Platinum-coated Titanium Electrodes Research Articles

Sustainable strategies of in-series AEM electrolysis and CEM electrolysis for the treatment of NF concentrates via ettringite-targeted mineral transition

A two-step ion exchange membrane electrolysis process was designed to recover divalent cations (Ca2+, Mg2+) and sulfate from nanofiltration concentrates (NFC) and investigate their removal performance and membrane fouling mechanism. As a result, the AEM electrolysis recovered divalent ions by generating calcium carbonate and magnesium hydroxide in the cathode chamber, while sulfate was enriched in the anode chamber. In the subsequent CEM electrolysis, desalination was achieved by adding chemicals to form ettringite precipitation in the cathode chamber. Meanwhile, the organics in nanofiltration concentrate were removed under the oxidation of platinum-coated titanium electrode and the precipitation adsorption of the cathode chamber. By comparing the desalination performance and organic matter removal, the dosage of ettringite was determined. When the Ca/S = 2.5 and Al/S = 1.0, it was beneficial to the recovery of ettringite. Furthermore, the membrane fouling mechanism was investigated to find that AEM fouling was more severe than CEM. Therefore, this study provides a technical idea and feasibility study for the treatment of municipal nanofiltration concentrate.

Influences of electrode distance and electrolysis time on phosphorus precipitation and composition during electrolysis of anaerobic digestion effluent

Global demand for phosphorus (P) is increasing, which has led to concerns over future drought and has driven efforts to recover P from wastewater streams for reuse. In this study, platinum-coated titanium electrodes were applied to the electrochemical precipitation of P from anaerobic digestion effluent that was collected from a domestic wastewater treatment plant. The influence of the electrode distance on P removal and precipitation was investigated. In addition, the influence of the electrolysis time on the chemical structure and composition of the P precipitate was evaluated from the viewpoint of utilising the P precipitate as fertiliser. Regardless of the electrode distance (10, 5 and 1 mm), PO43−, Ca2+ and Mg2+ were removed. The bulk solution pH increased during electrolysis because of the consumption of generated H+ as HCO3− transitioned to H2CO3 near the anode. A greater increase in the bulk solution pH was observed when the electrode distance was narrowed because of the enhanced H+ consumption. Narrowing the electrode distance reduced the energy consumption for P precipitation. The increase in the bulk solution pH with the narrowing electrode distance changed the dominant P precipitation pathway from onto the cathode to in the bulk solution. X-ray diffraction spectra of the precipitates showed that increasing the electrolysis time transformed amorphous P to hydroxyapatite and struvite. Most P existed in a citric acid-soluble form, which is recommended for use as a slow P release fertiliser. There were no significant changes in the citric acid-soluble P content of the precipitates with increasing electrolysis time. Therefore, increasing the electrolysis time has little influence on the suitability of the precipitate as a slow P release fertiliser.

Disinfection of Irrigation Water Using Titanium Electrodes

This work reports on the electrochemical disinfection of natural irrigation water collected from the Waiahole Ditch Irrigation System in Hawaii using a batch cell assembled with titanium electrodes as both anode and cathode. Disinfection experiments were performed by applying a polarity-reversing direct current between the two titanium electrodes. The naturally occurring concentration of chloride in the water was 1.84 mg l−1 and no other chemicals were added. The applied current density was varied between 0 mA cm−2 and 2 mA cm−2, and the half-period (T/2) of the polarity-reversing direct current was varied between 5 s and 60 s. The best disinfection performance was achieved at 2 mA cm−2 and T/2 = 10 s, requiring only 5 min of treatment for the complete disinfection of E. coli (4-log reduction). E. coli was inactivated by free chlorine species electrogenerated at the titanium electrodes. Hydrogen peroxide, short-lived oxidants, and direct electron transfer most likely had minor contributions to the disinfection process. During the disinfection experiments, the concentrations of disinfection byproducts (ClO3 −, CHCl3, CHBrCl2, CHBr2Cl, and CHBr3) were significantly lower than recommendations for drinking water. The titanium electrodes consumed less electrical energy than platinum-coated titanium electrodes because they needed a lower current density to achieve similar disinfection efficiency.

Impact of Process Parameters on the Diameter of Nanobubbles Generated by Electrolysis on Platinum-Coated Titanium Electrodes Using Box–Behnken Experimental Design

(1) The generation of nanobubbles by electrolysis is an interesting method of using electrical energy to form bubble nuclei, effectively creating a multiphase system. For every process, the effectiveness of nanobubble generation by electrolysis depends on various process parameters that impact should be determined. (2) In this work, the electrolytic generation of hydrogen and oxygen bubbles was performed in a self-built setup, in which a Nafion membrane separated two chambers. The generation of bubbles of both gases was investigated using Box–Behnken experimental design. Three independent variables were salt concentration, current density, and electrolysis time, while the dependent variables were Sauter diameters of generated bubbles. An ANOVA analysis and multivariate regression were carried out to propose a statistical and power model of nanobubble size as a process parameter function. (3) The generation of bubbles of hydrogen and oxygen by electrolysis showed that different factors or their combinations determine their size. The results presented in this work proved to be complementary to previous works reported in the literature. (4) The Sauter diameter of bubbles increases with salt concentration and stays constant with increasing current density in investigated range. The proposed correlations allow the Sauter diameters of nanobubbles generated during electrolysis to be predicted.

Removal of reactive azo dye using platinum-coated titanium electrodes with the electro-oxidation process

Removal of reactive azo dye using platinum-coated titanium electrodes with the electro-oxidation process

Electro-Oxidation of Humic Acids Using Platinum Electrodes: An Experimental Approach and Kinetic Modelling

Humic acids (HA) are a potential hazard to aquatic ecosystems and human health. Because biological treatment of contaminated water does not satisfactorily remove these pollutants, novel approaches are under evaluation. This work explores electrochemical oxidation of HA in aqueous solution in a lab-scale apparatus using platinum-coated titanium electrodes. We evaluated the effects of HA concentration, current density, chloride concentration and ionic strength on the rate of HA oxidation. The initial reaction rate method was used for determining the rate law of HA degradation. The results showed that the reaction rate was first-order relative to HA concentration, chloride concentration and current density. An appreciable effect of ionic strength was also observed, most likely due to the polyanionic character of HA. We propose a kinetic model that satisfactorily fits the experimental data.

Selection of electrode materials for membrane less fuel cells based on immiscible liquids

The possibility of using various materials as electrodes for membraneless fuel cells based on immiscible liquids, both from the standpoint of the thermodynamic possibility of the process and from the point of view of their corrosion resistance, is considered. The corrosion resistance of materials from alloys based on iron, as well as carbon was investigated for use as electrodes in membraneless fuel cells based on immiscible liquids. The possibility of using them instead of electrodes based on ruthenium and platinum in the studied alkaline aqueous ethanol system was shown. It was found that the highest electromotive force in the system occurs when using an activated carbon anode in the top ethanol phase and a carbon steel 10 cathodes in the bottom aqueous phase. The possibility of using activated carbon instead of a ruthenium-coated titanium electrode and platinum-coated titanium electrode, at almost equal exchange currents, will significantly reduce the cost of manufacturing a fuel cell. Thus under certain conditions, this type of fuel cell can compete with membrane fuel cells that have received industrial implementation

Utilisation of polarity inversion for phosphorus recovery in electrochemical precipitation with anaerobic digestion effluent

Phosphorus is a non-replaceable and limited resource, whose future drought is a matter of concern. Its recovery from wastewater has gained attention as a method of making the recovered phosphorus available for beneficial use. This study applied electrolysis with a platinum-coated titanium electrode to an actual anaerobic digestion effluent and investigated the phosphorus removal and precipitation characteristics with various current values. The separation of the phosphorus precipitate from the sludge residue and the usefulness of the polarity inversion to recover the phosphorus precipitate were evaluated. The availability of the recovered precipitate as a fertiliser was also demonstrated. The anaerobic digestion effluent after the centrifugal dehydration process with a coagulant was collected from a wastewater treatment plant. Phosphorus was precipitated as a form of calcium phosphate, including hydroxyapatite, which was confirmed by X-ray diffraction. The generated gases from the electrodes during the electrolysis floated and condensed the sludge residue, leading to successful separation of the phosphorus precipitate from the sludge residue. The polarity inversion successfully detached the phosphorus precipitate from the electrode, and at least 3 min polarity inversion was enough to detach the whole phosphorus precipitate. The submerging phosphorus precipitate contained abundant phosphorus (12.6%), in which citric-acid-soluble phosphorus accounted for 94.4%, and the utilisation of the precipitate as a slow-release phosphorus fertiliser was suggested.

Electroflotation of Escherichia coli Improves Detection Rates by Loop-Mediated Isothermal Amplification

Abstract. The power of portable molecular diagnostic systems for detection of pathogenic microorganisms in food and environmental samples is largely limited by small assay volumes (typically 1 to 5 µL), making direct detection of trace contamination (i.e., <104 CFU mL-1) unreliable. To improve detection limits for pathogens dispersed on an ecological scale, we developed a portable point-of-care (POC) sample preparation system using electroflotation (EF) to recover small quantities of these organisms from samples of hundreds of milliliters. Electrolysis reactions, supported on platinum-coated titanium electrodes, generate hydrogen and oxygen microbubbles that impel and displace suspended cells into a recovered concentrate. Samples were prepared by inoculating 380 mL of sterilized phosphate buffer (0.1 M, pH 6.6) with stock culture of ATCC 25922 to final concentrations ranging from 102 to 104 CFU mL-1. Samples were subjected to 10, 15, and 20 min durations of EF treatment under high and low turbulence conditions. We used a loop-mediated amplification (LAMP) assay with primers targeting a single-copy gene (glycerate kinase) in generic to evaluate the effects of EF treatment on concentration and recovery of detectable cell material. LAMP failed to detect in all untreated (control) samples at concentrations below 104 CFU mL-1 but was able to detect in 102 CFU mL-1 samples subjected to various conditions of EF treatment. Two-way ANOVA showed significant differences in detection rates between EF treatment durations for both high (p = 0.0019) and low turbulence (p = 0.002). Dunnett’s multiple comparison tests identified five process conditions resulting in significant (p < 0.05) differences in detection between treatments and the control. Keywords: Biotechnology, Electrolysis, Food pathogens, Microbubbles, Molecular diagnostics, Pathogen detection, POC sample preparation.

Electro-chemical mineralization of recalcitrant indole by platinum-coated titanium electrode: multi-response optimization, mechanistic and sludge disposal study

Indole is a highly recalcitrant aromatic heterocyclic organic compound consisting of a five-membered nitrogen-containing pyrrole ring fused to a six-membered benzene ring. This study presents the results of the electro-chemical mineralization of indole in an aqueous solution using platinum-coated titanium (Pt/Ti) electrode. A central composite design was used to investigate the effect of four parameters namely initial pH (pHo), current density (j), conductivity (k) and treatment time (t) at 5 levels. Multiple responses namely chemical oxygen demand (COD) removal (Y 1) and specific energy consumption (Y 2) were simultaneously maximized and minimized, respectively, by optimizing the parameters affecting the mineralization of indole by using the desirability function approach. At the operating conditions of pH 8.6, j = 161 A/m2, k = 6.7 mS/cm and t = 150 min, 83.8% COD removal with specific energy consumption of 36.3 kWh/kg of COD removed was observed. Ultra performance liquid chromatography, UV–visible spectroscopy, Fourier transform infrared spectroscopy and cyclic voltammetry of the indole solution were performed at the optimum condition of the treatment so as to report a plausible mechanism of indole degradation. Field emission scanning electron microscopy analysis of electrodes before and after treatment was performed for determining the changes on anode surface during the treatment. Thermal analysis of the solid residue (scum) obtained was also performed for exploring its disposal prospects. Present study shows that electro-chemical oxidation can be used for mineralization of nitrogenous heterocyclic compounds such as indole.

Generation of Sulfuric Acid and Sodium Hydroxide from the Sodium Sulphate Salt by Electro-Electrodialysis(EED)

The electro-electrodialysis process (EED) is used to generate H2SO4 and NaOH from sulphate sodium salt Na2SO4. The key phenomenon limiting the current efficiency of this process is the proton leakage through the anion selective membrane was not observed. The electro-electrodialysis was carried out with a three-compartment cell with two platinum-coated titanium electrodes separated by three compartments. The couple membrane used in this work is AFN and CMX. The experiments were carried out for four current densities 8.33 mA.cm-2 11.11mA.cm-2, 13.88mA.cm-2 and 27.77 mA.cm-2. For each current density, a voltage variation of cell and concentrations of H2SO4 and NaOH in the two compartments with the current density was used. The concentration of H2SO4 and NaOH increases with current density and with time, but higher for NaOH. The current efficiency increases with the current applied to the cell. The request for the electro-electrodialysis operation power was calculated in terms of the electrical energy consumed to produce H2SO4 and NaOH for 6 hours of electro-electrodialysis and it was found floating with the current applied and concentration sodium sulphate used and the concentration of H2SO4 and NaOH products, but is comparable for both initial concentrations of sodium sulfate.

Zirconium mesostructures immobilized in calcium alginate for phosphate removal

Eutrophication caused by the excessive supply of phosphate to water bodies has been considered as one of the most important environmental problems. In this study, the powder of zirconium mesostructure (ZM), which was prepared with the template of surfactant, was immobilized in calcium alginate for practical application and the resulting material was tested to evaluate the phosphate removal efficiency. Sorption isotherms and kinetic parameters were obtained by using the entrapped ZM beads with 30 to 60% of ZM. The maximum sorption capacity increased with the higher ZM content. Qmax in Langmuir isotherm was 51.74 mg/g for 60% of ZM with 7 mm of size. The smaller the particle size of the ZM beads, the faster the rate of phosphate removal, because the phosphate ions had less distance to reach the internal pores of the immobilized ZM beads. Chemical and electrochemical regeneration techniques were compared. Phosphates adsorbed on the ZM beads were effectively desorbed with NaCl, NaOH, and Na2SO4 solutions. An electrochemical regeneration system consisting of an anion exchange membrane between two platinum-coated titanium electrodes was successfully used to desorb and regenerate the phosphate-saturated ZM beads. Complete regeneration was reached under optimal experimental conditions. Chemical and electrochemical regeneration proved the reusability of the bead form of the entrapped ZM, and will enhance the economical performance of the phosphate treatment process.

Fabrication and Corrosion Behaviour of Platinum-Coated Titanium Electrodes from Low Temperature Molten Salt Electrolytes

The development of corrosion-resistant platinum coated titanium (Pt/Ti) electrodes for seawater electrolysis in the production of sodium hypochlorite is an important requirement. In this study a new ternary low temperature molten salt (LTMS) LiCl—NaCl—KCl system was chosen as the electrolyte. The direct current method of four Pt electrodes combined with a computer program was employed to measure the relationship between conductivity and temperature of the chosen electrolyte at various PtCl2 concentrations. The pulse current technique was used for fabrication of Pt/Ti electrodes from the chosen LTMS electrolyte at the temperature and PtCl2 concentration where the conductivity of the LTMS system was highest by changing the duty-cycle and plating current density. The morphology and composition of the Pt-coated layer was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Tafel plots, anodic polarization curves and electrochemical impedance spectroscopy (EIS) were employed to evaluate the corrosion behaviour of the Pt/Ti electrodes. The best quality Pt-coated electrodes were obtained from the pulse plating condition of Ton:Toff= 3:1 with a current density (iplat) of 127.5 mA cm−2. These had a higher Pt content, nobler corrosion potential (Ecorr), lower corrosion current density (icorr), lower passive current density (ipass) and higher impedance. Furthermore, AFM demonstrated that the best quality Pt/Ti electrode had the lowest surface roughness (Ra) with the finest grain size.

Polarization behaviour and lifetime of IrO2–Ta2O5–SnO2/Ti anodes in p-phenolsulfonic acid solutions for tin plating

Insoluble electrodes consisting of iridium and tantalum oxides thermally prepared on a titanium substrate have received much attention as oxygen evolution anodes in industrial electroplating processes. In commercial electrogalvanizing lines, the application of the IrO2±Ta2O5/ Ti anode has increased, replacing other insoluble anodes such as the platinum-coated titanium electrode, and a lifetime of more than 10 000 h has been demonstrated under severe operation conditions of 100Admy2 and 333K in practical use [1, 2]. The IrO2-based coating provides excellent catalytic and corrosion-resistant properties, if the electrolyte is an inorganic acid solution such as a sulfuric acid-based bath for electrogalvanizing. However, iridium oxide, along with other platinumgroup metals or their oxides, shows a high consumption rate if the electrolyte contains organic compounds [3, 4]. As a result, little has been done to develop the IrO2± Ta2O5/Ti anode for commercial electroplating lines using organic acid-based baths, for example, theFerrostan bath based on p-phenolsulfonic acid (PSA) for electrotinning. By contrast, we studied the electrochemical behavior of the IrO2±Ta2O5/Ti anode in a PSA solution in order to determine the real applicability of this anode for electrotinning lines [5]. The results indicated that PSA was oxidized at potentials less positive potential than that of oxygen evolution and the oxidation of PSA produced an organic ®lm that originated from the PSA on the anode during oxygen evolution. The organic ®lm on the anode adversely a€ected the electrocatalysis of the IrO2±Ta2O5 catalytic layer and caused a drastic decrease in the lifetime of the anode. However, it was also found that the addition of SnO2 on the outermost surface of the coating layer suppressed the accumulation of the organic ®lm, thus suggesting the prolongation of the anode lifetime in the PSA solution. It is, therefore, possible that the IrO2±Ta2O5 coating layer containing SnO2 has enhanced durability for use in the PSA-based tin plating bath. In this paper, the anodic polarization behaviour and lifetime for oxygen evolution of IrO2±Ta2O5±SnO2/Ti anodes in a PSA solution are reported. The manifested advantage of the SnO2 addition in the IrO2±Ta2O5 system to improve the anode lifetime is shown.

Electro-transport of sulphuric acid by electro-electrodialysis

This study concerns the electro-transport of sulphuric acid by electro-electrodialysis. The membrane is an RAI R1035 anion exchange membrane and the electrodes are two platinum-coated titanium electrodes. The transmembrane flux of sulphate ions is measured under a constant current, the sulphuric acid concentration being different on the anodic and on the cathodic side. The experimental values of the fluxes are compared with the values which can be calculated after integration of the Nernst-Planck electrodiffusion equation. The calculation requires the knowledge of the values of additional parameters (amount of sorbed acid, ratio between the diffusion coefficients of the proton and of the sulphate ion in the membrane), which have been determined experimentally.

Platinum-coated Titanium Electrodes for Cathodic Protection

Platinum-coated Titanium Electrodes for Cathodic Protection