Biotecnología ambiental

The various industrial sectors, as well as livestock and agricultural activities, are increasing the production of inputs to meet the demand of the worldwide demographic explosion, making a challenge the clean maintenance of water, soil, and air. Therefore, the search for solutions for a pollutant-free environment without compromising economic development has become extremely important. Thereby, biotechnological studies in order to solve environmental issues have been gaining extensive attention through the coupling of technology procedures to biological systems as sustainable solutions to remediate contaminated areas. In this sense, this review covers topics such as the role of Omics era in microbial environmental biotechnology for pollution control as well as the microbial fuel cell use in energy production. Moreover, phytoremediation and the perspective of applying chemical methods are approached as environmentally friendly tools for the pollutant control to improve remediation processes.Los diversos sectores industriales, así como las actividades ganaderas y agrícolas, están aumentando la producción de insumos para satisfacer la demanda de la explosión demográfica mundial, lo cual dificulta el mantenimiento limpio del agua, el suelo y el aire. Por lo tanto, la búsqueda de soluciones para un medio ambiente libre de contaminantes sin comprometer el desarrollo económico se ha vuelto extremadamente importante. De este modo, los estudios biotecnológicos para resolver problemas ambientales han recibido una gran atención a través del acoplamiento de procedimientos tecnológicos a sistemas biológicos como soluciones sostenibles para remediar áreas contaminadas. En este sentido, esta revisión cubre temas como el papel de la era Ómica en la biotecnología ambiental microbiana para el control de la contaminación, así como el uso de celdas de combustible microbianas en la producción de energía. Además, la fitorremediación y la perspectiva de aplicar métodos químicos se abordan como herramientas ecológicas para el control de contaminantes y mejorar los procesos de remediación

Pt–Sn/C catalysts prepared by sodium borohydride reduction for alcohol oxidation in fuel cells: Effect of the precursor addition order

A series of Pt–Sn/C catalysts used as anodes during ethanol oxidation are synthesized by a deposition process using NaBH4 as the reducing agent. The order in which the precursors are added affects the electrocatalytic activity and physical-chemical characteristics of the bimetallic catalysts, where the Pt–Sn catalyst prepared by co-precipitation of both metals functions best below a potential of 0.5 V and the catalyst prepared by sequential deposition of Sn and Pt (drying after Sn addition) is most active above a potential of 0.5 V. The electrochemical behavior of catalysts during ethanol oxidation in an acidic medium are characterized and monitored in a half-cell test at room temperature by cyclic voltammetry, chronoamperometry and anode potentiostatic polarization. Catalyst structure and chemical composition are investigated by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This behavior presented for best Pt–Sn catalyst can be attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn.The authors thank the Brazilian National Council of Technological and Scientific Development-CNPq (grants: 303630/2012-4, 402243/2012-9 and 310282/2013-6) for the scholarships and financial support for this work

Desenvolvimento de catalisadores para oxidação de glicerol

As células a combustível a etanol direto são amplamente estudadas e consideradas fontes de energia possíveis para aplicações em aparelhos portáteis e veículos em futuros próximos. Além de ser considerado um combustível verde, o etanol é mais seguro e tem maior densidade de energia quando comparado ao metanol e até mesmo outros tipos de combustíveis, sendo considerado um combustível potencial para células a combustível que operam a baixas temperaturas, este apresenta uma oxidação que envolve 12 elétrons por molécula oxidada, onde muitos intermediários adsorvidos e subprodutos são produzidos durante todo processo. Não esquecendo de destacar a difícil clivagem da ligação C-C à baixas temperaturas (< 100° C). Portanto, a urgência em desenvolver catalisadores com alta atividade eletrolítica para oxidação de etanol e glicerol, torne-se o ponto de partida para as pesquisas atualmente.

Methanol Electro-Oxidation on Carbon-Supported PtRu Nanowires

One of the key objectives in fuel cell technology is to improve the alcohol oxidation efficiency of Pt-based catalysts. A series of carbon-supported PtRu nanowires with different concentrations of Pt and Ru were prepared for application in methanol oxidation in acid media. The physicochemical properties and electrocatalytic activity of these catalysts during methanol oxidation are function on their structure, morphology and composition. A Pt60Ru40/C catalyst shows the best behaviour towards methanol electro-oxidation allowing decrease the onset potential approximately 0.2 V respect to others PtRu/C synthesised nanowires. The structural modification of Pt by Ru and synergetic character of RuPt are main factors that could contribute to reduction of energy necessary for electro-oxidation process. The Pt and PtRu nanowires have different sizes and distribution on the substrate. The average crystallite sizes, found by XRD, are in the 4.6–5.9 nm range and the lattice parameter is between 0.3903–0.3908 nm. Small differences with the values of the Pt/C catalyst were found. The XPS results show a prevailing presence of metallic Pt and Ru4+ species.The authors thank to CNPq (grants: 304419/2015-0, 402243/2012-9, 400443/2013-9, 407274/2013-8 and 310282/2013-6), CAPES and FAPITEC for the scholarships and financial support

Aminopropyltriethoxysilane functionalized MCM-41 and SBA-15 nanostructured materials for carbon dioxide adsorption

The design of effective CO2 capture materials is a current challenge. Here, we report the synthesis of aminosilanes-functionalized MCM-41 and SBA-15 materials with high efficiency toward carbon dioxide adsorption. The functionalization of the mesoporous silicas involves a post-synthesis method by impregnation with 3-aminopropyltriethoxysilane. The carbon dioxide adsorption capacities for the samples were carried out under ambient pressures. The results evidenced that aminosilanes with a terminal amine were functionalized through covalent coupling of this group onto the channels' surface in the ordered mesoporous silica. It means that the amine is anchored on the surface of the largest pores of the MCM-41 and SBA-15 supports. The Lagergren kinetic model evidenced the enhanced carbon dioxide adsorption capacity and stability of the functionalized ordered mesoporous molecular sieves.Keywords: 3-Aminopropyltriethoxysilane; Carbon dioxide; Functionalization; MCM-41; SBA-15.

\"Studies of boron-doped diamond eletrochemistry and of their surface modified with catalyst ofr the methanol and ethanol oxidation\"

Este trabalho mostra estudos das propriedades eletroquímicas do eletrodo de diamante dopado com boro (DDB) e descreve a utilização de eletrodos de DDB, modificados direta ou indiretamente pelo método Sol-gel, para a oxidação de metanol e de etanol em meio ácido. Do estudo das propriedades superficiais do diamante concluiu-se que a polarização catódica é bastante apropriada para um bom desempenho do material é que não introduz diferenças estruturais detectáveis no filme de DDB, indicando que a melhora na resposta eletroquímica é devida somente a mudanças superficiais. Entretanto, polarizações catódicas consecutivas e extensivas por longos períodos de tempo produzem uma erosão da superfície do eletrodo. Adicionalmente, estudos realizados usando voltametria cíclica e espectroscopia fotoeletrônica de raios X, mostraram que a superfície de eletrodos de DDB pré-tratados catodicamente tem um comportamento eletroquímico dinâmico, apresentando uma perda da reversibilidade para o sistema Fe(CN)63-/4- em função do tempo de exposição ao ar. Isto é devido, possivelmente, à perda de hidrogênio superficial decorrente da oxidação da superfície do eletrodo pelo oxigênio do ar. Este comportamento dinâmico da superfície do DDB é inversamente dependente ao teor de boro do eletrodo. Foi observado também que a quantidade de sítios ativos disponíveis na superfície do eletrodo é diretamente proporcional à dopagem do mesmo e deve ser conseqüência da quantidade de boro superficial. Desses estudos concluiu-se que todos os eletrodos de DDB com distintas dopagens usados nesta tese (300, 800, 2000 e 8000 ppm de B) apresentam uma superfície eletroquímica heterogênea (sítios ricos em boro que apresentariam uma alta condutividade e sítios de diamante com terminação hidrogênio com menor condutividade), quando polarizados catodicamente e parcialmente bloqueada (diamante com terminações oxigênio) quando polarizados anodicamente, formando arranjos de microeletrodos (provavelmente sítios ricos em boro). As superfícies do diamante foram modificadas diretamente com Pt, Pt-RuO2 e Pt-RuO2-RhO2 pelo método Sol-gel. Estes depósitos de catalisadores apresentavam tamanhos nanométricos e mostraram um bom contato elétrico com a superfície do diamante e elevada pureza, assim como, uma composição atômica bem controlada e uma distribuição homogênea na superfície do DDB. Os estudos da oxidação eletroquímica de metanol e de etanol sugerem fortemente que o envenenamento da superfície do eletrodo é grandemente inibido sobre o catalisador ternário Pt-RuO2-RhO2/DDB quando comparado com os eletrodos Pt-RuO2/DDB e Pt/DDB. Adicionalmente, esse eletrodo mostra uma excelente atividade catalítica para a oxidação de etanol, provavelmente devido à habilidade que o ródio tem para quebrar a ligação C-C somada ao mecanismo bifuncional que acontece no catalisador contendo Pt e Ru. Em seguida, realizaram-se modificações indiretas do DDB pela síntese de compósitos de pó de carbono modificados com metais e óxidos metálicos e posterior fixação usando uma solução de Nafion. A oxidação dos álcoois foi estudada por voltametria cíclica e curvas de polarização em estado estacionário (diagramas de Tafel). Os sistemas investigados incluíram misturas metálicas binárias, ternárias e quaternárias contendo Pt, Ru, Ir, Rh, PbOx, TaOx e MoOx num total de 16 sistemas diferentes. Assim, os melhores catalisadores para a oxidação de metanol foram: Pt-Ru-TaOx-PbOx > Pt-Ru-TaOx-MoOx ≈ Pt-Ru-MoOx-Ir enquanto que, para a oxidação de etanol foram Pt-Ru-TaOx-PbOx e Pt-Ru-PbOx-Rh. Consequentemente, catalisadores do tipo Pt-Ru-TaOx-M são promissores para futuras aplicações práticas. Finalmente, estudos preliminares realizados usando pó de DDB modificado diretamente com Pt-RuOx pelo método Sol-gel mostraram que este compósito apresenta uma excelente atividade catalítica para oxidação de metanol, que foi maior do que a observada sobre um catalisador comercial considerado como o estado da arte (Pt-Ru/C da E-TEK) nas mesmas condições experimentais. Desta forma, foi mostrada a possibilidade do uso de pó de DDB como suporte para eletrocatalisadores para aplicações em células a combustível que funcionem diretamente com álcoois.The electrochemical properties of boron-doped diamond (BDD) surfaces as well as studies of the oxidation of methanol and ethanol in acid media on BDD surfaces modified with catalysts by the Sol-gel method are presented here. Studies of the surface properties of BDD electrodes revealed that a cathodic polarization (-3,0 V vs. HESS, 30 min) is necessary for a good performance of the system while no important bulk structural differences are introduced in the film indicating that the enhanced electrochemical responses brought on by the cathodic pre-treatment is only due to superficial changes. Meanwhile, repeated and extensive cathodic polarizations led to severe erosion of the electrode surface. On the other hand, studies performed using cyclic voltammetry and X-ray photoelectron spectroscopy have shown that, after a cathodic pre-treatment, the BDD electrode surface presents a dynamic behaviour that results in a loss of the reversibility towards the Fe(CN)6 4−/3− redox couple as a function of the time exposed to atmospheric conditions. This dynamic behaviour must be associated to a loss of superficial hydrogen due to oxidation by the air and is inversely proportional to the BDD doping level suggesting that the boron content has a stabilizing effect on the H-terminated surface. It was also observed that the amount of electrochemical active sites of the BDD electrode has a direct dependence with the doping level (maybe due to the amount of superficial boron). From those studies, it was concluded that all BDD electrodes used in this work having different doping levels (300, 800, 2000 and 8000 ppm of boron) posses, after cathodic polarization, electrochemical heterogeneous surfaces (i.e. boron-rich sites with high conductivity and H-terminated diamond sites with lower conductivity) while after anodic polarization the surface is partially blocked by O-terminated diamond sites, resulting in a behaviour that resembles microelectrode arrays (probably formed by the few boron-rich sites). The BDD surface was also modified directly with Pt, Pt-RuO2 and Pt-RuO2-RhO2 using the Sol-gel method. These catalysts deposits have nanometric sizes, good electrical contact with the diamond surface and high purity. They also show a well controlled atomic composition and a homogeneous distribution on the BDD surface. Methanol and ethanol electrochemical oxidation studies on those modified electrodes suggested that poisoning of the surface by undesired intermediates (most xvi probably CO) is highly inhibited on the ternary catalyst Pt-RuO2-RhO2/BDD when compared with the Pt-RuO2/BDD and Pt/BDD responses. Additionally, the observed catalytic activity for ethanol oxidation was excellent, probably due to the rhodium ability to break the C-C bond which was added to the bifunctional mechanism operating in Pt-Ru catalysts. In the sequence, indirect modifications of the BDD surface were carried out by the production of carbon powder composites modified with metals and metallic oxides by the Sol-gel method and their subsequent anchoring to the BDD using a Nafionsolution. The alcohols oxidation on these electrodes was studied by cyclic voltammetry and steady-state polarization curves (Tafel plots). The investigated systems included binary, ternary and quaternary catalysts containing Pt, Ru, Ir, Rh, PbOx, TaOx and MoOx in a total of 16 different systems The higher catalytic activity towards methanol oxidation was observed in the sequence: Pt-Ru-TaOx-PbOx > Pt-Ru-TaOx-MoOx _ Pt-Ru-MoOx-Ir while for ethanol oxidation, the catalysts activity sequence was: Pt-Ru-TaOx-PbOx _ Pt-Ru-PbOx-Rh > Pt- Ru-Rh. Consequently, it was concluded that catalysts of the type Pt-Ru-TaOx-M are very promising systems to be used in future practical applications. Finally, preliminary studies carried out using BDD powder directly modified with Pt-RuOx by the Sol-gel method showed that this material has an excellent catalytic activity towards methanol oxidation reaction, being higher than that observed on a state of the art commercial catalyst (Pt-Ru/C from E-TEK) under the same experimental conditions. Thus, the feasibility of the use of BDD powder as catalysts support in direct-alcohol fuel cell systems was clearly established

Electroanalytical determination of N-nitrosamines in aqueous solution using a boron-doped diamond electrode

The electrochemical methods cyclic and square-wave voltammetry were applied to develop an electroanalytical procedure for the determination of N-nitrosamines (N-nitrosopyrrolidine, N-nitrosopiperidine and N-nitrosodiethylamine) in aqueous solutions. Cyclic voltammetry was used to evaluate the electrochemical behaviors of N-nitrosamines on boron-doped diamond electrodes. It was observed an irreversible electrooxidation peak located in approximately 1.8 V (vs. Ag/AgCl) for both N-nitrosamines. The optimal electrochemical response was obtained using the following square-wave voltammetry parameters: f = 250 Hz, E(sw) = 50 mV and E(s) = 2 mV using a Britton-Robinson buffer solution as electrolyte (pH 2). The detection and quantification limits determined for total N-nitrosamines were 6.0 x 10(-8) and 2.0 x 10(-7) mol L(-1), respectively