Mesostructured lead dioxide grown on titania nanotubes for diclofenac water removal through electrocatalytic and photoelectrocatalytic processes.

Mesostructured PbO2/TiO2 materials were synthesized to perform electrocatalysis (as electrooxidation, EO) and photoelectrocatalysis for removing diclofenac (DCF), 15 ppm concentration in 0.1 M NaSO4 solutions, at different pH conditions (3.0, 6.0 and 9.0) by applying 30 mA cm-2. Titania nanotubes (TiO2NTs)-based materials were prepared to synthetize with a massive PbO2 deposit on this support to obtain TiO2NTs/PbO2 and a TiO2NTs:PbO2 material consisting in a dispersed PbO2 deposit on TiO2-NTs that allowed the formation of a heterostructured surface of combined composition (TiO2 and PbO2). Organics removal (DCF and byproducts) was monitored through UV-vis spectrophotometry and high-performance liquid chromatography (HPLC) during degradation tests. TiO2NTs/PbO2 electrode was tested in both processes, removing DCF at neutral and alkaline solution conditions in EO while an unimportant photoactivity was registered at this material. Conversely, TiO2NTs:PbO2 was used as electrocatalytic material in EO experiments, achieving more than 50% of DCF removal at pH 6.0 by applying 30 mA cm-2. Also, for first time, the synergic effect was investigated when it was exposed to UV irradiation in photoelectrocatalytic experiments, enhancing its efficacy (⁓more than 20%) to remove DCF from a solution with 15 ppm over performance removals achieved (56%) when EO was applied under similar conditions. Chemical Oxygen Demand (COD) analyses showed that significantly higher DCF degradation is reached under photoelectrocatalysis, since COD values decrease a 76% against a 42% decrease achieved with electrocatalysis. Scavenging experiments showed a significant participation on the pharmaceutical oxidation process through the generation of photoholes (h+), hydroxyl radicals and sulfate-based oxidants.

Electrocatalytic oxidation of gaseous toluene in an all-solid cell using a foam Ti/Sb-SnO2/ß-PbO2 anode.

Mineralization of benzene, toluene, and xylene (BTX) with high efficiency at room temperature is still a challenge for the purification of indoor air. In this work, a foam Ti/Sb-SnO2/ß-PbO2 anode catalyst was prepared for electrocatalytically oxidizing gaseous toluene in an all-solid cell at ambient temperature. The complex Ti/Sb-SnO2/ß-PbO2 anode, which was prepared by sequentially deposing Sb-SnO2 and ß-PbO2 on a foam Ti substrate, shows high electrocatalytic oxidation efficiency of toluene (80%) at 7 hr of reaction and high CO2 selectivity (94.9%) under an optimized condition, i.e., a cell voltage of 2.0 V, relative humidity of 60% and a flow rate of 100 mL/min. The better catalytic performance can be ascribed to the high production rate of ⋅OH radicals from discharging adsorbed water and the inhibition of oxygen evolution on the surface of foam Ti/Sb-SnO2/ß-PbO2 anode when compared with the foam Ti/Sb-SnO2 anode. Our results demonstrate that prepared complex electrodes can be potentially used for electrocatalytic removal of gaseous toluene at room temperature with a good performance.

Electrodegradation of the Acid Green 28 dye using Ti/ß-PbO2 and Ti-Pt/ß-PbO2 anodes.

The statistical Response Surface Methodology (RSM) is applied to investigate the effect of different parameters (current density, j, NaCl concentration, [NaCl], pH, and temperature, θ) and their interactions on the electrochemical degradation of the Acid Green (AG) 28 dye using a Ti/ß-PbO2 or Ti-Pt/ß-PbO2 anode in a filter-press reactor. LC/MS is employed to identify intermediate compounds. For both anodes, the best experimental conditions are j = 50 mA cm(-2), [NaCl] = 1.5 g L(-1), pH = 5, and θ = 25 °C. After 3 h of electrolysis, a dye solution treated under these conditions presents the following parameters: electric charge per unit volume of the electrolyzed solution required for 90% decolorization (Q(90)) of 0.34-0.37 A h L(-1), %COD removal of ∼100%, specific energy consumption of 18-20 kW h m(-3), and %TOC removal of 32-33%. No loss of the ß-PbO2 film is observed during all the experiments. The ß-PbO2 films present excellent stability for solutions with pH ≥ 5 ([Pb(2+)] < 0.5 mg L(-1)). Chloroform is the only volatile organic halo compound present in the treated solution under those optimized conditions. Hydroxylated anthraquinone derivatives, aromatic chloramines, and naphthoquinones are formed during the electrolyses. The Ti/ß-PbO2 and Ti-Pt/ß-PbO2 anodes show significantly better performance than a commercial DSA anode for the electrochemical degradation of the AG 28 dye. The Ti/ß-PbO2 anode, prepared as described in this work, is an excellent option for the treatment of textile effluents because of its low cost of fabrication and good performance.

PbO2 reductive dissolution by dissolved Mn(III) in the presence of low molecular weight organic acids and humic acid.

Although Mn(III) complexes with organic ligands have been previously identified, the information about their stability and reactivity is scarce. In the present study, we analyzed the formation and stability of three different complexes: Mn(III)-citrate, Mn(III)-tartrate, and Mn(III)-humic acid (HA), as well as their reactivity toward an element of high environmental concern, lead (Pb).Our results indicate that the stability of studied complexes is highly dependent on pH. The Mn(III) complexes with citrate and tartrate degrade below pH 8, due to the electron transfer reaction between Mn(III) and the ligand, while the Mn(III)-HA complex's degradation is slower and less sensitive to pH. At pH 4, less than 40% of the initial Mn(III)-HA was found to be stable.The reactivity of the complexes was different depending on the ligand and its concentration. The Mn(III)-citrate and Mn(III)-tartrate complexes effectively reduced PbO2 and releases aqueous Pb2+, although significant differences were found with increasing ligand concentration. There was no evidence of the reduction of PbO2 by Mn(III) when it forms a complex with HA. This is likely due to the large size of HA moieties that prevent the Mn(III) component of the complex from getting close enough to the PbO2 surface to initiate electron transfer and lead to the reduction of Pb(IV) by HA itself.

PbO2 materials for electrochemical environmental engineering: A review on synthesis and applications.

Lead dioxide (PbO2) materials have been widely employed in various fields such as batteries, electrochemical engineering, and more recently environmental engineering as anode materials, due to their unique physicochemical properties. Key performances of PbO2 electrodes, such as energy efficiency and space-time yield, are influenced by morphological as well as compositional factors. Micro-nano structure regulation and decoration of metal/non-metal on PbO2 is an outstanding technique to revamp its electrocatalytic activities and enhance environmental engineering efficiency. The aim of this review is to comprehensively summarize the recent research progress in the morphology control, the structure constructions, and the element doping of PbO2 materials, further with many environmental application cases evaluated. Concerning electrochemical environmental engineering, the lead dioxide employed in chemical oxygen demand detection, ozone generators, and wastewater treatment has been comprehensively reviewed. In addition, the future research perspectives, challenges and the opportunities on PbO2 materials for environmental applications are proposed.

Electrochemical conversion of chromium from tannery effluents for potential reuse in industrial applications.

Electrochemical oxidation of trivalent chromium from leather tanning mud waste leachates (containing ca 6 g.L-1 Cr(III)) to its hexavalent form was carried out using a PbOx/Pb anode electrode in a prototype small (0.4 L) cylindrical batch electrochemical reactor. The PbOx/Pb anode was prepared by electrochemical anodization at constant current (75 mA cm-2 for 30 min) in a sulfuric acid solution and characterized by the cyclic voltammetry technique to investigate the effect of pH on the process. It was found that at pH = 3, Cr(III) oxidation prevails over the competing water oxidation-oxygen evolution reaction (OER), hence increasing the efficiency of the process. A detailed study of pH (0-3), current density (12-24 mA cm-2), and cell type (divided-undivided) effects on bulk electrolysis of Cr(III) leachates in the batch prototype reactor resulted in process optimization. At pH = 3, 12 mA cm-2 and a cathode inserted in a porous diaphragm envelope, nearly 70% conversion was achieved at a nearly 60% current efficiency, among the highest in the previously reported literature. The method (further optimized with an ion-selective membrane separator) could offer an attractive route for tannery Cr(III) conversion to Cr(VI) for reuse as an etchant or electroplating agent.

Electrochemical oxidation of chloramphenicol by modified Sm-PEG-PbO2 anodes: Performance and mechanism.

Chloramphenicol (CAP) is used extensively in industry and daily life, but its abuse has seriously affected the environment and public health. In this paper, a new composite PbO2 electrode was obtained through the modification Sm and polyethylene glycol (PEG), and an electrocatalytic oxidation technology of CAP degradation was investigated. The results showed that the catalytic degradation ability and industrial service life of the PEG-Sm-PbO2 composite electrode were significantly enhanced. Co-doping inhibited the growth of grains, resulting in the formation of refined pyramidal grains on the surface of the electrode, which increased the number of active spots. The industrial service life of the modified electrode was improved by 87.0%. In addition, the degradation effect under different conditions and mechanism of CAP were also explored. The optimal conditions for CAP degradation were explored, at which time the CAP degradation rate reached 99.1%. The degradation process was in accordance with the primary reaction kinetics, and the apparent rate constant of CAP at the PEG-Sm-PbO2 electrode was raised by 57.1% in comparison with the unmodified electrode, indicating that the modification facilitated the degradation of CAP in the electrode. Finally, two possible CAP degradation pathways were deduced. The results will provide technical support and a theoretical basis for the degradation of persistent organic pollutants.

Iron (III)-doped PbO2 and its application as electrocatalyst for decomposition of phthalocyanine dye.

The textile industry contributes significantly to environmental pollution through dyeing and finishing processes that release dyes into wastewater. Even small amounts of dyes can have harmful effects and cause negative impacts. These effluents have carcinogenic, toxic, and teratogenic properties and can take a long time to be naturally degraded through photo/bio-degradation processes. This work investigates degradation of Reactive Blue 21 (RB21) phthalocyanine dye using anodic oxidation process with PbO2 anode doped with iron III (0.1 M) (marked as Ti/PbO2-0.1Fe) and compared with pure PbO2. Ti/PbO2 films with and without doping were successfully prepared by electrodeposition technology on Ti substrates. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS) was used to characterize the electrode morphology. Also, linear scanning voltammetry (LSV) and cyclic voltammetry (CV) tests were conducted to investigate the electrochemical response of these electrodes. The influence of operational variables on the mineralization efficiency was studied as a function of pH, temperature, and current density. Doping Ti/PbO2 with Fe3+ (0.1 M) could reduce the particle to a smaller dimension and slightly increase the oxygen evolution potential (OEP). A large anodic peak was found for both electrodes prepared in the CV test, indicating that oxidation of the RB21 dye was easily achieved on the surface of the prepared anodes. No significant effect of initial pH on the mineralization of RB21 was observed. RB21 decolorization was more rapid at room temperature and increases with increasing current density. A possible degradation pathway for the anodic oxidation of RB21 in aqueous solution is proposed based on the identified reaction products. In general, it can be said that from the findings it was observed that the Ti/PbO2 and Ti/PbO2-0.1Fe electrodes show good performance on RB21 degradation. However, it was noted that the Ti/PbO2 electrode tends to deteriorate over time and exhibits poor substrate adhesion, while the Ti/PbO2-0.1Fe electrode displays superior substrate adhesion and stability.

Exploring specific biomarkers regarding neurobehavioral toxicity of lead dioxide nanoparticles in medaka fish in different water matrices.

Nano-scale lead dioxide (nPbO2) is an industrial metal oxide nanoparticle that can be also formed as a corrosion by-product from chlorination of Pb-containing plumbing materials. nPbO2 governs release of toxic lead ion in drinking water and receiving organisms; however, its modes of toxic action regarding neurobehavioral toxicity remain unclear. This study evaluated the toxicity mechanism of nPbO2 (10 and 20 mg/L) versus its released Pb(II)aq (100 µg/L) in terms of aqueous chemistry, bioavailability and neurobehavioral toxicity to medaka fish in different water matrices. In very hard water (VHW), dissolved salts enhanced the aggregation and sedimentation of nPbO2, resulting in higher bioavailability and altered locomotion of treated fish than those fish exposed to nPbO2 in soft water with humic acid (SW + HA). Transcriptomic results identified six differentially expressed genes with greater altered expression with nPbO2 than the control or Pb(II)aq exposure. With VHW exposure, nPbO2 caused greater altered expression of genes involved in cell adhesion (nlgn1 and epd), cell cytoskeleton (α1-tubulin), and relevant apoptosis (c-fos, birc5.1-a and casp3), as compared with SW + HA or Pb(II)aq exposure. This study provides novel molecular mechanistic insights into the neurobehavioral nanotoxicity using nPbO2 and medaka fish as surrogates, suggesting nPbO2 promotes neurobehavioral dysfunction, leading to adverse outcomes from gene alteration to the organismal level. The identified biomarkers responded specifically to the nPbO2-induced neurotoxicity in different water matrices can be used for evaluating toxicity risks of small metal oxide particulates on human or aquatic life under environmentally relevant exposures.

A cyclone reactor of electrochemical advanced oxidation processes using PbO2 anode and H2O2 electrosynthesis cathode.

Electrochemical advanced oxidation processes are promising tools for pollution abatement but most still lack practical engineering attempts and devices. A type of process intensification reactor for the electrochemical advanced oxidation processes is developed here. The cyclone continuous flow electrochemical reactor adopts a PbO2 anode and H2O2 electrosynthesis cathode together. A lab-scale cyclone continuous flow electrochemical reactor is fabricated and simulated, which is evaluated using the H-acid wastewater. The contributions of the PbO2 anode and H2O2 electrosynthesis cathode to pollutant degradation are discussed particularly. A 3-D model is developed to provide a visualized perspective on the reactor performances, including flow distribution, mass transfer, and current distribution. Pronounced signals of powerful radicals can be detected for the PbO2H2O2 cyclone reactor, including •OH, SO4•-, and 1O2. It exhibits excellent performances on mass transfer, electrical properties, organic degradation, and space-time yield. Such a strategy presents a promising engineering solution for scale-up and further development toward industrial application.

Fabrication of PbO2/PVDF/CC Composite and Employment for the Removal of Methyl Orange.

The in situ electrochemical oxidation process has received considerable attention for the removal of dye molecules and ammonium from textile dyeing and finishing wastewater. Nevertheless, the cost and durability of the catalytic anode have seriously limited industrial applications of this technique. In this work, the lab-based waste polyvinylidene fluoride membrane was employed to fabricate a novel lead dioxide/polyvinylidene fluoride/carbon cloth composite (PbO2/PVDF/CC) via integrated surface coating and electrodeposition processes. The influences of operating parameters (pH, Cl- concentration, current density, and initial concentration of pollutant) on the oxidation efficiency of PbO2/PVDF/CC were evaluated. Under optimal conditions, this composite achieves a 100% decolorization of methyl orange (MO), 99.48% removal of ammonium, and 94.46% conversion for ammonium-based nitrogen to N2, as well as an 82.55% removal of chemical oxygen demand (COD). At the coexistent condition of ammonium and MO, MO decolorization, ammonium, and COD removals still remain around 100%, 99.43%, and 77.33%, respectively. It can be assigned to the synergistic oxidation effect of hydroxyl radical and chloride species for MO and the chlorine oxidation action for ammonium. Based on the determination of various intermediates, MO is finally mineralized to CO2 and H2O, and ammonium is mainly converted to N2. The PbO2/PVDF/CC composite exhibits excellent stability and safety.

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.

Electrocatalysis degradation of coal tar wastewater using a novel hydrophobic benzalacetone modified lead dioxide electrode.

Coal tar wastewater is hard to degrade by traditional methods because of its toxic pollutant constituents and high concentration of aromatic hydrocarbons, especially phenolic substances. A new type of hydrophobic benzacetone modified PbO2 anode (BA-PbO2 electrodes) was used for the electrocatalytic treatment of coal tar wastewater in a continuous cycle reactor. The surface morphology, structure, valences of elements, hydrophobicity, hydroxyl radical (·OH) produced capacity, electrochemical properties and stability of BA-PbO2 electrodes were characterized by SEM (scanning electron microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), contact angle, a fluorescence probe test, an electrochemical workstation and accelerated life test, respectively. The BA-PbO2 electrodes exhibited a compact structure and finely dispersed crystallize size of 4.6 nm. The optimum degradation conditions of coal tar wastewater were as follows: current density of 90 mA cm-2, electrode gap of 1 cm and temperature at 25 °C with flow velocity of 80 L h-1. The chemical oxygen demand (COD) removal efficiency reached 92.39% after 240 min of degradation under the optimized conditions and the after-treatment COD value was 379.51 mg L-1 which was lower than the centralized emission standard (less than 400 mg L-1). These findings demonstrated the feasibility and efficiency of electrocatalytically degrading coal tar wastewater by BA-PbO2 electrodes. The possible mechanism and pathway for phenol a specific pollutant in coal tar wastewater were investigated by quantum chemistry calculations (Multiwfn) and gas chromatography-mass spectrometry (GC-MS). The toxicity of each intermediate was predicted by the ECOSAR program.

Electrochemical oxidation of chloramphenicol with lead dioxide-surfactant composites.

The PbO2 -2 wt.% sodium dodecyl sulfate composite formed from methanesulfonate electrolyte consists of 93.1% of α-phase PbO2 in contrast to the similar one synthesized from nitrate electrolyte, which contains 73.3% of ß phase. The electrocatalytic activity of the obtained composites in the oxygen evolution reaction and oxidation of chloramphenicol was investigated. It was found that the Tafel slope significantly exceeds the theoretical value, which indicates a decrease in the degree of filling of the electrode surface with oxygen-containing particles. In the presence of organic compound and chloride ions in the solution, irreversible adsorption of the intermediate is observed, which leads to additional blocking of active centers on the oxide surface, which are involved in the oxidation of organic substance. It was established that the maximum rate of chloramphenicol conversion is 83.5% and 85% at 50 and 80 mA cm-2 , respectively, under kinetic control. The heterogeneous oxidation rate constant of chloramphenicol is 0.0035 min-1 . Oxidation of chloramphenicol occurs through the formation of 4-(-2-amino-1,3-dihydroxy-propanyl)-nitrobenzene with cleavage of dichloroacetic acid. Next, the amino group is oxidized to the nitro group to form 4-(2-nitro-1,3-dihydroxy-propanyl)-nitrobenzene. Subsequent electrolysis produces nitrobenzoic acid, which is oxidized to benzoic acid, later hydroquinone, then benzoquinone and a set of aliphatic compounds. PRACTITIONER POINTS: The PbO2 -2 wt.% SDS composite consists of 93.1% of α phase of PbO2 in contrast to those synthesized from nitrate electrolyte. The Tafel slope indicates a decrease of surface filling with oxygen-containing particles. Irreversible adsorption of the intermediate is observed in the presence of chloride ions.

Formation of carbonaceous and nitrogenous iodinated disinfection byproducts from biofilm extracellular polymeric substances by the oxidation of iodide-containing waters with lead dioxide.

Lead dioxide (PbO2) is an important form of lead mineral scales in drinking water pipes. Iodide (I-) widely presents in source waters and can be thermodynamically oxidized by PbO2 to the reactive iodine species (I2/HOI). Biofilm extracellular polymeric substances (EPS) are nonnegligible precursors of disinfection byproducts (DBPs). The aim was to study the oxidation of I- by PbO2 and formation of iodinated DBPs (I-DBPs) from EPS. At a high molar ratio of PbO2 to I- (> 100), the observed rate constants of I- oxidation decreased as pH increased from 6.0 to 9.0 with an H+ dependence of 0.79, and the rate constant (k) was 1.6 × 1011 M-2.79 s-1. Most of formed I2/HOI (> 92%) was transformed to organic iodine in the presence of EPS. EPS had a lower formation potential (FP) of carbonaceous I-DBPs (C-IDBPs), while a higher that of nitrogenous I-DBPs (N-IDBPs) than HA, resulting in a higher Chinese Hamster Ovary cell cytotoxicity. Generally, the formation of I-DBPs decreased with the increase of pH due to the reduction of surface positive charge and electrochemical driving force. PbO2 dose and I- concentration also had a significant effect on the I-DBPs formation. EPS proteins had a higher FP of both C- and N-IDBPs than polysaccharides on account of more electrophilic sites and higher nitrogen content. In proteins, aspartic acid was the main contributor to triiodomethane and iodoacetic acids formation, whereas aspartic acid, asparagine and tyrosine were the major precursors of diiodoacetonitrile and diiodoacetamide. The study helps to improve the control strategy of I-DBPs when biofilm outbreaks in lead-containing water pipes.

Ferrate(VI) pretreatment of water containing natural organic matter, bromide, and iodide: A potential strategy to control soluble lead release from PbO2(s).

Lead dioxide (PbO2(s)) is a corrosion product of lead-containing plumbing materials in water distribution pipelines. The presence of reductants in water could cause the release of soluble lead (mainly Pb(II)) from PbO2(s). Lead in drinking water is detrimental to public health. This paper presents the first application of ferrate (FeVIO42-, Fe(VI)) to decreasing the generation of soluble lead in water containing PbO2(s) and common reducing constituents (e.g., natural organic matter (NOM), iodide (I-), and bromide (Br-)) at different pH conditions (i.e., 6.0, 7.0, and 8.0). The released soluble lead from PbO2(s) was found to be dominantly controlled by NOM in water, via the redox dissolution of PbO2(s) and the reduction of PbO2(s) by reducing moieties of NOM. The feasibility of both processes increased when pH decreased. The I- and Br- in water played minor roles in generating soluble lead. Fe(VI) reacted with reducing functional groups of NOM, as determined by 13C nuclear magnetic resonance spectroscopy. Water pretreatment with Fe(VI) inhibited the reaction of NOM with PbO2(s) and therefore, caused lower soluble lead concentrations compared to water samples without Fe(VI) treatment. This study indicates that Fe(VI) pretreatment is a potential approach to controlling soluble lead in drinking water.

A simple and rapid method for the determination of lead dioxide in minium by headspace gas chromatographic technique.

This paper demonstrated a simple and rapid approach for the determination of lead dioxide in minium using a headspace gas chromatographic (GC) technique. This new approach was based on the measurement of carbon dioxide from the redox reaction between lead dioxide and oxalic acid in a sealed headspace vial. The obtained results indicated that the new approach had good measurement accuracy (relative errors ≤8.71%) and precision (RSD ≤2.86%). Moreover, the limit of quantification (LOQ) and limit of detection (LOD) for this new approach were respectively 0.34% and 0.10%, and the recoveries ranged from 97.9 to 101.7%. The new approach is low-cost and reliable, which has potential for use in the analysis of lead dioxide in minium and related products.

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.

Electrocatalytic degradation of the herbicide metamitron using lead dioxide anode: influencing parameters, intermediates, and reaction pathways.

In the present study, the electrocatalytic degradation of triazine herbicide metamitron using Ti/PbO2-CeO2 composite anode was studied in detail. The effects of the current density, initial metamitron concentration, supporting electrolyte concentration, and initial pH value were investigated and optimized. The results revealed that an electrocatalytic approach possessed a high capability of metamitron removal in aqueous solution. After 120 min, the removal ratio of metamitron could reach 99.0% in 0.2 mol L-1 Na2SO4 solution containing 45 mg L-1 metamitron with the current density at 90 mA cm-2 and pH value at 5.0. The reaction followed the pseudo-first-order kinetics model. HPLC and HPLC-MS were employed to analyze the degradation by-products in the metamitron oxidization process, and the degradation pathway was also proposed, which was divided into two sub-routes according to the different initial attacking positions on metamitron by hydroxyl radicals. Therefore, the electrocatalytic approach was considered as a very promising technology in practical application for herbicide wastewater treatment.

Electrochemical Oxidation of Para-Aminophenol With Rare Earth Doped Lead Dioxide Electrodes: Kinetics Modeling and Mechanism.

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.