Electrocatalytic Oxidation Process Research Articles

Cis-bis(isothiocyanato)-bis(2,2′-bipyridyl-4,4′dicarboxylato)-Ru(II) (N719) dark-reactivity when bound to fluorine-doped tin oxide (FTO) or titanium dioxide (TiO 2) surfaces

The solar cell sensitizer cis-bis(isothiocyanato)-bis(2,2′-bipyridyl-4,4′dicarboxylato)-ruthenium(II) (N719) is adsorbed and investigated at two electrode surfaces: (i) at a bare fluorine-doped tin oxide (FTO) and (ii) at a nano-particulate anatase (TiO 2) film in contact with FTO. N719 is adsorbed from acetonitrile onto FTO surfaces giving poor quality partial or multi-layer coverage commencing at 10 −7 M concentration. In contrast, from 50% acetonitrile 50% t BuOH solution of N719 Langmuirian adsorption occurs with well-defined mono-layer coverage and a binding constant ca. 2 × 10 5 mol −1 dm 3. The adsorbed N719 exhibits voltammetric oxidation/back-reduction responses with E mid ≈ 0.56 (weaker) and 0.68 (dominant) V vs. Ag/AgCl (3 M KCl) and with chemically reversible characteristics at sufficiently high scan rates (ca. 16 V s −1). A chemical reaction step involving oxidised N719 at the electrode surface leads to the loss of electrochemical activity at slower scan rates with a first order chemical rate constant of ca. 2.4 s −1. The electro-catalytic oxidation of iodide is demonstrated for both the intact metal complex N719 and the reaction product formed after oxidation. When adsorbed onto TiO 2 (porous films made from approximately 9 nm diameter TiO 2 particles, Langmuirian binding constant ca. 10 5 mol −1 dm 3), immersed in acetonitrile (0.1 M NBu 4PF 6), and at sufficiently fast scan rates (ca. 16 V s −1), the N719 metal complex exhibits reversible voltammetric responses (with E mid ≈ 0.68 V vs. Ag/AgCl (3 M KCl)). At slower scan rates, the voltammetric response again appears irreversible, however, this time without significant degradation of the N719 metal complex at the TiO 2 surface. It is shown that the conduction mechanism via electron hopping becomes ineffective due to degradation of FTO-adsorbed N719. In the presence of iodide, the electro-catalytic iodide oxidation process (dark electro-catalysis) is shown to occur predominantly at the N719-modified FTO electrode surface. Implications of this dark-reactivity for the solar cell performance are discussed.

Electrocatalytic oxidation of methanol at platinum electrode modified with Eu–Fe cyanide-bridged binuclear complexes

The electrocatalytic oxidation of methanol at the platinum electrode modified with Eu–Fe cyanide-bridged binuclear complexes (Eu–Fe film) was investigated for the first time by cyclic voltammetry. Compared with the bare platinum electrode, the results showed that the modified electrode had excellent electrocatalytic activity for the oxidation of methanol; the oxidation peak potential shifted more negatively and the peak current increased about twenty times. The electrooxidation of methanol at the modified electrode with Eu–Fe cyanide-bridged binuclear complexes material exhibited the better tolerance capacity to poison of intermediate species; the peak current was proportional to the concentration of methanol in the range of 0.5–2.0 mol/L ( R 2 = 0.9991, n = 7), which was a comparatively wider linear range. Moreover, based on the linear relationship between the peak current and the square root of scan rate, electrocatalytic oxidation process of methanol was confirmed to be a diffusion control process. Furthermore, according to the counting of electron transfer number ( n α ) in the rate-limiting step and the slope of linear equation between acidity of electrolyte and the oxidation peak potential ( E p), the possible mechanism of the electrooxidation of methanol at the modified electrode was primarily discussed.

Rapid decolorization of azo dyes in aqueous solution by an ultrasound-assisted electrocatalytic oxidation process

In this study, we developed a novel ultrasound-assisted electrocatalytic oxidation (US–EO) process to decolorize azo dyes in aqueous solution. Rhodamine B was decolorized completely within several minutes in this developed US–EO system. Oxidation parameters such as applied potentials, power of the ultrasound, initial pH of the solution, and initial concentration of RhB were systematically studied and optimized. An obvious synergistic effect was found in decolorization of RhB by the US–EO process when comparing with either ultrasound (US) process or electrocatalytic oxidation (EO) one. Additionally, the decolorization of other azo dyes, such as methylene blue, reactive brilliant red X-3B, and methyl orange, were also effective in the US–EO system. The results indicated that US–EO system was effective for the decolorization of azo dyes, suggesting its great potential in dyeing wastewater treatment.

Differential pulse voltammetric simultaneous determination of noradrenalin and acetaminophen using a hematoxylin biosensor

A highly efficient noradrenalin (NA) biosensor was fabricated on the basis of hematoxylin electrodeposited on a glassy carbon electrode, GCE. The cyclic voltammetric responses of the hematoxylin biosensor at various scan rates, which were obtained in a 0.25 mmol L −1 NA solution, showed the characteristic shape typical of an EC cat process. The kinetic parameters such as electron transfer coefficient, α, the catalytic electron transfer rate constant, k′, and the standard catalytic electron transfer rate constant, k 0, for oxidation of NA at the hematoxylin biosensor surface were estimated using cyclic and RDE voltammetry. The peaks of differential pulse voltammetric (DPV) for NA and acetaminophen (AC) oxidation at the hematoxylin biosensor surface were clearly separated from each other when they co-exited in the physiological pH (pH 7.0). It was, therefore, possible to simultaneously determine NA and AC in the samples at a hematoxylin biosensor. Linear calibration curves were obtained for 5.0 × 10 −1 to 65.40 μmol L −1 and 65.40–274.20 μmol L −1 of NA, and for 12.00–59.10 μmol L −1 and 59.10–261.70 μmol L −1 of AC. The sensitivities of the biosensor to NA in the absence and presence of AC were found virtually the same, which indicates the fact that the electrocatalytic oxidation processes of NA are independent of AC and, therefore, simultaneous or independent measurements of the two analytes (NA and AC) are possible without any interference. The results of 16 successive measurements show an average voltammetric peak current of 1.13 ± 0.03 μA for an electrolyte solution containing 5.00 μmol L −1 NA. The hematoxylin biosensor has been satisfactorily used for the determination of NA and AC in pharmaceutical formulations. The results obtained, using the biosensor, are in very good agreement with those declared in the label of pharmaceutical inhalation products.

Electrocatalytic oxidation of the antiviral drug acyclovir on a copper nanoparticles-modified carbon paste electrode

The electrocatalytic oxidation of acyclovir (Zovirax) on two different copper-based electrodes: copper microparticles- and copper nanoparticles-modified carbon paste electrodes (denoted as micro-CPE and nano-CPE, respectively) was voltammetrically investigated. In the voltammogram recorded using micro-CPE, a single anodic oxidation peak appeared, while nano-CPE resulted in two overlapped anodic peaks. The anodic currents were related to the electrocatalytic oxidation of acyclovir via the electrogenerated active species of Cu(III) with an EC’ mechanism. Acyclovir was oxidized with higher rates at low potentials on nano-CPE compared to micro-CPE. This was related to the nanosize effect of copper nanoparticles. The constants of the electrocatalytic oxidation process and the diffusion coefficient of acyclovir were reported. A sensitive and time-saving determination procedure was developed for the analysis of acyclovir and the corresponding analytical parameters were reported. The proposed amperometric method was applied to the analysis of commercial pharmaceutical products (tablets and topical cream) and the results were in good agreement with the declared values.

Electrochemical Degradation of Herbicidal and Pure 2,4-Dichlorophenoxy Acetic Acid on Pb/PbO2 Modified Electrodes

Lead/lead oxide Pb/PbO2 modified electrodes was prepared for electrocatalytic oxidation of agrochemicals including herbicidal 2,4-D (albar super) and pure 2,4-dichlorophenoxy acetic acid. The results of electrocatalytic oxidation process of the agrochemical solutions were expressed in terms of the remaining concentration and COD removal. The different operating conditions of treatment process were investigated including current density, pH, temperature, time of electrolysis, type of conductive electrolyte, and its specific conductance. This electrode gives good results for the removal of agrochemicals and COD. Also, the results showed the best conductive electrolytes is NaCl. This observation was attributed to the small size of Na+ and contribution of Cl− ion in formation of OCl−.

Off-line coupled electrocatalytic oxidation and liquid phase polymer based retention (EO-LPR) techniques to remove arsenic from aqueous solutions

Electrochemistry and membrane ultrafiltration methods ( electro-oxidation and liquid phase polymer based retention technique, LPR, respectively) were off-line coupled to remove As(III) inorganic species from aqueous solutions. Our main objective was to achieve an efficient extraction of arsenic species by associating a polymer-assisted liquid phase retention procedure, based on the As(V) adsorption properties of cationic water-soluble polymers, with an electrocatalytic oxidation process of As(III) into its more easily removable analogue As(V). The electrocatalytic oxidation of As(III) to As(V) was performed in the presence of different water-soluble poly(quaternary ammonium) salts acting also as supporting electrolyte, i.e. poly(vinylbenzyl)trimethyl ammonium chloride, P(ClVBTA), poly[3-(methacryloylamine)propyl]trimethyl ammonium chloride, P(ClMPTA), and poly(4-vinyl-1-methylpyridinium bromide), P(BrVMP). After complete electrocatalytic conversion of As(III) into As(V), the mixtures were introduced into an LPR cell to remove the As(V)-polymer adducts. Using P(ClMPTA), P(ClVBTA), or P(BrVMP) ammonium salts in a 20:1 polymer:As(III) mol ratio at pH 8, complete (100%) retention of the arsenic was achieved. Moreover, the As(V) retention efficiency turned out to be directly related to the net charge consumed during the electrochemical conversion of As(III) to As(V).

Application of electrochemical methods to aqueous reprocessing of spent nuclear fuel

Published data demonstrating the possibilities of electrochemical methods as applied to solving particular problems arising in various steps of industrial reprocessing of spent nuclear fuel using the Purex process are summarized. Attention is given to stabilization of U, Np, and Pu in required valence states in aqueous solutions and two-phase systems in the course of Pu stripping in the step of its separation from U, to efficient dissolution of PuO2, to isolation of noble metals from high-level liquid waste, and to breakdown of spent organic solvents and complexing agents. Progress in the industrial use of electrolysis, in search for new electrode materials, and in studies of the mechanisms of electrocatalytic oxidation processes is noted.

Electrochemical behaviors of amino acids at multiwall carbon nanotubes and Cu 2O modified carbon paste electrode

A carbon paste electrode modified with multiwall carbon nanotubes and copper(I) oxide (MWCNT–Cu 2O CPME) was fabricated, and the electrochemical behaviors of 19 kinds of natural amino acids at this modified electrode were studied. The experimental results showed that the various kinds of amino acids without any derivatization displayed obvious oxidation current responses at the modified electrode. It was also found that the current response values of amino acids were dependent mainly on pH values of buffer solutions. The phenomenon could be explained by the fact that the amino acids suffered complexation or electrocatalytic oxidation processes under different pH values. Six kinds of amino acids (arginine, tryptophan, histidine, threonine, serine, and tyrosine), which performed high-oxidation current responses in alkaline buffers, were selected to be detected simultaneously by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). These amino acids could be perfectly separated within 20 min, and their detection limits were as low as 10 −7 or 10 −8 mol L −1 magnitude (signal/noise ratio = 3). The above results demonstrated that MWCNT–Cu 2O CPME could be successfully employed as an electrochemical sensor for amino acids with some advantages of convenient preparation, high sensitivity, and good repeatability.

High Performance on the Degradation of Cationic Red X-GRL by Wet Electrocatalytic Oxidation Process

This paper explored a novel advanced oxidation process for dye wastewater treatment, wet electrocatalytic oxidation (WEO), using electrical current to promote the degradation of organic pollutants in mild wet air oxidation (WAO). At the conditions of T = 120 °C, PN2 = 0.50 MPa, PO2 = 0.28 MPa, and Cdye =1000 mg/L, the introduction of current density = 1.77 mA/cm2 greatly improved the performance of cationic red X-GRL oxidation. The effects of major operational factors including current density, conductivity, initial dye concentration, and oxygen pressure on dye degradation were studied and optimized. The instantaneous current efficiencies under different conditions by WEO were much beyond 100%, which indicated that a small current performed as catalysis more than direct oxidation. Besides, the degradation mechanism by WEO was discussed based on the analysis of hydroxyl radicals formed on both the anode and cathode. A probable degradation pathway was deduced with the help of Gaussian 03W for the purpose of...

Enhanced degradation of organic wastewater containing p-nitrophenol by a novel wet electrocatalytic oxidation process: Parameter optimization and degradation mechanism

This paper explored a novel advanced oxidation process (AOP) for wastewater treatment—wet electrocatalytic oxidation (WEO), which introduced a small current into wet air oxidation (WAO) to promote the formation of hydroxyl radical and accelerate the oxidation of organic pollutants. The results showed that this novel process could couple the advantages of both WAO and electrochemical oxidation (EO). The effects of major operational factors of WEO were studied at relatively moderate condition ( T = 100–160 °C, C = 1000 mg L −1, P O 2 = 4 TOD, P N 2 = 0.50 MPa, current density = 0–7.08 mA cm −2 and pH 2.7–10.6) aiming to p-nitrophenol (PNP) degradation, TOC and COD removal. The cost-effective operational parameters were found and the current efficiencies were highly beyond 100% with the maximum value of 386%. The degradation mechanism of WEO was carefully studied based on the formation of free radical. After the detail analysis of Hammett theory and quantitative structure-activity relationships (QSAR), the reaction pathway of hydroxyl radical with PNP was analyzed with the help of Gaussian 03W and the probable degradation pathway of PNP by WEO was deduced.

Electrodegradation of Methylene Blue Dye in Water and Wastewater using Lead Oxide/Titanium Modified Electrode

A modified electrode was prepared by the electrodeposition of a lead oxide layer on a titanium substrate. This electrode was used as an anode for electrocatalytic oxidation process of dyestuff in aqueous solution. The modified electrode was used for electrochemical degradation of methylene blue dye. The results of the electrocatalytic oxidation process of the dyestuff solutions were expressed in terms of the remaining dye concentration and chemical oxygen demand (COD) values. Different operating conditions and factors that affected the treatment process including current density, pH, initial dye concentration, conductive electrolyte and time of electrolysis were studied. The optimum operating conditions for the dye and modified electrode were investigated. This has resulted in complete removal of the dye and COD. The optimum conditions were applied to the treatment of methylene blue dye in real wastewater solutions. These results indicate that the suggested modified electrode was highly efficient in the treatment of effluents containing methylene blue dye with very slight effect of matrix. This electrochemical system is robust in structure and simple in operation. It has the potential to be developed as a feasible and an effective wastewater treatment process.

Electrochemical degradation of acid green dye in aqueous wastewater dyestuff solutions using a lead oxide coated titanium electrode

A modified electrode, which can be used as an anode for electrocatalytic oxidation processes of dyestuff in aqueous solutions, was fabricated by the electrodeposition of a lead oxide layer on a titanium substrate. The modified electrode was used for the electrochemical degradation of an acid green dye. The results of the electrocatalytic oxidation process of the dyestuff solutions were expressed in terms of the remaining dye concentration and chemical oxygen demand (COD) values. The different operating conditions of the treatment process were studied. The optimum operating conditions for the dye and modified electrode were determined, where good results for complete removal of the dye and COD were achieved. The optimum conditions were applied to the treatment of a sulfur black dye in true wastewater solutions.

Electrocatalytic activity of cobalt phthalocyanine stabilized by different matrixes.

The behavior of cobalt phthalocyanine complexes incorporated inside an hydrotalcite-like clay (HT) or a sonogel-carbon composite has been investigated in order to develop chemically modified electrodes suitable for use as amperometric detectors. The electrocatalytic oxidation process of cysteine at this new electrode has been studied by cyclic voltammetry. For comparison, the oxidation of cysteine catalyzed by the cobalt phthalocyanine complex as a redox mediator, either dissolved in solution or entrapped inside the HT structure, has been followed by polarography. The sonogel-carbon composite electrode is stable and its response is repeatable. Cysteine oxidation is actually induced by the electrogenerated Co(III) complex, and the relevant anodic peak current varies linearly with cysteine concentration within the range 9.0x10(-4) to 1.0x10(-2) mol L(-1).

Mechanistic Studies and Sensitive Determination of Norepinephrine at a Nafion/Lead-Ruthenium Oxide Pyrochlore Chemically Modified Electrode

Nafion/lead-ruthenium oxide pyrochlore (Pb2Ru1.75Pb0.25O7–y) chemically modified electrode (NCME) exhibits excellent electrocatalytic response towards the norepinephrine (NE) oxidation reaction. NE oxidation by CV studies show the following main features: i) electrochemical oxidation of NE to o-quinone derivative (A1), ii) intramolecular cyclization of o-quinone derivative to leucodopachrome derivative, iii) further oxidation to dopachrome (A2), and iv) formation of polymeric melanine like products. Controlled product analysis using UV-visible spectroscopy gives evidence of the participation of leucodopachrome derivative (λ=425 nm) intermediate. The electrocatalytic oxidation process of A1 is mediated by the electrochemically active RuVI present in the pyrochlore network. The electrocatalytic reaction follows the Michaelis-Menten type kinetics, similar to an enzymatic mechanism. The determination of NE on the NCME was performed using square-wave voltammetry. A linear calibration plot was obtained over 0–6 µM with a detection limit (3σ) of 7.44 nM. The NCME showed high stability and no marked interference in the presence of glucose, ascorbic acid, and oxalic acid.

Lead Dioxide Deposition and Electrocatalysis at Highly Boron-Doped Diamond Electrodes in the Presence of Ultrasound

Boron-doped diamond (BDD) is a versatile and novel electrode material which, due to its mechanical and chemical robustness, wide potential window, low background interference, and ease of chemical modification, is becoming an interesting alternative to conventional electrodes for a wide range of electrochemical applications. It is shown in this study that BDD is a good substrate for the ultrasound-enhanced electrodeposition of lead dioxide, producing strongly adhered electrically conducting deposits. Power ultrasound is used to enhance both the efficiency of the deposition procedure and the rate of the electrocatalytic ethylene glycol oxidation process at the -modified BDD electrode. The presence of high levels of aqueous organic material is shown to interfere with the lead dioxide deposition process. Under optimized insonation conditions the deposit, quantified by using cathodic stripping voltammetry, is shown to be mechanically stable. When used in conjunction with power ultrasound to perform the electrocatalytic oxidation of ethylene glycol two distinct types of oxidation processes at chemically rate limited and electrochemically rate limited, are observed. © 2001 The Electrochemical Society. All rights reserved.

Redox and electrocatalytic activity of copper in base at unusually low, premonolayer potentials

The assumption involved in this work is that the formation of monolayer (α) oxide species, which occurs on copper in base at 60 °C at ca. 0.5 V (RHE), is of little relevance to the electrocatalytic behaviour of the metal at low potentials. For many processes occurring at the interface in question the critical potential is ca. −0.1 V (RHE). This is the value where several electrocatalytic oxidation and reduction processes commence or terminate under potential sweep conditions; hydrous oxide films are reduced close to this value and it is possible to produce an active (but transient) state of the metal surface which exhibits a reversible redox response in this region. The results are rationalized in terms of the incipient hydrous oxide/adatom mediator model of electrocatalysis, and the nature of the active site material at the interface is discussed.

In situ UV–Vis spectroscopic study of the electrocatalytic oxidation of hypophosphite on a nickel electrode

The electrocatalytic oxidation of hypophosphite on a nickel electrode has been studied by means of in situ UV–Vis subtractive reflectance spectroscopy to obtain information about the anodic oxidation mechanism. An absorbency band around 245 nm, which was ascribed to the formation of an intermediate, · PHO − 2 , was observed in the electrocatalytic oxidation process. Accordingly, the electrocatalytic oxidation of hypophosphite might undergo a H abstraction of hypophosphite from the P–H bond to form the phosphorus-centered radical · PHO − 2 , which is subsequently reacted with water to form the final product, phosphite.

Voltammetric and amperometric studies of selected thiols and dimethyldisulfide using a screen‐printed carbon electrode modified with cobalt phthalocyanine: Studies towards a gas sensor

AbstractCyclic voltammetry was used to investigate the electrochemical behavior of hydrogen sulfide, methanethiol, ethanethiol and dimethyl‐disulfide at a cobalt phthalocyanine modified screen‐printed carbon electrode (SPE) in phosphate electrolytes of different pH values. The thiols and hydrogen sulfide were found to undergo electrocatalytic oxidation while dimethyldisulfide exhibited an electrocatalytic reduction reaction. These processes were considered to involve the central cobalt(II) ion in the phthalocyanine macrocycle. The possibility of monitoring the thiols by exploiting the electrocatalytic oxidation process and DMDS by the electrocatalytic reduction process was examined by amperometry. In one approach a bulk phosphate electrolyte, pH 12.0, was employed. The amperometric behavior of the low boiling liquids ethanethiol and DMDS were studied by making standard additions to a stirred solution; both species showed rapid response times at applied potentials of +0.15 V and −0.40 V, respectively. The gaseous thiols, hydrogen sulfide and methanethiol, were examined by bubbling these through the same bulk electrolyte and again rapid, reproducible and reversible signals were obtained. In another approach a gel was prepared by adding agarose to the same phosphate electrolyte and a thin layer was deposited over the working and counter/reference electrodes of a screen‐printed strip. This sensor showed favorable electrochemical characteristics for the gaseous species examined which suggested that the device had promise as an amperometric gas sensor.

Electrochemical oxidation of thiourea studied by use of in situ FTIR spectroscopy

The electrochemical oxidation of thiourea on a Pt electrode was studied at different potentials by use of voltammetry and in situ FTIR spectroscopy. It was found that during the first step the thiourea could be oxidized to the c,c′-dithiodiformamidinium ion in 1 M NaCl solution. It could be further oxidized at higher potentials to produce cyanamide, HSO − 4 and SO 2− 4 ions through an electrocatalytic oxidation process of chemisorbed sulphur taken on the surface of the platinum electrode.