Katlin Ivon Barrios Eguiluz

Sequence-specific electrochemical detection of Alicyclobacillus acidoterrestris DNA using electroconductive polymer-modified fluorine tin oxide electrodes

This study outlines the quantification of low levels of Alicyclobacillus acidoterrestris in pure cultures, since this bacterium is not inactivated by pasteurization and may remain in industrialized foods and beverages. Electroconductive polymer-modified fluorine tin oxide (FTO) electrodes and multiple nanoparticle labels were used for biosensing. The detection of A. acidoterrestris in pure cultures was performed by reverse transcription polymerase chain reaction (RT-PCR) and the sensitivity was further increased by asymmetric nested RT-PCR using electrochemical detection for quantification of the amplicon. The quantification of nested RT-PCR products by Ag/Au-based electrochemical detection was able to detect 2 colony forming units per mL (CFU mL(-1)) of spores in pure culture and low detection and quantification limits (7.07 and 23.6 nM, respectively) were obtained for the target A. acidoterrestris on the electrochemical detection bioassay.

Wet chemical synthesis of rare earth-doped barium titanate nanoparticles

Barium titanate (BaTiO3) is a common ferroelectric material with perovskite structure widely used for the production of a variety of electro-optical devices. When doping with rare earth elements, very interesting characteristics can be attributed to BaTiO3. Among the methods used to synthesize BaTiO3, wet chemical approaches are the most suitable for preparing homogenous and pure nanostructured materials. In this sense, the present article aims to summarize the state-of-the-art of the most relevant wet chemical routes for the synthesis of nanocrystalline BaTiO3 doped with rare earth (RE) ions (BaTiO3:RE), which include the following: sol–gel, sol–emulsion–gel, Pechini, solvothermal/hydrothermal, and co-precipitation methods. The influence of each method on morphology and particle size, as well as on the dielectric and/or luminescent properties of the powders is discussed.

Environmentally friendly sol - gel-based anticorrosive coatings on aluminum alloy 2024

Chromate coatings used as corrosion protection technologies for aluminum alloys are environmentally harmful and extremely toxic. This paper presents an investigation on the deposition of environmentally friendly cerium oxide-based anticorrosive coatings on aluminum alloy 2024 substrates by the sol - gel method. The influence of the calcination temperature on both the microstructural characteristics and the electrochemical corrosion performance was tested using scanning electron microscopy, X-ray diffraction, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), before and after, periods of immersion in saline corrosive solutions. The ceramic coatings synthesized at 200, 300 and 400 °C showed very resistive behaviors leading to both an efficient passivation of the alloy surfaces and good corrosion protection. This passivation was maintained for 30 days of immersion in saline solutions, as well as, when aggressive electrochemical polarization experiments (until 2.0 V versus saturated calomel electrode) were used. Very high resistances for the charge transfer (0.14-0.28 GΩ) and very low current density values (5 × 10 - 14 -5 × 10 - 11 A cm - 2) were estimated by EIS and potentiodynamic polarization, respectively, for coatings prepared at 200-400 °C. Thus, the coatings prepared in this study by the sol - gel method appear as an efficient treatment for the corrosion protection of aluminum alloys.

Photoelectrocatalytic degradation of indanthrene blue dye using Ti/Ru-based electrodes prepared by a modified Pechini method

Photoelectrodes were used to treat synthetic textile wastewater contaminated with indanthrene blue dye. Two media of treatment were used (NaCl and Na2SO4), with variations on temperature, pH, current density, dye and chloride concentration. A modified Pechini method was applied to obtain Ti/Ru-based electrodes (Ti, Ru, Ti0.5Ru0.5, Ti0.75Ru0.25 and Ti0.25Ru0.75) containing anatase TiO2 nanoparticles and a color degradation analysis was done. Physical (atomic force microscopy and X-ray diffractometry) and electrochemical characterizations (cyclic voltammetry) were considered. The condition that yielded highest color removal for the system presented 0.05 mol L-1 NaCl, 100 mA cm-2, 35 °C and pH 7, independent of the dye concentration for the Ti0.25Ru0.75 electrode.

Tratamentos dos efluentes gerados na produção de biodiesel

The wastewaters from biodiesel production contain as primarily wastes sodium or potassium soaps, fatty acids, glycerin, alcohol and other contaminants. In general, these waters are chemically unsuitable for release to any water body, so, it is necessary the adoption of techniques for the treatment of this effluent. In this review, electrochemical, biological, physicochemical, and combined treatments reported for the removal of the wastewater containing pollutants come from biodiesel production have been summarized. In addition, the recovery, the reuse, the energy production and the synthesis of new compounds from the organic matter contained in this kind of effluent are also reviewed.

Ultramicroelectrode array behavior of electrochemically partially blocked boron-doped diamond surface

Demonstra-se, pela primeira vez usando experimentos simples de voltametria ciclica, que a pre-polarizacao anodica de eletrodos de diamante dopado com boro (DDB) conduz a superficies parcialmente bloqueadas. Eletrodos de DDB anodicamente pre-polarizados, com diferentes niveis de dopagem de boro, apresentaram respostas de voltametria ciclica sigmoidais para o par redox ferro/ferricianeto a baixas velocidades de varredura (0,5 mV s –1 ). Por outro lado, quando os mesmos eletrodos sao pre-polarizados catodicamente, observaram-se respostas quase-reversiveis e reversiveis na mesma velocidade de varredura, correspondendo a superficies eletroquimicamente heterogeneas. Assim, as superficies de DDB podem atuar parcialmente bloqueadas ou com eletroatividade heterogenea, dependendo da polarizacao, anodica ou catodica, respectivamente.

Estudo da eletrocristalização de Ni e Ni-P sobre ultramicroeletrodo de platina

This work describes a comparative study of the electrocrystallization of Ni and Ni-P on Pt ultramicroelectrodes using chronoamperometric measurements. It was possible to confirm that in all cases a progressive nucleation was the predominant mechanism. Moreover, the application of the Atomistic Theory to the experimental rate of nuclei formation showed that the number of atoms in the critical nucleus was zero, except for Ni-P on Pt at low overpotentials were a value of one was observed. Furthermore, the physical characterisation of the different deposits on Pt by atomic force microscopy allowed observing the coalescence of the hemispherical nuclei of Ni and Ni-P at tmax thus confirming the results obtained from the current-time analysis.

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.

An Eco-Friendly Method of BaTiO3 Nanoparticle Synthesis Using Coconut Water

BaTiO3 nanoparticles were successfully synthesized by a new coconut water-based sol–gel method using Ba(CH3COO)2 and TiCl3 as the starting salts. The influence of the amount of coconut water and calcination conditions on the barium titanate crystallization was investigated. The resulting nanoparticles were characterized by thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, and Raman and Fourier transform infrared (FTIR) spectroscopies. The ferroelectric tetragonal single phase of BaTiO3 was obtained in samples prepared with a ratio of coconut water volume (mL)/BaTiO3 mass (g) of 25 : 2 and 30 : 2, calcined at 1100°C, which was confirmed by XRD measurements. Crystallites with an average size of about 31 nm for both samples were obtained, and microscopy images revealed the presence of particles in the range of 40 to 60 nm. Raman and FTIR spectra confirmed the dominant tetragonal phase of BaTiO3, meanwhile traces of BaCO3 were identified in FTIR spectra.

Synthesis of high-area chemically modified electrodes using microwave heating

Abstract The synthesis of dimensionally stable carbon-based chemically modified electrodes (CMEs) is a challenge. The synthesis method, the electrode composition, and the heating used influences various properties of the electrodes. Here, we show an innovative, low cost, and efficient heating method for the CMEs production. We deposited ternary ruthenium, antimony, and tantalum or bismuth oxides on carbon-felts by the Pechini method focusing on the influence of different heating methods (conventional and microwave) on their electrochemical and physical properties. The oxides synthesized using microwave heating coated completely the carbon-felts fibers, displaying homogeneous morphology, while maintaining their three-dimensional character. XRD and XRF analyses confirm the presence of the desired oxides on the coating surfaces and the experimental metal load values close to the nominal (87–91% for Ru, 3–6% for Sb, and 4–7% for Ta or Bi, respectively). The microwave-assisted method yields CMEs with electrochemical active areas 136-fold (for tantalum-based) and 153-fold (for bismuth-based) higher than the unmodified carbon felt. The service lifetime of the CMEs is almost twice as high when using microwave heating than when using conventional heating, which is attributed to the complete and homogeneous coating of the fibers obtained using this heating method. In contrast, the conventional heating led to the incomplete covering of the fibers and to CMEs with low stability. Therefore, the use of microwave heating for the CMEs synthesis reduces the production time at around 60%, thus decreasing the production costs and producing CMEs with improved quality and stability when compared to both conventional-made CMEs and unmodified electrodes.