Instantaneous Current Efficiency Research Articles

Effects of experimental parameters on 2,4-dichlorphenol degradation over Er-chitosan-PbO2 electrode

This study focused on the effects of 2,4-dichlorphenol (2,4-DCP) initial concentration, initial pH value, applied current density and supporting electrolyte in water on 2,4-DCP degradation over Er-chitosan-PbO(2) electrode in a batch reactor. The results showed that higher initial 2,4-DCP concentration promoted the instantaneous current efficiency (ICE) and average current efficiency (ACE), however, 2,4-DCP degradation rate was inhibited although the removal amount was increased. In the range of initial pH between 3.3 and 12.5, both the highest and the lowest pH conditions favored 2,4-DCP degradation. With the increase of applied current density (1-10 mA/cm(2)), 2,4-DCP degradation efficiency increased initially, however, no significant change was observed afterwards. An acidic condition and higher applied current density were more beneficial to COD removal. The removal efficiency of 2,4-DCP was increased when NaCl was used as the supporting electrolyte instead of Na(2)SO(4) or NaNO(3). The increase of supporting electrolyte (NaSO(4)) concentration (0.01-0.05 mol/L) advanced 2,4-DCP degradation, COD removal and ACE. However, obvious inhibitory effect was exhibited when NaSO(4) concentration increased over a certain value (0.1 mol/L). The activity of Er-chitosan-PbO(2) electrode for 2,4-DCP degradation kept steady after repeated use.

Electrochemical pretreatment of textile effluents and effect of electrode materials on the removal of organics

Abstract The aquatic environment around the textile industries in India was severely affected due to continuous discharge of effluents. In order to avoid further deterioration, the pollution control board of Tamil Nadu, India has enforced zero discharge concepts throughout the state. Consequently, most of the industries have opted membrane technology to recover water. The present study was aimed to find out the efficacy of electrochemical techniques as pretreatment methods to reverse osmosis (RO). The textile wastewater was initially treated by electrocoagulation to remove the suspended solids. After the electrocoagulation, the wastewater was further treated by electrooxidation for COD removal. Mild steel as anode was found to be effective for coagulation of suspended solids. For electrooxidation, graphite and RuO 2 /IrO 2 /TaO 2 coated titanium were used as electrodes. The efficiency of these electrode materials was evaluated in terms of chemical oxygen demand (COD) removal, instantaneous current efficiency (ICE) and electrooxidation index (EOI). The COD was removed to the extent of 90–93% using graphite and 54% with RuO 2 /IrO 2 /TaO 2 coated titanium electrodes. The current efficiency of 40% and 11% was achieved with graphite and RuO 2 /IrO 2 /TaO 2 coated titanium respectively. The degradation of organics was followed using GC–MS and the reason for incomplete degradation of organics in the presence of RuO 2 /IrO 2 /TaO 2 coated titanium was discussed.

Electrochemical regeneration of granular activated carbon saturated with organic compounds

Electrochemical regeneration of granular activated carbon (GAC) saturated with organic compounds was investigated using SnO 2/Ti anodes. Experiments were carried out under a semi-batch electrochemical reactor covering wide range in operating conditions. A kinetic model has been developed to describe the electrochemical regeneration and the performance indicators such as instantaneous current efficiency and regeneration efficiency were estimated. The proposed model has been effectively demonstrated for the regeneration of GAC saturated with organics present in the 4,4′-diamino stilbene-2,2′-disulfonic acid manufacturing wastewater. It has been observed from the present experiments that the applied current density has significant influence on adsorption capacity of regenerated GAC. A good agreement of the model predictions with the experimental observations shows that the proposed kinetic model can be used as a better design method for electrochemical regeneration of spent GAC.

Electrochemical oxidation of organic pollutants in water at metal oxide electrodes: A simple theoretical model including direct and indirect oxidation processes at the anodic surface

Abstract The electrochemical oxidation of organics in water at metal oxide electrodes was investigated with the aim to discuss the correlations between the instantaneous current efficiency ICE and operative conditions by considering both the hypothesis of a direct oxidation process and of an indirect process mediated by adsorbed hydroxyl radicals or chemisorbed “oxygen”, in order to explicit the main differences expected between these cases. Thus, a simple theoretical model was discussed, as an extension of previous studies of Comnnellis and co-workers which were focused on indirect oxidation paths [C. Comninellis, Electrochim. Acta 39 (1994) 1857; O. Simond, V. Schaller, Ch. Comninellis, Electrochim. Acta, 42 (1997) 2009], concerning both the cases of mass transfer control and oxidation reaction control and mixed kinetic regimes. A very good agreement, between theoretical predictions and experimental data pertaining to the electrochemical oxidation of oxalic and formic acid at IrO2–Ta2O5, was observed.

Lasing-induced reduction in core heating in high wall plug efficiency quantum cascade lasers

Quantum cascade (QC) laser core heating is a primary impediment to high device wall plug efficiency (WPE). Here, we demonstrate that efficient photon generation produces a quantifiable reduction in heating of the QC laser core temperature. By superimposing low duty cycle current pulses on a core-heating dc baseline, we observe the instantaneous threshold current and current efficiency evolution as the dc input is varied. From these measurements we recover the laser core temperature Tcore. Results agree well with calculations of Tcore based on measured thermal resistance and WPE. Using the same thermal model for a laser with negligible WPE, we show that the large WPE of the measured device—24% for an 80 K heat sink—results in a core temperature reduction of ∼15 K.

Anodic Degradation of CI Reactive Blue 221 Using Graphite and IrO2/TaO2/RuO2Coated Titanium Electrodes

Anodic degradation of the biorecalcitrant reactive dye CI Reactive Blue 221 was investigated using graphite and IrO2/TaO2/RuO2 coated titanium electrodes in a batch reactor setup. The decolorization and mineralization of the dye molecule was monitored by UV−visible spectrophotometric method and chemical oxygen demand (COD) and/or total organic carbon (TOC) measurements, respectively. The effect of different electrolytes and applied current density on the mineralization of CI Reactive Blue 221 in the presence of different electrode materials was studied. Though both the electrode materials were found to be effective for decolorization, complete mineralization of the dye was accomplished in the presence of graphite over a pH range of 6.0−8.0. The efficiency of the electrode material was evaluated in terms of instantaneous current efficiency (ICE), electrochemical oxidizability index (EOI), and specific energy consumption (Esp). The metabolites formed during the degradation reaction were identified using GC-MS, and the degradation pathway was proposed.

Color and COD Removal Using a Three-Dimensional Stacked Pt/Ti Screen Anode

This investigation examines the electrochemical removal of color and chemical oxygen demand (COD) from real textile wastewater using a stacked anode made of 10 Pt/Ti screens in an electrochemical flow-through reactor. Experiments were performed to evaluate the effect of the operating parameters, such as the applied current density, the arrangement of electrode position, and the volumetric flow rate of the solution among others, on the removal of color and COD in the wastewater. The removal efficiencies of color and COD reached 97 and 52%, respectively, under the conditions of using the electrode arrangement of type 1, at 0.08 A cm−2 , 0.1 M Cl − concentration, and the volumetric flow rate of 0.6 dm3 min−1 . Experimental results showed that the removal efficiencies of color and COD are greatly increased by adjusting the Cl− concentration to 0.1 M and the main pathway of color and COD removals was by the indirect oxidation of pollutants in the wastewater. The highest instantaneous current efficiency was 81.4% in this work. Optimal applied current density was determined as 0.08 A cm−2, while considering simultaneously the effectiveness of COD removal and the instantaneous current efficiency.

Electro-catalytic degradation of phenol on several metal-oxide anodes

Three kinds of Ti-based multilayer metal-oxide electrode, including Ti/SnO 2 + Sb 2O 3/PbO 2, Ti/SnO 2 + Sb 2O 3/MnO x and Ti/SnO 2 + Sb 2O 3/RuO 2 + PbO 2 electrodes, were prepared by thermal decomposition, and SnO 2 + Sb 2O 3 coatings were produced with a polymeric precursor method (PPM). The conversion of phenol was carried out with these electrodes as anodes under galvanostatic control. Samples during the electrolyses were characterized with UV–vis spectra and chromatography, and chemical oxygen demand (COD) and instantaneous current efficiency (ICE) for phenol degradation were also determined. The results show that phenol can be oxidized and degraded for all of the three anodes, and the oxidation reactions of phenol follow first-order kinetics, but there are considerable differences in the effectiveness and performance of electro-catalytic degradation. Phenol can be degraded relatively fast on the Ti/SnO 2 + Sb 2O 3/PbO 2 anode and the degradation rate of phenol is slower with the Ti/SnO 2 + Sb 2O 3/MnO x electrode, and the slowest with the Ti/SnO 2 + Sb 2O 3/RuO 2 + PbO 2 electrode, whose apparent rate constants are 2.49 × 10 −2, 1.42 × 10 −2 and 9.76 × 10 −3 min −1, respectively. The rates of electro-catalytic degradation relate to oxygen evolution potential, and the higher the oxygen evolution potential, the better the performance of electro-catalytic degradation. The potential for oxygen evolution at the Ti/SnO 2 + Sb 2O 3/PbO 2 anode is highest, then Ti/SnO 2 + Sb 2O 3/MnO x , following Ti/SnO 2 + Sb 2O 3/RuO 2 + PbO 2. The accelerated life tests at 60 °C and in 1.0 mol L −1 aqueous H 2SO 4 with an anodic current density of 4.0 A cm −2 show that the service life is prolonged when the SnO 2 + Sb 2O 3 interlayer coating are inserted between Ti substrate and active layers.

Electrochemical degradation of phenol using electrodes of Ti/RuO 2–Pt and Ti/IrO 2–Pt

Electrochemical degradation of phenol was evaluated at two typical anodes, Ti/RuO 2–Pt and Ti/IrO 2–Pt, for being a treatment method in toxic aromatic compounds. The influences of current density, dosage of NaCl, initial phenol concentration on electrochemical phenol degradation were investigated. It was found that Ti/RuO 2–Pt anode had a higher oxygen evolution potential than Ti/IrO 2–Pt anode, which will increase the current efficiency for electrochemical degradation, and the instantaneous current efficiency (ICE) was relatively higher at the initial time during phenol electrolysis. HOCl formed during electrolysis would play an important role on the oxidation of phenol. For the Ti/RuO 2–Pt anode, phenol concentration decreased from around 8 mg/L to zero after 30 min of electrolysis with 0.3 g/L NaCl as supporting electrolyte at the current density of 10 mA/cm 2. Although phenol could be completely electrochemical degraded at both Ti/RuO 2–Pt and Ti/IrO 2–Pt anodes, phenol degradation was slower at the Ti/IrO 2–Pt anode than at the Ti/RuO 2–Pt anode due to the fact that passivation was to be found at the Ti/IrO 2–Pt anode.

Treatment of wastewater from synthetic textile industry by electrocoagulation–electrooxidation

Treatment of wastewater from a textile industry that produces synthetic polyester cloths was studied employing electrochemical techniques. The sample was initially subjected to electrocoagulation to remove suspended solids. Mild steel and aluminum electrodes were tried as anodes; and aluminum was found to be effective for the removal of suspended solids. Using aluminum as anode, the chemical oxygen demand (COD) concentration of the effluent which was initially at the level of 1316 mg L −1 could be reduced to 429 mg L −1 by electrocoagulation. After electrocoagulation, the effluent was further subjected to electrooxidation using graphite and RuO2/IrO2/TaO2 coated titanium as anodes. During the electrooxidation tests, both COD and chloride ion were simultaneously estimated; and the effect of Cl − ion is discussed. The measurements have revealed the depletion of Cl − ion concentration implying the generation of free chlorine during electrooxidation. The depletion of Cl − ion concentration and the COD removal were observed to be comparatively high in the presence of graphite electrode. The effects of electrode materials and current density on COD removal are discussed. The instantaneous current efficiency (ICE), mass transfer coefficient and energy consumption were estimated. © 2008 Elsevier B.V. All rights reserved.

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...

Electrochemical incineration of chloromethylphenoxy herbicides in acid medium by anodic oxidation with boron-doped diamond electrode

The electrochemical degradation of saturated solutions of herbicides 4-chloro-2-methylphenoxyacetic acid, 2-(4-chlorophenoxy)-2-methylpropionic acid and 2-(4-chloro-2-methylphenoxy)propionic acid in 1 M HClO 4 on a boron-doped diamond (BDD) thin film anode has been studied by chronoamperometry, cyclic voltammetry and bulk electrolysis. At low anodic potentials polymeric products are formed causing the fouling and deactivation of BDD. This is reactivated at high potentials when water decomposes producing hydroxyl radical as strong oxidant of organics. Electrolyses in a batch recirculation system at constant current density ≥8 mA cm −2 yielded overall decontamination of all saturated solution. The effect of current density and herbicide concentration on the degradation rate of each compound, the specific charge required for its total mineralization and instantaneous current efficiency have been investigated. Experimental results have been compared with those predicted by a theoretical model based on a fast anodic oxidation of initial herbicides, showing that at 30 mA cm −2 their degradation processes are completely controlled by mass transfer. Kinetic analysis of the change of herbicide concentration with time during electrolysis, determined by high-performance liquid chromatography, revealed that all compounds follow a pseudo first-order reaction. Aromatic intermediates and generated carboxylic acids have been identified using this technique and a general pathway for the electrochemical incineration of all herbicides on BDD is proposed.

Dechlorination by combined electrochemical reduction and oxidation

Chlorophenols are typical priority pollutants listed by USEPA (U.S. Environmental Protection Agency). The removal of chlorophenol could be carried out by a combination of electrochemical reduction and oxidation method. Results showed that it was feasible to degrade contaminants containing chlorine atoms by electrochemical reduction to form phenol, which was further degraded on the anode by electrochemical oxidation. Chlorophenol removal rate was more than 90% by the combined electrochemical reduction and oxidation at current of 6 mA and pH 6. The hydrogen atom is a powerful reducing agent that reductively dechlorinates chlorophenols. The instantaneous current efficiency was calculated and the results indicated that cathodic reduction was the main contributor to the degradation of chlorophenol.

Electrochemical QCM Studies of CdTe Formation and Dissolution in Ammoniacal Basic Aqueous Electrolytes

The behavior of CdTe in deposition and dissolution in a basic ammoniacal aqueous media (pH 10.7) containing Cd(II) and Te(IV) species was investigated in situ using an electrochemical quartz crystal microbalance (QCM). The instantaneous current efficiency of CdTe deposition during potentiostatic cathodic electrolysis, under dark conditions, increased up to 80-90% at the beginning of the electrolysis, but later gradually decreased to ca. 60%, resulting in an overall efficiency of around 70%. In contrast, the overall current efficiency under illumination with visible light increased steeply to 100%. Two anodic waves appeared during the positive-going scan of a cyclic voltammogram in the CdTe deposition bath, and were assigned to (i) a two-electron decomposition of CdTe into Cd(II) ions and elemental Te followed by (ii) a four-electron dissolution of the resulting Te into Te(IV) ions. These observed phenomena are discussed using a potential-pH diagram devised for the system.

Electrochemical Degradation of Microcystin-LR

Microcystin-LR present in drinking water sources poses a considerable threat to human health. Conventional oxidation treatment systems, such as photocatalysis and ferrate oxidation, demonstrated the formation of by-products detectable in the treated microcystin-LR solution. This study investigated an electrochemical approach for microcystin-LR oxidation. The oxidation rate of microcystin-LR increased with the current; the oxidation rate was 0.219 min−1 and the half-life was 2.5 min at an applied current of 100 mA to treat 1.0 mgL−1 of microcystin-LR solution. These results were almost the same as those obtained from the photocatalytic oxidation of a 0.055 mgL−1 microcystin-LR solution. The average instantaneous current efficiency of currents from 30 to 150 mA was greatest at 100 mA because both the current and the microcystin-LR concentration limited the oxidation rate. In addition, no by-products were detected by HPLC, which suggests that the microcystin-LR can be decomposed completely by the indirect oxidation of the hydroxyl radicals formed during electrochemical treatment. We demonstrated that the electrochemical oxidation is a promising approach for the complete oxidation of microcystin-LR.

Electrochemical Oxidation of Polyhydroxybenzenes on Boron-Doped Diamond Anodes

The electrochemical oxidation of phenol (Ph), hydroquinone (HQ), and 1,2,4-trihydroxybenzene (THB) using a diamond thin-film anode has been studied. Within the parameter ranges used (temperature 15−60 °C, initial concentration 1.1−36 mmol dm-3, current density 15−60 mA cm-2), almost complete mineralization of the organic waste is obtained. Carbon dioxide is the sole final product, and the main intermediates are carboxylic acids C4 and C2. Both direct and mediated electrochemical oxidation processes are involved in the electrochemical treatment. Sulfates contained in the waste favor the formation of electrogenerated reagents (persulfates). The instantaneous current efficiency was found to depend only on the controlling mechanism (mass transfer or electrode kinetics). The current efficiency of the process is 1 if it is kinetically controlled and decreases linearly to 0 from the chemical oxygen demand limit value if it is diffusion controlled. Taking into account the information obtained in previous works and the results of the voltammetric and galvanostatic studies of the present work, a simple mechanistic model is proposed to justify the processes involved in the electrochemical oxidation of polyhydroxybenzenes.

Electro-Fenton 반응을 이용한 유독성 유기화합물 처리

The feasibility and efficiency of the hydrogen peroxide produced by an electrolysis cell reactor was investigated, From regulating voltages for the given reaction time, the concentration of the hydrogen peroxide was gradually increased with increasing voltages. Optimal voltage range was found to be 10～15 V. The concentration of hydrogen peroxide was much higher with oxygen gas than without oxygen gas in the cathodic chamber. But there was a little difference in the generating rate of hydrogen peroxide regardless of the presence of nitrogen gas. Under given conditions, the maximum value of ICE(Instantaneous Current Efficiency) was about 38%, and then current density was 74 <TEX>$mA/\textrm{cm}^2.$</TEX> The specific energy consumption was <TEX>$0.694[kWh/kg-H_2O_2].$</TEX> Since Esp (Specific Energy Consumption)was very little value, It did not demand high energy in this system. Using the hydrogen peroxide gained in the experiment, Fenton's reaction was conducted and the removal of nitrobenzene, 3-chlorophenol and dye wastewater was studied. This results were very similar to the Fenton's reaction by using commercial hydrogen peroxide.

A Multielectrode Electrochemical and Scanning Differential Electrochemical Mass Spectrometry Study of Methanol Oxidation on Electrodeposited PtxRuy

Methanol electro-oxidation was studied on a series of electrodeposited PtxRuy catalysts constructed as multielement band electrodes. A combination of electrochemical and scanning differential electrochemical mass spectrometry measurements were performed to evaluate the composition-dependence of methanol oxidation, methanol decomposition, CO2 current efficiency, and the product distribution at 25 and 50 °C. At 25 °C, cyclic voltammetry revealed that the presence of Ru led to enhanced methanol oxidation rates over that of pure Pt. Methanol decomposition showed a similar composition-dependence. Mass spectrometry measurements revealed the evolution of HCOOH and CO2 during methanol oxidation and allowed indirect determination of H2CO produced. Notably, these products were not observed during methanol decomposition. The most active electrode compositions and the highest instantaneous current efficiencies for the formation of CO2 were found to depend on several factors. At 25 °C, the maximum activity was ∼10% Ru...

Electrochemical degradation of surfactants by intermediates of water discharge at carbon-based electrodes

The electrochemical oxidation of anionic (sodium dodecylbenzenesulfonate) and cationic (hexadecyltrimethyl ammonium chloride) aqueous dilute surfactant solutions at a BDD (boron-doped diamond) electrode has been studied by batch electrolysis experiments and potentiodynamic measurements. In the potential region of water decomposition ( E>2.3 V vs. SHE), surfactants could be deactivated and oxidised with total organic carbon (TOC) removals up to 82% by the action of intermediates of water discharge (e.g. hydroxyl radicals). Of the investigated process parameters, the initial electrolyte pH had the highest impact on surfactant oxidation. An initial pH of 10 significantly enhanced the electrochemical oxidation of both surfactants. The process was not diffusion-controlled and instantaneous current efficiencies (ICE) for TOC removal were in all cases low, varying from 5 to 12% on average. The surfactant deactivation and oxidation potential of the BDD electrode was compared with other carbon-based electrodes. Applying an equal electrode surface, the BDD electrode showed much higher surfactant removals compared to plane graphite. Graphite granules and carbon felt suffered from abrasion, leading to additional carbon loading of the surfactant solutions. Based on the current electrolysis configuration, the specific energy requirement with the BDD electrode for the electrochemical oxidation of surfactants was estimated at 10–20 kW h m −3 effective wastewater.

The current efficiency during the cathodic period of reversing current in copper powder deposition and the overall current efficiency

The current efficiency during the cathodic period of reversing current in copper powder deposition was determined by measuring the quantity of hydrogen evolved. The diagrams from which the instantaneous and average current efficiencies for copper deposition can be extracted for any deposition time up to 30 min are given. A procedure for the calculation of the overall current efficiency is proposed. .