Improved Operation of Chloralkaline Reversible Cells with Mixed Metal Oxide Electrodes Made Using Microwaves.

This study focuses on the synthesis of mixed metal oxide anodes (MMOs) with the composition Ti/RuO2Sb2O4Ptx (where x = 0, 5, 10 mol) using hybrid microwave irradiation heating. The synthesized electrodes were characterized using scanning electron microscopy, X-ray energy-dispersive analysis, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. These electrodes were then evaluated in both bulk electrolytic and fuel cell tests within a reversible chloralkaline electrochemical cell. The configurations using the electrodes Ti/(RuO2)0.7-(Sb2O4)0.3 and Ti/(RuO2)66.5-(Sb2O4)28.5-Pt5 presented lower onset potential for oxygen and chlorine evolution reactions and reduced resistance to charge transfer compared to the Ti/(RuO2)63-(Sb2O4)27-Pt10 variant. These electrodes demonstrated notable performance in reversible electrochemical cells, achieving Coulombic efficiencies of up to 60% when operating in the electrolytic mode at current densities of 150 mA cm-2. They also reached maximum power densities of 1.2 mW cm-2 in the fuel cell. In both scenarios, the presence of platinum in the MMO coating positively influenced the process. Furthermore, a significant challenge encountered was crossover through the membranes, primarily associated with gaseous Cl2. This study advances our understanding of reversible electrochemical cells and presents possibilities for further exploration and refinement. It demonstrated that the synergy of innovative electrode synthesis strategies and electrochemical engineering can lead to promising and sustainable technologies for energy conversion.

Reducing citrus effluent toxicity: Biological-electrochemical treatment with diamond anode.

One challenge of the citrus industry is the treatment and disposal of its effluents due to their high toxicity, substantial organic load, and consequent resistance to conventional biotechnological processes. This study introduces a novel approach, using electrochemical oxidation with a boron-doped diamond anode to efficiently remove organic compounds from biodegraded pulp wash (treated using the fungus Pleurotus sajor-caju.) The findings reveal that employing a current density of 20 mA cm-2 achieves notable results, including a 44.1% reduction in color, a 70.0% decrease in chemical oxygen demand, an 88.0% reduction in turbidity, and an impressive 99.7% removal of total organic carbon (TOC) after 6 h of electrolysis. The energy consumption was estimated at 2.93 kWh g-1 of removed TOC. This sequential biological-electrochemical procedure not only significantly reduced the mortality rate (85%) of Danio rerio embryos but also reduced the incidence of morphologically altered parameters. Regarding acute toxicity (LC50) of the residue, the process demonstrated a mortality reduction of 6.97% for D. rerio and a 40.88% lethality decrease for Lactuca sativa seeds. The substantial reduction in toxicity and organic load observed in this study highlights the potential applicability of combined biological and electrochemical treatments for real agroindustrial residues or their effluents.

Effect of non-ionic surfactant in the solvothermal synthesis of anatase TiO2 nanoplates with a high percentage of exposed {001} facets and its role in the photocatalytic degradation of methylene blue dye.

The synthesis of anatase TiO2 nanoparticles with controlled morphology and increased {001} facets exposed without the presence of fluorine-derived substances is a challenge. Herein, we report a highly effective approach to fabricate anatase TiO2 nanoplates with exposed {001} facets and their exploitation as robust photocatalytic materials for dye remediation. These materials were synthesized under controlled hydrolysis and condensation reactions, using titanium (IV) n-butoxide in an ethanolic solution, with acetic and sulfuric acids, by a solvothermal method at 190 °C with or without the presence of the non-ionic surfactant Triton® X-100 and then characterized. During TiO2 crystal synthesis, the effect of a non-ionic surfactant on the TiO2 particle growth was investigated. Our results demonstrate that the proposed method can synthesize pure and crystalline anatase TiO2 square nanoplates that form nanostructured spheres with high surface area, uniformly sized mesopores, and exposed {001} facets. The presence of non-ionic surfactant increased the exposed {001} facets percentage of the formed nanoplates from 69 to 80%, decreased the crystallite thickness, but unaffected its crystalline phase and band gap energy. The kinetic constants (Ka e Kb) for the synthesized TiO2 anatase nanoplates are considerably higher than the commercial TiO2 anatase constant (Kc). The synthesized photocatalysts show higher efficiency in the photocatalytic removal of methylene blue (MB) than commercial TiO2 (for t = 120 min).

Toward efficient electrocatalytic degradation of iohexol using active anodes: A laser-made versus commercial anodes.

The X-ray iodinated contrast medium iohexol is frequently detected in aquatic environments due to its high persistence and the inefficiency of its degradation by conventional wastewater treatments. Hence, the challenge faced in this study is the development of an alternative electrochemical treatment using active anodes. We investigate the oxidation of iohexol (16.42 mg L-1) using different operating conditions, focusing on the role of different mixed metal oxide anodes in the treatment efficiency. The electrocatalytic efficiency of the Ti/RuO2-TiO2 anode prepared using a CO2 laser heating and an ionic liquid is compared with Ti/RuO2-TiO2-IrO2 and Ti/IrO2-Ta2O5 commercial anodes. The hypochlorite ions generated by the anodes are also analyzed. The effect of the electrolyte composition (NaCl, Na2SO4, and NaClO4) and current density (15, 30, and 50 mA cm-2) on the iohexol degradation is also studied. The Ti/RuO2-TiO2 laser-made anode is more efficient than the commercial anodes. After optimizing experimental parameters, this anode removes 95.5% of iohexol in 60 min and displays the highest kinetic rate (0.059 min-1) with the lowest energy consumption per order (0.21 kWh m-3order-1), using NaCl solution as the electrolyte and applying 15 mA cm-2. Additionally, iohexol-intensified groundwater was used to compare the efficiency of anodes. The Ti/RuO2-TiO2 is also more efficient in removing the organic charge from the real water matrix (21.7% TOC) than the commercial anodes. Notably, the iohexol removal achieved is higher than all electrochemical treatments already reported using state-of-the-art non-active anodes in lower electrolysis time. Therefore, data from this study indicate that the electrochemical degradation of iohexol using the Ti/RuO2-TiO2 anode is efficient and has excellent cost-effectiveness; thus, it is a promising approach in the degradation of iohexol from wastewater. Furthermore, the Ti/RuO2-TiO2 active anode is competitive and can be an excellent option for treating effluents contaminated with recalcitrant organic compounds such as iohexol.

Recent advances on modified reticulated vitreous carbon for water and wastewater treatment - A mini-review.

Recently, modifications on reticulated vitreous carbon (RVC) have attracted attention as a promising strategy to produce low-cost, stable, and highly active electrodes leading to significant advances in the water/wastewater treatment field compared with raw RVC. Modified RVC materials have been used as cathode, anode, and membrane. Improvements on physical and electrocatalytic properties are achieved by RVC modification via diverse strategies, including the deposition of metal oxides, the introduction of surface functional groups, and the formation of composites, which were used to remove organic contaminants and pathogens from water matrices, as summarized in this mini-review. This mini-review mainly focused on papers published from 2015 to 2020 that reported modified RVC electrodes to eliminate pollutants and pathogens from water matrices by electrochemical advanced oxidation processes. Likewise, news challenges and opportunities are discussed, and perspectives for the ongoing and future studies in this research field are also given.

Towards a higher photostability of ZnO photo-electrocatalysts in the degradation of organics by using MMO substrates.

In this work, it is proposed a novel strategy to increase the photostability of the ZnO photoelectrocatalyst under prolonged light irradiation, without the addition or deposition of metals and/or semiconductor oxides during their synthesis. This strategy is based on the use of a mixed metal oxide (MMO-Ru0.3Ti0.7O2) coating as the substrate for the electrodeposition of ZnO. To assess it, the electrodeposition of ZnO films on Ti and Ti/MMO substrates and the photoelectrocatalytic activity of these materials for the degradation of the herbicide clopyralid were studied. The results showed that the substrate directly influenced the photo-stability of the ZnO film. Under the incidence of UV light and polarization, the novel Ti/MMO/ZnO electrode showed greater photocurrent stability as compared to Ti/ZnO, which is a very important outcome because the behavior of these electrodes was similar when compared in terms of the degradation of clopyralid. Single electrolysis was not able to degrade efficiently clopyralid at the different potentials studied. However, the irradiation of UV light on the polarized surface of the Ti/ZnO and Ti/MMO/ZnO electrodes increased markedly the degradation rate of clopyralid. A synergistic effect was observed between light and electrode polarization, since the rate of degradation of clopyralid was twice as high in photoelectrocatalysis (PhEC) than in photocatalysis (PhC) and different intermediates were formed. From these results, mechanisms of degradation of clopyralid for the PhC and PhEC systems with the Ti/ZnO and Ti/MMO/ZnO electrodes were presented. Therefore, the Ti/MMO/ZnO electrode could be a cheap and simple alternative to be applied in the efficient photodegradation of organic pollutants, presenting the great advantage of having a facile synthesis and high capacity to work at relatively low potentials.

Novel Ti/RuO2IrO2 anode to reduce the dangerousness of antibiotic polluted urines by Fenton-based processes.

The treatment of hospital wastewater is very complex, so treating polluted human urine is a significant challenge. Here, we tested a novel MMO-Ti/RuO2IrO2 electrode to reduce the ecotoxicity risk of hospital urines contaminated with antibiotics. This electrode was used as the anode in electro-Fenton (EF) and photoelectro-Fenton (PhEF) processes. The results were compared with those obtained using the boron-doped diamond (BDD) anode, as well as those obtained by a conventional Fenton oxidation. In order to analyze the performance of the processes, the treatments were evaluated on the subject of Penicilin G (PenG) removal, toxicity (using a standardized method with Vibrio Fisheri), and antibiotic activity (Enterococcus faecalis as the target bacterium). The results reveal that PenG degrades in the following order: Fenton < EF < PhEF. The best results are found for the MMO-PhEF, which completely removed PenG, decreased 96% of toxicity, and completely removed antibiotic activity. Besides, for comparison, tests were performed with BDD, and results point out the higher convenience of the new electrode in terms of acceptable use of energy because the effluents generated can be further degraded in an urban wastewater treatment plant. Because of that, MMO-RuO2-IrO2 emerges as a promising cost-effective material for the pre-treatment of hospital urine effluents.

Improved 4-nitrophenol removal at Ti/RuO2-Sb2O4-TiO2 laser-made anodes.

In this study, binary and ternary mixed metal oxide anodes of Ti/RuO2-Sb2O4 and Ti/RuO2-Sb2O4-TiO2 were prepared using two different heating methods: conventional furnace and alternative CO2 laser heating. The produced anodes were physically and electrochemically characterized by using different techniques. The main difference found in the laser-made anodes was their more compact morphology, without the common deep cracks found in anodes made by typical thermal decomposition, which showed an important correlation with the prolonged accelerated service life. The correlation between the physicochemical properties of the anodes with their performance towards the 4-nitrophenol oxidations is discussed. The results demonstrated that the ternary anode (Ti/RuO2-Sb2O4-TiO2) is very promising, presenting a kinetic 5.7 times faster than the respective binary anode and the highest removal efficiency when compared with conventionally made anodes. Also, the lowest energy consumption per unit of mass of contaminant removed is seen for the laser-made Ti/RuO2-Sb2O4-TiO2 anode, which evidences the excellent cost-benefit of this anode material. Finally, some by-products were identified, and a degradation route is proposed. Graphical abstract.

Biodegradability improvement of clopyralid wastes through electrolysis using different diamond anodes.

The use of boron-doped (BDDs) anodes for efficient removal of complex organic molecules, such as organochlorine compounds, is well stated in the literature. However, the role of the different characteristics of this anode on the transformation of these type of contaminants into more biodegradable molecules is a topic of interest that need to be clarified when aimed an efficient combination of an electrochemical system as a previous step to biological treatment. In this work, improvement in the biodegradability of synthetic wastes polluted with clopyralid, as an organochlorine model compound, is studied after electrolysis with different BDDs in the presence of the two most common supporting electrolytes (containing sulfate or chloride ions). For that, clopyralid removal, mineralization, aromatics intermediates, short-chain carboxylic acids, and inorganic ions were monitored. Improved results were found in sulfate media for BDD with 200 ppm, capable of removing 88.7% of contaminants and 85% of TOC, resulting in an improvement in biodegradability of almost 7-fold compared to the initial sample. These findings point out that lower doping levels are preferable when coupling studied technologies.

Influence of the doping level of boron-doped diamond anodes on the removal of penicillin G from urine matrixes.

The objective of this study is to understand the influence of the characteristics of boron-doped diamond anodes on the degradation of Penicillin G contained in urine. Therefore, five commercial BDD anodes with different boron doping levels (100 ppm - 8000 ppm) were studied. These electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and electrolysis. The boron doping was found to correlate well with the electrochemical properties of the electrodes, and results indicate a different behavior in drug degradation. The improvement in the toxicity and the reduction of the antibiotic effect of urine were the most innovative inputs monitored. For this, the concentration of Penicillin G, the toxicity toward Vibrio fisheri, and the antibiotic effect in Enterococcus faecalis were monitored. The best results were found for the BDD with a boron content of 200 ppm, capable of removing 100% of the antibiotic, reducing toxicity by 90%, and eradicating the antibiotic effect. These results indicate that low doping levels are more efficient for urine removal by anodic oxidation.

A Comparative Study of the Catalytic Performance of Pt-Based Bi and Trimetallic Nanocatalysts Towards Methanol, Ethanol, Ethylene Glycol, and Glycerol Electro-Oxidation.

Carbon-supported platinum is used as an anode and cathode electrocatalyst in low-temperature fuel cells fueled with low-molecular-weight alcohols in fuel cells. The cost of Pt and its low activity towards the complete oxidation of these fuels are significant barriers to the widespread use of these types of fuel cells. Here, we report on the development of PtRhNi nanocatalysts supported on carbon made using a reduction chemistry method with different atomic rates. The catalytic activity of the developed catalysts towards the electro-oxidation of methanol, ethanol, ethylene glycol, and glycerol in acidic media was studied. The obtained catalysts performances were compared with both commercial Pt/C and binary Pt75Ni25/C catalyst. The nanostructures were characterized, employing inductively coupled plasma optical emission spectrometer, X-ray diffraction, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The binary catalyst presents a mean particle size of around 2 nm. Whereas the ternary catalysts present particles of similar size and with some large alloy and core-shell structures. The alcohol oxidation onset potential and the current density measured after 3600 s of chronoamperometry were used to classify the catalytic activity of the catalysts towards the oxidation of methanol, ethanol, ethylene glycol, and glycerol. The best PtRhNi/C catalyst composition (i.e., Pt43Rh43Ni14/C) presented the highest activity for alcohols oxidation compared with all catalysts studied, indicating the proper tuning composition influence in the catalytic activity. The enhanced activity of Pt43Rh43Ni14/C can be attributed to the synergic effect of trimetallic compounds, Pt, Ni, and Rh.

The Effect of Pt Loading on Catalytic Activity of Pb0.25@Ptx/C Nanocomposites Toward Ethanol Oxidation.

Here, we study the influence of the Pt loading and the particle size of Pb0.25@Ptx/C catalysts on their specific activity toward ethanol oxidation in acid media. High angle annular dark field-scanning transmission electron microscopy and electron energy loss spectroscopy data indicate the formation of Pb0.25@Ptx/C core-shell structures, which are well dispersed on carbon support, with spherical shapes and small particle sizes (2.9-6.6 nm). Cyclic voltammetry experiments confirm characteristic profiles of polycrystalline Pt for Pb0.25@Ptx/C structures. The specific activity of the catalysts toward ethanol oxidation reaction greatly depends on the Pt content on Pb core, and consequently, depends on the size of the nanoparticles. The optimum activity occurs with the lowest Pt load in the shell and smaller particle size. Enhancements in specific activity result from the higher number of nanoparticles available for the ethanol oxidation reaction and the tensile strain effect of Pt atoms on the surface expanded in Pb0.25@Pt0.75/C. The lower activity observed for the catalysts with loads of 35 and 50% wt. (Pb0.25@Pt1.5 and Pb0.25@Pt2.25/C, respectively) in comparison to Pt/C, could be explain by the larger particle sizes obtained at these catalysts. Moreover, the Pb0.25@Pt0.75/C catalyst has high electrochemical stability and should be more stable in direct ethanol fuel cells systems than monolithic Pt catalysts. This is because the Pt shell in Pb0.25@Pt0.75/C exhibits lower chemical potential (p < 0) than at Pt/C and at the other core-shell catalysts studied; thus, reducing its tendency to dissolve. The developed core-shell nanostructure is thus a potential candidate as high-performance anode catalyst for application in direct ethanol fuel cells.

Photoelectrolysis of clopyralid wastes with a novel laser-prepared MMO-RuO2TiO2 anode.

This paper studies the applicability of a novel laser-prepared mixed metal oxide (MMO-RuO2TiO2) anode in the photoelectrochemical degradation of clopyralid, a toxic and biorefractory herbicide. Results are compared to those obtained using the well-known boron-doped diamond (BDD) anode and demonstrate that, although the electrolysis with diamond is more effective than that obtained with the new electrode, the irradiation of UVC light makes the novel MMO material more effective in chloride media. It was explained in terms of the homolysis of hypochlorous acid/hypochlorite to form chloride and hydroxyl radicals. Photoelectrochemical degradation with MMO produced a marked synergistic effect in TOC removal, especially in the presence of chloride ions. On the contrary, for the BDD anode, at the tested conditions, antagonisms were found in both sulfate and chloride media. These important synergisms allows finding conditions in which the novel anode can be competitive with the BDD.

Influence of magnetic field on barium sulfate incrustation from aqueous solutions.

The formation of scales in the petroleum industry, such as those composed of calcium and barium sulfates, may reduce productivity since these sediments can partially or totally obstruct the pipes. The mitigation of these inorganic precipitates can be accomplished by using scale inhibitors or by non-intrusive physical technologies. Here, we investigated the influence of magnetic field on the incrustations of barium sulfate by analyzing the concentration of barium and sulfate ions, the solution flow rate, the capillary tube geometry, and the magnetic field intensity in a homemade experimental unit supported on the monitoring of the dynamic differential pressure. The results show that the saline concentration and the flow rate of the solutions and the geometry of the capillary tube have a significant influence on the dynamics of barium sulfate incrustation. The presence of the magnetic field tends to prolong the induction time of the barium sulfate precipitation. A semi-empirical model was used to describe the effect of the studied variables on the barium sulfate incrustation behavior. The X-ray diffraction data of the precipitated particles analyzed using the Rietveld method suggest that the use of the magnetic field favor the formation of more crystalline particles and with smaller crystallite size than those formed in the absence of a magnetic field. Optical and scanning electron microscopy measurements also corroborate with these findings. The results from this study suggest that magnetic fields can be of interest in practical crystallization processes of barium sulfate and successfully applied to decrease the speed of barium sulfate incrustation in pipelines.

Synthesis of Ni-SiO2/C Supported Platinum Catalysts for Improved Electrochemical Activity Towards Ethanol Oxidation.

A series of Pt/Ni-SiO2/C catalysts with different mass proportions of Ni-SiO2/C (0:100, 30:70, 50:50, 70:30 and 100:0) were prepared and studied towards ethanol electrochemical oxidation in acid medium. The support silica particles were initially synthesized via sol-gel and then modified with NiCl2. The Ni deposited on the silica surface plays a role promoting nucleation sites for the reduction of platinum. Pt was further chemically reduced onto Ni-SiO2 using formic acid and loaded onto carbon Vulcan XC-72 R. The Pt/Ni-SiO2/C catalysts were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, temperature-programmed reduction, X-ray photoelectron spectroscopy, transmission electron microscopy and inductively coupled plasma-optical emission spectroscopy. The physical characterizations reveal the formation of oxide-metal composite and strong interaction between Pt and the Ni-SiO2 composite. The Pt/Ni-SiO2/C catalyst with meso/macroporous structure exhibits higher electrocatalytic activity towards ethanol oxidation and better stability, after 48 h of electrolysis, than a commercial Pt/C catalyst. These improved features could be due to presence of Ni-SiO2 composite that promotes corrosion resistance of the support and prevents the aggregation of Pt nanoparticles and their detachment from the support. The low poisoning of the Pt/Ni-SiO2/C catalyst is probably due to the enhanced oxygen content on the composite surface. The high electrocatalytic activity and enhanced electrochemical stability of the Pt/Ni-SiO2/C catalyst make it promising for further fuel cell applications.

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.

Electrochemical and/or microbiological treatment of pyrolysis wastewater.

Electrochemical oxidation may be used as treatment to decompose partially or completely organic pollutants (wastewater) from industrial processes such as pyrolysis. Pyrolysis is a thermochemical process used to obtain bio-oil from biomasses, generating a liquid waste rich in organic compounds including aldehydes and phenols, which can be submitted to biological and electrochemical treatments in order to minimize its environmental impact. Thus, electrochemical systems employing dimensionally stable anodes (DSAs) have been proposed to enable biodegradation processes in subsurface environments. In order to investigate the organic compound degradation from residual coconut pyrolysis wastewater, ternary DSAs containing ruthenium, iridium and cerium synthetized by the 'ionic liquid method' at different calcination temperatures (500, 550, 600 and 700 °C) for the pretreatment of these compounds, were developed in order to allow posterior degradation by Pseudomonas sp., Bacillus sp. or Acinetobacter sp. bacteria. The electrode synthesized applying 500 °C displayed the highest voltammetric charge and was used in the pretreatment of pyrolysis effluent prior to microbial treatment. Regarding biological treatment, the Pseudomonas sp. exhibited high furfural degradation in wastewater samples electrochemically pretreated at 2.0 V. On the other hand, the use of Acinetobacter efficiently degraded phenolic compounds such as phenol, 4-methylphenol, 2,5-methylphenol, 4-ethylphenol and 3,5-methylphenol in both wastewater samples, with and without electrochemical pretreatment. Overall, the results indicate that the combination of both processes used in this study is relevant for the treatment of pyrolysis wastewater.

Electrochemical mineralization of cephalexin using a conductive diamond anode: A mechanistic and toxicity investigation.

The contamination of surface and ground water by antibiotics is of significant importance due to their potential chronic toxic effects to the aquatic and human lives. Thus, in this work, the electrochemical oxidation of cephalexin (CEX) was carried out in a one compartment filter-press flow cell using a boron-doped diamond (BDD) electrode as anode. During the electrolysis, the investigated variables were: supporting electrolyte (Na2SO4, NaCl, NaNO3, and Na2CO3) at constant ionic strength (0.1 M), pH (3, 7, 10, and without control), and current density (5, 10 and 20 mA cm-2). The oxidation and mineralization of CEX were assessed by high performance liquid chromatography, coupled to mass spectrometry and total organic carbon. The oxidation process of CEX was dependent on the type of electrolyte and on pH of the solution due to the distinct oxidant species electrogenerated; however, the conversion of CEX and its hydroxylated intermediates to CO2 depends only on their diffusion to the surface of the BDD. In the final stages of electrolysis, an accumulation of recalcitrant oxamic and oxalic carboxylic acids, was detected. Finally, the growth inhibition assay with Escherichia coli cells showed that the toxicity of CEX solution decreased along the electrochemical treatment due to the rupture of the ß-lactam ring of the antibiotic.

Morphological dependence of silver electrodeposits investigated by changing the ionic liquid solvent and the deposition parameters.

The low toxicity and environmentally compatible ionic liquids (ILs) are alternatives to the toxic and harmful cyanide-based baths used in industrial silver electrodeposition. Here, we report the successful galvanostatic electrodeposition of silver films using the air and water stable ILs 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIM]TfO) and 1-H-3-methylimidazolium hydrogen sulphate ([HMIM(+)][HSO4(-)]) as solvents and AgTfO as the source of silver. The electrochemical deposition parameters were thoughtfully studied by cyclic voltammetry before deposition. The electrodeposits were characterized by scanning electron microscopy coupled with X-ray energy dispersive spectroscopy and X-ray diffraction. Molecular dynamics (MD) simulations were used to investigate the structural dynamic and energetic properties of AgTfO in both ILs. Cyclic voltammetry experiments revealed that the reduction of silver is a diffusion-controlled process. The morphology of the silver coatings obtained in [EMIM]TfO is independent of the applied current density, resulting in nodular electrodeposits grouped as crystalline clusters. However, the current density significantly influences the morphology of silver electrodeposits obtained in [HMIM(+)][HSO4(-)], thus evolving from dendrites at 15 mA cm(-2) to the coexistence of dendrites and columnar shapes at 30 mA cm(-2). These differences are probably due to the greater interaction of Ag(+) with [HSO4(-)] than with TfO(-), as indicated by the MD simulations. The morphology of Ag deposits is independent of the electrodeposition temperature for both ILs, but higher values of temperature promoted increased cluster sizes. Pure face-centred cubic polycrystalline Ag was deposited on the films with crystallite sizes on the nanometre scale. The morphological dependence of Ag electrodeposits obtained in the [HMIM(+)][HSO4(-)] IL on the current density applied opens up the opportunity to produce different and predetermined Ag deposits.

Electrochemical oxidation and electroanalytical determination of xylitol at a boron-doped diamond electrode.

Xylitol is a reduced sugar with anticariogenic properties used by insulin-dependent diabetics, and which has attracted great attention of the pharmaceutical, cosmetics, food and dental industries. The detection of xylitol in different matrices is generally based on separation techniques. Alternatively, in this paper, the application of a boron-doped diamond (BDD) electrode allied to differing voltammetric techniques is presented to study the electrochemical behavior of xylitol, and to develop an analytical methodology for its determination in mouthwash. Xylitol undergoes two oxidation steps in an irreversible diffusion-controlled process (D=5.05 × 10(-5)cm(2)s(-1)). Differential pulse voltammetry studies revealed that the oxidation mechanism for peaks P1 (3.4 ≤ pH ≤ 8.0), and P2 (6.0 ≤ pH ≤ 9.0) involves transfer of 1H(+)/1e(-), and 1e(-) alone, respectively. The oxidation process P1 is mediated by the (•)OH generated at the BDD hydrogen-terminated surface. The maximum peak current was obtained at a pH of 7.0, and the electroanalytical method developed, (employing square wave voltammetry) yielded low detection (1.3 × 10(-6) mol L(-1)), and quantification (4.5 × 10(-6) mol L(-1)) limits, associated with good levels of repeatability (4.7%), and reproducibility (5.3%); thus demonstrating the viability of the methodology for detection of xylitol in biological samples containing low concentrations.