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Tartrazine (Trz) is one of the most widely used azoic dyes in the alimentary industry; it is added to a great variety of products, for this reason it is necessary to develop analytic methods and materials which allow its detection and quantification. For this purpose ultraviolet-visible spectrophotometry (UV-Vis), high performance liquid chromatography (HPLC), capillary electrophoresis and potentiometric and voltammetric sensors have been used. Potentiometric and voltammetric sensors have many advantages such as simplicity; rapid analysis and cost, besides most recently developed sensors are environmentally friendly and avoid the use of mercury which is toxic. In this regard, carbonaceous electrodes such as carbon paste electrodes have been employed due to its low cost, they are easy to manufacture and can be modified with a great diversity of materials an methods. Nanostructured materials such as bamboo-shaped multiwalled carbon nanotubes (BS-MWCNT) and Pt nanoparticles (Pt/NPs) allow great electrochemical activity and in this work are proposed to modify a CPE in order to detect and quantify Tartrazine samples. The electrochemical experiments were performed in a potentiostat/galvanostat AUTOLAB30, using NOVA 2.1 software, a typical three-electrode electrochemical cell was used. A Pt wire was employed as counter electrode; Ag/AgCl (3M NaCl) in a Luggin capillary as reference electrode, the working electrode was a CPE prepared by mixing graphite powder and mineral oil in a proportion 1:1, the CPE was modified by adding an aliquot of 5mL of BS-MWCNT dispersion and by adding an aliquot of 5mL of Pt/NPs and BS-MWCNT. Cyclic voltammograms obtained in 0.5M NaCl + 2.0x10-5 M Trz (adjusted to a pH=4.0) are shown in Figure 1. In the case of CPE, a peak due to Trz oxidation appears at 0.77V, the oxidation peak is positively shifted (0.15V) when BS-MWCNT are added and now appears at 0.92V, even though the oxidation potential is greater on BS-MWCNT the associated current is also greater. When the experiment is performed on BS-MWCNT + Pt/NPs the oxidation peak appears at 0.99V, the associated current in this last case is greater than in the previous cases, a great current leads to an improvement of some analytical parameters such as sensibility, which may help to detect and quantify Trz more accurately. S Food and Drug Administration Center for Food Safety and Applied Nutrition. (2003) U. S Department of Health and Human Services. López-de-Alba, P. L., López-Martínez, L., De-León-Rodríguez, L. M. Simultaneous Determination of Synthetic Dyes Tartrazine, Allura Red and Sunset Yellow by Differential Pulse Polarography and Partial Least Squares. A Multivariate Calibration Method. (2002). 14(3):197-205. Ramírez-Silva, T., Palomar-Pardavé, M. E. Gónzalez, I., Rojas-Hernández, A. (1995). Carbon Paste Electrodes with Electrolytic Binder: Influence of the Preparation Method. Electroanalysis. 7:184-188. Yu, L., Shi, M., Yue, X., Qu, L. (2016). Detection of Allura Red Based on the Composite of Poly (diallylmethylammonium chloride) Functionalized Graphene and Nickel Nanoparticles Modified Electrode. Sensors and Actuators B: Chemical. 225:398-404. Figure 1

Low temperature fuel cell technology is set to occupy a central role in powering society in the near future. Several challenges emerge in the preparation of electrocatalysts to improve the operation, use and commercialization of fuel cells. Bi-metallic nanostructures are potential materials to use as electrocatalysts in this application. This research studies the electrocatalytic activity of palladium-copper nanostructures supported on graphene oxide as electrocatalysts for the formic acid oxidation reaction (FAOR). The Pd-Cu nanostructures were synthesized through the impregnation method using tetrachloropalladium acid and sodium borohydride. The Pd and Cu precursors were mixed in appropriate quantities to obtain Pd:Cu molar 1:1 ratios. The Pd-Cu nanostructures were characterized via X-rays diffraction, XRD, transmission, TEM, and scanning electron, SEM, microscopies. The electrocatalytic activity of the Pd-Cu nanostructures was evaluated for the FAOR. Figure 1 shows the cyclic voltammetries used to determine the electroactive area using the CO adsorption/desorption. The FAOR is shown in Figure 1B, where Pd-Cu is the electrocatalyst displaying the largest anodic current density as compared with Pd and commercial Pd. Figure 1

Caffeic acid (CA) ia classified as a hydroxycinnamic acid having three acidity constants and low stability in aqueous medium. This work proposes the use of sodium dodecyl sulfate (SDS) surfactant to confer stability to CA, performing the electrochemical characterization of the H3CA species at pH 1.44 in aqueous media, in the presence and absence of SDS. This study was carried out by cyclic voltammetry (CV) recorded over a carbon paste electrode (CPE) vs Ag/AgCl, beginning the potential sweep at Ei=0 = 0.400 V in the anodic direction. In the absence of SDS, the CA presents an oxidation peak at 0.527 V, but when the potential sweep is switched it is possible to observe a cathodic peak at 0.498 V; this study shows that the CA oxidation process is controlled by diffusion according with the Randles-Sevcik equation. However, in the presence of SDS the CV presents an oxidation peak at 0.561 V, although when switching potential sweep it is possible to observe a cathodic peak at 0.546 V. There exists a 0.029 V potential difference betwen the anodic and cathodic peak in the absence of SDS, while in its presense the potential difference is smaller, namely, 0.015 V. The CA anodic peak, in the presence of SDS, increases to 18.1 mA. The study shows that in the presence of SDS the CA oxidation is controlled through adsorption.

Quinizarin (Qz) is 1,4-dihydroxy-9,10-anthraquinone, exhibiting important potential applications in medicine. However, this molecule typically exhibits low water solubility at room temperature. Recently, the supramolecular host–guest interactions have been the subject of very active research due to their wide spread applications in various areas like pharmaceuticals, sensors, etc. Cyclodextrins (CDs) have been the most extensively investigated due to their higher solubility in aqueous medium. This work proposes the use of β-cyclodextrin (β-CD) to increase the Qz´s solubility through a study carried out via cyclic voltammetry recorded over a carbon paste electrode (CPE) vs Ag/AgCl: the potential sweep started at −0.1 V in the anodic direction at 0.1 Vs−1 rate. The switching potential was recorded in −0.980 V at pH 12.794, in the CPE/66 µM Qz system. Quinizarin (Qz) cyclic voltammetry presented a sharp reduction peak at −0.756 V, with increasing β-CD concentration that evidences the formation of second reduction peak in such a way that the Qz now presents two sharp reduction peaks at −0.895 V and −0.683 V. The formation of a second reduction peak and the potential shift to more positive values is indicative of the of formation of the quinizarin-β cyclodextrin complex in aqueous solution.

Green and low-cost energy production is an important matter in today society because fossil fuels are running low and burning them is not an efficient process. Therefore, low temperature fuel cells arise as a promising technology, e.g. direct ethanol fuel cells (DEFCs) and direct formic acid fuel cells (DFAFCs). Palladium (Pd) has proven to be an excellent catalyst in the formic acid oxidation reaction (FAOR) and further investigation of methods for its’ synthesis at nanoscale is needed. Several studies have been performed on Pd and other metal nanoparticles (NPs) synthetized from aqueous media and deep eutectic solvents (DESs). The advantage of synthesizing NPs by electrodeposition from DESs over aqueous media is the diminution of oxygen or hydrogen evolution reaction. Thus, the aim of this investigation is to electrodeposit Pd NPs onto glassy carbon (GC) from ethaline and find out their relation to size and morphology to the applied potential. Hence, how these affect the efficiency of the DFAOR. Pd electrodeposition was obtained by chronoamperometry (CA), as shown in Figure 1B. The potentials were set according to the cathodic peak in the cyclic voltammetry (CV), see Figure 1A. All experiments were performed at 25 °C on ethaline media. In both cases, GC was used as the working electrode, silver and platinum wires were used as reference and counter electrodes, respectively. Electrodeposits were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDS) analysis. Furthermore, the Pd electrochemical response was measured by CV to obtain the electroactive area with carbon monoxide. FAOR was conducted by CV and tested by CA over 20 minutes. Figure 1

This research work studied Cu electrodeposition over a glassy carbon electrode (GC) using deep eutectic solventes (DESs) instead of conventional aqueous media to subsequently assess the electrodeposit catalytic properties during nitrates reduction. These are nitrogen’s most reduced form, typically present in residual waters from chemical industries, from human consumption and from agriculture, which represent a significant contamination problem; they are not at all easy to eliminate through conventional methods used in water treatment plants, because they can reach potable water sources provoking in humans the incidence of severe illnesses, like cancer among others. It has been shown, that catalysts based in Pd, Pt and Cu metal phases reduce the nitrate ions, where the Cu ones have been studied because of their attractive catalytic properties. There are various forms of synthesizing the Cu catalysts, where electrodeposition leads to better control of Cu nucleation and growth. Cu electrocristalization was carried out from DES to compare the influence of the medium over the nucleation and growth mechanism. The eutectic mixtures used were prepared from choline chloride as the ionic species while the hydrogen bond donnors were urea and ethylene glycol. Both the DES were prepared in a 1:2 molar ratio, taking particular care to establish the influence of the resulting liquid at the early stages of electrodeposition, which was studied from Cu (II) solutions. It was shown that its electrodeposition takes place through a separte stage during which Cu (II) reduces first to Cu (I). All media studied led to demonstrate that electrodeposition follows a nucleation and 3D diffusion controlled growth. The Cu (II) diffusion coefficient, the A (nucleation frequence) and N0 (number density of active sites) parameters were estimated from potentiostatic plots using the Heerman and Tarallo model. The nitrates reduction at different concentrations was studied via differential pulse voltammetry to determine analytical parameters, like sensibility, detection and quantification limits. The Cu-modified glassy carbon electrodes and a Cu bar served to reduce the nitrates, immersed in 100 mM NaCl supporting electrolyte at pH=1.4 set with HClO4 analytical grade, adding different KNO3 concentraciones. It was shown that in acid medium the nitrates ion can be quantified reliably. Figure 1

In the last decades, fuel cells have been considered as an alternative power source for electric portable devices. Direct formic acid fuel cells (DFAFC) have attracted particular interest, since formic acid is safe, environmentally-friendly and non toxic. Also, it exhibits high-energy density and fast oxidation kinetics compared with other fuels, such as methanol and ethanol [1]. Palladium electrocatalysts supported on different carbon materials have been widely used for the formic acid oxidation reaction (FAOR). However, further research is still necessary as Pd deactivates during the FAOR. In order to overcome this limitation, Pd-Metal alloys have been proposed [3-5]. Pd, and PdFe nanoparticles supported on the carbon nanofibers with and without functionalization (NFC and NFCox) have been used for the FAOR in acid media. Electrocatalysts were synthesized by the borohydride reduction method with a metal loading of 20 wt.%. The morphology, composition and structural properties of the electrocatalysts were studied by transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD). The ROAF was evaluated in acid media in a conventional three-electrode cell by means of cyclic voltammetry (VC) and chronoamperometry (CA). The electrochemical behavior of Pd-based electrocatalysts for the FAOR showed that the functionalization of carbon nanofibers (NFCox) increased the electrocatalytic activity of Pd and PdFe electrocatalysts compared with the same electrocatalysts supported on NFC, as shown in Figure 1. X. Yu, P. Pickup, Journal of Power Sources,. 182(124-132) (2008) K. Jiang, H. Xuan, S. Zou, W. Bin, Phys. Chem. Chem. Phys., 16(20360-20376) (2014) H. Meng, F. Xie, J. Chen, P. Kang, Journal of Materials Chemistry., 21(11352-11358) (2011) D. Morales, J. Ledesma, L. Godinez, H. Rodríguez, L. Álvarez, L. Arriaga, Journal of Power Sources., 195(461-465) (2010) L. Zhang, L. Wan, Y. Ma, Y. Chen, Y. Zhou, Y. Tang, T. Lu, Applied Catalyst B: Environmental., 138-139(229-235) (2013). Figure 1

Formic acid electrochemical oxidation was studied using an electrode formed by Pd electrodeposited on third generation TiO2 nanotubes (TiO2NTBs-Pd), see inset in Figure 1A, in an alkaline medium. The electrochemical response of TiO2NTBs-Pd electrode towards formic acid oxidation was better than those corresponding to Ti or TiO2 nanotubes, see Figure 1A. Figure 1 (B) shows the typical Pd voltammetric regarding both Pd oxide formation and its reduction. From CO adsorption, see Figure1B, the real area of Pd electrodeposited was measured. The formic acid oxidation on the TiO2NTBs-Pd electrode is shown in 1D. Figure 1

The corrosion behavior of pipeline steel grade API 5L X52 immersed in 1M HCl aqueous solution in the presence and absence of cefalotine, was evaluated using EIS and a rotating disk electrode. The effect of different experimental conditions namely: Cefalotine concentration, electrode rotation speed, temperature and immersion times on the corrosion inhibition efficiency (IE) of Cefalotine, were evaluated. It is shown that at stagnant conditions (0 rpm), the IE increased with inhibitor concentration, Fig. 1, reaching a value of ca. 87% at 25 ppm and 89% at 200 ppm. When the steel working electrode rotation speed was varied, it was found that for [Cefalotine] ≥ 25 ppm, the IE reached a maximum value, ca. 85%, at 40 rpm, however, it diminished to ca. 75% when the electrode rotation speed reached 1000 rpm. Furthermore, when the temperature of the corrosive media was increased from 25 to 45 °C, at stagnant conditions with 200 ppm cefalotine, the IE values remain to ca. ~80%. For stagnant conditions, 50 ppm cefalotine and 25 °C, an IE greater that 94% was found for the inhibitor even after 336 exposure hours to the corrosive media.

In the past decades, direct methanol fuel cell (DMFC) has attracted much interest for their significant advantages in portable and automobile applications, for this technology the anode electrocatalyst is the most important part. The Pt catalyst is widely recognized as the best catalyst for DMFC and one of the key objectives in fuel cell technology is to improve the electrochemical activity and reduce Pt loading of the electrocatalyst. One way to reduce the Pt content in the electrocatlyst is by synthetizing core–shell structural catalysts, in which only surface atoms are active in the catalytic reaction (i.e. Pt as shell). In this work, the modulating effect given by the composition of the core in AuxCuy@Pt/C for the methanol oxidation reaction (MOR) is analyzed. For this purpose, AuxCuy@Pt/C catalysts were prepared varying the Au:Cu percentage (i.e. 100:0%, 75:25%, 50:50%, 25:75%, 0:100%), the catalysts were prepared by a two-step method.

The objective of this research is the production of an epoxy coating blended with organic–inorganic hybrid nanocomposite applied over mild steel, as a self-healing corrosion protection of defects. A series of conducting polyaniline (PANI)–SBA15/Fluconazole nanocomposites materials are being prepared by an in situ chemical oxidative method of aniline monomers in the presence of SBA15/fluconazole complex nanorods which were synthesized previously with camphor-sulfonic acid (CSA) and ammonium peroxydisulfate (APS) as surfactant and initiator, respectively. A commercial epoxy coating was applied over samples afterwards. The synthesized materials were characterized by X-ray diffraction pattern (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM). To determine the best inhibitor concentration, the anti-corrosion behavior of the Fluconazole was studied in a ammonium sulfide-sodium chloride pH 7 solution, at a temperature of 25 ͦ C using electro-chemical techniques including electrochemical impedance spectroscopy (EIS) and polarization potentiodynamic. The electrochemical results show that this inhibitor has an effect on anodic region forming a passivation layer, and the best result was achieved with 150 ppm of Fluconazole. The next step was to prepare the SBA15/Fluconazole nanorods, and finally the PANI-SBA15/Fluconazole composite, and evaluate the self-healing effect over mild steel. It was found that the presence of SBA15/Fluconazole nanorods dispersed in the PANI matrix can significantly improve the corrosion protection and barrier effect performance of the epoxy coating due to the flaky shaped structure of the PANI–SBA15/Fluconazole nanocomposites, evaluated electrochemically.

Gold-palladium nanoparticles (NPs) have been used as catalysts due to their catalytic activity, selectivity and stability for a variety of reactions, such as the small organic molecule oxidations (i.e. ethanol). In the present contribution, the catalytic activity of Pd and Au-Pd core-shell (CS) NPs is investigated towards the ethanol oxidation (Figures 1A and 1B). The Au-Pd CS NPs were synthesised by a seed-mediated growth method, where PdCl4 2- is reduced at the surface of Au NPs in the presence of ascorbic acid. This method allows adjusting the average Pd shell thickness between 1 (CS1) and 10 (CS10) nm, by varying the amount of palladium chloride. Electrochemical studies in potassium hydroxide (KOH) containing electrolyte solutions with ethanol show that the current density of ethanol oxidation decreases as the shell thickness decreases. Correlation between catalytic activity and shell thickness will be discussed in terms of the structural parameters.

The electrochemical formation of atomic adlayers introduces significant changes in the electrocatalytic properties of electrode surfaces. In the present contribution, we study the surface properties of Au nanoparticles analysing the electrochemical responses associated to the copper underpotential deposition (upd) in acid pH. The Au nanoparticles were synthesised by the chemical method, using HAuCl4 and trisodium citrate with an average diameter of 19.2 ± 1.2 nm. Three-dimensional networks of Au nanoparticles were assembled via electrostatic layer-by-layer adsorption employing poly-L-Lysine (PLL) on In-doped SnO2 electrodes (ITO). The electrochemical studies in sulfuric acid (Figure 1A) show the voltammetry behavior, while (Figure 1B) in copper sulfate (CuSO4) show the potentiostatic current transients of Cu onto Au nanoparticles. Detailed electrochemical analysis of the responses showed that the average Cu coverage on a single Au nanoparticle is close to those observed at extended Au surfaces. These results demonstrate that each individual nanoparticle in the assembly participate in the electrochemical copper deposition.