Soluble Anode Research Articles

Removal of fluoride, SDS, ammonia and turbidity from semiconductor wastewater by combined electrocoagulation–electroflotation

Semiconductor industry effluents contain organic and inorganic pollutants, such as sodium dodecyl sulfate (SDS), fluoride and ammonia, at high levels which consists a major environmental issue. A combined EC–EF process is proposed as a post-treatment after precipitation for simultaneous clarification and removal of pollutants. In EC step, a hybrid Fe–Al was used as the soluble anode in order to avoid supplementary EC step. EC-Fe is more suitable for SDS removal; EC-Al is more suitable for fluoride removal, while EC with hybrid Al-Fe makes a good compromise. Clarification and ammonia oxidation were achieved in the EF step. Effects of anodic material, initial pH, current, anion nature, chloride concentration and initial pollutant concentration were studied. The final concentrations may reach 0.27, 6.23 and 0.22 mg L−1 for SDS, fluoride and ammonia respectively. These concentrations are far lower than the correspondent discharge limits. Similarly, the final turbidity was found 4.35 NTU which is lower than 5NTU and the treated water does not need further filtration before discharge. Furthermore, the EC-EF process proves to be sufficiently energy-efficient with less soluble electrode consumption.

Photo-induced anisotropy in ZnO/PVA nanocomposites prepared by modified electrochemical method in PMA matrix

Substantial photo-induced optical anisotropy was discovered in ZnO/PVA nanocomposites under the influence of external bicolor laser illumination. Zinc oxide nanoparticles were synthesized by electrolysis of a sodium chloride aqueous medium including poly-methacrylic acid (PMA) in a cell system having a soluble zinc anode. The structural analysis of the ZnO powder samples has been carried out by X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM). The polyvinyl alcohol (PVA) embedded ZnO films obtained from the powder samples possess larger grain sizes than those in powder form. The films were prepared from the same polymer matrix but elaborated with two different PVA contents which are respectively 15% and 30%. The photoinduced anisotropy was identified by using two bicolor Er: glass laser beams incident at different angles. Substantial influence of the technological processes on the embedded nanoparticle sizes and related birefringence was explored. The process of laser induced anisotropy shows an occurrence of birefringence saturation.

Electrodeposition of Co–W coatings from boron gluconate electrolyte with a soluble tungsten anode

Conditions were determined in which an active anodic dissolution of tungsten is observed in a borongluconate electrolyte used to obtain Co–W coatings (pH ~6.5) and the nature of critical currents of transition to the passivation was found, which makes it possible to use the tungsten anode as a soluble electrode. The anodic dissolution of tungsten occurs under these conditions with a current efficiency of 90–100%, which, in contrast to the case of a graphite anode, does not lead to an additional oxidation of the electrolyte components and polymerization in solution; in combination with the decrease in the concentration of tungstate ions, this reduces the electrolyte performance. It was shown that the use of a soluble tungsten anode in obtaining nanocrystalline cobalt–tungsten coating can improve the electrolyte performance due to the rise in the current efficiency of electrodeposition and to the increase in the microhardness of the coatings in comparison with the case of an insoluble graphite anode.

Treatment of drilling fluids wastewater by electrocoagulation

Electrocoagulation has been successfully used to treat a variety of industrial wastewaters. The goal is to form flocks of metal hydroxides within the effluent to be cleaned by electro-dissolution of soluble anodes. The present work deals with the removal of petroleum organic matter such as diesel from drilling fluids wastewater by the electrocoagulation technique using a direct current (DC) electrolytic cell. The cell is consisted of a rectangular Plexiglass container of dimension 12*12*15cm equipped with varied number of parallel horizontal meshed Aluminum anodes (9*9cm) and 115.2cm2 effective area, stainless steel (9*9cm) cathode. The electrodes were connected to a digit DC power supply (40V) with a multi-range ammeter connected in series and voltmeter connected in parallel with the cell. The percentage of COD removal was studied under different conditions by varying the following parameters: (1) electrolysis time, from 5 to 45min, (2) current density, from 0.008 to 0.034A/cm2, (3) number of parallel horizontal meshed Al anodes, (4) electrolyte concentration. The new anode design of electrocoagulation cell permits high efficiencies with lower energy consumption in comparison with the other cell design used in previous studies.

Tuning the Morphology of Te 1D Nanostructures By Template-Free Electrochemical Deposition in an Ionic Liquid

Tellurium and its alloys are used in many applications such as photoconductors, piezoelectric devices, thermoelectric generators and coolers [1]. For thermoelectric applications, the transport properties (thermal conductivity, electrical resistivity, Seebeck coefficient) of tellurium and its compounds can be improved by nanostructuring [2]. One-dimensional nanostructures like nanowires [3] and core-shell nanowires [4] are particularly promising due to the high phonon interface scattering and the blocking of the phonon conduction along the wire axis which lead to an increase of the thermoelectric conversion efficiency. Te nanowires can represent a base to create core-shell structures, being the core that could be further capped with a shell to get arrays of Te-based thermoelectric nanostructures like BiTe [5], AgTe [6] or LaTe [7]. Template assisted electrodeposition is a low cost technique widely used in literature for the synthesis of nanowires but implies several preparation steps and the removal of the template after the growth of the nanowires. The aim of this work is to develop a template free synthesis route that would be more convenient. For this purpose, Room-Temperature Ionic Liquids (RTILs) appear as promising solvents. Indeed, it has been highlighted that they can act as stabilizing agents for nanoparticles and nanostructured films synthesis [8]. In a previous work ([9]), our laboratory showed that Te nanowires can be obtained in an ionic liquid binary mixture: 1-ethyl-1-octyl-piperidinium bis(trifluoromethylsulfonyl)imide:1-ethyl-1-octyl-piperidinium bromide (EOPipTFSI:EOPipBr). In the present work, several morphologies were obtained by varying the synthesis parameters (applied fixed potential, Te(IV) concentration, electrolyte composition). Under charge transfer control, micrometer faceted grains are formed. Under diffusion control, the deposits are composed of nanowires, which are single crystalline as proven by SAED (Selected Area Electronic Diffraction) and TEM (Transmission Electron Microscopy) analyses. In highest tested overpotential conditions, nanowires turn progressively into crystallized hollow nanostructures (HNs) when the coulometric charge increases. This phenomenon is more accentuated at low concentration and disappears when using a soluble anode, showing that the formation of HNs is due to a limitation by species supply. The geometry of HNs, with a high surface to volume ratio, is particularly interesting to create high performances thermoelectric materials. Indeed, this geometry could further decrease the lattice part of the thermal diffusion coefficient by phonon confinement. By decreasing the bromide content of the electrolyte, hair-like single crystalline nanowires with a high aspect ratio can be obtained. HRTEM (High Resolution Transmission Electron Spectroscopy) analyses reveal a growth along the c-axis, with a smooth interface. No surface contaminants were observed by STEM (Scanning Transmission Electron Microscopy), proving that halogenide ions do not play the role of capping agents, unlike observed in other works [10].

Towards a Ni-P 3D Electrostatic Energy Harvesting MEMS for Medical Implants

This communication presents developments in electrodeposition of nickel phosphorous (Ni-P) alloy, allowing to fabricate innovative 3D MEMS dedicated to medical applications. Nickel electrodeposition is a very common technique used to produce metallic thick layers applied mainly as corrosion protective layers or for decorative purpose [1]. With the MEMS booming, Ni electrodeposition attracted researchers’ attention since it allows to create thick patterns when it is combined with lithography (micromolding process). Moreover, nickel mechanical properties make this material ideal for inertial MEMS. However, it presents ferromagnetic properties which are not compatible with Magnetic Resonance Imaging (MRI), thus preventing its use in implantable medical devices. By doping nickel with at least 10 wt % phosphorous, the material becomes amorphous [2] and loses its magnetic properties whereas maintaining pretty good mechanical properties for MEMS application. We present here a study of micromolded Ni-P deposits from a sulfate bath including characterizations of its mechanical and magnetic properties. Our aim is to use this material to fabricate a tri-dimensional electrostatic energy harvesting MEMS designed to power a leadless pacemaker (Fig.1) [3]. The MEMS fabrication method is based on layer-by-layer electrodeposition of structural (Ni-P alloy) and sacrificial metals (copper). Electrodeposits of Ni and Ni-P patterns of different dimensions were micromolded on a Ti/Cu seed layer sputtered on SiO2/Si or glass substrates. Ni and Ni-P deposits were obtained by direct current electrodeposition technique, using a sulfate bath solution consisting of nickel sulfate (197g/l), nickel chloride (5g/l), boric acid (25g/l) and phosphorous acid (0 – 20g/l). A nickel plate was used as soluble anode. Ni-P alloys were elaborated in different conditions by varying the concentration of phosphorous acid between 5g/L and 20g/L or the current density (10 – 100mA/cm²). The deposits thickness was measured by optical profilometry in order to deduce the deposition rate. The deposits were observed by Scanning Electron Microscope (SEM) and their composition were analyzed by Energy-Dispersive Spectroscopy (EDS). As seen for other types of sulfate bath, it was possible to dope nickel up to 20% wt P. For small phosphorous acid bath concentrations, the current density had a significant effect on the P content. (Fig.2). It was also observed that adding phosphorous acid reduced the deposition rate. Young's Modulus and Hardness of nickel films were measured conventionally by micro-indentation. Young's Modulus was also evaluated by vibrometry, by measuring the resonant frequency of cantilever beams and microbridges [4]. Young’s modulus was found to be between 130 and 160GPa, which correspond to usual values for electroplated nickel according to literature. We are currently performing the same tests for Ni-P deposits. Magnetic properties of Ni-P alloys were measured with an Alternating Gradient Force Magnetometer (AGFM) for Ni and Ni-P. For a 20 wt% P Ni-P alloy, the saturation magnetization is 1.5 mT (0.1 emu/g) corresponding to 400 times less the value of the nickel one (0.6T; 54 emu/g). This result is very promising for MRI compatibility of nickel-based MEMS. [1] Modern Electroplating, M. Schlesinger and M. Paunovic, Wiley (2010) 736 pages, ISBN: 978-0-470-16778-6 [2] A. M. Pillai, A. Rajendra, A. K. Sharma, Electrodeposited nickel–phosphorous (Ni–P) alloy coating: an in-depth study of its preparation, properties, and structural transitions; J Coat. Technol. Res. 9(6) 785-707 (2012) [3] S. Risquez, M. Woytasik, J. Wei, F. Parrain E. Lefeuvre, Design of a 3D Multilayer Out-of-plane Overlap Electrostatic Energy Harvesting MEMS for medical implant applications; Symposium on Design, Test, Integration & Packaging of MEMS/MOEMS (DTIP’2015), 27-30 avril 2015, Montpellier (France), pp 5-9 [4] T. Fritz, M. Griepentrog, W. Mokwa, U. Schnakenberg, Determination of Young's modulus of electroplated nickel, Electrochimica Acta 48(20–22) 3029-3035 (2003) Figure 1

Computational Approaches for Rational Design of Electrodes for Biofuel Cells and Biosensors Applications

Redox enzymes have been extensively exploited as electrocatalysts in biofuel cells and biosensors due to the advantages they have over commonly used inorganic catalysts. For example, they often have higher activity and selectivity than the inorganic catalysts and can operate at biologically benign conditions. However, additional improvements have to be made for the development of enzymatic electrodes with high activity, stability, and ease of production that can lead to broader applications of enzyme-based systems. Immobilization and optimal interaction of the proteins with the support material is one of the key components in the design of enzymatic electrodes. Therefore, rational design of the electrode surface provides one of the most promising routes for creating biofuel cells and biosensors with enhanced performances. Such a design, however, demands deeper understanding of the bio-nano interface interactions as well as efficient enzyme orientation, which can be achieved by the use of various computational approaches. Density Functional Theory (DFT) and docking simulations were used to gain a fundamental understanding of the role of different molecules explored as orienting and/or mediating agents in the design and operation of several enzymatic electrodes. Different computational approaches were first used to explain the role of 1,2-benzoquinone, 1,4-benzoquinone, and ubiquinone on the operation and mechanism of electron transfer in PQQ-dependent soluble glucose dehydrogenase anodes (1, 2). The same approach was also used to understand the role of bilirubin in the bilirubin-modified oxygen reducing bio-cathodes based on bilirubin oxidase. We further studied the interaction of unsubstituted phenothiazine with glucose, lactate and cholesterol oxidases. Namely, it has been shown that the hydrophobic phenothiazine can be utilized for efficient electron transfer in various oxidases. In addition, docking simulations were used to discuss the nature of the interactions between flavins and outer membrane cytochromes of Shewanella spp., which has practical implication in the development of microbial fuel cells. 1. Babanova S, Matanovic I, Atanassov P. Quinone-modified surfaces for enhanced enzyme-electrode interactions in PQQ-dependent glucose dehydrogenase anodes. Chem Electro Chem. 2014;1(11):2017–28. 2. Babanova S, Matanovic I, Chavez MS, Atanassov P. The role of quinones in electron transfer of PQQ-glucose de-hydrogenase anodes – mediation or orientation effect. J. Am. Chem. Soc. 2015;137(24):7754-7762. Figure 1

Tuning the morphology of Te one-dimensional nanostructures by template-free electrochemical deposition in an ionic liquid

Template-free electrodeposition of Te one-dimensional (1D) nanostructures was carried out from an ionic liquid binary mixture: 1-ethyl-1-octyl-piperidinium bis(trifluoromethylsulfonyl)imide:1-ethyl-1-octyl-piperidinium bromide (EOPipTFSI:EOPipBr 95:5 (mol%)). SAED and XRD analyses confirm the formation of Te 1D nanostructures with a hexagonal single crystalline structure following the [001] direction. A systematic study of the influence of synthesis parameters on the deposits morphology has shown that it is possible to control the shape and the dimensions of the deposited nanostructures. Specifically, the applied potential has a strong influence on the morphology of the deposits. Nanowires or hollow nanostructures can be obtained, depending on mass transport conditions, as confirmed by the use of a soluble anode.

Investigation on the Oxidation and Reduction of Titanium in Molten Salt with the Soluble TiC Anode

To reveal the oxidation process of titanium from TiC anode and the reduction mechanism of titanium ions in molten NaCl-KCl, the polarization curve of TiC anode in molten NaCl-KCl and cyclic voltammograms of the molten salt after polarization were studied. Investigation on the polarization curve shows that titanium can be oxidized and dissociated from the TiC anode at very low potential. The cyclic voltammograms demonstrated that the reduction reaction of titanium ions in the molten salt is a one-step process. By potentiostatic electrolysis, dendritic titanium is obtained on the steel plate. The work promotes the understanding on the process of electrochemical oxidization/dissociation of titanium from TiC anode and the reduction mechanism of titanium ions in molten salt.

The effect of nickel sulfate additives to microarc oxidation electrolytes on the composition and morphology of the surface layer of MAO coatings on VT1-0 titanium And VT5 alloy

The effect of nickel sulfate additives to microarc oxidation (MAO) electrolytes on the composition and morphology of the surface layer of MAO coatings on VT1-0 titanium and VT5 alloy has been studied. The possibility of the incorporation of nickel (nickel oxide) in MAO coatings formed on titanium alloys in nickel-containing acidic and alkaline electrolytes has been explored with a view to designing partially soluble titanium anodes. It has been found that the introduction of liquid glass (LG) in conjunction with nickel sulfate into MAO electrolytes reduces the time to ignition of microarc discharges and contributes to an improvement of the morphology of nickel-containing MAO coatings. The best result has been obtained for VT1-0 titanium in an electrolyte containing 1 g/L KOH, 3 g/L LG, and 3 g/L NiSO4 at an MAO treatment time of 60 min.

Microvia Filling in an Acidic Copper Planting Bath with Insoluble Anodes

Microvia filling of a printed circuit board (PCB) by acidic copper electroplating has been widely used in electronic industry. The filling mode of copper electrodeposition in microvia must be bottom-up form. Moreover, bottom-up filling phenomenon is believed to be related to the properties and interaction of plating additives. Especially, the interaction of three (accelerator, suppressor, leveler) components have significantly effect on copper filling performance. It was confirmed that soluble anodes (i.e., P-doped Cu anode) have disadvantage when they were used in the acidic copper plating bath. For instance, the shape of the soluble anodes are changeable with operating time, which may causes non-uniform current distribution to form unequal copper thickness on substrate. Therefore, a special functional insoluble anode was used to replace the soluble anode and conventional dimensionally stable anode (DSA) to maintain better bath stability. The disadvantage of soluble anode can be improved by using the novel DSA. In this work, a planting formula which was composed of chloride ions, suppressor (polyethylene glycol), leveler (quaternary ammonium species) and a novel accelerator instead of bis(3-sulfopropyl) disulfide (SPS). SPS is not appropriate for DSA system because of easy breakdown; therefore, we develop a novel accelerator, ACC, which has a longer lifetime and better performance for acceleration on copper deposition than SPS. Using DSA instead of P-doped Cu anode has another important contribution, that is, SPS reacts with the copper anode to produce Cu(I)-thiolate. The Cu(I)-thiolate is a strong accelerator in the presence of chloride ion. Cu(I)-thiolate will be accumulated in the copper plating bath to destroy the synergy between the suppressor and accelerator. DSA has no this issue because DSA has no copper. Herein, we will show that ACC combining with DSA can perform excellent copper fill in microvia.

Evaluación Electroquímica de Recubrimientos Zn-Fe depositados con corriente pulsante

Se presenta la caracterización electroquímica para evaluar la resistencia a la corrosión de un recubrimiento metálico Zn-Fe por vía electrolítica sobre sustratos de lámina de acero cold-rolled. Los recubrimientos se depositaron mediante un generador de funciones, un osciloscopio y una celda electrolítica de 50 ml, provista de un ánodo soluble de zinc puro. Los reactivos utilizados son de grado analítico, y las pruebas se realizaron a temperatura de 25oC. No se utilizaron agentes acomplejantes ni abrillantadores; para que el proceso sea ambientalmente limpio. La caracterización electroquímica se realizó con mediciones de potencial de circuito abierto, resistencia a la polarización lineal y Espectroscopia de Impedancia Electroquímica, los cuales muestran que dentro del rango de ciclo de trabajo desde el 87,5% al 97,5%; y con variación de frecuencias entre 40 Hz y 100 Hz, el efecto de la corriente pulsante inversa favorece la resistencia a la corrosión del recubrimiento para valores de frecuencia de 100 Hz; la muestra con mayor resistencia a la corrosión se obtuvo con un ciclo de trabajo de 90%, al tener la mayor pendiente en la curva de resistencia a la polarización lineal de las muestras analizadas.

Size effect of microhardness of nanocrystalline Co-W coatings produced from citrate and gluconate solutions

The influence of various electrodeposition conditions (current density, including volume current density, and hydrodynamic conditions in different electrode systems such as the Hull cell with a rotating cylinder electrode and a cell without stirring, including a soluble anode (W) and an insoluble anode (graphite)) on the microhardness of nanocrystalline Co-W coatings, obtained from citrate and gluconate electrolytes, is investigated. It has been shown that the volume deposition current density is a governing factor which influences the measured microhardness values due to the microhardness size effect, that is, the dependences of microhardness on electrodeposition surface area for a fixed current density and electrolyte volume. The conditions, e.g., volume current densities, for maximum microhardness are determined.

Microvia Filling in an Acidic Copper Planting Bath with Insoluble Anodes

Microvia filling of a printed circuit board (PCB) by acidic copper electroplating has been widely used in electronic industry. The filling mode of copper electrodeposition in microvia must be bottom-up form. Moreover, bottom-up filling phenomenon is believed to be related to the properties and interaction of plating additives. Especially, the interaction of three (accelerator, suppressor, leveler) components have significantly effect on copper filling performance. It was confirmed that soluble anodes (i.e., P-doped Cu anode) have disadvantage when they were used in the acidic copper plating bath. For instance, the shape of the soluble anodes are changeable with operating time, which may causes non-uniform current distribution to form unequal copper thickness on substrate. Therefore, a special functional insoluble anode was used to replace the soluble anode and conventional dimensionally stable anode (DSA) to maintain better bath stability. The disadvantage of soluble anode can be improved by using the novel DSA. In this work, a planting formula which was composed of chloride ions, suppressor (polyethylene glycol), leveler (quaternary ammonium species) and a novel accelerator instead of bis(3-sulfopropyl) disulfide (SPS). SPS is not appropriate for DSA system because of easy breakdown; therefore, we develop a novel accelerator, ACC, which has a longer lifetime and better performance for acceleration on copper deposition than SPS. Using DSA instead of P-doped Cu anode has another important contribution, that is, SPS reacts with the copper anode to produce Cu(I)-thiolate. The Cu(I)-thiolate is a strong accelerator in the presence of chloride ion. Cu(I)-thiolate will be accumulated in the copper plating bath to destroy the synergy between the suppressor and accelerator. DSA has no this issue because DSA has no copper. Herein, we will show that ACC combining with DSA can perform excellent copper fill in microvia.

The mathematical description for the electropolymerization of furan, pyrrole and thiophene derivatives in alkaline media

The electropolymerization of furan, pyrrole and thiophene in strong basic media was mathematically described. Two models for the cases of the insoluble and soluble anodes were described and analyzed by using the linear stability theory and bifurcation analysis and compared with the models for other cases of electropolymerization. The causes for the oscillatory behavior, monotonic instabilities and steady-state stability conditions were found.

Current Efficiency and Polarization Factors in the Electrolytic Process of Seawater Pretreatment

The performance of the electrode is the core technology of the electrolytic process of seawater pretreatment, and has the decisive influence on the systematic technological process and water quality. In the initial stage of electrolytic technology being applied in seawater pretreatment, soluble anodes, which use the aluminum, ferrum or other metal elements as the main ingredient, are chosen for most cases. And this method can effectively reduce the turbidity of raw seawater and sludge density index (SDI). While applying a variety of methods, the proportion of electrolytic aluminum, ferrum and other metal elements in the water can be effectively controlled. And this can increase the ratio of hydrolysate, but will also introduce the composition of soluble electrode into the seawater inevitably. At the same time, the use of soluble electrode will be consumed continuously with the production process, which is likely to add the cost of production. This study uses electrodes which contain a variety of precious metal (such as Ti, Ru, and Ir) oxide in the seawater pretreatment process, which is different from traditional chlor-alkali industry.

Study on the Cyclic Voltammetry Curve of Electrode in the Electrolytic Process of Seawater Pretreatment

The performance of the electrode is the core technology of the electrolytic process of seawater pretreatment, and has the decisive influence on the systematic technological process and water quality. In the initial stage of electrolytic technology being applied in seawater pretreatment, soluble anodes, which use the aluminum, ferrum or other metal elements as the main ingredient, are chosen for most cases. And this method can effectively reduce the turbidity of raw seawater and sludge density index (SDI). While applying a variety of methods, the proportion of electrolytic aluminum, ferrum and other metal elements in the water can be effectively controlled. And this can increase the ratio of hydrolysate, but will also introduce the composition of soluble electrode into the seawater inevitably. This study uses electrodes which contain a variety of precious metal (such as Ti, Ru, and Ir) oxide in the seawater pretreatment process, which is different from traditional chlor-alkali industry.

Anodic oxidation of 1,3-di(paratolyl)-5-paratoluidinomethyl-1,3,5-diazaphosphorinane on aluminum

1102 Aminomethylphosphines pertain to one of the rare types of easily available hybrid polyfunctional phosphine ligands. Aminomethylphosphine based systems are used as specific ligands in coordination chemistry for creating water soluble [1–3], chiral [4–6], polynuclear compounds and clusters [7–9] and also biomimetic catalysts of several electrochem ical processes [10–13]. The results of studies of elec trochemical properties of aminomethylphosphines, for the most part, cyclic diazaphosphorinanes, is described in [14–17]. The anodic behavior of para toluidinomethyl 1,3,5 diazaphosphorinane I (DP) was studied most thoroughly. As was shown earlier, the result of electrochemical oxidation of I depends on the anode material. Thus, when glassy carbon was used, the reaction products contained salts of diazaphos phorinanium II and spirotetraazaphosphonium III [14]. At the same time, the oxidation on platinum pro duced bicyclic dimer IV in place of product III [15]. On the other hand, the anodic oxidation of DP on mercury led to the formation of a complex with a new P, N ligand V [18]. In line with the possible forma tion of new types of metallocomplexes, it seemed interesting to study the oxidation of DP on a soluble anode such as aluminum, which is a р element, in contrast to mercury (d element). The results of this experiment are shown in this publication.

Electrocoagulation of colloidal biogenic selenium.

Colloidal elemental selenium (Se(0)) adversely affects membrane separation processes and aquatic ecosystems. As a solution to this problem, we investigated for the first time the removal potential of Se(0) by electrocoagulation process. Colloidal Se(0) was produced by a strain of Pseudomonas fluorescens and showed limited gravitational settling. Therefore, iron (Fe) and aluminum (Al) sacrificial electrodes were used in a batch reactor under galvanostatic conditions. The best Se(0) turbidity removal (97 %) was achieved using iron electrodes at 200 mA. Aluminum electrodes removed 96 % of colloidal Se(0) only at a higher current intensity (300 mA). At the best Se(0) removal efficiency, electrocoagulation using Fe electrode removed 93 % of the Se concentration, whereas with Al electrodes the Se removal efficiency reached only 54 %. Due to the less compact nature of the Al flocs, the Se-Al sediment was three times more voluminous than the Se-Fe sediment. The toxicity characteristic leaching procedure (TCLP) test showed that the Fe-Se sediment released Se below the regulatory level (1 mg L(-1)), whereas the Se concentration leached from the Al-Se sediment exceeded the limit by about 20 times. This might be related to the mineralogical nature of the sediments. Electron scanning micrographs showed Fe-Se sediments with a reticular structure, whereas the Al-Se sediments lacked an organized structure. Overall, the results obtained showed that the use of Fe electrodes as soluble anode in electrocoagulation constitutes a better option than Al electrodes for the electrochemical sedimentation of colloidal Se(0).

Use of a Soluble Anode in Electrodeposition of Thick Bismuth Telluride Layers

Integration of thermoelectric devices within an automotive heat exchanger could enable conversion of lost heat into electrical energy, contributing to improved total output from the engine. For this purpose, synthesis of thick bismuth telluride (Bi2Te3) films is required. Bismuth telluride has been produced by an electrochemical method in nitric acid with a sacrificial bismuth telluride anode as the source of cations. The binary layer grows on the working electrode while the counter-electrode, a Bi2Te3 disk obtained by high frequency melting, is oxidized to BiIII and TeIV. This process leads to auto-regeneration of the solution without modification of its composition. The thickness of films deposited by use of the Bi2Te3 anode was approximately 10 times that without. To demonstrate the utility of a soluble anode in electrochemical deposition, we report characterization of the composition and morphology of the films obtained under different experimental conditions. Perfectly dense and regular Bi2Te3 films (∼400 μm) with low internal stress and uniform composition across the cross-section were prepared. Their thermoelectric properties were assessed.