Preparation and characterization of carbon nanotube and Bi co-doped PbO2 electrode

B4C/Ce co-modified Ti/PbO2 dimensionally stable anode: Facile one-step electrodeposition preparation and highly efficient electrocatalytic degradation of tetracycline

The application of PbO2 for electrochemical oxidation technology is limited by its low electrocatalytic activity and short service life. Herein, based on the facile one-step electrodeposition, we prepared a boron carbide (B4C) and cerium (Ce) co-modified Ti/PbO2 (Ti/PbO2-B4C-Ce) electrode to overcome these shortcomings. Compared with Ti/PbO2 electrode, the denser surface is displayed by Ti/PbO2-B4C-Ce electrode. Meanwhile, electrochemical characterization indicates that the introduction of B4C and Ce significantly enhance the electrochemical performance of PbO2 electrode. In degradation experiments, under optimized conditions (current density 20 mA cm-2, pH 9, 0.15 M Na2SO4 and 30 °C), the fully degradation of tetracycline (TC) can be completed within 30 min. Furthermore, the trapping experiment demonstrates that ∙OH and SO4·- radicals have a synergistic effect in the degradation process of TC. Based on results of liquid chromatography-mass spectrometer, the generated ·OH preferentially attacks amides, phenols and conjugated double bond groups in TC. Importantly, Ti/PbO2-B4C-Ce electrode maintains a constant degradation efficiency even after 10 recycling tests, and its service life is 2.4 times of traditional Ti/PbO2 electrode. Hence, Ti/PbO2-B4C-Ce electrode is a promising electrode for degradation of organic wastewater containing amides, phenols, and conjugated double bond groups.

Fabrication of PbO2 Electrodes with Different Doses of Er Doping for Sulfonamides Degradation

In the present study, PbO₂ electrodes, doped with different doses of Er (0%, 0.5%, 1%, 2%, and 4%), were fabricated and characterized. Surface morphology characterization by SEM-EDS and XRD showed that Er was successfully doped into the PbO₂ catalyst layer and the particle size of Er-PbO₂ was reduced significantly. Electrochemical oxidation of sulfamerazine (SMR) in the Er-PbO₂ anode system obeyed te pseudo first-order kinetic model with the order of 2% Er-PbO₂ > 4% Er-PbO₂ > 1% Er-PbO₂ > 0.5% Er-PbO₂ > 0% PbO₂. For 2% Er-PbO₂, k_SMR was 1.39 h^-1, which was only 0.93 h^-1 for 0% PbO₂. Effects of different operational parameters on SMR degradation in 2% Er-PbO₂ anode system were investigated, including the initial pH of the electrolyte and current density. Under the situation of an initial pH of 3, a current density of 30 mA·cm^-2, a concentration of SMR 30 mg L^-1, and 0.2 M Na₂SO₄ used as supporting electrolyte, SMR was totally removed in 3 h, and COD mineralization efficiency was achieved 71.3% after 6 h electrolysis. Furthermore, the degradation pathway of SMR was proposed as combining the active sites identification by density functional calculation (DFT) and intermediates detection by LC-MS. Results showed that Er-PbO₂ has great potential for antibiotic wastewater treatment in practical applications.

Application of lead oxide electrodes in wastewater treatment: A review

Electrochemical oxidation (EO) based on hydroxyl radicals (·OH) generated on lead dioxide has become a typical advanced oxidation process (AOP). Titanium-based lead dioxide electrodes (PbO₂/Ti) play an increasingly important role in EO. To further improve the efficiency, the structure and properties of the lead dioxide active surface layer can be modified by doping transition metals, rare earth metals, nonmetals, etc. Here, we compare the common preparation methods of lead dioxide. The EO performance of lead dioxide in wastewater containing dyes, pesticides, drugs, landfill leachate, coal, petrochemicals, etc., is discussed along with their suitable operating conditions. Finally, the factors influencing the contaminant removal kinetics on lead dioxide are systematically analysed.

Preparation and electrochemical properties of a novel porous Ti/Sn-Sb-RuO x /β-PbO2/MnO2 anode for zinc electrowinning

MnO₂ coatings prepared in a sulfate system (S-MnO₂) and MnO₂ prepared in a nitrate system (N-MnO₂) were successfully deposited on porous Ti/Sn-Sb-RuO _x /β-PbO₂ substrates by electrodeposition, and their electrochemical properties were studied in detail. The bath composition plays a very important role in the MnO₂ coating prepared by electrodeposition at a low current density. The results of scanning electron microscopy show that a Ti/Sn-Sb-RuO _x /β-PbO₂/MnO₂ electrode has a rough morphology and the unit cell is very good. At the same time, the surface cracks in the S-MnO₂ coating are larger than those in the N-MnO₂ coating. In addition, the N-MnO₂ coating is composed of a fluffy sheet-like substance. The surface morphology of the N-MnO₂ coating is denser than that of the S-MnO₂ coating. The S-MnO₂ coating consists of irregularly stacked granular particles. Further, the main crystal phase of MnO₂ is γ type, and the main valence state of MnO₂ is +4. The results show that the oxygen evolution potential of the N-MnO₂ electrode is 63 mV lower than that of the S-MnO₂ electrode, indicating that the N-MnO₂ electrode has better oxygen evolution activity and electrochemical stability, which can also be confirmed by EIS test results. Under the accelerated life test conditions, the N-MnO₂ electrode has a better service life of 77 h at a current density of 1 A cm^-2 in 150 g L^-1 H₂SO₄ and 2 g L^-1 Cl^- solution.

PbO2 modified with TiO2-NTs composite materials with enhanced OER electrocatalytic activity for Zn electrowinning

The high oxygen evolution overpotential of the Pb-Ag anode is one of the main reasons for the high energy consumption in Zn electrowinning. PbO2, owing to its high conductivity, good corrosion resistance and low cost, is widely used as an excellent coating material. In present research, a novel composite Ti/TiO2-NTs/PbO2 material was synthesized through a facile anodization, annealing, electrochemical reduction and galvanostatic deposition. The surface morphology, internal structure and the mechanisms of TiO2-NTs enhancing electrochemical performance were discussed. The results show that the self-organized high aspect ratio TiO2-NTs with diameter of ∼120 nm and length of ∼8 μm were obtained on Ti substrate. The Ti/TiO2-NTs/PbO2 composite material exhibits excellent oxygen evolution performance and good stability in Zn electrowinning simulation solution (50 g L-1 Zn2+, 150 g L-1 H2SO4) at 35 °C. Its oxygen evolution overpotential is only 630 mV under current density 50 mA cm-2, which is 332 m lower than that of Pb-0.76 wt% Ag (η = 962 mV) and only increases 22 mV after 5000 cycles of CV scanning. Its outstanding electrochemical performance is mainly ascribed to the introduction of TiO2-NTs in Pb(CH3COO)2 media since it refines the crystal grains, increases the electrochemical surface area, greatly reduces the charge transfer resistance (25.4 Ω cm2 to 2.337 Ω cm2) and enhances corrosion resistance. Therefore, the Ti/TiO2-NTs/PbO2 material prepared in Pb(CH3COO)2 medium may be an ideal anode for Zn electrowinning.

Electrochemical degradation of three phthalate esters in synthetic wastewater by using a Ce-doped Ti/PbO2 electrode

A Ce-doped Ti/PbO₂ electrode was prepared in a deposition solution containing Ce³⁺ and Pb²⁺ ions by electrodeposition, and the surface morphology, crystal structure and elemental states were characterized by SEM, XRD and XPS. The electrode was used to investigate the simultaneous degradation of three phthalate esters (PAEs), i.e., dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP) in synthetic wastewaters. The results showed that the electrode exhibited excellent electrocatalytic activity and good reusability and stability, and the removal efficiencies of 5 mg L^-1 DBP, DMP and DEP in 0.05 M Na₂SO₄ (pH 7) reached 98.2%, 95.8% and 81.1% at current density of 25 mA cm^-2 after 10 h degradation, respectively. The degradation processes followed pseudo first-order kinetic model very well, and the observed rate constants of DBP, DEP and DMP were 0.42, 0.40 and 0.29 h^-1, respectively. The energy consumption in three PAEs degradation was also assessed. The main degradation products of the three PAEs were identified by using liquid chromatography-tandem mass spectrometry, and the possible degradation pathways mainly included dealkylation, hydroxyl addition, decarboxylation and benzene ring cleavage. This work is a promising candidate for efficient treatment of multiple PAEs in wastewater and protection of the aquatic ecological environment.

Hybrid electrocatalytic ozonation treatment of high-salinity organic wastewater using Ni-Ce/OMC particle electrodes

Hybrid electrocatalytic ozonation is an efficient method for degrading high-salinity organic wastewater that has excellent oxidation ability and is environmentally friendly. Furthermore, the high salt content of the wastewater provides electrolyte to support the process, which avoids secondary pollution caused by the addition of electrolyte. In this work, Ni_0.2-Ce_0.2/ordered mesoporous carbon (OMC)/granular active carbon (GAC) particle electrodes with a Ni:Ce weight ratio of 1:1 were synthesized using a simple method. The electrodes were characterized by transmission electron microscopy and electron paramagnetic resonance spectroscopy, as well as other techniques. The catalytic performance was investigated using cyclic voltammetry and AC impedance. Higher reduction and oxidation peak currents were obtained with the Ni_0.2-Ce_0.2/OMC catalyst than with Ni_0.2/OMC or Ce_0.2/OMC, indicating that the bimetallic catalyst has higher activity for the reduction of O₂ to H₂O₂ and the oxidation of O₃ to ·OH. The order of the k values-which represent the mass-transfer rate-was Ni_0.2-Ce_0.2/OMC (0.157) > Ni_0.2/OMC (0.017) > Ce_0.2/OMC (0.014). The results show that cooperation between Ni, Ce, and OMC promoted the dispersion of Ni and Ce and improved the catalytic performance. Ni_0.2-Ce_0.2/OMC enhances the catalytic reduction of O₂ to H₂O₂, and, in addition, Ce is able to rapidly store and release oxygen through Ce³⁺/Ce⁴⁺ conversions and reacting with O₃ to generate ·OH, which increases the oxidation capacity of the material. Under the optimal conditions the chemical oxygen demand removal for high-salinity organic wastewater using Ni_0.2-Ce_0.2/OMC/GAC particle electrodes reached 93.7%.

Electrochemical pretreatment of coal gasification wastewater with Bi-doped PbO2 electrode: Preparation of anode, efficiency and mechanism

Coal gasification wastewater (CGW) contains a large amount of toxic pollutants, which seriously affects the subsequent biochemical treatment. In order to investigate the efficiency of electrocatalytic oxidation on pretreatment of CGW, lead dioxide electrodes doped with PEG and Bi were successfully prepared. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were comprehensively used to characterize the lead dioxide electrode and the electrochemical performance was also tested by linear sweep voltammetry curve, cyclic voltammetry curve and AC impedance. Biodegradability and toxicity of CGW were evaluated by dehydrogenase activity and acute toxicity, respectively. Results showed that the doping of PEG and Bi significantly improved the electrochemical performance and catalytic oxidation performance of lead dioxide electrodes. The degradation rate of phenol by Sn-Sb/PbO₂ (PEG + Bi) electrode were 1.57 times of that by pure lead dioxide electrode. The removal of TOC and total phenols were 53.2% and 82.7%, respectively at 120 min under 40 mA cm^-2 by Sn-Sb/PbO₂ (PEG + Bi) electrode. The changes of biodegradability, biological toxicity and by-products were analyzed. Furthermore, 3,5-dimethylphenol was used as characteristic pollutant to study the degradation mechanism of phenolic pollutants in electrocatalytic system. According to the intermediate products detected by GC-MS, possible degradation pathways in electrocatalytic system were proposed.

Electrochemical behaviors and influence factors of copper and copper alloys cathode for electrocatalytic nitrate removal

The electrocatalytic activities of a series of copper alloys, Cu/Ni/Zn (Cu₆₀ Ni₁₅ Zn₂₅ ) and Cu/Zn (Cu₆₂ Zn₃₈ ), toward the reduction of nitrate were investigated, in comparison with that of pure copper. Electrochemical analysis showed that the copper alloy electrode exhibited higher electrochemical reduction rate of nitrate. The extreme difference (R) between the orthogonal experiments revealed that the NO 3 - - N concentration was the main determinant of the removal percentage, followed by the current density and electrolyte concentration, while the impact of the initial pH was minimal. The conditions of the electrolysis experiments with Cu/Ni/Zn and Cu/Zn cathodes were optimized as follows: a current density of 8 mA/cm² , a NaCl concentration of 2.0 g/L, and an initial pH of 3.0. The nitrate reduction reaction process with copper alloy cathodes was confirmed by electrochemical analysis and electrolysis experiments. Therefore, copper alloyed with Zn and Ni is a feasible option for practical application to the electrocatalytic reduction of nitrate. PRACTITIONER POINTS: Alloy of Cu, Zn, and Ni improved electrochemical nitrate reduction reaction. Electrochemical reduction of nitrate was confirmed in the presence of NaCl. The optimized current density with copper alloy cathodes was 6 mA/cm² . A feasible strategy was provided for the improving nitrate removal and minimizing by-products.

Recent electrochemical methods in electrochemical degradation of halogenated organics: a review

Halogenated organics are widely used in modern industry, agriculture, and medicine, and their large-scale emissions have led to soil and water pollution. Electrochemical methods are attractive and promising techniques for wastewater treatment and have been developed for degradation of halogenated organic pollutants under mild conditions. Electrochemical techniques are classified according to main reaction pathways: (i) electrochemical reduction, in which cleavage of C-X (X = F, Cl, Br, I) bonds to release halide ions and produce non-halogenated and non-toxic organics and (ii) electrochemical oxidation, in which halogenated organics are degraded by electrogenerated oxidants. The electrode material is crucial to the degradation efficiency of an electrochemical process. Much research has therefore been devoted to developing appropriate electrode materials for practical applications. This paper reviews recent developments in electrode materials for electrochemical degradation of halogenated organics. And at the end of this paper, the characteristics of new combination methods, such as photocatalysis, nanofiltration, and the use of biochemical method, are discussed.

Effect of coating method on the structure and properties of a novel PbO2 anode for electrochemical oxidation of Amaranth dye

This study deals with the electrochemical degradation of Amaranth in aqueous solution by means of stainless steel (SS) electrodes coated with a SiO_x interlayer deposited by Plasma Enhanced Chemical Vapour Deposition and a modified PbO₂ top layer deposited by continuous galvanostatic electrodeposition. The morphological characterization of the PbO₂ top-layer performed by Field Emission Scanning Electron Microscope put in evidence that the SiO_x, interlayer allows obtaining a more integrated PbO₂/SS electrode with a very homogeneous PbO₂ film. The composition of the lead oxide layer was investigated by X-ray Diffractometry, showing that the β-PbO₂/α-PbO₂ ratio in the top layer deposited on the SiO_x film was four times higher respect to the one deposited directly on the stainless steel surface. In addition, the electrochemical behaviour of SS/SiO_x/PbO₂ interfaces was studied by electrochemical impedance spectroscopy (EIS). The EIS results showed that the presence of SiO_x favors electron transfer within the oxide layer which improves electro-oxidation capability. Moreover, bulk electrolysis showed that over 100% colour removal and 84% COD removal, using SS/SiO_x/PbO₂ at acidic pH were reached after 300 min. High Performance Liquid Chromatography analysis was used for the quantitative determinations of initial Amaranth dye molecule removal and to evaluate its specific degradation rate. In order to evaluate the phototoxicity of treated solution with different by-products, different tests of germination were performed and proved that the electrochemical treatment with modified PbO₂ could be as an efficient technology for reducing hazardous wastewater toxicity and able to produce water available for reuse.

Electrochemical degradation of insecticide hexazinone with Bi-doped PbO2 electrode: Influencing factors, intermediates and degradation mechanism

Electrochemical degradation of hexazinone in aqueous solution using Bi-doped PbO₂ electrodes as anodes was investigated. The main influencing parameters on the electrocatalytic degradation of hexazinone were analyzed as function of initial hexazinone concentration, current density, initial pH value and Na₂SO₄ concentration. The experiment results showed that the electrochemical oxidization reaction of hexazinone fitted pseudo-first-order kinetics model. 99.9% of hexazinone can be decontaminated using Bi-doped PbO₂ electrode as anode for 120 min. Comparing with pure PbO₂ electrode, the Bi-doped PbO₂ electrodes possess higher hexazinone and COD removal ratio, higher ICE and lower energy consumption in the electrocatalytic degradation process. The results revealed that electrochemical oxidation using Bi-doped PbO₂ anodes was an efficient method for the elimination of hexazinone in aqueous solution. The electrocatalytic oxidization mechanism of hexazinone with Bi-doped PbO₂ anode was discussed, then the possible degradation pathway of hexazinone with two parallel sub-routes was elucidated according to 15 intermediates identified using HPLC-MS.

Temperature effects on the kinetics of a PbO2 electrosynthesis process in an alkaline bath

An electrochemical investigation of temperature on the electrosynthesis of lead dioxide in alkaline solutions was performed using a rotating disk electrode (RDE).

Electrosynthesis and performance of WC and Co3O4 co-doped α-PbO2 electrodes

α-PbO₂ uniformly co-doped with Co₃O₄ and WC particles was prepared as a functional electrode for oxygen evolution.

Fabrication and characterization of a novel PbO2 electrode with a CNT interlayer

A novel PbO₂ electrode (marked as CNT–PbO₂) with a carbon nanotube (CNT) interlayer was prepared by electrophoretic deposition and electro-deposition.

Electrocatalytic degradation of ibuprofen in aqueous solution by a cobalt-doped modified lead dioxide electrode: influencing factors and energy demand

PbO₂ electrode modified with Co exhibited higher electrochemical oxidation. The effects of HA, FA, OA and CA were investigated.

Fabrication and characterization of β-PbO2/α-PbO2/Sb–SnO2/TiO2nanotube array electrode and its application in electrochemical degradation of Acid Red G

A novel β-PbO₂/α-PbO₂/Sb–SnO₂/TiO₂nanotube array electrode was fabricated and investigated for the treatment of Acid Red G (ARG) in aqueous solution.

Study on the performance of an improved Ti/SnO2–Sb2O3/PbO2 based on porous titanium substrate compared with planar titanium substrate

A systematic study was carried out to investigate the preparation and characterization of porous Ti/SnO₂–Sb₂O₃/PbO₂. Porous titanium substrates contribute to the improvement in the performance of electrodes.