Descomposición térmica del nitrato de metilo

Tesis (Maestría en Ciencias con Especialidad en Físico Química) UANLUANLhttp://www.uanl.mx

Synthesis, characterization and cyclic voltammetry studies of helical carbon nanostructures produced by thermal decomposition of ethanol on Cu-foils

Cu-foils have been used intensively to fabricate graphene and other carbon nanostructures. Several routes have been implemented to improve the synthesis of such carbonaceous nanomaterials. We investigated the growth of carbon materials on Cu-foils by mapping the reactor in a chemical vapor deposition method. Several Cu-foils were pretreated by sonication to modify their surface and were placed alongside the reactor and exposed to a flow of ethanol vapor. After carbon materials deposition, the Cu-foils were analyzed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, and cyclic voltammetry (CV). It was demonstrated that the type of synthesized carbon nanostructure depends strongly on the position where the Cu-foils were placed. XRD characterizations revealed the presence of graphite materials, Cu, and CuO crystal structures. SEM characterizations revealed the presence of helical, herringbone and straight multiwalled carbon nanotubes with internal bamboo-shape morphology and formation of Cu nanoparticles. Important electrochemical properties of Cu-foils rich in helical carbon nanostructures were observed, suggesting this material can be used for redox reactions (RR) promotion. In addition, the hydrophobic properties were evaluated by contact angle measurements

DNA Biosensor Based on Double-Layer Discharge for the Detection of HPV Type 16

DNA electrochemical biosensors represent a feasible alternative for the diagnosis of different pathologies. In this work, the development of an electrochemical method for Human Papillomavirus-16 (HPV-16) sensing is reported based on potential relaxation measurements related to the discharge of a complex double layer of a DNA-modified gold electrode. The method used allows us to propose an equivalent circuit (EC) for a DNA/Au electrode, which was corroborated by electrochemical impedance spectroscopy (EIS) measurement. This model differs from the Randles circuit that is commonly used in double-layer simulations. The change in the potential relaxation and associated charge transfer resistance were used for sensing the DNA hybridization by using the redox pair Fe(CN)64-/Fe(CN)63+ as an electrochemical indicator. In order to determinate only the potential relaxation of the composed double layer, the faradic and double-layer current contributions were separated using a rectifier diode arrangement. A detection limit of 0.38 nM was obtained for the target HPV-16 DNA sequences. The biosensor showed a qualitative discrimination between a single-base mismatched sequence and the fully complementary HPV-16 DNA target. The results indicate that the discharge of the double-layer detection method can be used to develop an HPV DNA biosensor

Determination of Pb in Brickellia Veronicifolia for Anodic Stripping Voltammetry

The Electrochemical Society, find out more Determination of Pb in Brickellia Veronicifolia for Anodic Stripping Voltammetry Luis Tomás Félix1, Sergio Miguel Durón2, Verónica Ávila1, Hans Christian Correa1 and Miguel Mauricio Aguilera1 © 2018 ECS - The Electrochemical Society ECS Transactions, Volume 84, Number 1 Citation Luis Tomás Félix et al 2018 ECS Trans. 84 297 DownloadArticle PDF Download PDF 7 Total downloads Turn on MathJax Get permission to re-use this article Share this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on Mendeley Article information Abstract This study consists of the determination of lead concentration contained in soil and plant material (Brickellia veronicifolia) by means of Differential Pulse Anodic Stripping Voltammetry, using vitreous carbon as working electrode, SCE as reference and platinum as auxiliary. Samples were collected from sites near a tailings dam belonging to San Martín-Sombrerete-México; taking 12 sampling points and analyzing the lead content in soil and plant (root, stem, leaf), for determining the accumulation of this toxic element, in order to define its possible use as phytoextractant. The detection and quantification limits were 0.8 and 1.9 ppb respectively; it was found that the highest lead concentration was 1,115 ppm, which corresponds to 2.87 times the value established in NOM-147-SEMARNAT/SSA1-2004 for contaminated sites, while the plant accumulated 730 ppm with accumulation averages of 20-35% in root, 11-30% in stem and 37-58% in leaf, inferring that is an indicator plant of lead contamination in soil

One-pot synthesis of ZnO–Ag and ZnO–Co nanohybrid materials for photocatalytic applications

ZnO–Ag and ZnO–Co nanohybrid materials with different Ag and Co contents were successfully prepared through a simple one-pot method at room temperature in the absence of surfactants. This synthesis route is effective and environmentally friendly and can produce spherical nanoparticles with sizes between 7 and 20 nm. The nanohybrid materials were characterized by UV–vis spectroscopy, fluorescence spectroscopy, scanning electron microscopy–energy-dispersive X-ray analysis, X-ray diffraction, Fourier transform IR spectroscopy, and high-resolution transmission electron microscopy. Their photocatalytic activity was evidenced by discoloration of the synthetic diazo dye Bismarck brown Y; ZnO–Ag nanohybrid materials had greater efficiency for decolorization of the dye compared with ZnO–Co, ZnO, and TiO2. The enhanced photocatalytic activity of the ZnO–Ag nanohybrid material is due to three important aspects: (1) the oxygen vacancies present on the ZnO surface, (2) the efficient absorption of visible light due to the interaction of the semiconductor and the surface plasmon resonance of Ag, and (3) the effective separation of charges due to the formation of the Schottky barrier between ZnO and Ag, where Ag acts as an electron trap, and thereby reduces recombination. When the ZnO–Co nanohybrid is used, the addition of Co introduces intermediate energy levels between the valence and conduction bands on the semiconductor surface, which results in a recombination that reduces the photocatalytic activity, making the azo dye decolorization less efficient

Morphology and surface structure of nanocarbon allotropes: a comparative study

Different carbon allotropes, including vulcan carbon, multiwall carbon nanotubes, graphene, and nanodiamonds, were processed by chemical purification and treated in a mixture of H2SO4–HNO3. The materials were characterized by infrared and Raman spectroscopy as well as by scanning and transmission electron microscopy. Oxidative differences are indicated by Raman through the G band (∼1570 cm−1), D band (∼1340 cm−1), and G’ band (∼2684 cm−1). The crystal size (La) and purity, relative to the amorphous carbonaceous material, were studied as well, along with the morphological changes induced by the treatment

The use of artificial intelligence models in the prediction of optimum operational conditions for the treatment of dye wastewaters with similar structural characteristics

This work assesses the effectiveness of an artificial intelligence (AI) model based on an artificial neural networks (ANN) – genetic algorithm (GA) in the prediction of the behavior and optimization of the treatment of sulfate wastewaters with Bromophenol blue dye using an electro-oxidation (EO) process. Trials were made with a filter press-type reactor with a boron-doped diamond (BDD) anode. The ANN model was trained with 51 electrolytic experiments by using the electrolysis time, flow, current density, pH and dye concentration as input variables and the discoloration efficiency as the output one. The performance of ANN was measured with RMSE and MAPE values of 10.73 % and 8.81 %, respectively, calculated from real and predicted values. Optimum conditions determined by GA were reached for the inputs of 10 min, 11.9 L min−1, 31.25 mA cm−2, 2.8 and 41.25 mg L−1, giving a discoloration efficiency of 88.8 ± 0.3 %, close to 95.5 % predicted by the model. To validate the AI model, the same experimental conditions were applied to treat wastewaters with Bromothymol blue and Thymol blue, with analogous structures to Bromophenol blue, and a mixture of the three dyes by EO. In all cases, the loss of color decayed following a pseudo-first-order kinetics, with similar apparent rate constants. For the dye mixture, 69 % COD was reduced at 60 min, with 13 % average current efficiency and 0.26 kW h (g COD)-1 energy consumption. The AI model is a strong tool to design, control and operate the EO process with a BDD anode to treat wastewaters with similar dyes

Ir-Sn-Sb-O Electrocatalyst for Oxygen Evolution Reaction: Physicochemical Characterization and Performance in Water Electrolysis Single Cell with Solid Polymer Electrolyte

Mixed oxide Ir-Sn-Sb-O electrocatalyst was synthesized using thermal decomposition from chloride precursors in ethanol. Our previous results showed that Ir-Sn-Sb-O possesses electrocatalytic activity for an oxygen evolution reaction (OER) in acidic media. In the present work, the physicochemical characterization and performance of Ir-Sn-Sb-O in an electrolysis cell are reported. IrO2 supported on antimony doped tin oxide (ATO) was also considered in this study as a reference catalyst. Scanning electron microscopy (SEM) images indicated that Ir-Sn-Sb-O has a mixed morphology with nanometric size. Energy dispersive X-ray spectroscopy (EDS) showed a heterogeneous atomic distribution. Transmission electron microscopy (TEM) analysis resulted in particle sizes of IrO2 and ATO between 3 to >10 nm, while the Ir-Sn-Sb-O catalyst presented non-uniform particle sizes from 3 to 50 nm. X-ray diffraction (XRD) measurements indicated that synthesized mixed oxide consists of IrO2, IrOx, doped SnO2 phases and metallic Ir. The Ir-Sn-Sb-O mixed composition was corroborated by temperature programmed reduction (TPR) measurements. The performance of Ir-Sn-Sb-O in a single cell electrolyser showed better results for hydrogen production than IrO2/ATO using a mechanical mixture. Ir-Sn-Sb-O demonstrated an onset potential for water electrolysis close to 1.45 V on Ir-Sn-Sb-O and a current density near to 260 mA mg−1 at 1.8 V. The results suggest that the mixed oxide Ir-Sn-Sb-O has favorable properties for further applications in water electrolysers

Effect of molybdenum content on the morphology and electronic characteristics of Pd–MoOx nanomaterials and activity evaluation for ethylene glycol electro–oxidation

In this work, Pd–MoOx nanomaterials were developed changing the Mo/Pd precursor ratio and tested for ethylene glycol electro–oxidation reaction (EGOR) in alkaline medium. Mo atomic % compositions of 0, 15, 35, 45 and 75 at. % were evaluated. The increase of Mo at. % resulted in morphology changes due to the directing effect of hexadecyltrimethylammonium bromide (CTAB) on molybdenum passing from hemispheres to nanobelts + hemispheres (15 at. % Mo denoted as Pd85Mo15), then only nanobelts (35 at. % Mo, Pd65Mo35), and nanosheets (45 at. % Mo, Pd55Mo45), and hemispheres were newly obtained at the higher Mo concentration (75 at. % Mo, Pd25Mo75). The activity evaluation of EGOR at 60 °C indicated that Pd25Mo75 supported on Vulcan carbon (Pd25Mo75/C) displayed the highest current density (63.80 mA cm−2), and according with X–ray photoelectron spectroscopy (XPS) the highest activity of Pd25Mo75/C can be related to the abundance of Mo5+ species, which have oxygen vacancies with a single positive charge. Additionally, the analysis of O 1s core–level corroborated the abundance of oxygen with high number of defects sites. Thereby, it was found that Pd loading can be decreased without comprising the activity by increasing oxygen vacancies of MoOx as co–catalyst

Glucose microfluidic fuel cell using air as oxidant

A bioanode was constructed using glucose oxidase enzyme (GOx) supported on multiwalled-carbon nanotubes (MWCNTs) in the presence of glutaraldehyde (GA) (GOx/MWCNTs-GA) and evaluated in an air-breathing hybrid glucose microfluidic fuel cell (HG-μFC). The air-breathing HG-μFC operated under physiological conditions (5 mM glucose at pH 7 with an air-exposed cathode) delivers an open circuit value of 0.72 V with 610 μW cm−2 of maximum power density, and shows potential possibilities to develop future implantable applications