation

Aplicação da tecnologia eletroquímica para a remoção e monitoramento de metais pesados em efluentes aquosos

Heavy metals are present in industrial waste. These metals can generate a large environmental impact contaminating water, soil and plants. The chemical action of heavy metals has attracted environmental interest. In this context, this study aimed to test t he performance of electrochemical technologies for removing and quantifying heavy metals. First ly , the electroanalytical technique of stripping voltammetry with glassy carbon electrode (GC) was standardized in order to use this method for the quantificatio n of metals during their removal by electrocoagulation process (EC). A nalytical curves were evaluated to obtain reliability of the determin ation and quantification of Cd 2+ and Pb 2+ separately or in a mixture. Meanwhile , EC process was developed using an el ectrochemical cell in a continuous flow (EFC) for removing Pb 2+ and Cd 2+ . The se experiments were performed using Al parallel plates with 10 cm of diameter (  63.5 cm 2 ) . The optimization of conditions for removing Pb 2+ and Cd 2+ , dissolved in 2 L of solution at 151 L h - 1 , were studied by applying different values of current for 30 min. Cd 2+ and Pb 2+ concentrations were monitored during electrolysis using stripping voltammetry. The results showed that the removal of Pb 2 + was effective when the EC pro cess is used, obtaining removals of 98% in 30 min. This behavior is dependent on the applied current, which implies an increase in power consumption. From the results also verified that the stripping voltammetry technique is quite reliable deter mining Pb 2+ concentration , when compared with the measurements obtained by atomic absorption method (AA). In view of this, t he second objective of this study was to evaluate the removal of Cd 2+ and Pb 2+ (mixture solution) by EC . Removal efficiency increasing current was confirmed when 93% and 100% of Cd 2+ and Pb 2+ was removed after 30 min . The increase in the current promotes the oxidation of sacrificial electrodes, and consequently increased amount of coagulant, which influences the removal of heavy metals in solution. Adsortive voltammetry is a fast, reliable, economical and simple way to determine Cd 2+ and Pb 2+ during their removal. I t is more economical than those normally used, which require the use of toxic and expensive reagents. Our results demonstrated the potential use of electroanalytical techniques to monitor the course of environmental interventions. Thus, the application of the two techniques associated can be a reliable way to monitor environmental impacts due to the pollution of aquatic ecosystems by heavy metals.

Tecnologia eletroquímica como tratamento alternativo de efluentes derivados da indústria têxtil e petroquímica

In this work, the treatment of wastewater from the textile industry, containing dyes as Yellow Novacron (YN), Red Remazol BR (RRB) and Blue Novacron CD (NB), and also, the treatment of wastewater from petrochemical industry (produced water) were investigated by anodic oxidation (OA) with platinum anodes supported on titanium (Ti/Pt) and boron-doped diamond (DDB). Definitely, one of the main parameters of this kind of treatment is the type of electrocatalytic material used, since the mechanisms and products of some anodic reactions depend on it. The OA of synthetic effluents containing with RRB, NB and YN were investigated in order to find the best conditions for the removal of color and organic content of the dye. According to the experimental results, the process of OA is suitable for decolorization of wastewaters containing these textile dyes due to electrocatalytic properties of DDB and Pt anodes. Removal of the organic load was more efficient at DDB, in all cases; where the dyes were degraded to aliphatic carboxylic acids at the end of the electrolysis. Energy requirements for the removal of color during OA of solutions of RRB, NB and YN depends mainly on the operating conditions, for example, RRB passes of 3.30 kWh m-3 at 20 mA cm-2 for 4.28 kWh m-3 at 60 mA cm-2 (pH = 1); 15.23 kWh m-3 at 20 mA cm-2 to 24.75 kWh m-3 at 60 mA cm-2 (pH 4.5); 10.80 kWh m-3 at 20 mA cm-2 to 31.5 kWh m-3 at 60 mA cm-2 (pH = 8) (estimated data for volume of treated effluent). On the other hand, in the study of OA of produced water effluent generated by petrochemical industry, galvanostatic electrolysis using DDB led to the complete removal of COD (98%), due to large amounts of hydroxyl radicals and peroxodisulphates generated from the oxidation of water and sulfates in solution, respectively. Thus, the rate of COD removal increases with increasing applied current density (15-60 mAcm-2 ). Moreover, at Pt electrode, approximately 50% removal of the organic load was achieved by applying from 15 to 30 mAcm-2 while 80% of COD removal was achieved for 60 mAcm-2 . Thus, the results obtained in the application of this technology were satisfactory depending on the electrocatalytic materials and operating conditions used for removal of organic load (petrochemical and textile effluents) as well as for the removal of color (in the case of textile effluents). Therefore, the applicability of electrochemical treatment can be considered as a new alternative like pretreatment or treatment of effluents derived from textiles and petrochemical industries.

Estudo da eficiência eletroquímica para tratamento de chorume gerado em aterro sanitário brasileiro

This work was performing effluent degradation studies by electrochemical treatment. The electrochemical oxidation (EO) hydroquinone (H2Q) was carried out in acid medium, using PbO2 electrode by galvanostatic electrolysis, applying current densities of 10 and 30 mA/cm2 . The concentration of H2Q was monitored by differential pulse voltammetry (DPV). The experimental results showed that the galvanostatic electrolysis process performance significantly depends on the applied current density, achieving removal efficiencies of 100% and 80 % and 10 applying 30 mA/cm2 , respectively. Furthermore, the electroanalytical technique was effective in H2Q be used as a detection method. In order to test the efficiency of PbO2 electrode, the electrochemical treatment was conducted in an actual effluent, leachate from a landfill. The liquid waste leachate (600ml effluent) was treated in a batch electrochemical cell, with or without addition of NaCl by applying 7 mA/cm2 . The efficiency of EO was assessed against the removal of thermo-tolerant coliforms, total organic carbon (TOC), total phosphorus and metals (copper, cobalt, chromium, iron and nickel). These results showed that efficient removal of coliforms was obtained (100%), and was further decrease the concentration of heavy metals by the cathode processes. However, results were not satisfactory TOC, achieving low total removal of dissolved organic load. Because it is considered an effluent complex were developed other tests with this effluent to monitor a larger number of decontamination parameters (Turbidity, Total Solids, Color, Conductivity, Total Organic Carbon (TOC) and metals (barium, chromium, lithium, manganese and Zinc), comparing the efficiency of this type of electrochemical treatment (EO or electrocoagulation) using a flow cell. In this assay was compared to electro streaming. In the case of the OE, Ti/IrO2-TaO5 was used as the anode, however, the electrocoagulation process, aluminum electrodes were used; applying current densities of 10, 20 and 30 mA/cm2 in the presence and absence of NaCl as an electrolyte. The results showed that EO using Ti/IrO2–TaO5 was anode as efficient when Cl- was present in the effluent. In contrast, the electrocoagulation flow reduces the dissolved organic matter in the effluent, under certain experimental conditions.

Aplicação da oxidação eletroquímica no tratamento de efluentes contendo corantes reativos utilizando Ti/Pt e Ti/Pt-SnSb

The textile effluents are a complex mixture of many pollutants that contain high organic loads, severe color and toxic compounds. The high concentration of the textile effluent may cause increased chemical demand (COD) and biochemical (BOD) of oxygen, elevated temperature, acidity or alkalinity, causing damage and environmental problems. In addition to representing a serious threat to human health such effluent is also quite toxic to most aquatic organisms. And for this reason, one must meet the concentration limits for emission sources and sewage system. This study aimed to investigate the performance of electrochemical treatment of a textile effluent for the removal of color, turbidity, dissolved oxygen (DO) and dissolved organic matter by investigating the influence of experimental parameters such as the electrocatalyst materials (Ti/Pt and Ti/Pt-SnSb) and current density in order to compare their efficiency, energy consumption and cost. The dye Novacron Blue CD (NB) was employed in synthetic solution, while the dyes Remazol Yellow 3RS (RY 3RS) Remazol Red RR Gran (RR-RR Gran) and Navy Blue CL-R (NB CL-R) were used to generate simulated textile effluent laboratory. The results showed that the application of electrochemical oxidation process favors the elimination of color effectively independent the electrocatalytic material and current used, as well as treated effluent. However, the influence of electrocatalytic material was crucial to reduction of the organic matter in all cases.

Estudo da produção eletroquímica de espécies de cloro ativo para tratamento de efluentes sintéticos

The treatment of wastewater is essential to human health. One of the most important steps is the disinfection treatment which uses chlorine to eliminate bacteria as required by environmental agencies. However, the identification of potentially toxic byproducts generated by this method, such as trihalomethanes, has stimulated the development of new alternative disinfection technologies. Among them, heterogeneous photocatalysis, TiO2 photocatalysis and electrochemical disinfection are considered suitable alternatives to the chlorination method. Thus, the present dissertation analyzes the evolution of active chlorine species in a synthetic NaCl solution and it is tested to treat a synthetic solution of the dye Reactive Blue 19 using boron-doped diamond (BDD) and ruthenium oxide (Ti/Ru0.3Ti0.7O2) as anodes. The indirect electrochemical process was discussed in terms of mineralization of the total organic load and percentage of color removal in order to evaluate the applicability of electrochemical technology. Electrochemical experiments were carried out with different current densities (25, 50 and 75 mA.cm-2) during 120 minutes. On the other hand, other important parameter in this study was the influence of the proportion sp3/sp2 on BDD anode on the performance of the evolution of active chlorine species which was investigated by electrolytic techniques (linear polarization), with the intention of determining the related training oxidizing species and consumption energy to chemical or electrochemical reactions. From the results, it can be noted that the BDD electrode showed better efficiency throughout the electrochemical process.

Estudo da produção eletroquímica de espécies de cloro ativo para tratamento de efluentes sintéticos

The treatment of wastewater is essential to human health. One of the most important steps is the disinfection treatment which uses chlorine to eliminate bacteria as required by environmental agencies. However, the identification of potentially toxic byproducts generated by this method, such as trihalomethanes, has stimulated the development of new alternative disinfection technologies. Among them, heterogeneous photocatalysis, TiO2 photocatalysis and electrochemical disinfection are considered suitable alternatives to the chlorination method. Thus, the present dissertation analyzes the evolution of active chlorine species in a synthetic NaCl solution and it is tested to treat a synthetic solution of the dye Reactive Blue 19 using boron-doped diamond (BDD) and ruthenium oxide (Ti/Ru0.3Ti0.7O2) as anodes. The indirect electrochemical process was discussed in terms of mineralization of the total organic load and percentage of color removal in order to evaluate the applicability of electrochemical technology. Electrochemical experiments were carried out with different current densities (25, 50 and 75 mA.cm-2) during 120 minutes. On the other hand, other important parameter in this study was the influence of the proportion sp3/sp2 on BDD anode on the performance of the evolution of active chlorine species which was investigated by electrolytic techniques (linear polarization), with the intention of determining the related training oxidizing species and consumption energy to chemical or electrochemical reactions. From the results, it can be noted that the BDD electrode showed better efficiency throughout the electrochemical process.