Fabrication of a novel PbO2 electrode with a graphene nanosheet interlayer for electrochemical oxidation of 2-chlorophenol

Development of SDS-Modified PbO2 Anode Material Based on Ti3+ Self-Doping Black TiO2NTs Substrate as a Conductive Interlayer for Enhanced Electrocatalytic Oxidation of Methylene Blue

Efficient and stable electrode materials are urgently required for wastewater treatment in the electrocatalytic degradation of toxic and refractory organic pollutants. Ti3+ self-doping black TiO2 nanotube arrays (Ti/B-TiO2-NTs) as an interlayer were used for preparing a novel PbO2 electrode via an electrochemical reduction technology, and a sodium dodecyl sulfate (SDS)-modified PbO2 catalytic layer was successfully achieved via an electrochemical deposition technology. The physicochemical characterization tests showed that the Ti/B-TiO2-NTs/PbO2-SDS electrodes have a denser surface and finer grain size with the introduction of Ti3+ in the interlayer of Ti/TiO2-NTs and the addition of SDS in the active layer of PbO2. The electrochemical characterization results showed that the Ti3+ self-doping black Ti/TiO2-NTs/PbO2-SDS electrode had higher oxygen evolution potential (2.11 V vs. SCE), higher electrode stability, smaller charge-transfer resistance (6.74 Ω cm-2), and higher hydroxyl radical production activity, leading to it possessing better electrocatalytic properties. The above results indicated that the physicochemical and electrochemical characterization of the PbO2 electrode were all enhanced significantly with the introduction of Ti3+ and SDS. Furthermore, the Ti/B-TiO2-NTs/PbO2-SDS electrodes displayed the best performance on the degradation of methylene blue (MB) in simulated wastewater via bulk electrolysis. The removal efficiency of MB and the chemical oxygen demand (COD) could reach about 99.7% and 80.6% under the optimal conditions after 120 min, respectively. The pseudo-first-order kinetic constant of the Ti/B-TiO2-NTs/PbO2-SDS electrode was 0.03956 min-1, which was approximately 3.18 times faster than that of the Ti/TiO2-NTs/PbO2 electrode (0.01254 min-1). In addition, the Ti/B-TiO2-NTs/PbO2-SDS electrodes showed excellent stability and reusability. The degradation mechanism of MB was explored via the experimental identification of intermediates. In summary, the Ti3+ self-doping black Ti/TiO2-NTs/PbO2-SDS electrode is a promising electrode in treating wastewater.

Quick and accurate determination of hazardous phenolic compounds using CaCu2O3 nanorods based electrochemical sensor

In the present work, we report the fabrication of a novel electrochemical sensor based on nanostructured CaCu₂O₃ as electrode material for the simultaneous determination of 2-Aminophenol (o-AP), 2-Chlorophenol (o-CP) and 2-Nitrophenol (o-NP). Nanorods-shaped CaCu₂O₃ have been synthesized by chemical precipitation method and characterized by powder X-ray diffraction (XRD), X-ray photo-electron microscopy (XPS), field emission electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Glassy carbon electrodes (3 mm diameter) have been modified using CaCu₂O₃ nanorods by drop-casting method. Cyclic voltammetry (CV) studies at CaCu₂O₃/GCE exhibited excellent electrochemical behaviours towards the oxidation of 2-AP, 2-CP and 2-NP at different potentials well separated from each other. The CaCu₂O₃/GCE displayed the lowest detection limits of 5.74 nM (0.626 ppb), 1.38 nM (0.177 ppb) and 1.03 nM (0.143 ppb) for 2-AP, 2-CP and 2-NP respectively over wide measurable linear ranges of 175 nM-68 μM (2-AP), 50 nM-90 μM (2-CP) and 25 nM-32 μM (2-NP). Cyclic stability studies showed a loss of 7%, 13% and 14% from initial current responses after conducting 100 cycles of CV for 2-AP, 2-CP and 2-NP in PBS (pH 7.0) which indicated the excellent stability of the fabricated electrode. Reproducibility studies of six different CaCu₂O₃/GCEs exhibited good recoveries in the order of 3.23% (2-AP), 3.54% (2-CP) and 2.46% (2-NP) respectively. The fabricated electrode with excellent sensitivity, stability and reproducibility has been successfully applied for the determination of 2-AP, 2-CP and 2-NP simultaneously in tap water and agricultural water samples. Selectivity studies carried out on CaCu₂O₃/GCE revealed its ability to detect 4-aminophenol and 4-nitorphenol at different oxidation potentials. High performance liquid chromatography (HPLC) studies have been carried out to validate the practical utility of the fabricated sensor.

Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion

Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

Electrochemical Oxidation of Methyl Orange in an Active Carbon Packed Electrode Reactor (ACPER): Degradation Performance and Kinetic Simulation

The efficient removal and kinetic modelling of methyl orange (MO) degradation using an electrocatalytic oxidation method in an activated carbon (AC) packed electrode reactor (ACPER) were conducted. A significantly high (81.2%) chemical oxygen demand (COD) and 100.0% MO decolorization efficiency were observed under the experimental conditions of current density of 3.0 mA·cm⁻², flow velocity of 0.3 L·h⁻¹, and treatment duration of 1.68 h using a β-PbO₂/Ti anode. The high removal efficiency is ascribed to the anode expansion effect after AC packing. The anode expansion coefficient (λ) of the ACPER was calculated to be 0.63 from the cyclic voltammetry (CV) measurement, which means the further current utilization for MO oxidation. Based on the current utilization efficiency on anodic and particle electrode surfaces, a phase-reaction kinetics model was proposed for the simulation of MO COD removal efficiency. Our simulation results showed that the newly established average current efficiency (ACE) and energy consumption (E_sp) model well matched the MO experimental degradation data. Our work broadens the scope of the application of ACPER in the treatment industry wastewater containing organics and provides a new strategy for the energy utilization evaluation during the removal of organic matter by electrocatalytic oxidation.

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.

PbO2 electrode modified by graphene oxide to boost electrodegradation of 4-hydroxybenzophenone

4-Hydroxybenzophenone (4-OH-BP), a highly toxic and widely used pharmaceutical and personal care products (PPCPs), has been obtained growing concern recently. Electrochemical anodic oxidation technology has been confirmed efficient in eliminating organics from aqueous solution. In this work, we constructed two novel PbO₂ electrodes by modifying the middle or active layer with graphene oxide (GO) to degrade aquatic 4-OH-BP. Compared with the pristine PbO₂ electrode, the modification by GO could enhance the anchor of the active layer (PbO₂ particles) onto the middle layer and improve the isolation of the titanium matrix from the active layer and solution. Therefore, we might obtain the better performance of PbO₂ electrodes after modification. Under the experimental conditions optimized by the Box-Behnken design model, as we expected, two novel electrodes (with modified middle layer: 99.85%; with modified active layer: 100%) outperformed the pristine electrode (95.46%) for 4-OH-BP degradation. We proposed the catalytic mechanism of GO-modified electrodes for 4-OH-BP and the degradation pathway of 4-OH-BP and evaluated the toxicity of intermediates based on the quantitative structure-activity relationship model. Furthermore, two GO-modified PbO₂ electrodes consumed less energy than commercial boron-doped diamond electrode, reflecting the prominent practicability of GO-modified PbO₂ electrode.

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.

Preparation and characterization of ZnO/PEG-Co(II)-PbO2 nanocomposite electrode and an investigation of the electrocatalytic degradation of phenol

A ZnO/PEG (polyethylene glycol) -Co(II)-PbO₂ nanocomposite electrode was constructed by using the anodic electrodeposition method and used for the electrocatalytic degradation phenol. The results showed that the electrode surface formed numerous PbO₂ nanosphere structures, and the average size of a single nanosphere is approximately 0.4 μm. XRD and EDS results showed the active layer consisted of β-PbO₂, and contained small amounts of cobalt and carbon. The electrochemical measurements showed that the electrode possessed a lower activation energy (E_a = 17.517 kJ∙mol^-1) and charge transfer resistance (R_ct = 7.564 Ω cm²) and a larger exchange current density (i°=1.476 × 10^-4 mA cm^-2). The phenol degradation process was controlled by the adsorption process and kinetic parameters were obtained with an initial concentration of 100 mg L^-1. The electrode possessed a shorter half-life, larger reaction rate constant, and degradation efficiency (RE = 91.1 %) after 180 min. Reaction order was also calculated, and the degradation followed the pseudo-first-order reaction kinetics. HPLC results showed that the degradation pathway is as follows: firstly, phenol is gradually decomposed into o-diphenol, p-diphenol and benzoquinone under hydroxyl radicals attack. Then, benzoquinone is broken into maleic acid and fumaric acid. Finally, these acidic compounds are broken into oxalic acid, which is eventually mineralized.

Fabrication of Co/Pr co-doped Ti/PbO2 anode for efficiently electrocatalytic degradation of β-naphthoxyacetic acid

The existence of β-naphthoxyacetic acid (BNOA) pesticide in water system has aroused serious environmental problem because of its potential toxicity for humans and organisms. Therefore, exploiting an efficient method without secondary pollution is extremely urgent. Herein, a promising Ti/PbO₂-Co-Pr composite electrode has been successfully fabricated through simple one-step electrodeposition for efficiently electrocatalytic degradation of BNOA. Compared with Ti/PbO₂, Ti/PbO₂-Co and Ti/PbO₂-Pr electrodes, Ti/PbO₂-Co-Pr electrode with smaller pyramidal particles possesses higher oxygen evolution potential, excellent electrochemical stability and outstanding electrocatalytic activity. The optimal degradation condition is assessed by major parameters including temperature, initial pH, current density and Na₂SO₄ concentration. The degradation efficiency and chemical oxygen demand removal efficiency of BNOA reach up to 94.6% and 84.6%, respectively, under optimal condition (temperature 35 °C, initial pH 5, current density 12 mA cm^-2, Na₂SO₄ concentration 8.0 g L^-1 and electrolysis time 3 h). Furthermore, Ti/PbO₂-Co-Pr electrode presents economic energy consumption and superior repeatability. Finally, the possible degradation mechanism of BNOA is put forward according to the main intermediate products identified by liquid chromatography-mass spectrometer. The present research paves a new path to degrade BNOA pesticide wastewater with Ti/PbO₂-Co-Pr electrode.

Degradation of aqueous cefotaxime in electro-oxidation - electro-Fenton -persulfate system with Ti/CNT/SnO2-Sb-Er anode and Ni@NCNT cathode

Due to the potential threatening of antibiotics in aqueous environment, a novel electro-oxidation (EO) - electro-Fenton (EF) -persulfate (PS) system with the addition of peroxydisulfate and Fe²⁺ was installed for the degradation of cefotaxime. Ti/CNT/SnO₂-Sb-Er with an ultra-high oxygen evolution potential (2.15 V) and enhanced electrocatalytic surface area was adopted as anode. The OH production and electrode stability test demonstrated great improvement in the electrochemical performances. Ni@NCNT cathode was tested with higher H₂O₂ generation by the presence of nitrogen functionalities due to the acceleration of electron transfer of O₂ reduction. Experiment results indicated CNT and ErO₂ modification increased the molecular and TOC removal of cefotaxime. Coupling processes of EO-EF and EO-PS both resulted in shorter electrolysis time for complete cefotaxime removal, however, the mineralization ability of EO-PS process was lower than EO-EF, which might result from the immediate vanishing of PS. Thus, a further improved treatment EO-EF-PS system achieved an 81.6% TOC removal towards 50 mg L^-1 cefotaxime after 4 h electrolysis, under the optimal working condition Fe²⁺ = PS = 1 mM. The influence of current density and initial concentration on the performance of all processes was assessed. Methanol and tert-butanol were added in the system as OH and SO₄^- scavengers, which illustrating the mechanism of EO-EF-PS oxidizing process was the result of the two free radicals. Major intermediates were deduced and the degradation pathway of cefotaxime was analyzed. This research provides a potential coupling process with high antibiotic removal efficiency and effective materials for practical uses.

Facile and efficient 3-chlorophenol sensor development based on photolumenescent core-shell CdSe/ZnS quantum dots

Quantum dots (QDs) are semiconducting inorganic nanoparticles, tiny molecules of 2-10 nm sizes to strength the quantum confinements of electrons. The QDs are good enough to emit light onto electrons for exciting and returning to the ground state. Here, CdSe/ZnS core/shell QDs have been prepared and applied for electrochemical sensor development in this approach. Flat glassy carbon electrode (GCE) was coated with CdSe/ZnS QDs as very thin uniform layer to result of the selective and efficient sensor of 3-CP (3-chlorophenol). The significant analytical parameters were calculated from the calibration plot such as sensitivity (3.6392 µA µM-1 cm-2) and detection limit (26.09 ± 1.30 pM) with CdSe/ZnS/GCE sensor probe by electrochemical approach. The calibration curve was fitted with the regression co-efficient r2 = 0.9906 in the range of 0.1 nM ∼ 0.1 mM concentration, which denoted as linear dynamic range (LDR). Besides these, it was performed the reproducibility in short response time and successfully validated the fabricated sensor for 3-CP in the real environmental and extracted samples. It is introduced as a noble route to detect the environmental phenolic contaminants using CdSe/ZnS QDs modified sensor by electrochemical method for the safety of healthcare and environmental fields at broad scales.

Electrochemical degradation of safranine T in aqueous solution by Ti/PbO2 electrodes

The electrochemical degradation of safranine T (ST) in aqueous solution was studied. The effects of current density, initial concentration of ST, initial pH values, and Na2SO4 concentration on electrocatalytic degradation of ST in the aqueous solution by Ti/PbO2 electrode were analyzed. The experimental results showed that the electrochemical oxidization reaction of ST fitted a pseudo first order kinetics model. By using the Ti/ PbO2 electrode as the anode, 99.96% of ST can be eliminated at 120 min. It means that the electrochemical degradation of ST in aqueous solution by the Ti/PbO2 electrode was very effective. The optimal reaction conditions were as follows: current density, 40 mA cm−2; initial ST concentration, 100 mg L−1; Na2SO4 concentration, 0.20 mol L−1; initial pH, 6. It can be known from the test of UV–vis and HPLC in the reaction process that the intermediates will be generated, and the possible intermediate structure was studied by HPLC–MS test. However, with the progress of degradation reaction, the intermediates will eventually be oxidized into CO2 and H2O. Cyclic voltammetry and fluorescence experiments proved that ST was indirectly oxidized through the generation of hydroxyl radicals. Under the optimal reaction conditions, the energy required to completely remove ST was 17.92 kWh/m3.

BP-ANN Model Coupled with Particle Swarm Optimization for the Efficient Prediction of 2-Chlorophenol Removal in an Electro-Oxidation System

Electro-oxidation is an effective approach for the removal of 2-chlorophenol from wastewater. The modeling of the electrochemical process plays an important role in improving the efficiency of electrochemical treatment and increasing our understanding of electrochemical treatment without increasing the cost. The backpropagation artificial neural network (BP-ANN) model was applied to predict chemical oxygen demand (COD) removal efficiency and total energy consumption (TEC). Current density, pH, supporting electrolyte concentration, and oxidation-reduction potential (ORP) were used as input parameters in the 2-chlorophenol synthetic wastewater model. Prediction accuracy was increased by using particle swarm optimization coupled with BP-ANN to optimize weight and threshold values. The particle swarm optimization BP-ANN (PSO-BP-ANN) for the efficient prediction of COD removal efficiency and TEC for testing data showed high correlation coefficient of 0.99 and 0.9944 and a mean square error of 0.0015526 and 0.0023456. The weight matrix analysis indicated that the correlation of the five input parameters was a current density of 18.85%, an initial pH 21.11%, an electrolyte concentration 19.69%, an oxidation time of 21.30%, and an ORP of 19.05%. The analysis of removal kinetics indicated that oxidation-reduction potential (ORP) is closely correlated with the chemical oxygen demand (COD) and total energy consumption (TEC) of the electro-oxidation degradation of 2-chlorophenol in wastewater.

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.

Functionalized graphene with Co-ZIF adsorbed borate ions as an effective flame retardant and smoke suppression agent for epoxy resin

In order to reduce the fire risk of epoxy resin (EP), functionalized reduced graphene oxide (RGO) with Co-ZIF (zeolitic imidazolate frameworks-67) adsorbed borate ions (ZIF-67/RGO-B) was prepared. The results of transmission electron microscopy (TEM) showed that ZIF-67 was grown on the surface of RGO triumphantly. In addition, the structure of ZIF-67/RGO-B was not significantly changed compared with ZIF-67/RGO. Subsequently, ZIF-67/RGO-B was added into EP by a simple blending method. The combustion results showed that the heat and smoke production of EP composites were obviously reduced. In particular, compared with pure EP, the peak heat release rate (pHRR), the total heat release (THR) and the maximum value of smoke density (D_s,max) of the composite with 2 wt% ZIF-67/RGO-B were reduced by 65.1%, 41.1% and 66.0%, respectively. The main mechanism of ZIF-67/RGO-B for reducing the fire risk of EP was analyzed according to the results of the char analysis. This work provided a new type of modified RGO for reducing the fire hazard of EP.

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.

Magnetic Assembled Anode Combining PbO2 and Sb-SnO2 Organically as An Effective and Sustainable Electrocatalyst for Wastewater Treatment with Adjustable Attribution and Construction

A new electrode consisting of a Ti/PbO₂ shell as main electrode (ME) and numerous Fe₃O₄/Sb-SnO₂ granules as auxiliary electrodes (AEs) was developed for flexible electrochemical oxidation (EO) treatment of wastewater. Material and electrochemical characterizations were carried out to study the impacts of the loading amount of the AEs on the attribution and construction of the electrode. Lignin, a complex group of polymeric macromolecules, was selected as the representative actual contaminant to test the real EO capability of the assembled electrodes with different AE loading amounts. The stability and recyclability of the electrodes were also investigated. Results showed that the roughness and the surface area of the electrode were increased with the increased loading amount of AEs, while improvement of the electrode properties was achieved only with the appropriate amounts of AEs. The optimum AE loading (such as 0.25 and 0.5 g on 6 cm² ME) boosted the EO performance of the anode toward lignin by ∼20%, making the electrode more capable in benzene ring opening. Excessive AEs were found to be unavailing, which only increased the percentage of the less accessible catalytic active sites. Moreover, a preliminary operating mechanism of this 2.5D electrode was proposed to evaluate the effect of AEs and further reveal the relationships of structure and activity of the 2.5D electrode. Finally, the electrode's lifetime was lengthened and further boosted via loading AEs and the subsequent recycling of AEs.

Preparation of the CNTs/AG/ITO electrode with high electro-catalytic activity for 2-chlorophenol degradation and the potential risks from intermediates

A novel carbon nanotubes (CNTs)/agarose (AG)/ITO electrode with high electro-catalytic activity was prepared using a simple sol-gel method. Characterization results showed that the prepared CNTs/AG membrane, coated on the ITO conductive glass, was consisted of C and O. The electro-catalytic degradation for 2-chlorophenol (2-CP) and the influence factors were investigated. The results meant that electro-catalytic degradation for 2-CP was highly dependent on pH, bias voltage, and catalyst dosage. At pH 2, 4 V bias voltage, and 5 wt% CNTs dosage, the electro-catalytic efficiency of CNTs/AG/ITO electrode for 2-CP (20 mg/L) achieved 98% within 180 min. Afterwards, the electro-catalytic properties of recycling electrode, roles of the generated reactive oxygen species, and the reaction pathways were also investigated and proposed. In addition, the toxicities of the generated intermediates from the electro-catalytic degradation were calculated by easy methods. The results indicated that the toxicities of some intermediates were higher than the parent pollutant, especially the formation of 2-CP dimer which was seldom reported in the advanced oxidation process. The findings of using AG as the carrier and conductive adhesive for catalytic material and the assessment methods for the possible increasing risks from the intermediates were reported firstly in this paper.

Hydrophobic networked PbO2 electrode for electrochemical oxidation of paracetamol drug and degradation mechanism kinetics

A hydrophobic networked PbO₂ electrode was deposited on mesh titanium substrate and utilized for the electrochemical elimination towards paracetamol drug. Three dimensional growth mechanism of PbO₂ layer provided more loading capacity of active materials and network structure greatly reduced the mass transfer for the electrochemical degradation. The active electrochemical surface area based on voltammetric charge quantity of networked PbO₂ electrode is about 2.1 times for traditional PbO₂ electrode while lower charge transfer resistance (6.78 Ω cm²) could be achieved on networked PbO₂ electrode. The electrochemical incineration kinetics of paracetamol drug followed a pseudo first-order behavior and the corresponding rate constant were 0.354, 0.658 and 0.880 h^-1 for traditional, networked PbO₂ and boron doped diamond electrode. Higher electrochemical elimination kinetics could be achieved on networked PbO₂ electrode and the performance can be equal to boron doped diamond electrode in result. Based on the quantification of reactive oxidants (hydroxyl radicals), the utilization rate of hydroxyl radicals could reach as high as 90% on networked PbO₂ electrode. The enhancement of excellent electrochemical oxidation capacity towards paracetamol drug was related to the properties of higher loading capacity, enhanced mass transfer and hydrophobic surface. The possible degradation mechanism and pathway of paracetamol on networked PbO₂ electrode were proposed in details accordingly based on the intermediate products.