Electrochemical degradation of chloramphenicol with a novel Al doped PbO2 electrode: Performance, kinetics and degradation mechanism

Electrochemical chlorine evolution reaction to improve the desalination of sea sand

Sea sand, a vital sand and gravel resource, is rich in chloride, which causes corrosion of steel reinforcements. This study investigates the effect of the electrochemical chlorine evolution reaction (CER) on the desalination of sea sand. The results indicate that the chlorine removal efficiency (RE) of sea sand increased from 48.76 to 56.40 % under optimal conditions: a current density of 15 mA/cm2, an electrolysis time of 1 min, and a sodium sulphate-supported electrolyte concentration of 0.05 mol/L. After 30 days of resting, the dissolved chlorine content in sea sand was 0.154 %, which was 21.03 % lower than that of the control group. The electrically active chlorine-mediated desalination process demonstrated excellent dechlorination ability, facilitated the transformation of metal and organic chlorine into liquid and gaseous forms, and reduced the slow release of chloride from sea sand. Therefore, CER is expected to be an efficient method for sea sand desalination.

PANI/GO and Sm co-modified Ti/PbO2 dimensionally stable anode for highly efficient amoxicillin degradation: Performance assessment, impact parameters and degradation mechanism

The abuse and uncontrolled discharge of antibiotics present a severe threat to environment and human health, necessitating the development of efficient and sustainable treatment technology. In this work, we employ a facile one-step electrodeposition method to prepare polyaniline/graphite oxide (PANI/GO) and samarium (Sm) co-modified Ti/PbO2 (Ti/PbO2-PANI/GO-Sm) electrode for the degradation of amoxicillin (AMX). Compared with traditional Ti/PbO2 electrode, Ti/PbO2-PANI/GO-Sm electrode exhibits more excellent oxygen evolution potential (2.63 V) and longer service life (56 h). In degradation experiment, under optimized conditions (50 mg L-1 AMX, 20 mA cm-2, pH 3, 0.050 M Na2SO4, 25 °C), Ti/PbO2-PANI/GO-Sm electrode achieves remarkable removal efficiencies of 88.76% for AMX and 79.92% for chemical oxygen demand at 90 min. In addition, trapping experiment confirms that ·OH plays a major role in the degradation process. Based on theoretical calculation and liquid chromatography-mass spectrometer results, the heterocyclic portion of AMX molecule is more susceptible to ·OH attacks. Thus, this novel electrode offers a sustainable and efficient solution to address environmental challenges posed by antibiotic-contaminated wastewater.

Electrochemical oxidation of Florfenicol in aqueous solution with mixed metal oxide electrode: Operational factors, reaction by-products and toxicity evaluation

Veterinary antibiotics have become an emerging pollutant in water and wastewater sources due to excess usage, toxicity and resistance to traditional water and wastewater treatment. The present study explored the degradation of a model antibiotic- Florfenicol (FF) using electrochemical oxidation (EO) with Ti-RuO2/IrO2 anode. The anode material was characterized using SEM-EDS studies expressing stable structure and optimal interaction of the neighboring metal oxides with each other. The EDS results showed the presence of Ru, Ir, Ti, O and C elements with 6.44%, 2.57%, 9.61%, 52.74% and 28.64% atomic weight percentages, respectively. Optimization studies revealed pH 5, 30 mA cm-2 current density and 0.05 M Na2SO4 for 5 mg L-1 FF achieved 90% TOC removal within 360 min treatment time. The degradation followed pseudo-first order kinetics. LC-Q-TOF-MS studies revealed six predominant byproducts illustrating hydroxylation, deflourination, and dechlorination to be the major degradation mechanisms during the electrochemical oxidation of FF. Ion chromatography studies revealed an increase in Cl-, F- and NO3- ions as treatment time progressed with Cl- decreasing after the initial phase of the treatment. Toxicity studies using Zebrafish (Danio rerio) embryo showed the treated sample to be toxic inducing developmental disorders such as pericardial edema, yolk sac edema, spinal curvature and tail malformation at 96 h post fertilization (hpf). Compared to control, delayed hatching and coagulation were observed in treated embryos. Overall, this study sets the stage for understanding the effect of mixed metal oxide (MMO) anodes on the degradation of veterinary antibiotic-polluted water and wastewater sources using electrochemical oxidation.

Preparation of Ti3C2Tx modified rare earth doped PbO2 electrodes for efficient removal of sulfamethoxazole

In this study, we deposited Ti3C2Tx-modified, rare-earth-doped PbO2 on the surface of a carbon fabric via electrodeposition. The surface morphology and electronic structure of the electrode were characterized with SEM, XRD and XPS. The layered Ti3C2Tx did not change the structure of β-PbO2, and at the same time, it improved the crystallinity of the material and reduced the grains of PbO2. Electrochemical experiments showed that the addition of Ti3C2Tx increased the electrochemical activity of the electrode and produced more H2O2, which contributed to the degradation of pollutants. The efficiency of sulfamethoxazole (SMX) degradation reached 95% after 120 min at pH 3 with a current density of 50 mA/cm2. Moreover, the electrode has good cycling performance, and the degradation efficiency was still 80% after 120 min after 10 cycles of recycling. Based on the intermediates identified by HPLC‒MS, a mechanism for SMX degradation was proposed. Our results will provide a new idea for the development of efficient electrocatalytic degradation of antibiotics.

Additive manufacturing-derived free-standing 3D pyrolytic carbon electrodes for sustainable microbial electrochemical production of H2O2

Producing H2O2 via microbial electrosynthesis is a cost-effective and environmentally favorable alternative to the costly and environmentally hazardous anthraquinone method. However, most studies have relied on carbon electrodes with two-dimensional (2D) surfaces (e.g., graphite), which have limited surface area and active sites, resulting in suboptimal H2O2 production. In this study, we demonstrate the enhanced efficiency of microbial H2O2 synthesis using three-dimensional (3D) electrodes produced through additive manufacturing technology due to their larger surface area than conventional carbon electrodes with 2D surfaces. This work innovatively combines 3D printed pyrolytic carbon (3D PyrC) electrodes with highly defined outer geometry and internal mesh structures derived from additive manufacturing with high-temperature resin precursors followed by pyrolysis with microbial electrochemical platform technology to achieve efficient H2O2 synthesis. The 3D PyrC electrode produced a maximum of 129.2 mg L-1 of H2O2 in 12 h, which was 2.3-6.9 times greater than conventional electrodes (e.g., graphite and carbon felt). Furthermore, the scalability, reusability and mechanical properties of the 3D PyrC electrode were exemplary, showcasing its practical viability for large-scale applications. Beyond H2O2 synthesis, the study explored the application of the 3D PyrC electrode in the bio-electro-Fenton process, demonstrating its efficacy as a tertiary treatment technology for the removal of micropollutants. This dual functionality underscores the versatility of the 3D PyrC electrode in addressing both the synthesis of valuable chemicals and environmental remediation. This study shows a novel electrode design for efficient, sustainable synthesis of H2O2 and subsequent environmental remediation.

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

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

Photoelectrocatalytic treatment of municipal wastewater with emerging concern pollutants using modified multi-layer catalytic anode

Municipal wastewater contains emergent chemical and biological pollutants that are resistant to conventional wastewater treatments. Therefore, the focus of the current study was to address the challenge of removing emergent chemical and biological pollutants present in municipal wastewater. To achieve this, a photo electro-catalytic (PEC) treatment approach was employed, focusing on the removal of both micro and biological pollutants that are of emergent concern, as well as the reduction of Chemical Oxidation Demand (COD) and Total Organic Carbon (TOC). The treatment involved the use of a modified multi-layer catalytic anode photo-electroactive anode as an effective anode for PEC treatment of municipal wastewater. In the continuous mode of operation, %COD removal was optimized for the treatment of municipal wastewater under Ultra-Violet C (UVc), 280 nm, and Visible (Vis) radiation, 400 nm. Therefore, a comparative study was performed to investigate the effect of Vis radiation on %COD removal, micropollutants removal, and disinfection of municipal wastewater. Micropollutants present in municipal wastewater were effectively oxidized/degraded with the highest reduction rate between 100% and 80% under the influence of UVc and Vis radiation respectively by the PEC treatment process. Disinfection of various microorganisms present in the wastewater with the effect of UVc and Vis assisted PEC treatment was also monitored. Overall, 75-80% of the disinfection of municipal wastewater was contributed by the modified multi-layer catalytic anode. The UVc in the PEC system, contributes approximately 20-25% to the overall disinfection of municipal wastewater.

Highly applicable dual-cathode electro-Fenton system with self-adjusting pH and ferrous species

Due to the high dependence on the pH of influent water and the level of ferrous species, the applicability of the electro-Fenton (EF) system is poor. A highly applicable dual-cathode (DC) EF system with self-adjusting pH and ferrous species is proposed: gas diffusion electrode (GDE) for generation H₂O₂ and Fe/S doped multi-walled carbon nanotubes (Fe/S-MWCNT) modification active cathode (AC) for adjusting pH and iron species. The strong synergistic enhancement effect between two cathodes (synergy factor up to 90.3%) improves the catalytic activity of this composite system about 12.4 times higher than that of cathode alone. Impressively, AC has the ability of self-regulate to shift towards the optimal Fenton pH (around 3.0) without adding reagents. Even pH can be adjusted from 9.0 to 3.4 within 60 min. This characteristic gives the system a wide range of pH applications, while avoiding the disadvantage of the high cost of traditional EF in pre-acidification. Furthermore, DC has a high and stable ferrous species supply, and the iron leaching amount is about twice less than that of heterogeneous EF system. Long-term stability of the DC system and its easy activity regeneration exhibit the potential of environmental remediation in 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.

Preparation of Porous Ti/RuO2-IrO2@Pt, Ti/RuO2-TiO2@Pt and Ti/Y2O3-RuO2-TiO2@Pt Anodes for Efficient Electrocatalytic Decomposition of Tetracycline

Electrocatalytic oxidation (ECO) has attracted attention because of its high efficiency and environmental friendliness in water treatment. The preparation of anodes with high catalytic activity and long service lifetimes is a core part of electrocatalytic oxidation technology. Here, porous Ti/RuO₂-IrO₂@Pt, Ti/RuO₂-TiO₂@Pt, and Ti/Y₂O₃-RuO₂-TiO₂@Pt anodes were fabricated by means of modified micro-emulsion and vacuum impregnation methods with high porosity titanium plates as substrates. The scanning electron microscopy (SEM) images showed that RuO₂-IrO₂@Pt, RuO₂-TiO₂@Pt, and Y₂O₃-RuO₂-TiO₂@Pt nanoparticles were coated on the inner surface of the as-prepared anodes to form the active layer. Electrochemical analysis revealed that the high porosity substrate could result in a large electrochemically active area, and a long service life (60 h at 2 A cm^-2 current density, 1 mol L^-1 H₂SO₄ as the electrolyte, and 40 °C). The degradation experiments conducted on tetracycline hydrochloride (TC) showed that the porous Ti/Y₂O₃-RuO₂-TiO₂@Pt had the highest degradation efficiency for tetracycline, reaching 100% removal in 10 min with the lowest energy consumption of 167 kWh kg^-1 TOC. The reaction was consistent with the pseudo-primary kinetics results with a k value of 0.5480 mol L^-1 s^-1, which was 16 times higher than that of the commercial Ti/RuO₂-IrO₂ electrode. The fluorospectrophotometry studies verified that the degradation and mineralization of tetracycline were mainly ascribed to the •OH generated in the electrocatalytic oxidation process. This study thus presents a series of alternative anodes for future industrial wastewater treatment.

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.

Electrocatalytic degradation of methyl orange and 4-nitrophenol on a Ti/TiO2-NTA/La-PbO2 electrode: electrode characterization and operating parameters

The anode material plays a crucial role in the process of electrochemical oxidation. Herein, a TiO₂ nanotube arrays (TiO₂-NTA) intermediate layer and La-PbO₂ catalytic layer were synthesized on a Ti surface by the electrochemical anodic oxidation and electrochemical deposition technology, respectively. The prepared Ti/TiO₂-NTA/La-PbO₂ electrode was used as an electrocatalytic oxidation anode for pollutant degradation. Scanning electron microscopy (SEM) analysis showed that the TiO₂-NTA layer possessed a highly ordered and well-aligned nanotube array morphology, and the La-PbO₂ layer with angular cone cluster was uniform and tightly bonded. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis indicated that the intermediate layer primarily consisted of the anatase crystal structure of TiO₂ and the catalyst layer was made of La-PbO₂. Electrochemical analysis revealed that Ti/TiO₂-NTA/La-PbO₂ electrode exhibited higher oxidation peak current, electrochemical active surface area, and oxygen evolution potential (OEP, 1.64 V). Using methyl orange and 4-nitrophenol as model pollutants, electrocatalytic properties of the prepared Ti/TiO₂-NTA/La-PbO₂ electrode were systematically investigated under different conditions, and the electrochemical degradation fitted well with the pseudo-first-order kinetics model. Efficient anodic oxidation of model pollutants was mainly attributed to the indirect oxidation mediated by hydroxyl radicals (•OH). The total organic carbon (TOC) removal efficiency of methyl orange and 4-nitrophenol was 70.2 and 72.8%, and low energy consumption (2.50 and 1.89 kWh g^-1) was achieved after 240 min of electrolysis under the conditions of initial concentration of model pollutant, electrode spacing, and electrolyte concentration were 50 mg L^-1, 2 cm, and 0.1 mol L^-1, respectively. This work provided a new strategy to develop the high-efficiency electrode for refractory pollutants degradation.

Cobalt-bismuth bimetallic composite anchored on carbon derived from cigarette butts as peroxymonosulfate activator for rapid removal of chloramphenicol

Chloramphenicol (CAP) is a typical kind of antibiotics, which has posed a severe threat to nature and human beings due to its wide application. In this study, cobalt-bismuth bimetallic composite anchored on carbon derived from cigarette butts (Co-Bi@CCB) was prepared to activate peroxymonosulfate (PMS) for the removal of CAP. Our results demonstrated Co-Bi@CCB not only possessed excellent catalytic performance, but also significantly limited metal ions dissolution. Over 98% of CAP (10 mg/L) was degraded in the presence of Co-Bi@CCB (0.05 g/L) and PMS (1 mM) within 20 min at pH = 7. Quenching tests and electron paramagnetic resonance (EPR) spectrometry confirmed that SO₄^•-, ^•OH, and ¹O₂ led to the rapid decomposition of CAP. Combined with X-ray photoelectron spectroscopy (XPS) of Co-Bi@CCB before and after reaction, the mechanism of PMS activation was deduced. Finally, the possible pathways of CAP degradation was further speculated according to the intermediates determination by high-performance liquid chromatography equipped with high resolution mass spectrometer (HPLC-HRMS). Thus, the present study provides a new strategy to utilize discarded cigarette butts (recycled materials) as a carrier to fabricate novel and efficient catalysts to activate PMS for the removal of organic contaminants.

Energy-efficient electrochemical treatment of paracetamol using a PbO2 anode based on pulse electrodeposition strategy: Kinetics, energy consumption and mechanism

The purpose of this research is to study the pulse electrochemical oxidation of paracetamol (PCT) using a novel PbO₂ anode based on pulse electrodeposition strategy (PbO₂-PE). The pulse electrodeposition strategy used to prepare a PbO₂ anode resulted in rougher surface, higher directional specificity of β(101) and more redox couples of Pb⁴⁺/Pb²⁺. Additionally, the oxygen evolution potential (OEP) and charge transfer resistance were also improved. When compared to direct current electrochemical oxidation process, pulse electrolysis in had a slightly higher PCT removal efficiency and active species (·OH and active chlorine) production, while 72.04% of energy consumption was saved. The effects of operating parameters on PCT degradation efficiency and specific energy consumption were studied. The findings suggested that the pulse electrochemical oxidation of PCT followed a pseudo-first-order kinetic model, with PCT removal reaching 98.63% after 60 min of electrolysis under optimal conditions. Possible mechanisms describing reaction pathways for PCT were also proposed. Finally, combinating with the economic feasibility and safety evaluation, we could conclude that pulse electrolysis with a PbO₂-PE electrode was a promising option for improving the practicability of electrochemical treatment for refractory organic wastewater.

Elaboration of Highly Modified Stainless Steel/Lead Dioxide Anodes for Enhanced Electrochemical Degradation of Ampicillin in Water

Lead dioxide-based electrodes have shown a great performance in the electrochemical treatment of organic wastewater. In the present study, modified PbO2 anodes supported on stainless steel (SS) with a titanium oxide interlayer such as SS/TiO2/PbO2 and SS/TiO2/PbO2-10% Boron (B) were prepared by the sol–gel spin-coating technique. The morphological and structural properties of the prepared electrodes were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). It was found that the SS/TiO2/PbO2-10% B anode led to a rougher active surface, larger specific surface area, and therefore stronger ability to generate powerful oxidizing agents. The electrochemical impedance spectroscopy (EIS) measurements showed that the modified PbO2 anodes displayed a lower charge transfer resistance Rct. The influence of the introduction of a TiO2 intermediate layer and the boron doping of a PbO2 active surface layer on the electrochemical degradation of ampicillin (AMP) antibiotic have been investigated by chemical oxygen demand measurements and HPLC analysis. Although HPLC analysis showed that the degradation process of AMP with SS/PbO2 was slightly faster than the modified PbO2 anodes, the results revealed that SS/TiO2/PbO2-10%B was the most efficient and economical anode toward the pollutant degradation due to its physico-chemical properties. At the end of the electrolysis, the chemical oxygen demand (COD), the average current efficiency (ACE) and the energy consumption (EC) reached, respectively, 69.23%, 60.30% and 0.056 kWh (g COD)−1, making SS/TiO2/PbO2-10%B a promising anode for the degradation of ampicillin antibiotic in aqueous solutions.

Removal of chloramphenicol antibiotics in natural and engineered water systems: Review of reaction mechanisms and product toxicity

Chloramphenicol antibiotics are widely applied in human and veterinary medicine. They experience natural attenuation and/or chemical degradation during oxidative water treatment. However, the environmental risks posed by the transformation products of such organic contaminants remain largely unknown from the literature. As such, this review aims to summarize and analyze the elimination efficiency, reaction mechanisms, and resulting product risks of three typical chloramphenicol antibiotics (chloramphenicol, thiamphenicol, and florfenicol) from these transformation processes. The obtained results suggest that limited attenuation of these micropollutants is observed during hydrolysis, biodegradation, and photolysis. Comparatively, prominent abatement of these compounds is accomplished using advanced oxidation processes; however, efficient mineralization is still difficult given the formation of recalcitrant products. The in silico prediction on the multi-endpoint toxicity and biodegradability of different products is systematically performed. Most of the transformation products are estimated with acute and chronic aquatic toxicity, genotoxicity, and developmental toxicity. Furthermore, the overall reaction mechanisms of these contaminants induced by multiple oxidizing species are revealed. Overall, this review unveils the non-overlooked and serious secondary risks and biodegradability recalcitrance of the degradation products of chloramphenicol antibiotics using a combined experimental and theoretical method. Strategic improvements of current treatment technologies are strongly recommended for complete water decontamination.

Decontamination of wastewater containing contaminants of emerging concern by electrooxidation and Fenton-based processes - A review on the relevance of materials and methods

In recent years, there has been an increasingly growing interest regarding the use of electrochemical advanced oxidation processes (EAOPs) which are considered highly promising alternative treatment techniques for addressing environmental issues related to pollutants of emerging concern. In EAOPs, electrogenerated oxidizing agents, such as hydroxyl radical (HO^•), can react non-selectively with a wide range of organic compounds, degrading and mineralizing their structures to unharmful molecules like CO₂, H₂O, and inorganic ions. To this date, a broad spectrum of advanced electrocatalysts have been developed and applied for the treatment of compounds of interest in different matrices, specifically aiming at enhancing the degradation performance. New combined methods have also been employed as alternative treatment techniques targeted at circumventing the major obstacles encountered in Fenton-based processes, such as high costs and energy consumption, which still contribute significantly toward inhibiting the large-scale application of these processes. First, some fundamental aspects of EAOPs will be presented. Further, we will provide an overview of electrode materials which have been recently developed and reported in the literature, highlighting different anode and cathode structures employed in EAOPs, their main advantages and disadvantages, as well as their contribution to the performance of the treatment processes. The influence of operating parameters, such as initial concentrations, pH effect, temperature, supporting electrolyte, and radiation source, on the treatment processes were also studied. Finally, hybrid techniques which have been reported in the literature and critically assess the most recent techniques used for evaluating the degradation efficiency of the treatment processes.

Electro-Chemical Degradation of Norfloxacin Using a PbO2-NF Anode Prepared by the Electrodeposition of PbO2 onto the Substrate of Nickel Foam

A novel three-dimensional network nickel foam/PbO2 combination electrode (PbO2-NF) with high electrochemical degradation efficiency to norfloxacin was successfully fabricated through the electrodeposition of PbO2 on the substrate of nickel foam. The characterization of an PbO2-NF electrode, including surface morphology, elemental components, electrochemical performance, and stability was performed. In electrochemical oxidation tests, the removal efficiency of norfloxacin (initial concentration for 50 mg/L) on PbO2-NF reached 88.64% within 60 min of electrolysis, whereas that of pure nickel foam was only 30%. In the presence of PbO2-NF, the optimum current density, solution pH, electrode spacing for norfloxacin degradation were 30 mA/cm2, 11, and 3 cm, respectively. The electric energy consumption for 80% norfloxacin was approximately 5 Wh/L. Therefore, these results provide a new anode to improve the removal of norfloxacin in the wastewater with high efficiency and low energy consumption.

Electrochemical Reduction and Oxidation of Chlorinated Aromatic Compounds Enhanced by the Fe-ZSM-5 Catalyst: Kinetics and Mechanisms

Devising cost-effective electrochemical catalyst system for the efficient degradation of chlorinated aromatic compounds is urgently needed for environmental pollution control. Herein, a Fe-ZSM-5 zeolite was used as a suspended catalyst to facilitate the degradation of lindane as a model chlorinated pesticide in an electrochemical system consisting of the commercial DSA (Ti/RuO₂-IrO₂) anode and graphite cathode. It was found that the Fe-ZSM-5 zeolite greatly accelerated the degradation of lindane, with the degradation rate constant more than 8 times higher than that without Fe-ZSM-5. In addition, the Fe-ZSM-5 zeolite widened the working pH range from 3 to 11, while efficient degradation of lindane in the absence of Fe-ZSM-5 was only obtained at pH ≤ 5. The degradation of lindane was primarily due to reductive dechlorination mediated by atomic H* followed by ^•OH oxidation. Fe-ZSM-5 zeolite could enrich lindane, H*, and ^•OH on its surface, thus provided a suitable local environment for lindane degradation. The Fe-ZSM-5 zeolite exhibited high stability and reusability, and reduced the energy consumption. This research provides a potential reduction-oxidation strategy for removing organochlorine compounds through a cost-efficient Fe-ZSM-5 catalytic electrochemical system.

Performance and mechanism of removal of antibiotics and antibiotic resistance genes from wastewater by electrochemical carbon nanotube membranes

Electrochemical carbon nanotube (CNT) and carboxylated carbon nanotube (CNT-COOH) membranes were prepared by vacuum filtration for the removal of antibiotics and antibiotic resistance genes (ARGs) from water. Scanning electron microscopy and energy-dispersive spectroscopy were used to analyze the performances of the two electrochemical membranes in the removal of antibiotics and ARGs, to determine the effects of different factors on removal rates, and to explore the mechanisms of the removal of antibiotics and ARGs. The results showed that CNT-COOH formed a porous mesh structure on the surface of polytetrafluoroethylene membrane and contained more oxygen than CNT. The electrochemical CNT-COOH membrane showed higher antibiotic and ARG removal rates than the electrochemical CNT membrane, with an antibiotics removal rate of 82% after 60 min of reaction and an ARGs concentration decrease by 1.85 log. The removal rate of antibiotics and ARGs increased with the increase in electrolyte concentration and anode voltage but decreased with the increase in the influent flow rate. The removal rate of antibiotics decreased with the increase in pH, while the best removal rates of ARGs were observed in a neutral environment. The degradation mechanism of antibiotics on the electrochemical CNT-COOH membrane was analyzed, and possible antibiotic degradation pathways were proposed. The removal of antibiotics and ARGs mainly occurred through electrochemical degradation, where hydroxyl radicals (-OH) played a dominant role.

Fluidized ZnO@BCFPs Particle Electrodes for Efficient Degradation and Detoxification of Metronidazole in 3D Electro-Peroxone Process

A novel material of self-shaped ZnO-embedded biomass carbon foam pellets (ZnO@BCFPs) was successfully synthesized and used as fluidized particle electrodes in three-dimensional (3D) electro-peroxone systems for metronidazole degradation. Compared with 3D and 2D + O₃ systems, the energy consumption was greatly reduced and the removal efficiencies of metronidazole were improved in the 3D + O₃ system. The degradation rate constants increased from 0.0369 min^-1 and 0.0337 min^-1 to 0.0553 min^-1, respectively. The removal efficiencies of metronidazole and total organic carbon reached 100% and 50.5% within 60 min under optimal conditions. It indicated that adding ZnO@BCFPs particle electrodes was beneficial to simultaneous adsorption and degradation of metronidazole due to improving mass transfer of metronidazole and forming numerous tiny electrolytic cells. In addition, the process of metronidazole degradation in 3D electro-peroxone systems involved hydroxyethyl cleavage, hydroxylation, nitro-reduction, N-denitrification and ring-opening. The active species of ·OH and ·O₂^- played an important role. Furthermore, the acute toxicity LD₅₀ and the bioconcentration factor of intermediate products decreased with the increasing reaction time.

Advances of Drugs Electroanalysis Based on Direct Electrochemical Redox on Electrodes: A Review

The strong development of mankind is inseparable from the proper use of drugs, and the electroanalytical research of drugs occupies an important position in the field of analytical chemistry. This review mainly elaborates the research progress of drugs electroanalysis based on direct electrochemical redox on various electrodes for the recent decade from 2011 to 2021. At first, we summarize some frequently used electrochemical data processing and electrochemical mechanism research derivation methods in the literature. Then, according to the drug therapeutic and application/usage purposes, the research progress of drugs electrochemical analysis is classified and discussed, where we focus on drugs electrochemical reaction mechanism. At the same time, the comparisons of electrochemical sensing performance of the drugs on various electrodes from recent studies are listed, so that readers can more intuitively compare and understand the electroanalytical sensing performance of each modified electrode for each of the drug. Finally, this review discusses the shortcomings and prospects of the drugs electroanalysis based on direct electrochemical redox research.

Formation of stable imine intermediates in the coexistence of sulfamethoxazole and humic acid by electrochemical oxidation

The electrochemical degradation performance of sulfamethoxazole (SMX) was studied in the presence of humic acid (HA) by using a Ti/Ti₄O₇/β-PbO₂ anode. The electrochemical degradation efficiency of SMX decreased from 93.4% to 45.8% in 50 min after the addition of 25 mg L^-1 HA. The pseudo-first-order kinetic rate constant decreased by 71.4%, and the E_EO value increased from 63.8 Wh L^-1 to 90.9 Wh L^-1. HA and its degradation intermediates could compete for free radicals, especially for ·OH, with SMX. The analytical results obtained using UPLC-ESI-Q-TOF-MS showed that 18 degradation intermediates were identified in the coexistence of SMX and HA. Four imine intermediates were formed through the reactions between the aniline moieties of SMX and quinone groups in the HA structure through covalent bonds. Furthermore, the relative abundances of the intermediates demonstrated that the imine intermediates were complex and stable during electrochemical degradation.

Photodegradation of chloramphenicol in micro-polluted water using a circulatory thin-layer inclined plate reactor

This study describes the photodegradation of chloramphenicol (CAP) in micro-polluted water with a thin-layer inclined plate reactor. Under simulated sunlight irradiation, the effect of reaction parameters including solution pH, initial CAP concentration, and co-existed humic acid (HA) or chloride was evaluated. The photodegradation of CAP was independent of initial pH in the range of 6.0-9.0, but sharply decreased by 25.5% with the increase of initial CAP concentration from 0.4 to 1.0 mg/L. The presence of HA exhibited a significant inhibitory effect, while Cl^- promoted the photoreaction. In this study, CAP was degraded through both direct and indirect photolysis, in which ¹O₂ was the main reactive species responsible for the indirect route. Its steady-state concentration in the micro-polluted water was determined to be 1.40 × 10^-13 mol/L. Transformation intermediates were identified to propose the degradation pathway of CAP, which substantially met the density functional theory (DFT) calculation results. Moreover, four other pharmaceuticals including tetracycline, doxycycline, oxytetracycline, and minocycline were also successfully photodegraded during 5 h irradiation. Therefore, the designed circulatory thin-layer inclined plate reactor is suggested to be effectively applied to the decontamination of organic micro-polluted water.

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.

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.

Catalytic ozonation of chloramphenicol with manganese-copper oxides/maghemite in solution: Empirical kinetics model, degradation pathway, catalytic mechanism, and antibacterial activity

The composite material of manganese-copper oxide/maghemite (Mn_xCu_yO_z/γ-Fe₂O₃) was synthesized by the co-precipitation-calcination method. With the initial concentration of 0.2 g/L Mn_xCu_yO_z/γ-Fe₂O₃ and 10 mg/L O₃, the chloramphenicol (CAP, 10 mg/L) could be completely degraded, which was about 2.22 times of that treated with ozonation alone. The contribution of O₃ and hydroxyl radical (•OH) for CAP degradation in the catalytic process was 6.9% and 93.1%, respectively. According to the effects of catalyst dosage, ozone dosage, and pH on the catalytic performance of Mn_xCu_yO_z/γ-Fe₂O₃, a predictive empirical model was developed for the ozonation with the Mn_xCu_yO_z/γ-Fe₂O₃ system. The HCO₃^-/CO₃^2- and phosphates in solution could inhibit the degradation of CAP with the inhibition ratios 8.45% and 13.8%, respectively. The HCO₃^-/CO₃^2- could compete with CAP and react with •OH, and the phosphates were considered as poisons for catalysts by blocking the surface active sites to inhibit ozone decomposition. The intermediates and possible degradation pathways were detected and proposed. The catalytic ozonation could effectively control the toxicity of the treated solution, but the toxicity was still not negligible. Furthermore, Mn_xCu_yO_z/γ-Fe₂O₃ could be easily and efficiently separated from the reaction system with an external magnet, and it possessed excellent reusability and stability.

Process Optimization of Electrochemical Treatment of COD and Total Nitrogen Containing Wastewater

In this work, an electrochemical method for chemical oxygen demand (COD) and total nitrogen (TN, including ammonia, nitrate, and nitrite) removal from wastewater using a divided electrolysis cell was developed, and its process optimization was investigated. This process could effectively relieve the common issue of NO₃^-/NO₂^- over-reduction or NH₄⁺ over-oxidation by combining cathodic NO₃^-/NO₂^- reduction with anodic COD/NH₄⁺ oxidation. The activity and selectivity performances toward pollutant removal of the electrode materials were investigated by electrochemical measurements and constant potential electrolysis, suggesting that Ti electrode exhibited the best NO₃^-/NO₂^- reduction and N₂ production efficiencies. In-situ Fourier transform infrared spectroscopy was used to study the in-situ electrochemical information of pollutants conversion on electrode surfaces and propose their reaction pathways. The effects of main operating parameters (i.e., initial pH value, Cl^- concentration, and current density) on the removal efficiencies of COD and TN were studied. Under optimal conditions, COD and TN removal efficiencies from simulated wastewater reached 92.7% and 82.0%, respectively. Additionally, reaction kinetics were investigated to describe the COD and TN removal. Results indicated that COD removal followed pseudo-first-order model; meanwhile, TN removal followed zero-order kinetics with a presence of NH₄⁺ and then followed pseudo-first-order kinetics when NH₄⁺ was completely removed. For actual pharmaceutical wastewater treatment, 79.1% COD and 87.0% TN were removed after 120 min electrolysis; and no NH₄⁺ or NO₂^- was detected.

Efficiency of an up-flow Anaerobic Sludge Blanket reactor coupled with an electrochemical system to remove chloramphenicol in swine wastewater

The application and design of treatment systems in wastewater are necessary due to antibiotics' potential toxicity and resistant genes on residual effluent. This work evaluated a coupled bio-electrochemical system to reduce chloramphenicol (CAP) and chemical oxygen demand (COD) on swine wastewater (SWW). SWW characterization found CAP of <10 μg/L and 17,434 mg/L of COD. The coupled system consisted of preliminary use of an Up-flow Anaerobic Sludge Blanket Reactor (UASB) followed by electrooxidation (EO). The UASB reactor (primary stage) was operated for three months at an organic load of 8.76 kg of COD/m³d and 50 mg CAP/L as initial concentration. In EO, we carried out a 2² (time operation and intensity) factorial design with a central composite design; we tried two Ti cathodes and one anode of Ti/PbO₂. Optimal conditions obtained in the EO process were 240 min of operation time and 1.51 A of current intensity. It was possible to eliminate 44% of COD and 64.2% of CAP in the preliminary stage. On bio-electrochemicals, total COD and CAP removal were 82.35 and >99.99%, respectively. This coupled system can be applied to eliminate antibiotics and other organic pollutants in agricultural, industrial, municipal, and other wastewaters.

Influence of dimethylphenol isomers on electrochemical degradation: Kinetics, intermediates, and DFT calculation

Dimethylphenol isomers (DMP) pose a great threat to the environment, and the electrooxidation (EO) process proves to be an extraordinarily effective method to degrade DMP. However, the EO performance is affected by the molecular structure of DMP and the adopted experimental parameters. In this study, the effects of 2,4-DMP and 2,6-DMP on the working potential, limiting current density (J_lim), and pH were systematically analysed, with Ti-mesh plates used as the cathode and Ti/PbO₂ as the anode. The peak potentials of 2,4-DMP and 2,6-DMP were determined to be 0.83 V and 0.77 V by cyclic voltammetry, with J_lim were 2.5 mA·cm^-2 and 2.0 mA·cm^-2, respectively. The whole process exhibited pseudo-first-order kinetics, and the kinetic constants (K) for the degradation of 2,4-DMP and 2,6-DMP were determined to be 0.0041 min^-1 and 0.0150 min^-1, respectively. Additionally, the optimal initial pH value for 2,4-DMP and 2,6-DMP was 5.0, where the highest hydroxyl (OH) radical density, as determined by the electron spin technique (ESR), was achieved at a higher current density. Comparatively, the OH radical density in the 2,6-DMP solution was lower than that in 2,4-DMP. In situ Fourier infrared (FT-IR) spectroscopy, GC-MS, and density functional theory (DFT) were employed to explore three possible degradation pathways. The main intermediates for 2,4-DMP degradation were determined to be quinone and ether, while that for 2,6-DMP degradation was quinone. According to the results of this study, the molecular structure (different methyl group positions on the benzene ring) has a great influence on the EO process.

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 β 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.

Co/Sm-modified Ti/PbO2 anode for atrazine degradation: Effective electrocatalytic performance and degradation mechanism

In this work, Ti/PbO₂-Co-Sm electrode has been successfully prepared using electrodeposition and further applied for the electrocatalysis of atrazine (ATZ) herbicide wastewater. As expected, Ti/PbO₂-Co-Sm electrode displays highest oxygen evolution potential, lowest charge transfer resistance, longest service lifetime and most effective electrocatalytic activity compared with Ti/PbO₂, Ti/PbO₂-Sm and Ti/PbO₂-Co electrodes. Orthogonal and single factor experiments are designed to optimize the condition of ATZ degradation. The maximum degradation efficiency of 92.6% and COD removal efficiency of 84.5% are achieved in electrolysis time 3 h under the optimum condition (current density 20 mA cm^-2, Na₂SO₄ concentration 8.0 g L^-1, pH 5 and temperature 35 °C). In addition, Ti/PbO₂-Co-Sm electrode exhibits admirable recyclability in degradation progress. The degradation of ATZ is accomplished by indirect electrochemical oxidation and ∙OH is tested as the main active substance in ATZ oxidation. The possible degradation mechanism of ATZ has been proposed according to the degradation intermediates detected by LC-MS. This research suggests that Ti/PbO₂-Co-Sm is a promising electrode for ATZ degradation.

Scaling-up of microbial electrosynthesis with multiple electrodes for in situ production of hydrogen peroxide

Microbial electrosynthesis system (MES) has recently been shown to be a promising alternative way for realizing in situ and energy-saving synthesis of hydrogen peroxide (H₂O₂). Although promising, the scaling-up feasibility of such a process is rarely reported. In this study, a 20-L up-scaled two-chamber MES reactor was developed and investigated for in situ and efficient H₂O₂ electrosynthesis. Maximum H₂O₂ production rate of 10.82 mg L⁻¹ h⁻¹ and cumulative H₂O₂ concentration of 454.44 mg L⁻¹ within 42 h were obtained with an input voltage of 0.6 V, cathodic aeration velocity of 0.045 mL min⁻¹ mL⁻¹, 50 mM Na₂SO₄, and initial pH 3. The electrical energy consumption regarding direct input voltage was only 0.239 kWh kg⁻¹ H₂O₂, which was further much lower compared with laboratory-scale systems. The obtained results suggested that the future industrialization of MES technology for in situ synthesis of H₂O₂ and further application in environmental remediation have broad prospects.

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Up-scaled microbial electrosynthesis with multiple electrodes to synthesize H₂O₂

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The H₂O₂ yield was higher than that of laboratory-scale systems using graphite cathode

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Energy consumption was lower than that of laboratory-scale (bio)electrochemical systems

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Systematic evaluation of the influence of operating parameters on H₂O₂ production