Samples of PM10 and PM2.5 were collected using High Vol and MiniVol devices on the platform of a subway station in Mexico City and in an outdoor location close to it, using such devices. Soluble ...extractable organic matter (SEOM) and water solubility of metals were determined. Elemental composition and solubility of trace metals were determined and individual aerosol particles were studied with scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The concentration levels in both sizes were similar during all days with the exception of weekends, especially on Sunday when activity decreases due to lower trains’ frequency. The largest particles concentrations in the subway were found from 06:00 to 14:00 and the lowest concentrations were registered from 22:00 to 06:00. Concentrations of PM2.5 ranging between 60 μg m−3 and 93 μg m−3 (10% and 90% percentile) in the subway were 6% larger than outside, whereas PM10 were 20% larger than outside ranging from 88 μg m−3 to 145 μg m−3. Greater Fe, Cu, Ni, Cr and Mn concentrations were quantified in the subway samples as compared to the airborne particles by up to 2.5, 9, 1.8, 2.0 and 2.6 times, respectively. Even when the solubility percent of these metals in the subway PM was smaller than in the outdoor airborne particles, metals’ concentrations were greater. SEM and EDS exhibit the presence of many individual particles with a large metal content in the subway samples. Correlation analysis showed the influence of outdoor PM in the subway aerosols, but characterization revealed also important differences in the presence of metals and SEOM, due to underground sources such as friction, brake system, and metals from sparking. This means that a large number of commuters are exposed during labor days to large toxic metals concentrations as they transit.
► First attempt to study in depth the air quality in the underground system in Mexico. ► Elemental speciation was done to assess the underground’s microenvironment. ► This is a comparative study broaching several world underground systems. ► Water solubility of the metals incorporated into the PM particles was determined. ► SEM micrographs and EDX analysis revealed important aspects of morphology.
Choline chloride based-deep eutectic solvents (DES), namely: choline chloride (ChCl): urea (U), reline, ChCl: glycerol (G), and ChCl: ethylene glycol (EG), ethaline, were used as leaching media for ...the cathode powder of spent Ni-MH batteries. It is shown that the best metal extraction was obtained with the reline DES. The resulting solution was used as electrolytic bath for the electrochemical deposition of a Ni–Co alloy onto a glassy carbon electrode (GCE). A theoretical model that involves the simultaneous presence of two contributions, to the total current density, namely: three-dimensional nucleation and diffusion-controlled growth of the bimetallic phases, and the residual water reduction on the growing surfaces of the bimetallic (Ni–Co) nuclei, was implemented for the analysis of the potentiostatic current density transients. From this analysis, the potential dependence of kinetic parameters was obtained. SEM images of the GCE, after the potentiostatic electrodeposition, showed the formation of nuclei distributed all over the substrate surface. From EDX and XRD analysis it is shown that these nuclei were composed by Ni, Co and oxygen.
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•Reline was used as leaching media of cathode powder of Ni-MH spent batteries.•Resulting liquor was used as electrolytic bath for Ni–Co alloy electrodeposition.•Ni–Co electrodeposition mechanism and kinetics onto glassy carbon was assessed.•3D nucleation of Ni–Co and water reduction occurs simultaneously.•Reline is a green alternative for metal recovery from spent batteries.
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•Co electrochemical nucleation and growth at different temperatures was studied.•The exchange current density and transfer coefficient were assessed.•From i-t plots the mechanism and ...kinetics of Co nucleation were assessed.•Mechanism involved the proton reduction onto Co growing surfaces.•SEM showed that the cobalt nuclei are bigger as the temperature increases.
From potentiodynamic and potentiostatic experiments, the cobalt electrochemical nucleation and growth process, onto the glassy carbon electrode surfaces, from an aqueous solution containing 10−2M CoCl2 and 1M NH4Cl (pH=4.66) at different temperatures (15–60°C) is reported. It was found that while the equilibrium potential moves to more negative values as the temperature of the system was increased, the contrary was observed for the nucleation overpotential, ηnucleation, required for the onset of cobalt nucleation onto the surfaces of vitreous carbon. From Tafel plots recorded at the different temperatures considered, both: the transfer coefficient, α, and the exchange current density, j0, associated with the Co(II)/Co(0) system were assessed, and from the Arrhenius plot (ln j0 vs. T−1) the activation energy for Co(II) reduction of (27.9±0.3) kJmol−1 was estimated. From analysis of the potentiostatic current density transients according with the formalism proposed by Palomar-Pardavé et al. (Electrochim. Acta 50 (2005) 4736-4745), the total current density was de-convoluted into individual contributions, due to formation of multiple mass-transfer controlled 3D Co nuclei and that associated to the proton reduction occurring simultaneously on the growing surface of the Co nuclei. The latter contribution was practically null at 10°C, however, it drastically increased as the temperature of the system did, provoking that the cathodic efficiency for Co deposition diminished. Furthermore, it was found that both the number density of active sites, N0, and the nucleation rate, A, for Co nucleation depend exponentially with ηnucleation, regardless of temperature, except at 60°C where N0 diminished linearly with ηnucleation. From variations of the Co(II) ions diffusion coefficient with temperature, a value of (8.5±0.2) kJmol−1 was obtained for the activation energy for bulk diffusion. SEM analysis showed that the cobalt nuclei are bigger as the temperature increases; however, the coverage of the electrode surfaces becomes lower.
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•PM2.5 concentrations at station platforms are 2–5 times greater than outdoors.•The greater the depth, the greater the PM2.5 concentrations, as well as species.•Iron, Mn, Cr and other ...metals come from wheel/rail mechanical abrasion.•Most abundant metals in subway aerosols are Fe >>Cu > Zn > Mn > Pb > Cr > V>Ni.•Bioavailability using ALF was Zn > Pb > V > Ni > Cu > Mn > Cr in subway PM2.5.
PM2.5 that have been related to public health risks, were collected during two seasons with High-Vol samplers in platforms of a Mexican subway station, which interconnects through transfers three lines having different depths. The objective was to study the influence of depth on the PM2.5 concentrations and their species. PM2.5 concentrations in cold-dry and warm-dry seasons presented statistical differences, being in average 57 and 66 μgm−3 respectively, in the shallower line 9; 90 μgm−3 and 111 μgm−3 in line 1; and 104 and 122 μgm−3in the deepest line 7. During the cold-dry season and warm-dry season PM2.5concentrations in the subway environment were respectively up to 3.5 times and up to 5 times greater than in the ambient air. Like PM2.5, metals analyzed with an OES-ICP presented higher concentrations in deeper lines as well as PAHs quantified with CG-MS, which ranged from 4.5 to 11.7 ngm−3. High PM2.5, metals and organic toxic concentrations found in deeper lines of the subway environment represent a risk for commuters endorsing the need for ventilation systems to reduce them. Zn, Pb, V and Ni in subway particles presented the highest solubility in artificial lysosomal fluid suggesting high bioavailability in the lung fluids.
Palladium nanoparticles (PdNPs) were formed and supported onto the surface of a glassy carbon electrode (GCE) from a single potentiostatic step using palladium chloride (PdCl2) as the precursor salt, ...dissolved in a deep eutectic mixture formed by 2-Hydroxy-N,N,N-trimethylethanaminium chloride (choline chloride) and diaminomethanal (urea). Analysis of the potentiostatic current density transients allows to accurately establish the amount of Pd deposited on the GCE surface required to determine the so-called mass activity, as defined by the ratio between methanoic acid (formic acid) oxidation current and palladium mass electrodeposited on the electrode. From SEM analysis of the GCE surface modified with PdNPs, it was found that PdNPs were distributed uniformly over the electrode surface, having an average size of (60 ± 9) nm. EDX and XPS analysis confirm a core-shell morphology constituted by a Pd core surrounded by a palladium (II) Hydroxide- palladium (II) oxide (Pd(OH)2-PdO) shell. The GCE modified with PdNPs (GCE/PdNPs) were used to oxidize formic acid from aqueous electrolytic baths added with perchloric acid (HClO4) or sulfuric acid (H2SO4). It was shown that the maximum mass activity depended on both, the nature of the electrolytic bath and the applied potential for the PdNPs electrodeposition. However, the best mass activity ((5085 ± 129) mA mgPd−1) was achieved with the GCE/PdNPs, formed at −700 mV vs. the silver quasi reference electrode (Ag QRE), immersed in the HClO4 electrolytic bath, even when the formic acid concentration was half that used in the H2SO4 electrolytic bath. Furthermore, the mass activities of the PdNPs reported in this work rank high among other values reported in the literature for nanoparticles based on palladium but synthesized with more complex and expensive processes, having the advantage of being obtained by a simple, rapid, and cost-effective electrochemical method.
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•PdNPs were electrodeposited onto GCE from a deep eutectic solvent.•Pd@Pd(OH)2 was the core-shell structure from SEM and XPS.•Pd@Pd(OH)2 mass activity towards FAOR in acid media was evaluated.•Pd@Pd(OH)2 exhibited outstanding mass activity toward FAOR.
This work deals with the electrochemical synthesis and characterization of nickel nanoparticles, NiNPs, onto a glassy carbon electrode, GCE, from a deep eutectic solvent prepared by mixing choline ...chloride and urea in 1:2 M ratio at 60 °C. From the potentiodynamic study, up to 3 energetically different reduction stages can be identified during the Ni(II) reduction process. Two of them (R1 and R2) are mass-transfer controlled process. A crossover between the cathodic and anodic voltammetric scans, characteristic of nucleation processes was clearly observed. From this singular point, the equilibrium potential, Eeq ((-505 ± 5) mV vs. Ag QRE) of the system Ni(II)/Ni(0) was measured. From Tafel plots, the exchange current density of the nickel deposition (j0 = (1.7 ± 0.3) μAcm−2) and its corresponding energy transfer coefficient (α = 0.79 ± 0.2) were obtained. From analysis of potentiostatic current density transients, it was possible to deconvolve the different individual contributions to the total current, namely: i) multiple 3D nucleation and mass transfer controlled-growth of NiNPs and ii) residual water reduction on the growing surfaces of the NiNPs. Furthermore, from integration of the respective j-t plots of each of these contributions it was possible to note that the amount of charge of each process depends of the deposition time and the applied potential and can be controlled by a suitable selection of these experimental variables. Due to water presence, the reduction to hydrogen and hydroxyl ions, precipitation of Ni(OH)2 (s) on the surfaces of the NiNPs, is likely to occur. SEM and HRTE images, taken on the GCE surfaces after potentiostatic deposition of nickel on the R1 potential zone, show the formation of NiNPs all over the surface. Moreover, XPS analysis of the electrode surface indicates the presence of metallic nickel, Ni(0), and NiO/Ni(OH)2 compounds. However, XPS spectra recorded from the same surfaces after a sputtering process, revealed the presence of pure Ni(0), which confirms that the NiNPs obtained after electrodeposition are core-shell type with a core formed by metallic nickel and a thin shell of NiO/Ni(OH)2 (ad).
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•Ni nanoparticles, NiNPs, were electrodeposited from a deep eutectic solvent.•From Tafel plots, the exchange current density and energy transfer were obtained.•The mechanism and kinetics were assessed from analysis of j-t plots.•Total current involves 3D nucleation and residual water reduction on the NiNPs.•Charge of each process depends of time and the applied potential.
► API X52 steel corrosion in H
2SO
4 was evaluated with EIS. ► The corrosion inhibition efficiency of six thiadiazole compounds were evaluated. ► The alkyl chain length of these compounds was related ...to their corrosion IE. ► 2-Amino-5-undecyl-1,3,4-thiadiazole, IC-11, was the best inhibitor at 100
ppm. ► IC-11 corrosion inhibition lasted over 90% for at least 720
h.
The corrosion inhibition efficiency of 2 amino 5 alkyl 1,3,4 thiadiazole compounds with different alkyl chain lengths, namely: 2 ethyl, 3
n propyl, 5
n penthyl, 7 hepthyl, 11 undecyl and 13 tridecyl, was evaluated in the system steel/1
M H
2SO
4. These compounds were synthesized, characterized by FT-IR and NMR spectroscopy analysis and evaluated using electrochemical impedance spectroscopy and SEM analysis. The results showed that the inhibition mechanism involves blockage of the steel surface by the inhibitor molecules by a Langmuir-type adsorption process and that the alkyl chain length plays an important role in the inhibition efficiency of the synthesized inhibitors.
Pd and PdM (M = Fe or Co) nanostructured electrocatalysts were synthesized by the impregnation method and supported on carbon black Vulcan XC-72R for the formic acid oxidation reaction, FAOR, in acid ...medium. Nitrates or chlorides were used as Fe and Co precursors to study the counter ion role on the physicochemical features and electrochemical performance of the electrocatalysts. TEM analysis showed that PdM was deposited on the carbon material with a particle size around 2–3 nm. From XRD, peaks associated with the fcc palladium planes were observed along with evidence of PdM alloy formation, particularly when the nitrate salts were used as metal precursors. Furthermore, XPS analyses indicated that nitrates promote the metal oxide formation to a greater extent than chlorides, mainly for Pd. PdCo electrocatalyst obtained from nitrates exhibited the highest performance for FAOR with a steady state current density of 451 and 313 μA cm−2 at 200 and 400 mV respectively, which is in both cases, 3 times larger than that developed for a commercial Pd/C catalyst.
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•Pd and PdM (M = Fe and Co) electrocatalysts were synthesized by impregnation method.•Nitrates or chlorides were used as Fe and Co precursors.•XRD and TEM showed formation of Pd and PdM alloy nanoparticles.•Nitrates favored metal oxides formation.•PdCo-N/C exhibited the highest performance for FAOR.
The mechanism and kinetics of zinc electrochemical nucleation and growth onto glassy carbon surface, from Zn(II) ions dissolved in the choline chloride (ChCl)–urea eutectic mixture, reline, at ...different temperatures,
T
, within the 303 to 363 K range, are reported for the first time. From the potentiodynamic study, the exchange current density,
j
0
, and the energy transfer coefficient, α, of the Zn(II)
DES
+ 2e
−
GCE/Zn(s)
↔ Zn
(s)
reaction were estimated as a function of
T
. It was found that while
j
0
depends exponentially on
T
, α= 0.12 ± 0.02 remains almost constant. Furthermore, the activation energy,
E
*
= (33 ± 0.2) kJmol
−1
, of this reaction was assessed from the Arrhenius-type plot (ln
j
0
vs.
T
−1
). Analysis of the potentiostatic current density transients allowed to establish that the zinc electrodeposition mechanism occurs via the simultaneous presence of a Langmuir-type adsorption–desorption equilibrium, an instantaneous nucleation process with two-dimensional (2D) growth limited by the rate of lattice incorporation, and a diffusion-controlled three-dimensional nucleation and growth contribution (3D), which is particularly notorious at 348 K. This is the first time that a 2D-3D nucleation transition has been observed during the electrochemical deposition of metals from deep eutectic solvents (DES). From the 2D nucleation process contribution to the total current density, it was possible to determine the surface roughness factor and the electrochemically active surface area of the glassy carbon electrode (GCE). The time evolution of the Zn monolayer formation onto the GCE was also reported.
The alloys of the aluminum bronze system contain 5–14wt% Al that can be heat treated giving as result of different microstructures that were characterized by optical microscopy and scanning electron ...microscopy. This work aimed at investigating the influence of the microstructures of a Cu-9Al-3Ag alloy obtained after normalizing and annealing heat treatments, on the corrosion behavior in a saline medium containing 0.5 M sodium chloride, NaCl. The corrosion effect on the phases compounding the overall microstructures as result of immersing the samples in the corrosive medium was evaluated using cyclic voltammetry, potentiodynamic polarization curves, and electrochemical impedance spectroscopy. The results showed that normalizing and annealing heat treatments redefined the distribution of the α phase and, in addition led to formation of proeutectoid pearlite (α + γ
2
), which is a microstructural constituent configured similarly to that present in diverse carbon steels, though in this case displaying a sequence of alternate lamellae of α and γ
2
, respectively. From the results of the linear polarization plots, the maximum anodic potentials became apparent, just like the regions where the trend of the graph gave the impression that passivation were to gain control. Likewise, the Tafel plots and impedance tests evidenced that the as-cast and normalized samples exhibited a better resistance to corrosion, at variance with the results of the annealed sample.
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