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Electrocatalytic oxidation of aromatic pollutants (aniline, Methyl Orange, Eriochrome blue SE) is studied on lead dioxide, boron doped diamond, and ruthenium- and titanium-oxide-based anodes (DSA, dimensionally stable anode). The catalytic properties of the tested materials are studied using cyclic voltammetry and galvanostatic electrolysis. The activity of electrodes toward the electrochemical conversion of organics is shown to increase in the sequence of DSA Methyl Orange > aniline for all electrodes. The oxidation process of the compounds corresponds to the pseudo-first-order reaction kinetics. The apparent rate constant grows at an increase in the applied current density and decrease in the initial pollutant concentration. The formation of both •OH and $${\text{SO}}_{4}^{{2\centerdot {\kern 1pt} - }}$$ radicals is confirmed by the free radical quenching studies; their contribution to the Eriochrome blue SE dye destruction process is evaluated.

The charge-discharge characteristics and the aging mechanism of PbO2 layers doped with bismuth in contact with sulfuric acid solutions were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers (non-doped and doped with Bi) were electrodeposited on gold substrate from aqueous solutions of Pb(NO3)2 dissolved in nitric acid and they were investigated in sulfuric acid media. Based on the electrochemical and the mass change responses, it is concluded that during the electrodeposition, bismuth influences the structure of the PbO2 formed. Bi(III) also inhibits the oxidation of lead sulfate and affects the reduction kinetics of lead dioxide. During successive cyclization (aging), the presence of bismuth accelerates the hydration of PbO2.

The charge-discharge characteristics and the aging mechanism of PbO2 layers in contact with sulfuric acid solutions of different concentrations (1.5–5.0 M) were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers were electrodeposited on gold substrate from aqueous solutions of Pb(NO3)2 dissolved in nitric acid. Based on the electrochemical and the mass change responses, it was found that in more concentrated solutions of H2SO4, the main reduction reaction was the transformation of lead dioxide to lead sulfate. However, in less concentrated sulfuric acid media, the transformation of lead dioxide to lead(II) ion became the main reaction. These Pb2+ ions transformed into lead sulfate crystals later by a chemical reaction. Because the electrochemical oxidation of lead sulfate is less favourable in sulfuric acid medium of higher concentrations, thus, PbO2 layers cannot be tested by continuous cyclization, which is necessary to study their aging parameters. Therefore, a delay step before each cyclic voltammogram was applied while the non-conductive lead sulfate dissolves or alternatively, by applying a pre-oxidation step prior to each cyclic voltammetry experiment to produce electrochemically significant amount of lead dioxide which can be reduced during the following negative potential sweep.

Lead dioxide was extracted from used batteries, and used to synthesize the following intermediate oxides by heating at different temperatures: Pb12O19, Pb12O17, and Pb3O4. Each of the prepared intermediate oxide was subject to sulfuric acid with 1.28 g cm–3. X-ray diffraction (XRD) results showed that the sample prepared from Pb12O19 only had a pattern similar to that of the starting PbO2 with α-PbO2 and β-PbO2 phases. The measurements of H+ proton diffusion coefficient (DH+) of the different samples showed that the sample prepared from Pb12O19 had better electrochemical performances than the starting PbO2. This kinetics reflects the proton insertion mechanism in PbO2, i.e. the sample prepared from Pb12O19 has a large amount of structural water in OH– hydroxyl form. This amount contributes more in the PbO2 reduction mechanism. In addition, the DH+ value of the sample prepared from Pb12O19 is significantly higher than that of starting PbO2, which confirms this hypothesis. X-ray diffraction analysis, thermogravimetric and differential thermogravimetry analysis, and cyclic voltammetry reduction at different scanning rates were used to investigate the samples. This work contributes to environment preservation by recycling of used lead dioxide and reduction of the hazard of its disposal on water. Scopus

Selected cathodes, including carbon paper (C) and plates of titanium (Ti), iron (Fe), copper (Cu) and aluminum (Al), combined with a Ti/PbO2 anode (a lead dioxide electrodeposited on titanium plate) were employed for studying quick nitrate removal from neutral water in this work. Cathode materials, current densities and the presence of chloride ions (Cl−) in water were investigated as to the effects on nitrate removal. Nitrate and two main reduction products, i.e. nitrite and ammonia, were measured using ion chromatography. The results showed that the nitrate removal efficiency decreased in the order of cathode materials: C > Ti ≈ Fe > Cu > Al. The optimum removal was achieved to be 47.7% for a 50 mg-N/L nitrate solution by using carbon paper cathode and Ti/PbO2 anode after 120-min electrolysis with a current density of 40 mA/cm2. The subsequent experimental results showed that the current density of 20 mA/cm2 is also high enough for achieving a considerable nitrate removal. Moreover, the presence of Cl− in water was proven to have no significant effect on nitrate removal but be able to promote the destruction of nitrite and ammonia ions, resulting in the virtual decrease in nitrate and total nitrogen. By a designed experiment, the nitrate removal pathway was confirmed to include a reciprocating reduction (of nitrate) and oxidation (of nitrite and ammonia), both of which can lead to the removal of nitrate as well as total nitrogen from nitrate-containing wastewater by generation of nitrogen. cathodes and anodes may play different roles.

Intermediate oxides are synthesized by heating fresh lead dioxide obtained from commercial positive plates of lead-acid batteries. These oxides are soaked in sulfuric acid with 1.28 s g under stirring for 1 h. The obtained powders are analyzed using X-ray diffraction and chemical analysis. The samples are discharged with a cathodic current of 1 mA in sulfuric acid with 1.28 s g, and the capacity is determined. It is found that lead dioxide obtained from PbO1.55 is more active than the fresh sample. It shows an increase in capacity of 17%. This is due to the increase in the quantity of structural water as given by the chemical and thermal analyses.

The influence of manganese ions on the electrodeposition process of lead dioxide on the glassy carbon electrode (GCE) in the lead nitrate solution was investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results show that the electrodeposition process of lead dioxide was inhibited by the addition of manganese ions. However, the nucleation model is not influenced by the addition of manganese ions and the electrodeposition process still fits the instantaneous nucleation model with three-dimensional growth according to Scharifker—Hills’ model.

The comparative study of electrocatalytic activity of DSA, lead dioxide and F-PbO2 has been performed. It has been shown that the processes of electrochemical oxidation of nitroanilines on investigated materials occur qualitatively the same and differ only in the rate. This suggests the invariability of the mechanism of their oxidation on different materials that allows one for a correct comparison of their electrocatalytic activity. The maximum interest for the electrochemical destruction of nitroanilines represents lead dioxide electrodes modified by fluorine to which a rate constant of p-nitroaniline oxidation increases in 3 times compared with nonmodified electrodes.

An investigation on lead dioxide electrodeposition from methane­sul­fonate electrolytes additionally containing Ni 2+ is reported. It is shown that the lead dioxide electrodes micromodified by nickel have different physico­chem­ical properties vs . nonmodified PbO 2 -anodes, that are formed during the depo­sition. The electrocatalytical reactivity of the electrodes involved in com­par­ison to both the oxygen evolution, as well as to the electrooxidation of 2,4- -dichlorophenoxyacetic (2,4-D) acid is investigated. The processes of electro­chemical oxidation of 2,4-D on various materials occur qualitatively with the same mechanism and differ only in the reaction rate. It is shown that the Ni-PbO 2 -anode possesses the highest electrocatalytic activity: the destruction rate of 2,4-D on it increases 1.5 times in comparison with the unmodified lead diox­ide. The chemical oxygen demand ( COD ) of a 0.4 mM solution of 2,4-D, det­ermined by the dichromate method, is 90.0 mg dm -3 which is 94 % of the theor­etical value.

An innovative process was proposed for recovering lead from spent lead paste, and it produced less pollution and used less energy than the traditional process. First, lead dioxide in lead paste was reduced by glucose under hydrothermal conditions. The effects of the reaction time, glucose excess coefficient, temperature and pH on the hydrothermal reduction were systematically investigated. Under the optimized reduction conditions (i.e., temperature of 175 °C, time of 120 min, glucose excess coefficient of 3.0 and pH of 5.5), 99.9% reduction ratio of lead dioxide is achieved, and only the PbO·PbSO4 and PbSO4 phases are observed in the reducing residue. Subsequently, the reducing residue is desulfurized in a NaOH solution, and approximately 99.40% of the sulfur is removed. The main lead phase in the desulfurization residue is 3PbO·H2O.

Thick lead dioxide layers were electrodeposited on gold and platinum substrates from aqueous solutions of Pb(NO3)2 dissolved in nitric acid and perchloric acid, respectively. The electrodeposition was carried out using cyclic voltammetry and chronoamperometry experiments. The mass changes during PbO2-film formation and dissolution were followed by in situ electrochemical quartz crystal microbalance (EQCM). The electrodeposition of lead dioxide on several types of substrates and in different electrolytes has been widely investigated; however, the mechanism of its dissolution has not been explored, yet. The rate of the reactions occurring during the reduction of the film can be very different depending on the substrates, the electrolytes, the applied potential, and the scan rate. The sweep rate and pH have a small effect on reversibility but highly influences the properties and the deposited mass of lead dioxide layer. At lower concentrations of nitric acid, the PbO2 can be reduced in a larger potential range which is most likely related to the variation of the conductivity of the deposited layer as well as on the nature of the intermediate species.

The polydopamine (PDA) coating was used to modify the surface of the PbO2/TiO2 nanotube arrays (PTNAs) by impregnation method. The obtained PDA-PbO2/TiO2 nanotube arrays (PPTNAs) coating exhibited a sandwich structure and used as anode for photoelectrochemical degradation of toluene. Generally, due to the symmetric structure and conjugation of methyl with benzene ring, the degradation of toluene was difficult to carry on. Our results show that the rate of toluene degradation can reach up to 66% at the surface of PPTNAs coating anode, it is much higher than that of the TiO2 nanotube arrays coating anode, 17%. The reduction product at cathode, hydrogen, was also measured, which is one of the valuable source of energy. In the coupled effect of applied voltage and photocatalysis on the PPTNAs anode, the degradation of toluene was carried out smoothly. The introduction of lead dioxide nanoparticles on the coated anode possessed favorable electronic conductivity in strong acid, which is benefit for a high rate of electrons transportation at the interface of TiO2 and lead dioxide. The excellent corrosion resistance of PPTNAs coating further ensured the effective degradation of toluene with long-term stability. Meanwhile, the unique adhesion of the outer PDA coating increased the contact opportunities between toluene molecules and the anode surface, and enhanced the photocatalytic activity of the PPTNAs coating anode. The applied voltage suppressed the recombination of electron-hole pairs and provided abundant reaction sites. All of these increased the photo-electro catalysis of toluene degradation. The new fabricated anode material shows good prospective application of cleaning up refractory pollutants and the resource utilization.

The development of efficient electrocatalytic systems for CO2 conversion with high current density and high Faradaic efficiency simultaneously is crucially important but challenging. Herein, we described the first study of the electrochemical reduction of CO2 into HCOOH over commercial lead dioxide (PbO2) as the electrode in ionic liquid (IL)-containing catholytes. It was found that 1-benzyl-3-methylimidazolium tetrafluoroborate ([Bzmim]BF4) was the best IL to enhance the efficiency of the PbO2 electrode in the electroreduction of CO2 to HCOOH. In a ternary electrolyte consisting of [Bzmim]BF4 (14.7 wt%), H2O (11.7 wt%) and acetonitrile, the PbO2 electrode showed an excellent performance in electroreduction of CO2 into HCOOH with high Faradaic efficiency (95.5%) and very high current density (40.8 mA cm−2) simultaneously.

β-Lead dioxide is prepared by chemical and electrochemical routes. The chemical sample is obtained by dissolving lead tetra-acetate in distilled water at room temperature. The electrochemical sample is prepared by oxidizing cured plates in sulfuric acid with 1.05 g cm−3 specific gravity. The two powders are indexed as β-PbO2. The sample prepared by chemical route presents smaller crystallite size. When cycling the two powders up to 100 cycles between 0.5 and 1.5 V versus Hg/Hg2SO4 reference electrode, the electrochemical sample presents higher values of anodic and cathodic peak current densities and higher discharge capacity. Thermal analysis and electrochemical techniques are used to explain this difference in activity between the two samples.

Titanium dioxide nanotubes (TiO2-Nts) array morphology and its high specific surface area provide a suitable substrate for PbO2 electrodeposition. PbO2 was effectively dispersed on the whole nanotubes surface, including both their walls and mouths (electrocatalyst of the type: Ti/TiO2-Nts::PbO2). Scanning electron microscopy and EDS microanalyses showed that PbO2 grows from the bottom to the surface of the nanotubes, firstly covering their walls. A simple growth mechanism previously proposed was confirmed by electrochemical methods. Cyclic voltammetry characterization of Ti/TiO2-Nts::PbO2 electrodes (2 cm2 geometric area) allowed to obtain the double layer capacitances that were directly related to PbO2 electroactive area, indicating that it grows inversely with deposition time. Also, electrocatalytic features (high oxygen evolution overpotential, open-edge morphologies and larger network structures to PbO2 crystals formed) depend on the PbO2 dispersion as well as electrodeposition time. Their electrooxidation properties were tested for electrolysis of 15 ppm methyl red (MR) and 50 ppm p-nitrophenol (PNP) acidic aqueous solutions at a current density of 30 mA cm− 2. Results clearly showed the effect of PbO2 deposition time on the electrocatalytic area and on the electrooxidation of PNP and MR. That is, Ti/TiO2-Nts::PbO2 with the shortest electrodeposition time has the highest surface and active area, efficiently degrading MR (100% of discoloration and 90% of organic removal) and PNP (90% of concentration removal after 3.5 h) in solutions. HPLC analyses of the final samples showed that carboxylic acids are the main remnant of electrooxidation.

Graphite-supported α- and β-PbO2 electrodes (PbO2@G) were prepared by electrochemical deposition at appropriate potentials with regard to Pb(II)/PbO2 redox couple under alkaline and acidic conditions, respectively, for studying the direct electro-oxidation of ammonia in aqueous solutions. Results of surface characterization including scanning electron microscopy (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) indicated the presence of polymorphs of PbO2@G. Cyclic voltammetry (CV) of the electrolyte containing NH3 indicated mediation of electron transfer by PbO2. At the onset potential of ca. +1.0 to +1.45 V (vs. Hg/HgO), a pathway of NH3 oxidation to nitrogen byproducts, namely, N2, NO2−, and NO3− was proposed. The removal efficiency and selective conversion of ammonia (0.1 M Na2SO4, pH 11, 25 °C) on PbO2@G was determined based on controlled potential experiments.

In this study, the electrochemical removal of pyrrole as a non-basic nitrogen compound in diesel model fuel was investigated using platinum (Pt), graphite (Gr), carbon paper (CP), lead/lead dioxide (Pb/PbO2), and tin/tin dioxide (Sn/SnO2) working electrodes in a divided cell. Electrochemical analysis such as cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectrometry, and Tafel test was utilized to determine different behavior of electrodes. According to gas chromatography results, pyrrole removal efficiency at a constant current density of 17 mA cm−2 during 6 h was in the range of 83%–100% for Sn/SnO2 and CP electrodes, respectively. The denitrification reaction using CP, Gr, and Sn/SnO2 electrodes was diffusion-controlled regarding data extracted from cyclic voltammetry at various scan rates. However, the adsorption mechanism was dominated by Pt and Pb/PbO2 electrodes. Tafel analysis demonstrated that the electrocatalytic activity of electrodes is as follows: Pt > CP > Gr > Pb/PbO2 > Sn/SnO2. Besides, the formation of polypyrrole and low oxygen evolution potential diminished Pt pyrrole removal efficiency. Carbon-based electrodes with pyrrole oxidation potential near Pt electrode and higher oxygen evolution potential can be utilized as efficient and cost-effective electrodes in the denitrification process.

In the present work, we have synthesized ZrO2 doped PbO2 nanocomposites by hydrothermal method using Zirconium nitrate hydrate [Zr(NO3)4·5H2O] and lead nitrate [Pb(NO3)2] as a precursor. The results show that the amount of Iodine (I) and the NaOH concentration plays an important role in the formation of hexagonal structure. The quantum confinement regime (QCR), phase analysis, purity and morphology are investigated by X-ray diffraction (XRD), Ultraviolet–visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR), High resolution transmission electron microscopy (HRTEM), Energy dispersive X-ray spectroscopy (EDX), μ-Raman spectroscopy, The photocatalytic activity was evaluated by the degradation of methylene blue (MB) dye under UV and visible light solar irradiation. Due to the quantum confinement effect of nanocrystals, this nanocomposite could be potential building blocks to construct functional devices and for the main cladding materials for water-cooled reactors.

In this work, the electrochemical degradation of antibiotic enrofloxacin (ENR) has been investigated by using a Ti/SnO 2 -Sb/La-PbO 2 anode, which demonstrated good performance. The effect of the current density, pH, inorganic anions and humic acid (HA) on the reaction kinetics has been systematically studied. The increase of current density and initial Cl − concentration exerted a prominent effect on the degradation of ENR, while the presence of NO 3 − and HA was found to show an inhibition. The total organic carbon removal rate, defluorination rate and energy cost were 95.1%, 95.3%, and 2.1 Wh/L, respectively, at a current density of 8 mA/cm 2 . The toxicity of the reaction products of ENR towards Vibrio fischeri initially increased slightly and then rapidly reduced to non-toxicity over time. A total of seven aromatic intermediate products of ENR degradation were identified and the different structural changes to the ENR molecule included decarboxylation, substitution of –COOH by –OH group, formation of a ketone group on the piperazine ring, cleavage of the quinolone and piperazine rings, formation of an amide group, and loss of piperazinyl group. Based on the identified products, a reaction mechanism has been proposed wherein hydroxyl radicals attack and open the piperazine and quinolone rings substructures. The products formed after ring opening were further oxidized to CO 2 , H 2 O, NO 3 − , and F − , reaching almost complete mineralization of ENR.

Lead dioxide has absorbed much attention for its good resistance to corrosion, high electronic conductivity, good stability, long lifetime, low cost as electrode material. However, there still exist problems about the selection of electrolyte, which may bring trouble in energy conservation and environmental protection. The present study was to provide more environmentally electrolyte of methanesulfonic acid (MSA) and evaluate MSA effect on electrosynthesis of lead dioxide by using rotating disk electrode (RDE) and scanning electron microscope (SEM) as well as X-ray diffraction (XRD) so as to make sure suitable concentration of MSA and to gain more environmental and energy benefit. The results show that methanesulfonic acid has great influence on the electrodeposition of lead dioxide and adequately characterise the PbO2 synthesized on Pt electrode surface. By controlling the composition of the electrodeposition bath at MSA concentration 0.1 M and Pb(II) 0.2 M can we get better reversible process, longer electrode lifetime and more satisfactory environmental protection.

Modified PbO2 electrodes were prepared by electrodeposition in the presence of ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([Emim]BF4). The electro-catalytic performance of the prepared electrodes for the electrochemical degradation of phenol in aqueous solution was investigated. The COD removal of phenol simulated wastewater followed pseudo-first-order rate kinetics. The rate constant with [Emim]BF4-modified PbO2 electrodes was 0.007 39 min−1, higher than 0.003 83 min−1 obtained with non-modified PbO2 electrodes. The microstructure of the electrodes was characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The electrochemical properties were investigated by Mott-Schottky, steady-state polarization and linear sweep voltammetry techniques. Results indicate that PbO2 coatings with compact and regular morphology, a higher degree of crystallinity and higher content of oxygen in crystal lattice are anodically grown on Ti substrate from electrolyte containing [Emim]BF4. Steady-state polarization tests show that oxygen evolution overpotential on modified electrodes is significantly higher than that on non-modified ones. Mott-Schottky tests reveal a markedly lower content of oxygen vacancy in modified PbO2 samples as compared with the non-modified ones. It is suggested that the enhanced electro-catalytic activity of the [Emim]BF4-modified PbO2 electrodes towards phenol degradation arises largely from its lower content of oxygen vacancy, which decreases the probability of oxygen transferring from more effective •OH into less desirable Olat at the electrode surface.

In this work, lead dioxide coatings deposited from nitrate electrolytes containing nickel ions as an additive are investigated. It is shown that lead dioxide electrodes micromodified with nickel are formed upon the deposition that differ from conventional PbO2 anodes in their physicochemical properties. It is established that modifying lead dioxide with nickel leads to a considerable growth in the number of labile oxygencontaining species at the electrode surface, which, in turn, results in an increased electrocatalytic activity of the coating.

In this study, La and Ce doped PbO2 electrodes were prepared and the characteristic of the electrodes were discussed with the help of structure analysis. The catalytic effects of the doped electrodes were explored through the degradation of para-aminophenol wastewater. The results showed that the para-aminophenol removal was 96.96%, 89.34%, and 77.55% after 180 min treatment with Ce-PbO2, La-PbO2, and PbO2, respectively. The para-aminophenol enhanced degradation mechanism was discussed with rare earth element doping electrodes and a kinetic model was established based on radical reactions mechanism with genetic algorithm (GA) calculation. The reaction constants of these electrodes were calculated and the results showed that the reaction constant of Ce-PbO2 electrode was the highest, which indicated that Ce-PbO2 electrode could have a better treatment effect. The EE/O was used as the index of energy consumption efficiency and the results were calculated and compared. This paper could provide basic data and technique reference of the prediction the oxidation reaction process of different electrodes for the electrochemical oxidation application in wastewater treatment.

In this work, a three-dimension grapnene-PbO2 (3DG-PbO2) composite anode was prepared using coelectrodeposition technology for electrocatalytic oxidation of perfluorooctane sulfonate (PFOS). The effect of 3DG on the surface morphology, structure and electrocatalytic activity of PbO2 electrode was investigated. The results indicated that the 3DG-PbO2-0.08 anode (3DG concentration in electrodeposition solution was 0.08 g L−1) possessed the best electrocatalytic activity due to its stronger ·OH radicals generation capacity, more active sites and smaller charge-transfer resistance. The degradation rate constant of PFOS on 3DG-PbO2-0.08 anode was 2.33 times than that of pure PbO2 anode. Additionally, the by-products formed in electrocatalytic degradation of PFOS were identified and a PFOS degradation pathway was proposed accordingly, which was dominated by the dissociation of –CF2- groups via the attack of ·OH radicals. Finally, the toxicity evolution of degradation solution was examined to evaluate the ecological risk of electrocatalytic oxidation of PFOS by acute toxicity assays to zebrafish embryos.

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.

Ti/TiO2-NTs/Ag2O/PbO2 anode was prepared by electrodeposition technique and characterized by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), linear sweep voltammetry (LSV), and accelerated life test. Electrochemical oxidation of persistent organic pollutant wastewater perfluorooctane sulfonate (PFOS) was carried out with the novel PbO2 anode. Ti/TiO2-NTs/Ag2O/PbO2 anode exhibited a pyramid structure, which was the typical PbO2 electrodes prepared using electrochemical deposition method. XRD spectra indicated that diffraction peaks of PbO2 coating conformed to that of JCPDS (Joint Committee on Powder Diffraction Standards) card for β-PbO2. Ti/TiO2-NTs/Ag2O/PbO2 anode showed high oxygen evolution potential, and longer life service, compared with Ti/PbO2 and Ti/TiO2-NTs/PbO2 anodes. The degradation ratio of PFOS (90 mL of 0.0929 mmol L−1) was 74.87%, with a pseudo first-order kinetic constant of 0.0165 min−1 and a half-life of 43.18 min−1 at a constant current density of 30 mA cm−2 after 180 min of electrolysis. PFOS oxidation yielded sulfate, fluoride, and perfluorocarboxyl anions (i.e., C3F7COO−, C4F9COO−, C5F11COO−, C6F13COO−, and C7F15COO−). The electrospray ionization (ESI) mass spectrum confirmed that oxygen in the intermediate products originated from a heavy-oxygen water electrolyte, and the degradation of PFOS was initiated by the dissociation of a sulfonic group. A possible mechanism was revealed; that was, PFOS was desulfated at the anode to form C8F17· and then transformed into C8F17OH, followed by intramolecular rearrangement and hydrolysis reactions to form C7F15COO−. Kolbe decarboxylation occurred in C7F15COO− at the anode to generate C7F15·, which evolved into C6F13COO− in a similar way and the CF2 unit fell off from C7F15COO−. PFOS was gradually degraded into short-chain perfluorocarboxyl anions by repeating the CF2 unzipping cycle.

The kinetics of PbO2 electrodeposition from nitrate electrolytes containing nickel ions, and the influence of deposition conditions on the physicochemical properties of obtained materials, have been investigated. This study reveals that the mechanism of Ni2+/PbO2 electrodeposition is not in conflict with that of PbO2 formation in the absence of foreign species that we described earlier. Accordingly, electrochemical formation of PbO2 occurs in four stages, two of which are electron transfer steps while the other two are chemical reactions involving formation and decay of soluble intermediates consisting of 3 and 4-valent lead species. We observed an inhibition of Pb2+ electrooxidation in the presence of Ni2+ that is attributable to partial blocking of the active surface sites by the adsorbed foreign cations. Interestingly though, blocked active sites that inhibit the growth of PbO2 show, at the same time, a high activity for O2 evolution. Changing of the electrolyte composition and conditions of electrodeposition of PbO2 (deposition potential, temperature and pH) significantly influences the physicochemical properties of the PbO2 deposits. In particular, the phase and chemical composition, the crystallographic orientation, the content of structural water and the nature of adsorbed oxygen-containing particles on the electrode surface. Concerning the last point, bearing direct relevance to the electrocatalytic properties, we noted that Ni2+/PbO2 electrodes feature a significant increase in the amount of labile oxygen intermediates on the electrode surface which are responsible of a high electrocatalytic activity in the O2 evolution reaction.

The determination of the electrocatalytic activity and selectivity of electrodes with respect to the target process is considered to be of interest both in the theoretical aspect for the development of electrocatalysis theory and in application for efficient electrocatalysts which can be used in electrochemical systems for wastewater treatment. The purpose of the given work was to identify the relationship between the chemical and phase composition of materials based on lead dioxide, their physicochemical properties, and their electrocatalytic activity. The main research methods were quasi-stationary polarization and impedance spectroscopy, photocolorimetry, fluorescent and spectrophotometry in the UV and visible regions, atomic absorption spectroscopy, and high performance liquid chromatography (analysis of the solutions). It was shown that the modification of lead dioxide by ionic additives results in significant changes in the electrocatalytic activity of the system in respect to the oxygen evolution reaction and electrochemical oxidation reactions of organic compounds. It was found that, at low polarizations, the oxygen evolution reaction is limited by the electrochemical desorption step (the second electron transfer), and its overpotential at PbO2-modified electrodes increases in the order that coincides with the dependence in which the number of oxygen-containing particles strongly bound to the electrode surface increases. It was found that the rate of oxidation of organic substances on the anode materials involved is directly proportional to the amount of oxygen-containing radicals formed on the electrode during the water oxidation.

It was shown that the presence of titanium dioxide nanoparticles with an average size of 14 nm in methanesulfonate electrolytes leads to acceleration of the electrolytic deposition and crystallization of lead dioxide. It was established that the process results in the formation of PbO2–TiO2 nanocomposites the composition and structure of which depend on the composition of the suspension electrolyte and the hydrodynamic conditions of electrodeposition.

In this study, degradation of an industrial textile dye by electrochemical oxidation (EO) approach has been performed in an aqueous medium. The galvanostatic electrolysis, through the use of the platinum supported on Ti (Ti/Pt), lead dioxide (Pb/PbO 2 ) and TiO 2 -nanotubes decorated with PbO 2 supported on Ti (Ti/TiO 2 -nanotubes/PbO 2 ) anodes, were conducted in an electrochemical flow cell with 1.0 L of solution containing 250 mg dm −3 of the textile dye Acid Blue 113 (AB113) using Na 2 SO 4 as supporting electrolyte, applying 20, 40 and 60 mA cm −2 . Large disk electrodes of Ti/TiO 2 -Nanotubes/PbO 2 (65 cm 2 of geometrical area) were successfully synthesized by anodization and electrodeposition procedures. The electrolytic process was monitored by the UV–visible spectrometry and the chemical oxygen demand (COD). The results showed that the AB113 was successfully degraded by hydroxyl radicals electrogenerated from water discharge on the Ti/TiO 2 -Nanotubes/PbO 2 electrode surface. Compared with Ti/Pt and Pb/PbO 2 , the Ti/TiO 2 -Nanotubes/PbO 2 anode showed a better performance to remove the AB113. It provided a higher oxidation rate, higher current efficiency and consumed less energy than the galvanostatic electrolysis using the other electrodes.

In this study, we aimed to establish the optimum reductive leaching process with diluted acetic acid for the lead dioxide recovery from lead-acid battery paste. The effects of various reducing agents, acid concentrations, pulp densities, reaction temperatures, and leaching times on the dissolution of lead dioxide were investigated. Lead dioxide dissolution by reductive acidic media is a chemically controlled process with activation energy of 44.51 +/- 1.23 kJ/mol. After leaching, lead acetate ions were precipitated with chromic acid as the lead chromate (PbCrO4) compound. Lead acetate salt was also precipitated from the leaching solution using a crystallization method. These lead compounds can potentially be used in many industries (e.g., pigment application to detect the poisonous gas hydrogen sulfide). Our findings indicate that this process could be effective in leaching lead dioxide.

This paper reports a new method of direct recovery of highly pure lead oxide (PbO) from waste lead pastes and lead grids of spent lead–acid batteries via catalytic conversion, desulfurization, and recrystallization processes in sequence. On the basis of the analytical results of lead (Pb) and lead dioxide (PbO2) contents in the scrap lead paste, a certain amount of waste lead grid was used as a reductant to transform the excess PbO2 into lead sulfate (PbSO4). This paper systematically studies the influence of the concentration of sulfuric acid (H2SO4) and catalyst and the reaction temperature on the catalytic process. The desulfurization of the obtained PbSO4 and the recrystallization of PbO in sodium hydroxide (NaOH) solutions of different concentrations are also investigated. Furthermore, electrochemical experimental results show that the prepared α-PbO with high purity provides slightly superior electrochemical performance to the existing lead oxide obtained by the Shimadzu ball-milling method during t...

A new class of glass and vitroceramic electrodes with applications for rechargeable batteries was obtained by a melt quenching method. The structural characterization of the samples having the x Pb·(100− x )PbO 2 composition, where x =0, 10, 20, 30, 40 and 50 mol% Pb, was performed by UV–vis and FTIR spectroscopies investigations. UV–vis and FTIR data reveal that the excess of lead content in the host matrix generates the transformation and/or disintegration of [PbO 6 ] octahedral structural units into [PbO 4 ] structural units or Pb 2+ ions and non-bonding oxygen ions centers. The electrochemical performances of the glass and vitroceramics electrodes were investigated by cyclic voltammetry. The shapes of the cyclic voltammograms and redox peaks depend on the electrolyte solution concentration and the lead content in host matrix. Differences between these waves are determined by the type of electrochemically active species existing in the glass or glass ceramics. The improved performance of the vitroceramic electrodes is attributed to the presence of the lead metallic phase that seems to offer an easier route for the charge process of the electrodes. Thus, the presence of these phases generates more electrochemically active species, inhibits the secondary reactions implying PbO, takes up the ionic conduction of the larger electrolyte solution and increases the charge/discharge rate of the electrochemical processes.

PbO2 nanowires that were approximately 200 nm in diameter were obtained by template electrodeposition using an anodic aluminum oxide membrane. A proton exchange membrane (PEM) water electrolyzer with an anode made of this PbO2 nanowire, a cathode made of carbon supported platinum, and Nafion®-117 membrane operating at a current density of 1.5 A cm−2, an ozone current efficiency of 20% was achieved, and did not attenuate significantly during a 30-day period.

Lead sulfate, lead dioxide and lead oxide are the main components of lead paste in a spent lead-acid battery. In addition, there are a few impurities in spent lead paste, which have great influence on the performance of the new battery; therefore, it is necessary to remove them. In this study, a novel approach with low temperature burning and hydrometallurgical processing with NH4AC is developed to recover lead from spent lead paste. First, some of the impurities are converted to metal oxides by the calcination of spent lead paste at low temperature. Second, the metal oxides are transformed into soluble sulphates by the reaction between the calcination products and dilute H2SO4 and H2O2 (5.0%). Then, the solids are separated from the solution by filtration; the solids are mainly PbSO4, BaSO4 and CaSO4. NH4AC is used as the leaching solution for PbSO4, and CO2 is introduced to obtain pure PbCO3. Under the optimized leaching conditions (leaching temperature at 40 °C for 20 min, 10.0 wt% NH4AC), the lead recovery ratio is about 99.9%. The calcination product of lead carbonate is PbO, and high-purity lead oxide is obtained. The initial discharge capacity of high-purity lead oxide is about 158 mA h g−1, and the capacity loss is less than 2% after 80 cycles.

A Co-doped modified PbO2 electrode was prepared to electrocatalytically oxidize IBU in aqueous solution. The effects of initial IBU concentration (40–320 mg L−1), initial pH (4–10), current density (3–30 mA cm−2), natural organic matter and small molecular organic acid were investigated. The structure, morphology and electrochemical properties of the electrode were studied by X-ray diffraction, scanning electron microscopy, linear sweep voltammetry and cyclic voltammograms. The doping of Co may decrease the particle size and increase the lifetime of PbO2, which favors the electrocatalytic activity. The results indicated that the Co-PbO2 electrode exhibited a highly effective oxidation capacity for IBU. After 60 min of electrolysis, the removal of IBU and COD at a current density of 3 mA cm−2 for 80 mg L−1 of IBU reached 98.7% and 32.1%, respectively, and the degradation of COD was 53.6% after 180 min of reaction. The reaction apparently followed a first-order kinetics model. When the IBU initial concentration was 80 mg L−1, the highest reaction rate and energy efficiency were observed. Considering the energy demand and space efficiency, the applied current density of 3 mA cm−2 was the most suitable. Lower pH favored degradation because the oxygen evolution reaction was restrained. The addition of low concentrations (10 mg L−1) of humic acid and fulvic acid could promote the degradation of IBU, whereas high concentrations (20–40 mg L−1) inhibited the degradation of IBU. Moreover, the addition of oxalic acid and citric acid (0.1–0.5 mmol L−1) could inhibit IBU degradation. Finally, the possible reaction pathways were proposed.

An electrochemical investigation of temperature on the electrosynthesis of lead dioxide in alkaline solutions was performed using a rotating disk electrode (RDE). In the Pb(II)-containing alkaline solution, the reaction taking place at 0.6 VSCE is under the mixed control of ionic transport and charge transfer. The Koutechy–Levich equation was used to calculate the kinetics of the PbO2 electrodeposition process at 0.6 VSCE. The results indicate that temperature has a positive influence on the diffusion of Pb(II). Moreover, temperature has a positive influence on the apparent heterogeneous rate constant of Pb(II) oxidation reactions within a temperature range of 25–40 °C. XRD and SEM results show that PbO2 synthesized in the alkaline solution consists of pure α phase within a temperature range of 25–45 °C. The intensity of the (200) crystallographic plane shows the same variation in the calculated apparent heterogeneous rate constant k of the PbO2 electrodeposition process. The deposits are composed of rounded nanocrystallites when the temperatures of solutions are lower than 40 °C, but the deposits synthesized at 40 °C and 45 °C exhibit rod-like crystallites.

The anodic oxidation of syringic acid aqueous solutions has been comparatively studied using lead dioxide (PbO2) and boron-doped diamond (BDD) anodes in an electrolytic cell. The influence of several operating parameters such as current density and SA concentration on the performance of both systems has been investigated and the energy consumption has been also evaluated. Galvanostatic electrolyses always cause concomitant generation of hydroxyl radicals that lead to the SA destruction. The efficiency of the electrochemical process increases at lower current density and higher SA initial concentration while it decreases with the COD removal progress. The performance of the BDD anode is always better than that of PbO2, requiring shorter electrolysis time to reach overall mineralization, due to the high amounts of effective hydroxyl radicals generated from water oxidation at each anode, which lead to a higher current efficiency and a lower specific energy consumption when BDD anode was used. A possible reaction mechanism for SA oxidation with ˙OH was proposed. The kinetics decay for the SA degradation on the PbO2 anode follows a pseudo-first order reaction with a rate constant of 8.3 10−3 min−1 for a japp value of 15 mA cm−2.

Pyromorphite is one of the important end member lead apatites that has potential applications in environment remediation. The thermal behavior of natural pyromorphite, Pb10(PO4)6Cl2, has been investigated up to 1373 K at room-pressure using a powder X-ray diffraction device equipped with a heating system. Pyromorphite experiences melting and decomposing at 1373 K into lead phosphate (Pb3(PO4)2), and lead dioxide (PbO2) with reaction with air. The fit of the temperature&ndash, volume data yields a linear volume expansion coefficient &alpha, V = 4.5 (&plusmn, 0.02) &times, 10&minus, 5 K&minus, 1. The linear expansion coefficients for lattice parameters present the anisotropic thermal expansibility, i.e., &alpha, a = (&plusmn, 0.06) &times, 1 and &alpha, c = 2.2 (&plusmn, 1. We looked into the crystal chemistry and proposed an expression to quantitatively evaluate the structural evolution of pyromorphite upon high temperature by calculating the twist angle of the Pb(1)O6 metaprism, which decreases at elevated temperatures. A distinct drop of the twist angle was observed at ~1100&ndash, 1200 K, which might be a sign for the phase transition to a low symmetric subgroup. The variation of the twist angle is more sensitive than that of the unit cell, therefore, it can be applied to monitor the structural and phase changes of apatite group materials in general.