Traitement électrochimique d' eaux usées chargées de phénol : étude comparative sur des électrodes de dioxyde de plomb et de platine

Electrochemical treatment of waste water containing phenol: a comparative study on lead dioxide and platinum electrodes. The objective of this work was to study the efficiency of the Pb/PbO₂ electrode for decomposing the molecule of phenol, then to compare it to a platinum model electrode. Preliminary investigations by cyclic voltammetry showed that the Pb/PbO₂ anode presents a good chemical and electrochemical stability and possesses a high oxygen overvoltage. The study also showed that the electrochemical oxidation of phenol on Pt and PbO₂ in acidic media is a complex process. Long-time electrolysis was carried out using a three potential-plateau program with different values of the oxidation potentials and different concentrations of phenol. The obtained results showed that the transformation of phenol is total on the Pb/PbO₂ anode and that it is partial on Pt. On the other hand an increase in the phenol concentration decreases the rate of its conversion on the electrodes.     

Influence of F‐ doping on the microstructure,surface morphology and electrochemical properties of the lead dioxide electrode

The lead dioxide electrode (PbO₂) with Ti substrate and SnO₂‐Sb₂O₅ intermediate layer was doped by F^‐ ion through the potentiostatic anode co‐deposition method. The content of F in the coating can be controlled by adjusting deposition potential. The effect of F^‐ doping on the composition, surface morphology and electrochemical properties of the PbO₂ electrode was characterized by X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectroscopy and electrochemical measurement methods. The results have confirmed that the content of β‐PbO₂ increases with increasing that of F, and the doping can make the β‐PbO₂ grains become fine and the electrode surface become smooth; the specific surface areas and conductivity increase, and the initial potential of oxygen evolution shifts toward positive direction compared with the free‐doped PbO₂ electrode; the oxygen evolution potential increases with the increasing of the F^‐content in the PbO₂ film electrode. The bulk electrolysis result demonstrated that the performances of the F‐PbO₂ electrode for anodic oxidation aniline have been improved to some extent. Copyright © 2012 John Wiley & Sons, Ltd.     

Removal of pesticide chlorobenzene by anodic degradation: Variable effects and mechanism

The oxidation of chlorobenzene (CB) was studied by electrochemical electrolysis using boron-doped diamond (BDD), PbO₂ or platine (Pt) as anode and graphite bar as cathode. The effect of applied current density, supporting electrolyte and initial pH value were also studied. The results demonstrated that BDD anode had the best effectiveness and accomplishment of electrochemical degradation of CB compared to PbO₂ and Pt anodes. For a current density of 20 mA/cm² and at pH = 3, the elimination of COD and TOC were about 97% and 98%, respectively, after 360 min of electrolysis with the BDD anode. Pseudo-first order kinetics appears to be the most appropriate to describe the degradation of chlorobenzene. The electrochemical mechanism of chlorobenzene on BDD was proposed based on the identified intermediates.     

Study on the electrocatalytic degradation of 4-chlorophenol on PbO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript> composite electrode and its electrochemical property

PbO₂–ZrO₂ composite electrodes were prepared by anodic electrodeposition in the lead nitrate solution. The electrochemical property of this electrode was studied by cyclic voltammetry, polarization curves and open-circuit potential–time curves. The results show that PbO₂–ZrO₂ composite electrodes possess higher oxygen evolution overpotential and better anti-corrosion performance than traditional PbO₂ electrodes. Electrocatalytic oxidation of 4-chlorophenol (4-CPs) in aqueous solution was studied to evaluate the applications of this electrode in environmental protection. The influence of experimental parameters on the COD removal efficiency was studied on PbO₂–ZrO₂ composite electrodes as a function of the current density, initial concentration of the 4-CPs, initial pH, supporting electrolyte concentration and electrolysis time. The results show that the 4-CPs removal efficiency in 0.1 mol L^–1 Na₂SO₄ solution containing 8 mmol L^–1 4-CPs could reach 89.2% with the current density at 200 mA cm^–2 and pH value at 6.5 after 4 h. Compared with traditional PbO₂ anodes, the PbO₂–ZrO₂ composite electrodes show higher instantaneous current efficiency with degradation of 4-CPs. The experimental results demonstrate that the PbO₂–ZrO₂ composite electrodes possess the excellent electrocatalytic activity in refractory pollutants degradation.     

Microwave activation of electrochemical processes: enhanced PbO2 electrodeposition, stripping and electrocatalysis

Microwave activation of electrochemical processes has recently been introduced as a new technique for the enhancement and control of processes at electrode|solution (electrolyte) interfaces. This methodology is extended to processes at glassy carbon and boron-doped diamond electrodes. Deposition of both Pb metal and PbO₂ from an aqueous solution of Pb²⁺ (0.1 M HNO₃) are affected by microwave radiation. The formation of PbO₂ on anodically pre-treated boron-doped diamond is demonstrated to change from kinetically sluggish and poorly defined at room temperature to nearly diffusion controlled and well defined in the presence of microwave activation. Calibration of the temperature at the electrode|solution (electrolyte) interface with the Fe^3+/2+ (0.1 M HNO₃) redox system allows the experimentally observed effects to be identified as predominantly thermal in nature and therefore consistent with a localized heating effect at the electrode|solution interface. The microwave-activated deposition of PbO₂ on boron-doped diamond remains facile in the presence of excess oxidizable organic compounds such as ethylene glycol. An increase of the current for the electrocatalytic oxidation of ethylene glycol at PbO₂/boron-doped diamond electrodes in the presence of microwave radiation is observed. Preliminary results suggest that the electrodissolution of solid microparticles of PbO₂ abrasively attached to the surface of a glassy carbon electrode is also enhanced in the presence of microwave radiation. Electronic Publication     

Electrochemical oxidation of dyes on oxide lead anode with the involvement of active oxygen species

Kinetics and selectivity of oxidation of dyes (Methyl Orange and Chrome Dark Blue) on a lead dioxide (Pb/PbO₂) anode at various current densities, substrate concentrations, and pH values with the use of various active oxygen species was studied. It was shown that the electrochemical oxidation of dyes on the Pb/PbO₂ anode occurs rather effectively under the chosen conditions. The mineralization efficiency in 5 h was 51 to 89.5 and 93 to 100% for, respectively, Methyl Orange and Chrome Dark Blue, depending on the electrolysis conditions.     

Investigation on electro-catalytic oxidation properties of carbon nanotube–Ce-modified PbO2 electrode and its application for degradation of m-nitrophenol

In this work a carbon nanotube–Ce-modified PbO₂ (CNT–Ce–PbO₂) electrode was prepared by electrodeposition method, and compared with pure PbO₂, Ce–PbO₂, and CNT–PbO₂ electrodes. The direct and indirect oxidation capacities of prepared electrodes in electro-catalytic oxidation processes were investigated by cyclic voltammetry and hydroxyl radical production tests, respectively. The electro-catalytic activity of electrodes was examined by electro-catalytic oxidation of a model pollutant of m-nitrophenol (m-NP). Besides, high-performance liquid chromatography (HPLC) was also employed to identify the products resulting from the electro-catalytic oxidation of m-NP and the degradation mechanism of m-NP was proposed. Results show that the CNT–Ce–PbO₂ anode has higher direct and indirect oxidation capacities than pure PbO₂, Ce–PbO₂, and CNT–PbO₂ anodes. In the electro-catalytic oxidation of m-NP, the m-NP can be oxidized and degraded at all anodes, and the oxidation reactions of m-NP follow first-order kinetics. m-NP and TOC removal efficiencies are about 0.987 and 0.622 after electrolysis of 120 min and a maximum first-order rate constant of 0.036 min⁻¹ is achieved at the CNT–Ce–PbO₂ anode, which are obviously higher than those of the other three kinds of anodes.     

苯酚在热氧化法制备的SnO2/Ti 电极上的电氧化研究

A SnO₂/Ti electrode prepared by thermal oxidation was used as the anode for galvanostatic electrolysis in acidic solution containing phenol, the time-dependances of phenol concentration,chemical oxygen demand in solution(COD)and instantaneous current efficiency were determined during electrolysis.The results show that with the SnO₂/Ti anode instead of Pt,the COD significantly decreases at the same charge passage, and average current efficiency of oxidation increases by three times The mechanism for phenol oxidation at two electrodes was discussed.     

Electrochemical oxidation of phenol on boron-doped diamond electrode

The process of phenol oxidation on a boron-doped diamond electrode (BDD) is studied in acidic electrolytes under different conditions of generation of active oxygen forms (AOFs). The scheme of phenol oxidation known from the literature for other electrode materials is confirmed. Phenol is oxidized through a number of intermediates (benzoquinone, carboxylic acids) to carbon dioxide and water. Comparative analysis of phenol oxidation rate constants is performed as dependent on the electrolysis conditions: direct anodic oxidation, with oxygen bubbling, and addition of H₂O₂. A scheme is confirmed according to which active radicals (OH^·, HO₂^·, HO₂⁻) are formed on a BDD anode that can oxidize the substrate which leads to formation of organic radicals interacting with each other and forming condensation products. Processes with participation of free radicals (chain-radical mechanism) play an important role in electrochemical oxidation on BDD. Intermediates and polymeric substances (polyphenols, quinone structures, and resins) are formed. An excess of the oxidant (H₂O₂) promotes a more effective oxidation of organic radicals and accordingly inhibition of the condensation process.     

A mini-review of recent progress in lead dioxide electrocatalyst for degradation of toxic organic pollutants

Lead dioxide (PbO₂) electrocatalyst as a non-active anode have been extensively investigated in recent years with environmental objectives for the degradation of organic pollutants. Degradation of organics at the surface of the PbO₂ anode by direct and indirect oxidation mechanisms proceeds to complete mineralization under optimal conditions. However, for conventional Ti/PbO₂ anodes, low oxygen evolution potential (OEP), short service time, lead leakage, mass transfer limitation and, low active surface area are still the most important disadvantages that need much study. Development of PbO₂ electrocatalysts with a three-dimensional structure, use of innovative intermediate layers, and doping of the main electrocatalyst active layer with the aim of increasing active sites are among the new strategies for upgrading PbO₂ anodes. Focusing on articles published since 2021, this review presents current efforts by researchers to improve the electrocatalytic performance, stability and, environmental safety of PbO₂ anodes for improved degradation of environmental pollutants.     

电解液对全铅单液流电池电极性能的影响

研究Pb(II)和H+离子浓度对全铅单液流电池正、负电极在复合石墨基体上电化学行为的影响.结果表明,PbO2正极和Pb负极的电极过程受电化学和扩散混合控制.Pb(II)氧化沉积成PbO2时出现成核环,铅负极成核过电位小,充放电电压差远小于PbO2正极,电池极化主要来自PbO2正极.增加H+浓度有利于降低PbO2正极和Pb负极的极化,但析氧、析氢副反应和腐蚀加重.增大Pb(II)浓度有利于抑制析氧,但PbO2正极充电电压升高,充放电电压差增大.Pb(II)浓度较低时,充放电过程中PbO2沉积层少许脱落,充电电压进一步降低且更趋平稳.为此,电解液中HBF4浓度以2 mol L-1为宜,Pb(II)浓度应在0.9 mol L-1以上.     

Electrochemical perfluoroalkoxylation of aromatic compounds

New approaches to the electrochemical synthesis of aryl perfluoroalkyl ethers based on a) the electrooxidation of perfluorocarboxylic acid on a consumable PbO₂ anode and b) the simultaneous anodic oxidation of the “aromatic compound-alkaline perfluoroalkoholate” system on a platinum electrode were proposed.     

Oxidation processes at mercury electrodes for tetraphenyllead and related compounds in dichloromethane

Two oxidation waves are observed at mercury electrodes for tetraphenyllead in dichloromethane. The mechanisms of the oxidation processes have been investigated by dc and differential pulse polarography. The first wave is a broad two-electron step and represents the summation of a number of processes related to mercury exchange and halide abstraction. The exchange reactions are as follows: 2 Φ₄Pb + Hg→2Φ₃Pb⁺ + Φ₂Hg+2e^? 2 Φ₃Pb⁺ + Hg→2Φ₂Pb²⁺ + Φ₂Hg+2e^? Dichloroethane and HgCl₂ are identified as products of controlled potential electrolysis experiments as well as Φ₂Hg and Φ₂PbCl₂ implying that the coordinatively unsaturated Φ₃Pb⁺ and/or Φ₂Pb²⁺ react with the solvent dichloromethane and abstract chloride. The second oxidation process is the two electron step. Φ₂Hg+Hg→2 ΦHg⁺ + 2e^?Tetraalkyllead compounds (tetramethyl, tetraethyl, tetrabutyl) also give rise to related electrode processes at mercury electrodes and polarographic techniques may form the basis of a method for their analytical determination if separated chromatographically prior to detection.     

Determination of nanomolar lead (II) using H<Subscript>2</Subscript>O<Subscript>2</Subscript>-oxidized activated carbon modified electrode

The virgin activated carbon (AC) was oxidized by 30% H₂O₂ under the ultrasonic condition for 6 h (denoted as AC-6). The electrochemical response of Pb²⁺ at the AC-6 modified paste electrode was investigated, suggesting that AC-6 shows much higher accumulation efficiency to trace levels of Pb²⁺. Based on this, a sensitive and convenient electrochemical method was developed for the determination of Pb²⁺ utilizing the excellent properties of AC-6. In pH 3.6 HAc-NaAc buffer, Pb²⁺ was easily accumulate at the surface of AC-6 modified paste electrode, then reduced to Pb at −1.20 V. During the following anodic sweep, the reduced Pb was oxidized and resulted in an oxidation stripping peak at −0.58 V. The stripping peak current is proportional to the concentration of Pb²⁺ over the range from the 8.0 × 10⁻⁹ to 2.0 × 10⁻⁶ mol l⁻¹, and the limit of detection is as low as 2.0 × 10⁻⁹ mol l⁻¹. Finally, this newly-developed method was successfully employed to determine Pb²⁺ in water samples.     

Fabrication of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–PbO<Subscript>2</Subscript> electrode and its performance in electrochemical advanced oxidation processes

Owing to its high oxygen evolution potential, PbO₂ electrode is one of the candidates for electrochemical advanced oxidation processes (EAOPs). To further improve its performance as EAOP electrode, a Ga₂O₃-doped PbO₂ electrode (Ga₂O₃–PbO₂ electrode) was fabricated by the composite plating method. SEM and XRD results showed that the crystalline in the coating of Ga₂O₃–PbO₂ electrode is more uniform and in smaller size than that in the undoped PbO₂ electrode, which provided a higher specific surface area. The electrochemical studies showed that the Ga₂O₃–PbO₂ electrode had higher oxygen evolution potential (OEP) and smaller electrode surface impedance, which is a benefit for the formation of hydroxyl radicals (·OH). The electrochemically degradation test using bromocresol green sodium (BG) solution and glucose solution as the simulated wastewater showed that the kinetics of electrochemical catalytic degradation is a pseudo-first-order reaction, and the reaction rate constant on Ga₂O₃–PbO₂ electrode was 2 times accelerated.     

Kinetics of the Electrocatalytic Oxidation of 2,2-Dimethylolpropionaldehyde

A new method of synthesis 2,2-dimethylolpropionic acid from 2,2-dimethylolpropionaldehyde was put forward. The electrochemical oxidation behavior of 2,2-dimethylolpropionaldehyde has been investigated on a Ti/SnO₂ + Sb₂O₄/PbO₂ electrode by cyclic voltammetry (CV) and stable polarization curves in sulfuric acid. The results showed that it was an irreversible reaction controlled by diffusion. The formation mechanism of 2,2-dimethylolpropionic acid in the sulfuric acid was then proposed and the transfer coefficients of the reaction were calculated. It was concluded that RCHO+ỌH_ads→RCHOỌH_ads was the rate-determining step in the electrolysis process. The rate of this step obtained from the assumed process agrees well with experiment.     

On the Utilization of Boron Doped Diamond Electrode as a Sensor for Parathion and as an Anode for Electrochemical Combustion Of Parathion

This work proposes the utilization of a boron doped diamond (BDD) electrode as a sensor for pesticides and as well as an anode for electrochemical combustion of Parathion in spiked, pure and natural waters. The square‐wave voltammetry was selected as the electroanalytical technique and the Britton–Robinson buffer as the electrolyte. The electrochemical reduction responses of Parathion were analyzed and compared with those previously obtained using a hanging mercury electrode (HMDE). The detection and quantification limits were calculated from the analytical curves both for BDD and HMDE in Milli‐Q water (2.4 and 7.9 μg L^?1 and 3.9 and 12.8 μg L^?1 respectively) showing only a slight improvement when used BDD. However, if the application involves polluted natural waters the improvement is accentuated due to the very low adsorption characteristics of BDD, which prevent the fouling of electrode surface by organic pollutants. The BDD was also used as anode for electrochemical remediation of Parathion contamination. In this case, electrolysis was carried out in high positive potential (3.0 V) and lead the electrochemical combustion of Parathion to CO₂ and H₂O, as measured by the diminishing of total organic carbon in the electrolyte.     

Oxidation of toluene on Bi-doped PbO<Subscript>2</Subscript> studied by electrochemical impedance spectroscopy and UV spectrophotometry

Oxidation of organics in the potential region of O₂ evolution is supposed to proceed through the oxidation of water to hydroxyl radicals, which then may either be further oxidized to give molecular oxygen or interact with organic molecules in an oxygen transfer reaction. Therefore, the electrode material must ensure (1) the preferential adsorption of the organic compound, (2) the production of adsorbed hydroxyl radicals able to react with this compound in a selective oxidation reaction (with as little as possible oxygen evolution), and (3) a long-term stability. In the present paper, the oxidative decomposition of toluene in sulfuric acid solution on PbO₂ coatings deposited on Ti substrate from acidic nitrate + fluoride baths containing Pb²⁺ and Bi³⁺ is investigated by voltammetry, electrochemical impedance spectroscopy, and UV spectrophotometry. The chemical composition and structure of the catalytic coatings is characterized with X-ray photoelectron spectroscopy and X-ray diffraction. The catalytic activity is estimated both from current density vs potential and polarization resistance vs potential plots using measurements on the same electrodes in sulfuric acid without toluene to eliminate the oxygen evolution reaction that proceeds in parallel to the oxidation of toluene. A skeletal reaction mechanism of the process is proposed to account for the steady-state and transient response of the catalytic electrodes during oxidation of toluene.     

Indirect electrochemical oxidation of aniline in acid electrolyte with active oxygen species

Kinetics and selectivity of the aniline oxidation on a boron-doped diamond electrode and lead dioxide anode (Pb/PbO₂) in an acid electrolyte were studied under various generation conditions of active oxygen species. The resulting kinetic dependences can be described by a pseudo-first-order equation. The apparent rate constants of the process were determined for two electrolysis modes: direct anodic oxidation and oxidation with addition of hydrogen peroxide. UV spectroscopy was used to determine that the aniline destruction process occurs via formation of a number of intermediate products (benzoquinone, carboxylic acids). It was shown that the aniline destruction process can occur with a rather high efficiency (~80–90%) on the electrode types under study.     

Activity of Pt anode catalyst modified by underpotential deposited Pb in a direct formic acid fuel cell

We characterized the electrocatalytic activity of platinum electrode modified by underpotential deposited lead (PtPb_upd) for a formic acid (HCOOH) oxidation and investigated the influence on the power performance of direct formic acid fuel cells (DFAFC). Based on the electrochemical analysis using cyclic voltammetry and chronoamperometry, PtPb_upd electrode modified by underpotential deposition (UPD) exhibited significantly enhanced catalytic activity for HCOOH oxidation below anodic overpotential of 0.4 V (vs. SCE). Multi-layered PtPb_upd electrode structure of Pt/Pb_upd/Pt resulted in more stable and enhanced performance using 50% reduced loading of anode catalyst. The performance of multi-layered PtPb_upd anode is about 120 mW/cm² at 0.4 V and it also showed a sustainable cell activity of 0.52 V at an application of constant current loading of 110 mA/cm².