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

Electrochemical degradation of toluene-2,4-diamine by graphene oxide-modified Ti/Sb-SnO2/α-PbO2/β-PbO2 anode: Performance and mechanism

The formidable toluene-2,4-diamine (TDA), a potential human carcinogenic pollutant, environmental challenge necessitates investigating an efficient technology and clarifying its removal mechanism. Accordingly, we prepared a graphene oxide-modified PbO2 anode (Ti/Sb-SnO2/α-PbO2/GO-β-PbO2) to degrade TDA using electrochemical oxidation technology given its high oxidation capacity and green feature. The Ti/Sb-SnO2/α-PbO2/GO-β-PbO2 attained 100 % TDA and 82.7 % COD removal efficiency after 3.0 h electrolysis for its high oxygen evolution overpotential (2.08 V vs.SCE), superior ⋅OH generation capacity, and hydrophobic surface (121.2°). The quenching experiments and EPR tests all confirmed the vital role of both ⋅OH and SO4·-, resulting in the oxidation of the benzene ring and amino group. Moreover, the (Ti/Sb-SnO2/α-PbO2/GO-β-PbO2 also presented an improved stability with the accelerated lifetime prolonged by about 50.8 %. Therefore, this work provides a toolbox for treating TDA wastewater and a good reference for fabricating PbO2 anode via a facile yet effective method.

A comprehensive review of PbO2 electrodes in electrocatalytic degradation of organic pollutants

This paper provides a systematic review of recent advancements in PbO2 electrodes for the electrocatalytic degradation of organic pollutants, emphasizing innovative breakthroughs and key technological optimizations in this domain. This work analyzes PbO2 electrode fabrication methods, assessing strengths/weaknesses, and summarizes recent advances in surface modification. Atomic-scale strategies such as elemental doping, composite oxides, and nanomaterial coupling, enhance its catalytic performance. Kinetic modeling and characterization confirm the improved efficiency and durability in organic contaminant mineralization. Kinetic and experimental analyses demonstrate the high efficiency and stability of modified PbO2 electrodes in degrading organic pollutants. Industrial feasibility analysis indicates that the PbO2 electrode demonstrates technical robustness, economic viability, and scalability for industrial implementation. This work elucidates direct/indirect oxidation mechanisms in electrocatalysis, revealing correlations between surface reactive sites and active oxidant generation, guiding electrode design optimization. Looking ahead, this paper proposes innovative trajectories for PbO2 electrode technology, such as exploring novel modified materials, intelligently designing hierarchical architectures, and integrating advanced systems with smart control. These directions aim to promote its widespread use in environmental protection for more efficient and eco-friendly organic pollutant treatment. This review enriches the theoretical framework for PbO2 electrode electrocatalytic degradation of organic contaminants and offers references and inspirations for future research.

Anodic oxidation using 3D carbon felt/PbO2 anode: a electron transfer-mediated system for degradation of Rhodamine B

This study investigates the use of porous structured carbon felt (CF) as a substrate for the preparation a lead dioxide (CF/PbO2) anode for the electrochemical oxidation of Rhodamine B (RhB). Compared to traditional titanium-based lead dioxide (Ti/PbO2) and graphite sheet-based lead dioxide (GS/PbO2) anodes, the CF/PbO2 anode exhibited superior electrocatalytic activity, achieving a RhB degradation efficiency exceeding 99%. After 10 cycles, the electrocatalytic activity of CF/PbO2 anode remained robust, with a degradation efficiency of over 97%. Fluorescence spectroscopy, quenching experiments, and electrochemical tests indicate that the electrochemical oxidation behaviour on CF/PbO2 and GS/PbO2 anodes was governed by direct electron transfer, while indirect oxidation via •HO radicals was pivotal for the Ti/PbO2 anode. LC-MS analysis identified the intermediates of RhB degradation, contributing to the proposed degradation pathway. This study provides an efficient anode for the electrochemical degradation of organic pollutants in water.

In situ grown petal-like La-doped FeCo-layered double hydroxide on carbon felt for enhanced moxifloxacin hydrochloride removal via heterogeneous electro-Fenton process

In this study, a petal-like ternary metal-layered double hydroxide (FeCoLa-LDH) was synthesized through a facile one-step hydrothermal method and in situ grown on carbon felt (CF). The FeCoLa-LDH/CF composite electrode was applied in a heterogeneous electro-Fenton (HEF) system for the degradation of moxifloxacin hydrochloride (MOX). Characterization revealed that La-doped FeCo-LDH/CF exhibited petal-like layered structure rather than particle's structure, with higher surface defect degree and an increased electroactive surface area (ESA) compared to FeCo-LDH/CF. The composite electrode effectively degraded MOX across a pH range of 3-9. Under optimal conditions, it achieved a degradation efficiency of 92.2% within 45 min and 96.8% within 120 min. After 120 min, 82.4% of the chemical oxygen demand (COD) was removed. The superior degradation performance was primarily attributed to La doping, which enhanced electron transfer between Co2+/Co3+ and Fe2+/Fe3+, promoting in situ H2O2 generation and causing rapid conversion of H2O2 to hydroxyl radical(•OH) on the electrode surface. Radical quenching experiments confirmed that •OH was the primary reactive species. The possible MOX degradation pathways were elucidated through liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) calculations, and a catalytic mechanism of HEF process was proposed. Moreover, the electrode maintained 82.8% efficiency after five cycles, with lower ion leaching and broader pollutant applicability. Moreover, good degradation efficiencies of MOX were still observed in actual water bodies. Toxicity tests confirmed that MOX degradation intermediate products had low plant toxicity. This study provides a promising high-performance cathode for antibiotic removal from wastewater.

Bibliometric analysis and systematic review of electrochemical methods for environmental remediation

Electrochemical methods are increasingly favored for remediating polluted environments due to their environmental compatibility and reagent-saving features. However, a comprehensive understanding of recent progress, mechanisms, and trends in these methods is currently lacking. Web of Science (WoS) databases were utilized for searching the primary data to understand the knowledge structure and research trends of publications on electrochemical methods and to unveil certain hotspots and future trends of electrochemical methods research. The original data were sampled from 9080 publications in those databases with the search deadline of June 1st, 2022. CiteSpace and VOSviewer software facilitated data visualization and analysis of document quantities, source journals, institutions, authors, and keywords. We discussed principles, influencing factors, and progress related to seven major electrochemical methods. Notably, publications on this subject have experienced significant growth since 2007. The most frequently-investigated areas in electrochemical methods included novel materials development, heavy metal remediation, organic pollutant degradation, and removal mechanism identification. "Advanced oxidation process" and "Nanocomposite" are currently trending topics. The major remediation mechanisms are adsorption, oxidation, and reduction. The efficiency of electrochemical systems is influenced by material properties, system configuration, electron transfer efficiency, and power density. Electro-Fenton exhibits significant advantages in achieving synergistic effects of anodic oxidation and electro-adsorption among the seven techniques. Future research should prioritize the improvement of electron transfer efficiency, the optimization of electrode materials, the exploration of emerging technology coupling, and the reduction in system operation and maintenance costs.

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.

Photocatalytic degradation of drugs and dyes using a maching learning approach

The waste management industry uses an increasing number of mathematical prediction models to accurately forecast the behavior of organic pollutants during catalytic degradation. With the increasing quantity of waste generated, these models are critical for reinforcing the efficiency of wastewater treatment strategies. The application of machine-learning techniques in recent years has notably improved predictive models for waste management, which are essential for mitigating the impact of toxic commercial waste on global water supply. Organic contaminants, dyes, pesticides, surfactants, petroleum by-products, and prescription drugs pose risks to human health. Because traditional techniques face challenges in ensuring water quality, modern strategies are vital. Machine learning has emerged as a valuable tool for predicting the photocatalytic degradation of medicinal drugs and dyes, providing a promising avenue for addressing urgent demands in removing organic pollutants from wastewater. This research investigates the synergistic application of photocatalysis and machine learning for pollutant degradation, showcasing a sustainable solution with promising effects on environmental remediation and computational efficiency. This study contributes to green chemistry by providing a clever framework for addressing present-day water pollution challenges and achieving era-driven answers.

Boosted electrocatalytic oxidation of organophosphorus pesticides by a novel high-efficiency CeO2-Doped PbO2 anode: An electrochemical study, parameter optimization and degradation mechanisms

This article presents a novel and highly efficient electrocatalytic degradation method for two significant organophosphorus pesticides, fenitrothion (FEN), and methyl parathion (MPN), using a Ti/β-PbO2-CeO2 modified anode (indirect oxidation). A comprehensive electrochemical investigation was also carried out to gain new insight into the redox behavior and destruction pathway of these pesticides (direct oxidation). The study also explores the effects of various operating parameters, such as initial solution pH, applied current density, and initial pesticides concentration, on the conversion-paired electrocatalytic removal process. To further enhance the degradation efficiency, a new configuration of the electrochemical cell was designed, employing two types of electrodes and two independent power supply devices. The conversion paired electrocatalytic degradation process of these pesticides involves first the direct reduction of FEN (or MPN) on a graphite cathode and then the indirect oxidation of reduced FEN (or MPN) by hydroxyl radicals electro generated on the Ti/β-PbO2-CeO2 anode. The synergism of these two processes together will effectively lead to FEN (or MPN) degradation. The degradation percentages of 98% for FEN and 95% for MPN at the optimal conditions for the electrochemical degradation of these pesticides were achieved at pH = 7, initial concentration 50 mg L-1, with a current density of 90 mA cm-2 for direct reduction and 11 mA cm-2 for indirect oxidation. Overall, this study presents a promising and efficient approach for the remediation of organophosphorus pesticide-contaminated environments, offering valuable insights into the electrochemical degradation process and highlighting the potential for practical application in wastewater treatment and environmental protection.

Sustainable application of electrocatalytic and photo-electrocatalytic oxidation systems for water and wastewater treatment: a review

Wastewater treatment and reuse have risen as a solution to the water crisis plaguing the world. Global warming-induced climate change, population explosion and fast depletion of groundwater resources are going to exacerbate the present global water problems for the forthcoming future. In this scenario, advanced electrochemical oxidation process (EAOP) utilising electrocatalytic (EC) and photoelectrocatalytic (PEC) technologies have caught hold of the interest of the scientific community. The interest stems from the global water management plans to scale down centralised water and wastewater treatment systems to decentralised and semicentralised treatment systems for better usage efficiency and less resource wastage. In an age of rising water pollution caused by contaminants of emerging concern (CECs), EC and PEC systems were found to be capable of optimal mineralisation of these pollutants rendering them environmentally benign. The present review treads into the conventional electrochemical treatment systems to identify their drawbacks and analyses the scope of the EC and PEC to mitigate them. Probable electrode materials, potential catalysts and optimal operational conditions for such applications were also examined. The review also discusses the possible retrospective application of EC and PEC as point-of-use and point-of-entry treatment systems during the transition from conventional centralised systems to decentralised and semi-centralised water and wastewater treatment systems.

Y-mediated optimization of 3DG-PbO2 anode for electrochemical degradation of PFOS

In our previous study, the three-dimensional graphene-modified PbO2 (3DG-PbO2) anode was prepared for the effective degradation of perfluorooctanesulfonat (PFOS) by the electrochemical oxidation process. However, the mineralization efficiency of PFOS at the 3DG-PbO2 anode still needs to be further improved due to the recalcitrance of PFOS. Thus, in this study, the yttrium (Y) was doped into the 3DG-PbO2 film to further improve the electrochemical activity of the PbO2 anode. To optimize the doping amount of Y, three Y and 3DG codoped PbO2 anodes were fabricated with different Y3+ concentrations of 5, 15, and 30 mM in the electroplating solution, which were named Y/3DG-PbO2-5, Y/3DG-PbO2-15 and Y/3DG-PbO2-30, respectively. The results of morphological, structural, and electrochemical characterization revealed that doping Y into the 3DG-PbO2 anode further refined the β-PbO2 crystals, increased the oxygen evolution overpotential and active sites, and reduced the electron transfer resistance, resulting in a superior electrocatalytic activity. Among all the prepared anodes, the Y/3DG-PbO2-15 anode exhibited the best activity for electrochemical oxidation of PFOS. After 120 min of electrolysis, the TOC removal efficiency was 80.89% with Y/3DG-PbO2-15 anode, greatly higher than 69.13% with 3DG-PbO2 anode. In addition, the effect of operating parameters on PFOS removal was analyzed by response surface, and the obtained optimum values of current density, initial PFOS concentration, pH, and Na2SO4 concentration were 50 mA/cm2, 12.21 mg/L, 5.39, and 0.01 M, respectively. Under the optimal conditions, the PFOS removal efficiency reached up to 97.16% after 40 min of electrolysis. The results of the present study confirmed that the Y/3DG-PbO2 was a promising anode for electrocatalytic oxidation of persistent organic pollutants.

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.

An integrated process for wet scrubber wastewater treatment using electrooxidation and pressure-driven membrane filtration

In this study, the electrooxidation (EO) and membrane processes were used for chemical oxygen demand (COD) and total phenol (TPh) removal from wet scrubber wastewater (WSW). EO experiments were carried out using Al, Fe, SS, Ti, graphite, active carbon cloth electrodes and Box-Behnken design were used for optimization of maximum COD and TPh removal efficiency. Moreover, membrane filtration experiments were conducted to EO process using nanofiltration (NF270) and reverse osmosis membranes (SW30 and BW30). The maximum COD (55%) and TPh (50%) removal efficiency was achieved at pH of 8, 150 A/m² current density, and 180 min reaction time in EO process. Membrane filtration results showed that COD removal efficiency was the highest for SW30 membrane (95.18%) compared to BW30 (91.15%) and NF270 (80.11%) membranes. TPh removal efficiency in the NF270, BW30, and SW30 membranes was 27.08%, 96.06%, and 98.02%, respectively. The effect of microbial cell viability of the raw and treated wet scrubber wastewater after electrooxidation and membrane filtration was also investigated using E. coli. In addition to these, biofilm inhibition of the raw wet scrubber wastewater and the treated WSW after EO and membrane filtration were tested and the highest biofilm inhibition was found as 76.43% and 72.58% against S. aureus and P. aeruginosa, respectively, in 1/20 diluted samples of the raw WSW. This study suggests that the integrated process using EO and pressure-driven membrane methods are an efficient strategy for COD and TPh removal from WSW.

Removal of phenol from wastewater by electrochemical bromination in a flow reactor

Electrochemical methods have been widely applied in the treatment of phenol wastewater for the past few years. However, conventional electrochemical advanced oxidation processes (EAOPs) generally encounter the problem of electrode passivation and the energy consumption required for mineralization is high. In this work, we reported the treatment of phenol wastewater by electrochemical bromination method in a flow electrolysis cell. The Ti/Sb-SnO₂/PbO₂ electrode was prepared and used as anode. The experiments were carried out under different initial pH, KBr concentrations, current densities, and volumetric flow rates. The generated 2,4,6-tribromophenol (TBP) could be easily separated from the electrode surface and electrolyte. The brominated intermediates were identified by GC/MS. The removal efficiencies for phenol and COD were 100% and 82.7%, respectively, under the best operational conditions (current density of 40 mA cm^-2, KBr concentration of 0.074 mol L^-1, initial pH of 1.0, and volumetric flow rate of 114 mL min^-1). Furthermore, our electrochemical bromination method offered a high apparent current efficiency (ACE) of 276.6% and a low energy consumption (EC) of 4.54 × 10^-3 kWh gCOD^-1 after 40 min of electrolysis time, indicating that this process was suitable for phenol wastewater treatment.

Fabrication and characterization of Ti/polyaniline-Co/PbO2-Co for efficient electrochemical degradation of cephalexin in secondary effluents

The traditional interlayer of PbO₂ electrode possessed many problems, such as short service lifetime and limited specific surface area. Herein, a novel and efficient Ti/polyaniline-Co/PbO₂-Co electrode was conctructed employing cyclic voltammetry to introduce a Co-doped polyaniline interlayer and anodic electrodeposition to synthetize a β-PbO₂-Co active layer. Compared with pristine PbO₂ electrode, Ti/polyaniline-Co/PbO₂-Co exhibited more compact crystalline shape and higher active sites amounts. Pratically, the electrochemical degradation of 5 mg L^-1 cephalexin in real secondary effluents was effectively achieved by the novel anode with 87.42% cephalexin removal and 71.8% COD mineralization after 120 min of 15 mA cm^-2 electrolysis. The hydroxyl radical production and electrochemical stability were increased by 3.16 and 3.27 times respectively. The cephalexin degradation pathway was investigated by combining a density functional theory-based theoretical approach and LC-QTrap-MS/MS. The most likely cleavage point of the β-lactam ring was the O=C-N bond, whose attack would produce small molecular compounds containing the thiazole and 4, 6-thiazine rings. Further oxidation produced inorganic ions; quantitative investigations indicated the amino groups to undergo decomposition to form aqueous NH₄⁺, which was further oxidized to NO₃^-. The accumulation of NO₃^- and SO₄^2-, combined with a decrease in toxicity toward Escherichia coli, demonstrated the efficient mineralization of cephalexin on the Ti/polyaniline-Co/PbO₂-Co electrode.

Electrochemical degradation of antibiotic enoxacin using a novel PbO2 electrode with a graphene nanoplatelets inter-layer: Characteristics, efficiency and mechanism

A novel PbO₂ electrode was fabricated by adding graphene nanoplatelets (GNP) inter-layer into β-PbO₂ active layer (called GNP-PbO₂) and utilized to degradation of antibiotic enoxacin (ENO). The GNP-PbO₂ electrode had a much rougher surface than the typical PbO₂ electrode, with smaller crystal size and lower charge-transfer resistance at the electrode/electrolyte interface. Notably, the GNP inter-layer increased the oxygen evolution potential of PbO₂ electrode (2.05 V vs. SCE), which was very beneficial to inhibit oxygen evolution and promote ·OH production. The relatively best operating parameters for ENO removal and energy efficiency were current density of 20 mA cm^-2, initial pH of 7, initial ENO concentration of 100 mg L^-1 and electrode distance of 4 cm. Furthermore, indirect radical oxidation was found to be the main way during electrolysis process. Based on the observed analysis of intermediate products, the main reaction pathways of ENO included hydroxylation, defluorination and piperazine ring-opening. Finally, combinating with the electro-oxidation capability, stability and safety evaluation, we can conclude that GNP-PbO₂ is a promising anode for treatment of various organic pollutants in wastewater.