PbO2 Anode Research Articles

Polystyrene microsphere assisted synthesis of a Co/PEG comodified PbO2 anode and its electrocatalytic oxidation performance

• The Co-PEG-PbO 2 electrode was prepared by PS-assisted electrodeposition. • The electrode possess porous structure and high electrocatalytic performance. • The degradation of p-chlorophenol follows the CE mechanism. Highly performed electrode is one of the key factors affecting the efficiency of oxidation toward organic pollutants. To improve the electrocatalytic performance and stability of PbO 2 electrode, a Co-PEG-PbO 2 electrode modified by Co 2+ ion and polyethylene glycol (PEG 6000) was prepared by polystyrene microspheres assisted electrodeposition combined with surface structure adjustment and active substance doping, and used for the effective degradation of p-chlorophenol in water. The results showed that the Co-PEG-PbO 2 electrode surface was composed of small spherical particles β-PbO 2 , containing a small amount of Co 2 O 3 and PEG, and its grain size (8.985 nm) was the smallest in the same series of electrodes. The electrochemical tests results showed that the oxygen evolution reaction in Na 2 SO 4 solution was a sequential two-step charge transfer process, which was controlled by charge transfer and diffusion. The electrode had smaller oxygen evolution potential (1.40 V), larger exchange current density (j 0 = 1.164 × 10 −4 mA · cm −2 ), smaller charge transfer resistance (0.8778 Ω · cm 2 ) and larger concentration polarization resistance (1.335 Ω · cm 2 ), indicating that the Co-PEG-PbO 2 electrode had better electrocatalytic performance. The degradation of p-chlorophenol was controlled by diffusion and was oxidized by strong oxidizing · OH, which conforms to CE mechanism. Within the same degradation time, the electrode had a higher p-chlorophenol removal efficiency η (97.34%), higher TOC removal efficiency (64.25%), higher mineralization current efficiency (23.45%), and lower cell voltage. The accelerated life test showed that Co-PEG-PbO 2 electrode had the longest service life (280 min), which was 2.8, 1.8 and 2 times of PbO 2 electrode, Co-PbO 2 electrode and PEG-PbO 2 electrode, respectively. The electrocatalytic activity and stability of PbO 2 electrode can be effectively improved by structural adjustment and co-doping with Co 2+ and PEG, which can be used for the effective degradation of p-chlorophenol.

Electrochemical Ni-EDTA degradation and Ni removal from electroless plating wastewaters using an innovative Ni-doped PbO2 anode: Optimization and mechanism

In this work, a novel Ni-doped PbO2 anode (Ni-PbO2) was prepared via a co-electrodeposition method and used to remove Ni-ethylenediaminetetraacetic acid (Ni-EDTA) from solutions typical of electroless nickel plating wastewater. Compared with a pure PbO2 electrode, Ni doping increased the oxygen evolution potential as well as the reactive surface area and reactive site concentration and reduced the electron transfer resistance thereby resulting in superior Ni-EDTA degradation performance. The 1% Ni-doped PbO2 electrode exhibited the best electrochemical oxidation activity with a Ni-EDTA removal efficiency of 96.5 ± 1.2%, a Ni removal efficiency of 52.1 ± 1.4% and an energy consumption of 2.6 kWh m−3. Further investigations revealed that 1% Ni doping enhanced both direct oxidation and hydroxyl radical mediated oxidation processes involved in Ni-EDTA degradation. A mechanism for Ni-EDTA degradation is proposed based on the identified products. The free nickel ion concentration initially increased as a result of the degradation of Ni-EDTA complexes and subsequently decreased as a consequence of nickel electrodeposition on the cathode surface. Further characterization of the cathode deposits by X-ray diffraction and X-ray photoelectron spectra indicated that the deposition products were a mixture of Ni0, NiO and Ni(OH)2 with elemental Ni accounting for roughly 80% of the deposited nickel. Results of this study pave the way for the application of anodic oxidation processes for efficient degradation of Ni-containing complexes and recovery of Ni from nickel-containing wastewaters.

Electrochemical degradation performance and mechanism of dibutyl phthalate with hydrophobic PbO2 electrode

A polytetrafluoroethylene (PTFE) doped PbO2 anode with a highly hydrophobicity was fabricated by electrodeposition method. In this process, vertically aligned TiO2 nanotubes (TiO2NTs) are formed by the anodic oxidation of Ti plates as an intermediate layer for PbO2 electrodeposition. The characterization of the electrodes indicated that PTFE was successfully introduced to the electrode surface, the TiO2NTs were completely covered with β-PbO2 particles and gave it a large surface area, which also limited the growth of its crystal particles. Compared with the conventional Ti/PbO2 and Ti/TiO2NTs/PbO2 electrode, the Ti/TiO2NTs/PbO2-PTFE electrode has enhanced surface hydrophobicity, higher oxygen evolution potential, lower electrochemical impedance, with more active sites, and generate more hydroxyl radicals (·OH), which were enhanced by the addition of PTFE nanoparticles. The electrocatalytic performance of the three electrodes were investigated using dibutyl phthalate (DBP) as the model pollutant. The efficiency of the DBP removal of the three electrodes was in the order: Ti/TiO2NTs/PbO2-PTFE > Ti/TiO2NTs/PbO2 > Ti/PbO2. The degradation process followed the pseudo-first-order kinetic model well, with rate constants of 0.1326, 0.1266, and 0.1041 h−1 for the three electrodes, respectively. The lowest energy consumption (6.1 kWh g−1) was obtained after 8 h of DBP treatment using Ti/TiO2NTs/PbO2-PTFE compared to Ti/TiO2NTs/PbO2 (6.7 kWh g−1) and Ti/PbO2 (7.4 kWh g−1) electrodes. Moreover, the effects of current density, initial pH and electrolyte concentration were investigated. Finally, the products of the DBP degradation process were verified based on gas chromatography-mass spectrometry analysis, and possible degradation pathways were described.

Enhancing the stability and electrocatalytic activity of Ti-based PbO2 anodes by introduction of an arc-sprayed TiN interlayer

Ti/TiN/PbO2 electrodes were prepared using an arc-sprayed TiN interlayer on Ti substrates, followed by the anodic electrodeposition of a PbO2 catalytic surface layer on it. In order to investigate the positive effect of the TiN interlayer on the stability and electrocatalytic activity of the anodes, microstructural, surface roughness, adhesion evaluation, accelerated life and electrochemical performance tests and electrooxidation experiments of phenol simulated wastewater were conducted and compared with Ti/PbO2 anodes without the interlayer. The experimental results demonstrated that the arc-sprayed TiN interlayer with a thickness of 140–180 μm had a higher surface roughness and hardness than that of its titanium substrate. The coatings forming the electrode were firmly bonded to the substrate. The conductivity of the Ti-based PbO2 anode containing the TiN interlayer was significantly improved. The PbO2 surface coating achieved a faster deposition rate and finer grains, which produce a number of anode active sites and the electrocatalytic performance was boosted with a removal rate of phenol of up to 85.2%, which was higher than that of Ti/PbO2 by 30.6%. Simultaneously, the anode stability was also significantly enhanced, i.e., the Ti/TiN/PbO2 anode constructed by introducing the TiN interlayer exhibited excellent stability and electrocatalytic performance. The high-performance anode obtained relied not only on the presence of the arc-sprayed TiN interlayer, which significantly improved the overall physicochemical properties of the electrode, but also on the kinetic rate of the electrocrystallization growth of the refined PbO2 coating that was accelerated.

Fabrication of In2O3 doped PbO2 anode and its application for electrochemical degradation of norfloxacin in aqueous solutions

To improve the electrochemical activity and stability of PbO2 electrode, In2O3 particles were doped into β-PbO2 active layer by composite electrodeposition technology. When the In2O3 concentration in electrodeposition solution was 2 mM, the In2O3-PbO2 electrode had larger specific surface area, tighter crystal structure, higher oxygen evolution potential (2.09 V vs. SCE), smaller charge transfer resistance (64.32 Ω/cm2), stronger ability to generate hydroxyl radicals (0.213 μM/min) and thereby the better electrocatalytic activity and stability. In electrochemical oxidation of norfloxacin (NOR), the NOR removal rate at the In2O3-PbO2 anode was 1.388 times faster than that at pristine PbO2 electrode. Additionally, the effects of current density, initial pH, initial NOR concentration and electrolyte concentration on NOR removal efficiency were investigated by the principle of single variable. With the increase of current density and the decrease of initial NOR concentration, the NOR removal efficiency increased significantly; the better degradation effect was obtained under pH 3 and Na2SO4 concentration of 0.2 M. Finally, the degradation mechanism of NOR was discussed and five possible degradation pathways were proposed.

Fabrication of a Ti/PbO2 electrode with Sb doped SnO2 nanoflowers as the middle layer for the degradation of methylene blue, norfloxacin and p-dihydroxybenzene

In the preparation of Sb-SnO2 internal layer of PbO2 electrode, the traditional thermal decomposition method has many problems, such as environmental pollution, short service life and low catalytic activity. Herein, a three-dimensional (3D) Sb doped SnO2 nanoflowers interlayer with good conductivity was prepared on the titanium substrate by the hydrothermal strategy to fabricate a novel PbO2 electrode (Ti/Sb-SnO2NFs/PbO2). Compared to the traditional PbO2 anode, a more compact and undulating 3D morphology of Ti/Sb-SnO2NFs/PbO2 electrode exhibited a higher total and inner active sites and stronger ·OH generation ability. Specifically, three typical organics, methylene blue (MB), norfloxacin (NOR) and p-dihydroxybenzene (p-DHB), were effectively degraded by the novel Ti/Sb-SnO2NFs/PbO2 electrode with economic energy consumption and the degradation mechanism of MB was also investigated. This 3D interlayer also improved the anode stability and safety with the lifetime prolonged about 2.70 times (from 30.1 h to 81.3 h). Consequently, this work offers a meaningful method to prepare PbO2 anode with high catalytic activity and good stability for wastewater treatment.

Improved degradation of diuron herbicide and pesticide wastewater treatment in a three-dimensional electrochemical reactor equipped with PbO2 anodes and granular activated carbon particle electrodes

The electrocatalytic performance of porous carbon felt/PbO2 and planar titanium/PbO2 anodes in a three-dimensional electrochemical reactor (3DER) equipped with granular activated carbon (GAC) particle has been studied for synergistic degradation of diuron herbicide (DIU) and treatment of pesticide wastewater. The results showed that porous carbon felt/PbO2 anode in addition to high stability can provide around three times more surface area than titanium/PbO2 for degradation reactions. Optimization of DIU degradation in 3DER system with carbon felt/PbO2 anode was performed by a five-level rotatable central composite design. The TOC mineralization rate under optimal conditions (pH = 4.7, current density = 13.5 mA cm−2, Na2SO4 concentration = 0.04 M and DIU concentration = 40 mg L−1) for the 3ٍِDER system with carbon felt/PbO2 and titanium/PbO2 anodes after 50 min were 100% and 63.8%, respectively. However, the electrocatalytic efficiency of carbon felt/PbO2 and titanium/PbO2 anodes in the absence of GAC particles to remove TOC was 85.5 and 42.7%, respectively. The energy consumed in the 3DER system equipped with carbon felt/PbO2 anode was 2.28 times less than the 3DER system with titanium/PbO2. The contribution of direct and indirect oxidation of DIU in 3DER degradation systems was determined by radical scavenging technique. The safety of the anodes was evaluated for Pb2+ leakage. The DIU degradation pathway was proposed based on the intermediates identified by LC-MS. The performance of optimized 3DER systems was evaluated for treatment of real pesticide wastewater. The chemical oxygen demand (COD) removal efficiency after 300 min of reaction in the 3DER system with carbon felt/PbO2 and titanium/PbO2 electrodes was 95% and 62.5%, respectively.

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.

Electrochemical study of a novel high-efficiency PbO2 anode based on a cerium-graphene oxide co-doping strategy: Electrodeposition mechanism, parameter optimization, and degradation pathways

A novel and efficient Ti/SnO2-Sb/PbO2-GO-Ce electrode was successfully fabricated based on the co-deposition of Ce ions and graphene oxide (GO) into β-PbO2 crystals and used as an anode for electrocatalytic oxidation of phenol. The electrodeposition mechanism, parameter optimization, mechanism analysis, and potential degradation pathways were discussed in depth. The co-doping of GO and Ce resulted in the high directional specificity of β(301), orderly and dense grain arrangement of PbO2 crystals. At the same time, the oxygen evolution potential, •OH generation capacity and lifetime were also improved. The effects of experimental parameters on phenol removal efficiency were evaluated, including the applied current density, electrode gap, supporting electrolyte, initial NaCl concentration, initial pH, and initial phenol concentration. Under the optimal conditions, the removal efficiency of phenol can reach 375.6 g m-2 h-1 for 20 min electrolysis, which is about 1.2 times that of the pure PbO2 electrode. The active oxygen species (•OH, ClO- and HClO) were important attributes to the degradation of phenol. Additionally, a potential degradation pathway for phenol was proposed. After 10 successive recycles, there was no significant difference of the electro-generated •OH, cell voltage and phenol removal rate, which confirms the stability and admirable reusability of Ti/SnO2-Sb/PbO2-GO-Ce electrode.

Enhanced perfluorooctane acid mineralization by electrochemical oxidation using Ti3+ self-doping TiO2 nanotube arrays anode

Perfluorooctanoic acid (PFOA) is of increasing concern due to its worldwide application and extremely environmental persistence. Herein, we demonstrated the electrochemical degradation of PFOA with high efficiency using the Ti3+ self-doping TiO2 nanotube arrays (Ti3+/TiO2-NTA) anode. The fabricated Ti3+/TiO2-NTA anode exhibited vertically aligned uniform nanotubes structure, and was demonstrated good performance on the electrochemical degradation of PFOA in water. The degradation rate, total organic carbon (TOC) removal rate and defluorination rate of PFOA reached 98.1 %, 93.3 % and 74.8 %, respectively, after electrolysis for 90 min at low current density of 2 mA cm−2. The energy consumption (7.6 Wh L−1) of this electrochemical oxidation system using Ti3+/TiO2-NTA anode for PFOA degradation was about 1 order of magnitude lower than using traditional PbO2 anodes. Cathodic polarization could effectively prolong the electrocatalytic activity of the anode by regenerating Ti3+ sites. PFOA molecular was underwent a rapidly mineralization to CO2 and F−, with only low concentration of short-chain perflfluorocarboxylic acids (PFCAs) intermediates identified. A possible electrochemical degradation mechanism of PFOA was proposed, in which the initial direct electron transfer (DET) on the anode to yield PFOA free radicals (C7F15COO•) and hydroxyl radicals (•OH) oxidation were greatly enhanced. This presented study provides a novel approach for the purification of the recalcitrant PFOA from wastewaters.

Interpretation of high perchlorate generated during electrochemical disinfection in presence of chloride at BDD anodes

Perchlorate is a disinfection by-product (DBP) of serious health concern. Herein, the long sought mechanism of high perchlorate production during electrochemical disinfection at boron-doped diamond (BDD) anode in the presence of chloride was elucidated. The generated perchlorate at BDD during electrochemical disinfection (in 10 mM NaCl) in 60 min reached 0.125 mM, which was 830 times higher than the EPA standard. In contrast, perchlorate at PbO2 and SnO2 anodes was below the detection limit. Further experiments employing NaClO3 revealed that the conversion ratio from ClO3− to ClO4− in 10 h at BDD (98%) was considerably higher than PbO2 (13%) and SnO2 (12%). Such significant difference among anodes was fully interpreted with a two-step mechanism. The first step is essential to produce ·ClO3 by oxidizing ClO3− at electrodes. Otherwise, the conversion to perchlorate would be impossible even with excessive ·OH, which was verified with the photocatalysis process. The second step is the perchlorate generation with radical reaction between ·ClO3 and ·OH, where the primary role of ·OH was substantiated by scavenging test. Interestingly, the capability of perchlorate production was correlated with free ·OH instead of the total amount of ·OH. Despite the similar abilities of electron transfer between anodes and ClO3−, much higher free ·OH exists at BDD anode than at PbO2 and SnO2 anodes through chronoamperometry experiments and work function characterization, which reasonably provides interpretation of high perchlorate production at BDD anode.

Electrocatalytic degradation of diuron herbicide using three-dimensional carbon felt/β-PbO2 anode as a highly porous electrode: Influencing factors and degradation mechanisms

Traditional planar PbO2 anodes have been used extensively for the electrocatalytic degradation process. However, by using porous PbO2 anodes that have a three-dimensional architecture, the efficiency of the process can be significantly upgraded. In the current study, carbon felt (CF) with a highly porous structure and a conventional planar graphite sheet (G) were used as electrode substrate for PbO2 anodes. Both CF/β-PbO2 and G/β-PbO2 anodes were prepared by the anodic deposition method. The main properties of the electrodes were characterized by XRD, EDX-mapping, FESEM, and BET-BJH techniques. The electrocatalytic degradation of diuron using three-dimensional porous CF/β-PbO2 anode was modeled and optimized by a rotatable central composite design. After optimizing the process, the ability of porous CF/β-PbO2 and planar G/β-PbO2 anodes to degrade and mineralize diuron was compared. The electrocatalytic degradation of the diuron was well described by a quadratic model (R2 > 0.99). Under optimal conditions, the kinetics of diuron removal using CF/β-PbO2 anode was 3 times faster than the G/β-PbO2 anode. The energy consumed for the complete mineralization of diuron using CF/β-PbO2 anode was 2077 kWh kg−1 TOC. However, the G/β-PbO2 anode removed only 65% of the TOC by consuming 54% more energy. The CF/β-PbO2 had more stability (115 vs. 91 h), larger surface area (1.6287 vs. 0.8565 m2 g−1), and higher oxygen evolution potential (1.89 vs. 1.84 V) compared to the G/β-PbO2. In the proposed pathways for diuron degradation, the aromatic ring and groups of carbonyl, dimethyl urea, and amide were the main targets for HO• radical attacks.

Synergetic electrocatalytic degradation of isophorone by active oxygen species generated in the gas diffusion electrode and PbO2 anode

Significant efforts have been made to achieve efficient H2O2 generation via oxygen reduction reaction (ORR). Here, the acetylene black (AB)-based gas diffusion electrodes (GDEs) modified by PTFE were fabricated and applied in a closed autoclave for H2O2 generation for the first time. The surface morphology, BET, XPS, cyclic voltammetry curves and linear scanning voltammetry curves of GDEs were all characterized. Additionally, the H2O2 generation experiments of GDEs and the relationship between H2O2 yield and BET surface area (SBET), double layer capacitance (Cdl) were all investigated. It could be found that the SBET and Cdl of GDEs kept a good linear relationship with H2O2 content, and 2#GDE (AB:PTFE = 1:3) possessed the optimal H2O2 generation capacity. Also, the effect of oxygen pressure and current density on H2O2 production was evaluated detailedly, indicating higher oxygen pressure was beneficial to the H2O2 generation and the preferable current density was 20 mA cm−2 due to the side reactions. And all the H2O2 electro-generation experiments exhibited a higher oxygen utilization efficiency (0.77%–2.93%). Finally, the efficient and synergetic electro-catalytic degradation of isophorone was achieved by self-made PbO2 anode and GDE.

Anodic oxidation of organic pollutants: Anode fabrication, process hybrid and environmental applications

Abstract This review summarizes the recent progress in anodic oxidation of organic pollutant for water and wastewater treatment. It supplies the advances in anodes fabrication to improve the anodic performance by different modifications and preparation strategies, focusing on non-active anodes including boron-doped diamond (BDD), PbO2, SnO2 and Ti-based anode (e.g., Ti4O7, blue titanium oxide). Meanwhile, the tendency of anodic oxidation coupled or combined with other processes (adsorption, membrane separation, biological treatment and advanced oxidation process) for pretreatment or advanced treatment of organic pollutant is presented. Finally, anodic oxidation for environmental application is briefly described; several challenges need to be overcome and perspectives for future study are critically proposed.

Fabrication of sulfur-doped TiO2 nanotube array as a conductive interlayer of PbO2 anode for efficient electrochemical oxidation of organic pollutants

Efficient and stable anode materials are in high demand for the electrochemical oxidation of toxic and persistent organic pollutants in wastewater treatment. Herein, a highly structured and conductive sulfur-doped TiO2 nanotubes was fabricated as an interlayer for the Ti-based PbO2 anode (S-TiO2 NTA-PbO2). The novel S-TiO2 NTA-PbO2 anode exhibited a better electrochemical oxidation capability and hydroxyl radical production activity for organic degradation than the parent interlayer-based anode without S-doping and the well-reported PbO2 anode. A nearly 100% of methylene blue (MB, 20 mg L-1) was degraded on the S-TiO2 NTA-PbO2 anode in 90 min. A quenching experiment revealed that direct oxidation on the anode surface contributed about 50% of the MB degradation and played a crucial role in the complete mineralization of MB. The stable and conductive S-TiO2 NTA interlayer enabled the high reactivity and stability of the composite anode, as exhibited by the cyclic tests. Moreover, the S-TiO2 NTA-PbO2 anode was versatile enough to degrade various industrial pollutants, including 4-chlorophenol, p-nitrophenol and bisphenol A. This work on the new conductive S-doped TiO2 NTA interlayer also provides a new method for the design and fabrication of highly effective and stable anodes for electrochemical treatment of industrial wastewater.

Preparation and characterization of Nano-SiC doped PbO2 electrode for degradation of toluene diamine

A novel PbO2 electrode with nano-SiC modified (Ti/SiC–PbO2) was fabricated through electrodeposition to enhance the anode oxidation ability and stability. The microstructure, composition and morphology of the anodes were characterized by SEM, EDX, XRD and XPS. The results demonstrate the successful doping of nano-SiC on the catalytic coating layer with much smaller and uniform β-PbO2 grains. The electrochemical properties of the anodes were explored by CV, EIS, LSV, Tafel and Mott-Schottky curves. Toluene diamine (TDA) was degraded by electrochemical oxidation technology on the prepared electrodes. The higher oxygen evolution over-potential (about 2.11 V vs. SCE) and lower charge transfer resistance of the Ti/SiC–PbO2 electrode endow it with a satisfactory COD removal efficiency and economical current efficiency at different initial TDA concentrations. The accelerated lifetime of the Ti/SiC–PbO2 anode was 61.8 h at 2 A/cm2 in 4.0 mol/L H2SO4 solution, and it is approximately 3.07 times longer than the traditional PbO2 electrode, indicating its high stability. These results demonstrate a promising potential of the Ti/SiC–PbO2 electrode in addressing water pollution issues.

Affordable PbO2 anode on conductive polymer‑carbon composite substrates for non-heavy duty use

Abstract The feasibility of using polymer‑carbon composite material (PCCM) substrate, instead of titanium substrate, for the preparation of PbO2 electrode was explored. The preparation procedure was optimized to maximize the performance of the PbO2 anodes. Our investigation shows that introducing α-PbO2 interlayer could significantly enhance the bonding of the surface β-PbO2 with the substrate. The addition of fluoride ions in the electrodeposition electrolyte could refine the grain size of the β-PbO2, resulting in a dense and smooth surface to enhance the service life of the composite anode. Therefore, the electrode PCCM\α\F−-β-PbO2, which had a α-PbO2 interlayer and a fluoride doped β-PbO2 surface layer, showed the longest accelerating life. The results of experiments also showed that the current density and deposition time significantly affected the surface morphologies of the PbO2 composite electrode. The optimal condition for the deposition of F−-β-PbO2 surface layer was 1 h of operation at 10 mA/cm2 current density, and this condition allowed to offer the electrode with a compact surface to prevent the penetration of caustic electrolyte and an appropriate thickness to avoid the strong internal stress. It was also found that the PCCM\α\F−-β-PbO2 exhibited the same electrocatalytic activity as that of the Ti-substrate counterpart electrode for the electrochemical oxidation of 2,4-dichlorophenol. This study indicates that the PCCM substrate can be used as an alternative substrate for the preparation of affordable PbO2 anode for non-heavy duty applications.

Electrocatalytic oxidation of PCP-Na by a novel nano-PbO2 anode: degradation mechanism and toxicity assessment

This study aims at investigating the electrocatalytic oxidation of sodium pentachlorophenate (PCP-Na) using a novel nano-PbO2 powder anode. The nano-PbO2 powder (marked as HL-PbO2) was prepared by a simple hydrolysis process, and hydrothermal treatment was followed to improve the activity of HL-PbO2. The HL-PbO2 treated for 24h by hydrothermal process (HL/HT-PbO2-24) was confirmed to possess higher crystallinity, higher oxygen evolution potential, and more active sites, resulting in stronger OH radical generation capacity and higher electrochemical activity. Compared with conventional electrodeposited PbO2 (ED-PbO2) anode, the HL/HT-PbO2-24 anode showed higher PCP-Na degradation rate. Under the same operating conditions, the mineralization current efficiency at HL/HT-PbO2-24 was 2.7 times than that at ED-PbO2. Five intermediates were detected in PCP-Na degradation solution and possible degradation mechanism of PCP-Na was discussed. In addition, the acute toxicity of PCP-Na degradation solution to zebrafish embryos and the oxidative stress induced in zebrafish embryos/larvae were studied to evaluate the ecological security of electrocatalytic oxidation of PCP-Na.

Electro- and photo-electrooxidation of 2,4,5-trichlorophenoxiacetic acid (2,4,5-T) in aqueous media with PbO2, Sb-doped SnO2, BDD and TiO2-NTs anodes: A comparative study

Abstract In this work, the 2,4,5-T degradation in aqueous media was studied by electro- (EC) and photoelectrochemical (PEC) oxidation methods, which are two of the most important advanced oxidation processes (AOPs) for wastewater treatment. Both EC and PEC experiments were carried out in a single compartment cell under galvanostatic conditions (30 mA cm−2) at 298 K by using 0.05 M Na2SO4 + 200 ppm 2,4,5-T at pH 3 and pH 9, as model solutions. EC oxidation was performed using Sb-doped SnO2, PbO2 and boron doped diamond (BDD) as anodic materials. Besides these anodes, TiO2 in a nanotubular structure (TiO2 NTs) with or without PbO2 dispersed nanoparticles (TiO2::PbO2) were also used for PEC oxidation process. In all cases, the electrolyzed solutions were periodically analyzed by UV–vis spectrophotometry (232 or 235 nm) and liquid chromatography (HPLC) for 2,4,5-T as well as the oxidation by-products. The mineralization level was occasionally measured by using total organic carbon (TOC). For PEC experiments the photocurrent response variations with potential in 0.5 M H2SO4 were obtained by the linear scanning voltammetry (LSV) method at a slow potential sweep (5 mV s−1). Results clearly showed that at 30 mA cm−2, the 2,4,5-T was 100% oxidized on Sb-doped SnO2 and 95% on PbO2 after 120 min of electrolysis, which allow to assume the EC as an adequate treatment method to remove this herbicide from wastewaters. HPLC results showed the formation of aromatic intermediates such as 2,4,5-trichlorophenol (2,4,5-TCP) and 2,5-dihydroxyquinone (2,5-DHQ) followed by the formation of carboxylic acid such as hydroxyacetic acid. For these cases, alkaline media (pH 9) was better than acidic media (pH 3) in about one magnitude order in the apparent rate constant (k). On the other hand, photochemical activity results showed that PEC on TiO2-NTs::PbO2 had higher photocurrent density values than on naked TiO2 NTs as photoanodes. These electrodes also had the better photo conversion efficiencies (η), which strongly suggests the occurrence of a “co-catalysis” effect due to an electronic transfer assisted by the closed contact between TiO2 and PbO2. This fact was supported by the PEC oxidation of 2,4,5-T in aqueous solution, whose k value was slightly lower than that observed for bulk material.

Electrocatalytic degradation of perfluoroocatane sulfonate (PFOS) on a 3D graphene-lead dioxide (3DG-PbO2) composite anode: Electrode characterization, degradation mechanism and toxicity

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.