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This review summarizes recent advances in the development of pyrolyzed M–N–C catalysts for the oxygen reduction reaction, focusing on activity, stability, and the reactivity descriptors proposed for the rational design of pyrolyzed M–N–C catalysts. We discuss the last advances in achieving high catalytic activity and stability and the new insights into the characterization of FeN4 active sites by Mossbauer spectroscopy in combination with Density Functional Theory (DFT) calculations of the Fe–N–C catalysts. In addition, we present the different reactivity descriptors proposed in the literature for the rational design of Fe–N–C pyrolyzed materials: (i) structural descriptors determined by X-Ray Photoelectron Spectroscopy (XPS) and Mossbauer spectroscopy and (ii) the redox potential of the active center MNx.

In this work, the use of neodymium electrodes as a basis for the immobilization of magnetite nanoparticles has been carried out. The sensitivity and detection limit to H2O2 are 2.4 × 104 μA M−1 and 1.8 × 10−5 M, respectively. The amount of peroxide in a contact lens liquid was also determined; there was a discrepancy between the manufacturer reported and the experimental measured values less than 2% of error. For the use of a biosensor in glucose detection, the sensitivity and detection limit are 938 μA M−1 and 9 mM, respectively. In both cases, the most notable is the increase in reuse of the electrode of up to 10 times without loss of sensitivity and its excellent performance after 1-month aging.

We have systematically studied the catalytic activity of a series of substituted bisphenanthroline Cu complexes adsorbed on glassy carbon electrodes for the oxygen reduction reaction (ORR) in aqueo...

Peroxydisulfate (PDS, S2O82−)-based advanced oxidation processes have been developed as an alternative to those based on OH, as PDS activation yields a much more stable radical like SO4 − that can maintain the oxidation ability of water treatment systems for longer time. Here, the electrochemical PDS activation has been investigated using reticulated vitreous carbon (RVC) substrate modified with Fe3O4 nanoparticles (NPs) as cathode. The NPs were exhaustively characterized by different surface analysis techniques (TEM, SEM) and Mossbauer spectroscopy. Cyclic voltammetry and linear sweep voltammetry with a rotating disk electrode allowed concluding that the main electrocatalytic role in the cathodic PDS activation to SO4 − corresponded to the Fe(II) active sites continuously promoted upon cathodic polarization. These sites were less catalytic for O2 reduction reaction, although it was still feasible with n = 2.7 electrons as determined from Koutecky-Levich analysis. Both cathodic reactions followed an inner-sphere reaction mechanism. The Fe3O4-modified RVC cathodes were employed to electrolyze Methylene Blue aqueous solutions at pH 3.5, employing different current values and PDS concentrations. Dissolved O2 was purged to impede the competitive cathodic H2O2 production and Fenton’s reaction. The occurrence of dye adsorption/electrosorption on the cathode reduced the mass transport limitations, enhancing the reaction between SO4 − and organic molecules. The best operation conditions to reach total and fast color removal at 18 min were 2 mM PDS and 10 mA, yielding > 80% TOC abatement at 45 min. Reproducible degradation profiles were found after 5 runs, thereby ensuring the stability of the Fe3O4-modified RVC, with no iron sludge production.

9 pags., 6 figs., 2 tabs., Pyrolyzed non-precious metal catalysts (NPMCs) are promising materials to replace platinum-based catalysts in the cathode of the fuel cells. These catalysts present high catalytic activity both in alkaline and acid media for the oxygen reduction reaction (ORR). These catalysts are essentially heterogeneous as they can present different types of active sites. MNx structures have been proposed as the most active for the ORR, similar to those of the MN4 structures of metal porphyrins and phthalocyanines. Several parameters have been proposed as reactivity descriptors to correlate the structure of these materials with their catalytic activity, such as the amount of MNx and of pyridinic nitrogens in the graphitic structure. In this study, we have explored the metal center redox potential of the catalyst as an overall reactivity descriptor. We have investigated this descriptor for pyrolyzed and intact catalysts for the ORR in acid and basic media. We have found that for all catalysts tested, there is a linear correlation between the redox potential of the catalyst and the catalytic activity expressed as (log i)). The activity increases as the redox potential becomes more positive. The correlation gives a straight line of slope close to +0.12 V/decade which agrees with the theoretical slope proposed in a previous publication assuming the adsorbed M − O follows a Langmuir isotherm and that the redox potential is directly linked to the M − O binding energy. The Tafel plots present two slopes, at low and high overpotentials. Based on these results, we proposed two different mechanisms. The low Tafel slopes of −60 mV appear at potentials where the surface concentration of M(II) active sites is potential dependent (close to the onset potential). At higher overpotentials the surface coverage of M(II) becomes constant and the slope changes to −0.120 V/decade., This work was supported by Fondecyt Regular Projects 1161117,1181037, Fondecyt Postdoctoral Projects 3170330 and 3180509, andConicyt Scholarship 21160955.

In the search for new quinoid compounds endowed with potential anticancer activity, the synthesis of novel heterodimers containing the cytotoxic 7-phenylaminoisoquinolinequinone and 2-phenylaminonaphthoquinone pharmacophores, connected through methylene and ethylene spacers, is reported. The heterodimers were prepared from their respective isoquinoline and naphthoquinones and 4,4&prime, diaminodiphenyl alkenes. The access to the target heterodimers and their corresponding monomers was performed both through oxidative amination reactions assisted by ultrasound and CeCl3&middot, 7H2O catalysis &ldquo, in water&rdquo, This eco-friendly procedure was successfully extended to the one-pot synthesis of homodimers derived from the 7-phenylaminoisoquinolinequinone pharmacophore. The electrochemical properties of the monomers and dimers were determined by cyclic and square wave voltammetry. The number of electrons transferred during the oxidation process, associated to the redox potential EI1/2, was determined by controlled potential coulometry.

Multilayers of polyaniline (PAni) and PAni/nanotubes-TiO2 composite were compared for corrosive protection on carbon steel and welded carbon steel. The layer porosity, morphology and thickness were characterized. PAni coating showed the best protection when a layer of 2 μm was deposited on steel surface. In spite of the good anticorrosive behaviour of PAni, when the layer thickness was increased up to 4.5 μm a decrease in the anticorrosive behaviour is detected due to the development of mechanical tensions which increase the porosity of the film. However, the addition of TiO2 nanotubes to PAni coatings shows an interesting ability to inhibit this undesirable mechanical effect, showing a good anticorrosive behaviour and lower porosity when thickness layer is increased. The morphological and electrochemical tests of the samples showed good resistance against degradation in chloride medium and in the salt spray analysis, promoting improvement of corrosion protection in an aggressive corrosion medium.

We studied the adsorption/degradation process of methylene blue in a Fenton like process using iron oxide nanoparticles as a source of Fe2+ ions, where the nanoparticles were prepared via a facile electrochemical synthesis method. The degradation kinetics were studied using 2 g L−1 of catalyst and 100 ppm of pollutant at pH 3.5. The influence of temperature on this process was evaluated using two different setups: conventional heating in a thermostatic bath and selective heating using an alternating magnetic field. The magnetic induction heating process led to a greater degradation of the pollutant compared with the thermostatic bath. In addition, the optimal concentration of Fe2+ in solution was evaluated in a Fenton homogeneous process to achieve the same degradation efficiency when using a nanoparticle-assisted Fenton-like process. A concentration of 0.5 ppm Fe2+ in solution yielded the same degradation achieved by using 2 g L−1 of iron oxide nanoparticles. The kinetic analysis fit the pseudo-first-order kinetics and indicated a linear increase in the apparent rate constant with increasing temperature. The activation energy of the degradation process obtained by fitting the Arrhenius equation was 58 kJ mol−1.

A novel method to obtain catalytic bio-nanocomposites based on chitosan containing different amounts of gold nanoparticles generated in situ is reported. The formation of gold nanoparticles takes place in solid phase assisted by a heating induced process. This method only involves the use of chitosan biopolymer and a gold salt precursor. Unlike other methods the addition of external reducing and stabilizing agents to generate gold nanoparticles, is not needed because these roles are played by chitosan. Therefore, the striking properties of chitosan (e.g., high functionality, biodegradability and biocompatibility) are profited, in order to design a facile and green route of synthesis. Additionally, the described method allows to vary the amount and size of the gold nanoparticles contained in the bio-nanocomposite by using different gold ion compositions and temperatures of heating process. Finally, the bio-nanocomposite performance as heterogeneous catalyst on the reduction of p-nitrophenol (4-NP) to p-aminophenol (4-AP) as a model system was assessed. The results showed a significant catalytic effect that increases as the content of gold nanoparticles in the bio-nanocomposite also increases.

Electrochemical sensors have been developed for the determination of selenium (Se (IV)) using glassy carbon electrodes modified with gold nanoparticles (AuNPs) obtained electrochemically (GC/AuNPs/E) and chemically (GC/AuNPs/C) using square wave anodic stripping voltammetry (SWASV). GC/AuNPs/E was characterized by cyclic voltammetry (CV), atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray dispersion spectrometry (EDS). The results indicate a homogeneous distribution of AuNPs with a 75 ± 20 nm particle size distribution. The chemically prepared AuNPs were characterized by transmission electron microscopy (TEM) and UV–vis spectroscopy (Surface Plasmon Band), and the results indicate that the AuNPs have a spherical shape (7.4 ± 1.3 nm). GC/AuNPs/C was prepared using a drop coating technique and was characterized by CV. The optimum conditions for the prepared electrodes were as follows: accumulation potential of −0.80 V ( E acc ), accumulation time ( t acc ) of 120 s, and a frequency of 15 Hz. A linear range was observed from 10 to 50 μg L −1 with a limit of detection (LOD) of 0.120 μg L −1 for GC/AuNPs/E, and a linear range was observed from 15 to 55 μg L −1 with a LOD of 0.175 μg L −1 for GC/AuNPs/C. The proposed procedure was validated with the TM-15 certified reference material, and good accuracy and precision were observed. In addition, this approach was applied to seawater samples with satisfactory results.

Steel reinforcement in concrete is protected from corrosion by passivation due to the high alkalinity of the cement pore solution, but the presence of aggressive ions as Cl− could induce pitting corrosion processes thus decreasing the durability of the structure. This also occurs for prestressing concretes but the risk to suffer pitting corrosion in presence of aggressive ions, and hence stress corrosion cracking (SCC), increases due to the external mechanical load. The study of the corrosion processes by classical methods involves the determination of pitting potential (E pit) or the polarization resistance monitoring during long periods (i corr). However, the large number of parameters, which could potentially influence the determination of the E pit or the i corr values, result in a great variety of results in literature. The present study proposes a simple and reliable method to evaluate the susceptibility to suffer pitting corrosion process and stress corrosion cracking by the induction of pitting corrosion process by cyclic voltammetry. The pitting corrosion intensity is evaluated by means of the charge during the corrosion process, and related with the weight loss and the decrease of the mechanical properties of the steel under external load. The results show a linear and a volcano trend when pitting corrosion process and stress corrosion cracking are respectively evaluated.

Corrosion of zinc in aqueous methanesulfonic acid has been evaluated over a wide range of concentrations of acid (0.5–5 mol dm−3), dissolved zinc (0.5–2 mol dm−3), and electrolyte temperature (22–50 °C). The corrosion rate of zinc, in terms of weight loss and the volume of hydrogen evolved, varied with time and it was found to be highly dependent on the surface state and electrolyte conditions. With an initial active layer of zinc present, the corrosion rate rapidly increased following a decline when the proton concentration in the solution decreased to ca. 0.56 mol dm−3. Organic and inorganic inhibitors were added to the electrolyte to suppress the zinc corrosion in 1 mol dm−3 methanesulfonic acid. The strong adsorption and blocking effects of cationic organic adsorption inhibitors, such as cetyltrimethyl ammonium bromide and butyltriphenyl phosphonium chloride, led to a significant decrease in zinc corrosion over a 10 h immersion period. With the addition of indium and lead ions inhibitors, the zinc surface showed less activity. Zinc corrosion continued to a smaller extent in the presence of these metallic inhibitors during the first few hours, but the metallic layer of the inhibitors did not cover the surface completely resulting in continued hydrogen evolution and making the inhibitors less effective at longer times.

In classical volcano correlations in electrocatalysis, the shape of (log io) plots versus the binding energy of the reactant to active sites, the maximum activity is associated to a situation where the surface coverage of reactant species is equal to 0.5 corresponding to a free energy of adsorption of the reactant equal to zero. When studying electrochemical reactions catalysed by macrocyclic transition metal complexes adsorbed on graphite electrodes, volcano correlations are found when plotting the activity versus the formal potential of the catalyst for several reactions, assuming that the formal potential is somehow related to the free energy of the adsorption of the reacting molecule. In this work we offer an interpretation different from that given in the literature for these correlations for the electrooxidation of hydrazine. The highest catalytic activity is achieved when the formal potential of the catalyst approaches the N2H4/N2 reversible potential. In contrast, if log i (normalized for the actual surface concentrations of Fe(II) active sites at constant potential) is plotted versus the difference between the Fe(II)/(I) formal potential of the catalysts and the standard potential of the N2H4/N2 reaction, the correlation is linear with a slope close to 2RT/F. Keywords: Falling region, Tuning formal potential, Design best catalyst, Surface redox catalysis

An efficient and inexpensive catalyst for the oxygen reduction reaction (ORR) is the key missing component for large-scale development of fuel cells. Bio-inspired tethered electrocatalysts could be the solution to this problematic reaction. Either unsubstituted Fe phthalocyanine (FePc) or Fe hexadecachloro-phthalocyanine (16(Cl)FePc) was anchored to carbon nanotubes (CNTs) via a pyridine axial ligand. The results show that the fifth coordination plays a major role in increasing the catalytic activity of FePc and 16(Cl)FePc for the ORR. The coordination also allows the decoupling of the metal centre from the carbon support, thus changing the geometrical and electronic structure and hindering the production of HO. The pentacoordinated catalysts were stable in acidic pH according to the rotating disk analysis, but the activity of the hexadecachloro compound was not higher than that of the unsubstituted phthalocyanine. Cl atoms reduced the coupling between O and Fe, mismatching the energy of the frontier orbitals and lowering the activity towards the reduction of O.

A film of iridium and tin dioxides doped with antimony oxide (IrO2-SnO2-Sb2O5) was deposited onto Ti mesh and plate substrates by the Pechini method. The electrode surface morphology and composition were characterized by SEM-EDS. The ternary oxide coating was used for the anodic oxidation of methyl orange (MO) azo dye. Linear sweep voltammetry was used to identify the electrode potentials that favour MO degradation. Batch electrolyses were then carried out at a constant electrode potential of 1.5, 1.75 and 2.0V vs. SHE using either a three-electrode batch cell or a flow reactor. The dye solutions were totally decolorized via reactive oxygen species, such as OH, H2O2 and O3 formed in situ from water oxidation at the Ti/IrO2-SnO2-Sb2O5 surface.

The preparation of PbO2 coatings on reticulated vitreous carbon (RVC) has been carried out at constant current from electrolytic baths containing aqueous Pb(II) and methanesulfonic acid (MSA, CH3SO3H). The morphological and structural analysis of the RVC/PbO2 deposits carried out by scanning electron microscopy (SEM) and X-ray diffraction revealed that a thick (100 ?m), homogeneous, nanostructured ?-PbO2 film can be successfully formed. As a result, three-dimensional ?-PbO2 structures were obtained, being particularly interesting for their use as anodes in wastewater treatment. The high oxidation ability of these anodes has been verified by the electro-oxidation of Methyl Orange aqueous solutions. Quick decolourisation was achieved, with total colour removal in less than 60 min at 600 mA due to the production of large amounts of reactive OH radicals from the oxidation of water at high anodic potentials. The progressive mineralisation of the solutions was also ascertained from the total organic carbon (TOC) removal, which was much quicker at a higher applied current. All the coated RVC electrodes exhibited excellent long-term stability and remained unaltered after prolonged electrolyses. In addition, novel PbO2 composite coatings were prepared in the presence of hydrothermally synthesized titanate nanotubes (TiNT). The SEM images showed the presence of TiNT agglomerates along the PbO2 surface, which led to higher anodic current in the cyclic voltammetries carried out with Methyl Orange solutions. It is suggested that TiNT favour the adsorption of the organic molecules, facilitating the contact with the OH radicals and thus accelerating the electro-oxidation process. This was confirmed by the faster TOC removal compared to that yielded by the RVC/PbO2, being 45% instead of 24% at 120 min

Electrodeposition methods have been used to obtain polypyrrole and polyaniline polymer layers, bilayers and blends of these polymers on carbon steel by passivation of the steel surface in the electrodeposition solution (oxalic acid and monomer) between −0.5 and 0.3 V versus Ag/AgCl and subsequent electrodeposition using different techniques (potentiodynamic, galvanostatic and potentiostatic). The results obtained indicate that prepassivation gives rise to adherent polymer layers with excellent corrosion resistance. Of all the bilayers obtained, the best results are yielded with those in which polyaniline is deposited as the base for the deposition of polypyrrole. The electrodeposition of Zn microparticles on the previously deposited polymer layers promotes a great improvement in the corrosion current in highly aggressive solutions such as NaCl due to the effect of Zn as an anodic corrosion inhibitor. The drop in the corrosion rate depends on the amount of Zn deposited on the polymer layer, up to a certain point after which the protective effect ceases to be observed.

Following an adapted three-step seed-mediated method, we synthesize colloidal Au thin and long (L > 100 nm) nanorods (NRs) and characterize the metallic nanostructures evolving from the initial Au nanoparticle (NPs) seeds to thiolate-functionalized NRs, using HRTEM and ultraviolet, visible, and near-infrared absorption spectroscopy (UV-vis-NIR). For the long NRs we analyze the role of several solvents and rod concentration on the spectral features of the assembled products, which are further studied with simulated spectra. Superimposed to a broad resonance in the range 700-900 nm, which corresponds to short (L < 100 nm) interacting nanorods, the growth of long nanorods is clearly identified with the emergence of a robust resonance at 960 nm, linked to the three half-wavelength antenna plasmon mode. This mode is enhanced when the nanorod concentration decreases and splits into two peaks when the thiolate coverage chemically modifies the rod surface by a thin layer of nanometer size. This behavior is explained with a dielectric model based on ab initio calculations of thiolate-gold cluster surfaces., We gratefully acknowledge the support of the Basque Departamento de Educacion and the UPV/EHU (Grant No.IT-366-07) and Spanish Ministry of Economy and Competitiveness MINECO (FIS2013-48286-C2-1-P and FIS2013-41184-P) and the ETORTEK research program funded by the Basque Departamento de Industria and the Diputacion Foral de Guipuzcoa (nanoGUNE 2014). F.J. Recio thanks a Fondecyt 3130538 Postdoctoral Grant.

Well-dispersed magnetite nanoparticles of different sizes between 15 and 43 nm were synthesized by an electrochemical method in a controlled manner by simply changing the synthesis temperature. These nanoparticles were used as a reusable adsorbent to remove Cr(VI) from aqueous solution. The recovery efficiency was found to be highly dependent on environmental parameters, such as temperature and pH. In addition, it was demonstrated that the initial concentrations of both Cr(VI) and magnetite nanoparticles strongly influence the removal capability of these nanomaterials. Remarkably, the nanoparticle size has a key role on the Cr(VI) adsorption efficiency, which gradually increases as the diameter decreases due to the augmentation of the surface area. The low aggregation in the case of small particles that results from the low magnetization saturation values also contributes to the enhancement of the surface area available for Cr(VI) adsorption. In contrast, nanoparticles with larger sizes are more easily manipulated by a magnet, and the efficiency is largely maintained after five cycles. The adsorption process fits the Langmuir isotherm model well, and the reaction was found to follow a pseudo-second-order rate., The authors are grateful to the Spanish Ministry of Science and Innovation (MAT2012-37109-C02-02, MAT2013-47878-C2-1-R and CSD2008-00023).

Nanostructured nickel was electrodeposited on a stainless steel plate. The convective-diffusion mass transfer to this nanostructured electrode was compared to that of a planar, mirror polished solid nickel electrode using the limiting current technique, for the reduction of ferricyanide, hexacyanoferrate (III) ion in an undivided cell. The effect of introducing a turbulence promoter into the electrolyte channel was also evaluated for each electrode under steady state conditions. At a Reynolds number of 700, the product of mass transfer coefficient and active electrode area, kLA for the nanostructured nickel electrode increases over 11 times compared to the mirror polished planar nickel electrode. In the presence of a turbulence promoter, the nanostructured nickel electrode shows an approximately 23 times increase in kLA compared to the planar mirror polished nickel electrode. The dimensionless mass transfer correlations Sh=aRebScdLee are compared to others in the literature. © 2012 Elsevier Ltd., J. Recio, P. Herrasti and L. Vazquez are grateful to the Spanish Ministry of Science and Innovation (MAT2009-C02-02, FIS2009-12964-C05-04) for financial support. L. Vazquez also acknowledges the Comunidad Autónoma de Madrid project S2009/PPQ-1642, AVANSENS.

The critical conditions for hydrogen embrittlement (HE) risk of high strength galvanized steel (HSGS) wires and tendons exposed to alkaline concrete pore solutions have been evaluated by means of electrochemical and mechanical testing. There is a relationship between the hydrogen embrittlement risk in HSGS and the length of hydrogen evolution process in alkaline media. The galvanized steel suffers anodic dissolution simultaneously to the hydrogen evolution which does not stop until the passivation process is completed. HSGS wires exposed to a very high alkaline media have showed HE risk with loss in mechanical properties only if long periods with hydrogen evolution process take place with a simultaneous intensive galvanized coating reduction.

We have correlated the in vitro results of testing the susceptibility of Cryptococcus neoformans to fluconazole with the clinical outcome after fluconazole maintenance therapy in patients with AIDS-associated cryptococcal disease. A total of 28 isolates of C. neoformans from 25 patients (24 AIDS patients) were tested. The MICs were determined by the broth microdilution technique by following the modified guidelines described in National Committee for Clinical Standards (NCCLS) document M27-A, e.g., use of yeast nitrogen base medium and a final inoculum of 10 4 CFU/ml. The fluconazole MIC at which 50% of isolates are inhibited (MIC 50 ) and MIC 90 , obtained spectrophotometrically after 48 h of incubation, were 4 and 16 μg/ml, respectively. Of the 25 patients studied, 4 died of active cryptococcal disease and 2 died of other causes. Therapeutic failure was observed in five patients who were infected with isolates for which fluconazole MICs were ≥16 μg/ml. Four of these patients had previously had oropharyngeal candidiasis (OPC); three had previously had episodes of cryptococcal infection, and all five treatment failure patients had high cryptococcal antigen titers in either serum or cerebrospinal fluid (titers, >1:4,000). Although 14 of the 18 patients who responded to fluconazole therapy had previously had OPC infections, they each had only a single episode of cryptococcal infection. It appears that the clinical outcome after fluconazole maintenance therapy may be better when the infecting C. neoformans strain is inhibited by lower concentrations of fluconazole for eradication (MICs

We performed a prospective study to compare the Etest and the microdilution method (NCCLS guidelines) for determining the MICs of fluconazole, itraconazole, flucytosine and amphotericin B for 35 strains of Cryptococcus neoformans. For the microdilution method (MDM) RPMI 1640 medium with 2% glucose was used for fluconazole, itraconazole and flucytosine, and Antibiotic Medium 3 for amphotericin B. For the Etest, RPMI 1640 medium with 2% glucose and solidified with 1.5% agar was used for the four antifungal agents. Amphotericin B was also tested on Antibiotic Medium 3 solidified with 1.5% agar. Fluconazole and flucytosine MICs by the Etest showed good correlation with the broth MDM (81.1 and 89.2% agreement within two dilutions, respectively). With the tested population of itraconazole- and amphotericin B-susceptible isolates, the MIC agreement for itraconazole was 54%; amphotericin B showed the lowest agreement (8.1% on Antibiotic Medium 3 and 13.5% on RPMI).

Hematology and serum biochem­ ical data are presented for the Egyptian mon­ goose, Herpestes ichneumon, caught in Doñana National Park, southwestern Spain