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Sludge management is an integral process of an effluent treatment plant (ETP). This study aimed at using the electro-Fenton (EF) process for pretreatment of a cattle-based slaughterhouse ETP sludge to enhance biogas production from anaerobic digestion. EF-oxidation experiments were conducted in 0.5 L beakers with mild-steel electrodes, to study the effect of factors, viz., H2O2 concentration, current density and reaction time on soluble chemical oxygen demand (sCOD) concentration, soluble extracellular polymeric substances (sEPS) concentration and volatile suspended solids (VSS) removal efficiency. This was followed by the quantification of biogas production from the raw and pretreated sludge in anaerobic digestion (AD). Experimental conditions for the EF process were optimized using response surface methodology (RSM). At optimized experimental conditions, EF pretreatment resulted in an increase in sCOD and sEPS concentrations, from 0.91 g/L to 6.1 g/L and 0.18 g/L to 1.4 g/L, respectively. VSS removal efficiency was 68.1%. Batch anaerobic digestion studies demonstrated an enhancement in the specific biogas yield, from 110 NmL/g-VS to 460 NmL/g-VS. [ABSTRACT FROM AUTHOR]

As an easily obtained organic waste, by-product acetic acid could be an appropriate co-substrate with blue algae wastes (increase C/N ratio of substrates) for co-fermentation of PHA production. However, there are still acrylic acid and other chemicals in by-product acetic acid, which could cause severe inhibition for fermenting microorganisms during PHA production process. The current study represented that alkali pretreatment (pH level of 12) is a more favorable method compared with thermal pretreatment (80 ℃ for 30 min) for breaking cell walls of blue algae. It seemed that there was no synergistic effect of the combination of thermal and alkali pretreatment methods (temperature of 80 ℃ and pH level of 12). Optimal parameters during electro-fenton process for removal of inhibitors in by-product acetic acid were under current of 0.5 A, pH level of 3 and reaction time of 120 min. Both the highest dry weight of PHA and PHA concentration were achieved by applying blue algae and by-product acetic acid (after pretreatment) as co-substrates (mixed ratio of 3:1, stirring speed of 200 r/min, 24 h), indicating that using by-product acetic acid (after pretreatment) as co-substrate could increase C/N ratio and promote PHA production successfully. The current study could offer new insights for improving PHA production by co-fermentation. [Display omitted] • Alkali pretreatment is a more favorable method compared with thermal pretreatment. • There was no synergistic effect of the combination of thermal and alkali pretreatment. • Optimal parameters for removal of inhibitors in by-product acetic acid were determined. • By-product acetic acid (after pretreatment) as co-substrate could promote PHA production. [ABSTRACT FROM AUTHOR]

Electrochemical advanced oxidation processes are the most promising methods for destroying and degrading organic and inorganic pollutants present in produced water effluents. This study presents the electro‐oxidation process using graphite electrodes and electro‐Fenton process using iron electrodes for the treatment of real produced water. The effect of operating parameters such as current density on chemical oxygen demand (COD) removal efficiency was addressed. The result showed that electro‐Fenton process was more efficient than electro‐oxidation process where it gave 98% as maximum COD removal efficiency with energy consumption of 1.9 kWh/dm3 at H2O2 concentration of 12 mM, current density of 10 mA/cm2, temperature of 25°C, pH of 3, and treatment time of 80 min compared with 96.9% as maximum COD removal efficiency with energy consumption of 3 kWh/dm3 at pH of 6, current density of 10 mA/cm2, temperature of 40°C, and reaction time of 80 min when using electro‐oxidation process. These results demonstrated that electrochemical technologies are very promising methods for the treatment of produced water from oil/gas industry, so it can be safely disposed of or effectively reused for injection and irrigation. [ABSTRACT FROM AUTHOR]

Redwater is a highly toxic waste generated during the purification of 2,4,6-trinitrotoluene (TNT), one of the most widely used military explosives. Redwater treatment is difficult because of its high chemical oxygen demand (COD) and strong red color. In this study, we present a comprehensive study on the treatment of the actual TNT redwater by a combination of chemical coagulation and electro-Fenton process. The pretreatment by traditional coagulation using poly-aluminum chloride (PAC) was investigated at different operation conditions of solution pH (4–11), PAC concentration (500–3500 mg/L), flocculant concentration (0–3.5 mg/L), times for coagulation (0–7 min) and flocculation (0–4 min), and stirring speed (100–700 rpm). This pretreatment could removal 52.84% of COD, 53.22% of color, 36.76% of TSS, and 25.88% of total nitrogen under optimal conditions (i.e., pH 7.0, PAC dosage of 2500 mg/L, anion flocculant dosage of 1.25 mg/L, coagulation time of 4 min, flocculation time of 1 min, and stirring speed of 500 rpm). The pretreated redwater was then subjected to an electro-Fenton process using Pt/Ti as anode and carbon felt as the cathode. The effects of solution pH (2–6), iron content (0.05–1 mM), current intensity (8.33–33.33 mA/cm2) and reaction times (0–200 min) on the electro-Fenton treatment were investigated. Under optimal condition (i.e., pH 3.0, Fe(II) concentration of 0.1 mM, current intensity of 16.67 mA/cm2, and reaction time of 120 min), the removal efficiency reached 87.07, 96.2, 72.94, and 50.26% for COD, color, TSS, and total nitrogen, respectively. UV-Vis spectroscopy results confirmed the role of electro-Fenton for the effective removal of aromatic nitro compounds in the redwater. These results suggest that the combination of coagulation and electro-Fenton process could be a promising technology for treating TNT redwater. [ABSTRACT FROM AUTHOR]

The electro-Fenton process is based on the generation of hydroxyl radicals (OH•) from hydroxide peroxide (H2O2) generated in situ by an oxygen reduction reaction (ORR). Catalysts based on carbon gels have aroused the interest of researchers as ORR catalysts due to their textural, chemical and even electrical properties. In this work, we synthesized metal-free electrocatalysts based on carbon gels doped with graphene oxide, which were conformed to a working electrode. The catalysts were prepared from organic-gel-based inks using painted (brush) and screen-printed methods free of binders. These new methods of electrode preparation were compared with the conventional pasted method on graphite supports using a binder. All these materials were tested for the electro-Fenton degradation of amoxicillin using a homemade magnetite coated with carbon (Fe3O4/C) as a Fenton catalyst. All catalysts showed very good behavior, but the one prepared by ink painting (brush) was the best one. The degradation of amoxicillin was close to 90% under optimal conditions ([Fe3O4/C] = 100 mg L−1, −0.55 V) with the catalyst prepared using the painted method with a brush, which had 14.59 mA cm−2 as JK and a H2O2 electrogeneration close to 100% at the optimal voltage. These results show that carbon-gel-based electrocatalysts are not only very good at this type of application but can be adhered to graphite free of binders, thus enhancing all their catalytic properties.

Abstract The use of microfluidic electrochemical reactors has been introduced several decades ago, but their application in the field of wastewater treatment is more recent (2010). The parallel development of electrochemical advanced oxidation processes (EAOPs) as promising technologies for effluent treatment make them good candidates to be implemented as thin film cells. This allows favoring the mass transfer, which is particularly interesting for heterogenous electro‐oxidation. Moreover, the energy requirement is reduced, while there is possibility to treat low‐conductivity solutions. This review intends to provide instructions on the main operating parameters to be optimized during the EAOPs treatment. Directions on engineering aspects have been given to overcome the main drawbacks of microreactors, such as fouling, scaling, and low treatment capacity, based on recent encouraging results given in literature. The promising development of hybrid processes that combine electroseparation with electroconversion would also benefit from such reactor designs.

Emerging contaminants (ECs) are concerned worldwide due to their ubiquitous, persistence, high toxicity and low treatment efficiency in conventional processes. Meanwhile, the electro-Fenton (EF) technique has gained significant attention owing to its high efficiency and environmental compatibility for the degradation of ECs. Nevertheless, the EF process has suffered low Faraday efficiency, high cost and poor mass transfer, mainly in the low efficiency of Fe3+/Fe2+ cycle, insufficient capacity of oxygen reduction and limitation of low pH. The ways to improve EF efficiency include adding catalysts, optimizing electrode materials, and coupling other technologies. Among them, cathode material is the key factor affecting EF efficiency. In recent years, researchers have carried out a large number of related studies, among which carbonaceous materials (CMs) have become one of the most promising EF cathode materials due to their excellent performance advantages. Many works on the preparation and modification of novel carbon materials have been paid attention to, but lacks a systematic review report summarizing carbon cathode in EF process. Aiming at this issue, this paper summarizes the modification of CMs to improve H 2 O 2 electrogeneration, strengthen Fe3+/Fe2+ cycle efficiency, and broaden pH window, respectively. Besides, the development of biochar materials is summarized, and the existing shortcomings and future development directions in the field of cathode EF are briefly discussed. [Display omitted] • Cathode material is a key factor affecting cathode electro-Fenton efficiency. • Various carbonaceous cathodes for emerging contaminants degradation are summarized. • Cathode modification for H 2 O 2 generation, Fe3+/Fe2+ cycle and pH window are reviewed. • The development of biochar materials as electro-Fenton cathode is introduced. • The shortcomings and future research directions for electro-Fenton are proposed. [ABSTRACT FROM AUTHOR]

Introducing the source, water quality and harm of landfill leachate, and introduces an u environment-friendly technology" 一electrochemical method, which can effectively remove refractory and toxic organics in landfill leachate・ Electrochemical technologies in landfill leachate treatment mainly include electrocoagulation, electrooxidation, electro・Fenton and coupling of electrochemical technology with other technologies. Their principles, characteristics, treatment effects and application prospects are analyzed. [ABSTRACT FROM AUTHOR]

In this study, Firstly, an Electro-Fenton (EF) system was established by converting the biochar products obtained by pyrolysis from the mixed furniture waste biomass to electrodes of without modification (raw) and after thermal modification. The modification variables of biochars were determined as: gas type (N2,CO2), temperature (500-900°C) and time (1-4 h). In the EF system, the effects of modified biochar electrodes used as cathodes on peroxide production-current efficiency (CE) and dye removal efficiency were examined and the most effective biochar electrode and modification conditions were determined. In the study, pH:3, EF time: 0.5 hours, cathodic potential:2 V, catalyst (FeSO4) concentration:0.2 mM, electrolyte (Na2SO4) concentration: 50 mM as EF conditions and Astrazon blue aqueous solution (50 mg/L) were chosen as a model contaminant. Among the electrodes, the most effective electrode was determined as the electrode (CO2-700-1), which was thermally modified in CO2 gas at 700°C for 1 hour. In addition, the energy efficiency and economic results of the study were analyzed. When the electrodes are evaluated in terms of treatment cost for 100% dye removal in the EF system, it is found that the treatment cost obtained with the electrode (CO2-700-1) is 68.2% lower than the raw electrode (N2-350-4). It was observed that the dye removal efficiency of the regenerated electrode did not change after 10 cycles. [ABSTRACT FROM AUTHOR]

The fast and complete removal of the anti-cancer drug cytarabine (CYT) from water was studied, for the first time, by the electro-Fenton process using a BDD anode and carbon felt cathode. A catalytic amount (10−4 M) of ferrous iron was initially added to the solution as catalyst and it was electrochemically regenerated in the process. Complete degradation of 0.1 mM (24.3 mg L−1) CYT was achieved quickly in 15 min at 300 mA constant current electrolysis by hydroxyl radicals (●OH) electrocatalytically generated in the system. Almost complete mineralization (91.14% TOC removal) of the solution was obtained after 4 h of treatment. The mineralization current efficiency (MCE) and energy consumption (EC) during the mineralization process were evaluated. The absolute (second order) rate constant for the hydroxylation reaction of CYT by hydroxyl radicals was assessed by applying the competition kinetics method and found to be 5.35 × 109 M−1 s−1. The formation and evolution of oxidation reaction intermediates, short-chain carboxylic acids and inorganic ions were identified by gas chromatography-mass spectrometry, high performance liquid chromatography and ion chromatography analyses, respectively. Based on the identified intermediate and end-products, a plausible mineralization pathway for the oxidation of CYT by hydroxyl radicals is proposed. [ABSTRACT FROM AUTHOR]

The negative environmental impact by the presence of organic contaminants in industrial and domestic effluents requires the development of treatment technologies. In this work, recent advances of three important electrochemical advanced oxidation processes (EAOPs) are presented. The review focuses on recent electro-oxidation (EO), electro-Fenton (EF), and photoassisted electro-Fenton (PA-EF) studies aimed to treat effluents contaminated with dyes, pharmaceuticals, and pesticides. The fundamentals of the three EAOPs are briefly described in the first part of the corresponding section. Later, changes in degradation with increasing current and pH are presented. Then, the use of different electrode materials involved in the electrochemical generation of •OH radicals is discussed showing the superiority of BDD. Approaches such as the way in which iron is added for the EF and PA-EF processes as well as different irradiation sources for PA-EF are also examined and finally, recently reported hybrid systems, as well as novel arrangements and electrochemical reactors, are presented along with information on energy consumption and the intermediates produced during the EO, EF, and PA-EF treatments. From the literature review, the EO process proved to be more efficient for simpler chemical organic molecules, while for more complex molecules the EF and PA-EF processes seem to be more suitable. [ABSTRACT FROM AUTHOR]

A weak aspect of the electro-Fenton (EF) oxidation of contaminants is the dependence of the Fenton reaction on acidic pH values. Therefore, the rationale of this work was to develop a novel catalyst capable of promoting the EF oxidation process at near-neutral and basic pH values. In this framework, rhombohedral FeCO3 was synthesized hydrothermally and used as a catalyst in the EF oxidation of p-benzoquinone (BQ). The catalyst was characterized using various surface and spectroscopic methods. Moreover, the effects of applied current (100–500 mA), time (1–9 h), catalyst dosage (0.25–1.00 g L−1), and initial concentration of BQ (0.50–1.00 mM) on the total organic carbon removal efficiency were determined. The results indicated that a 400 mA current was sufficient for a 95% total organic carbon removal and that the increase in catalyst dosage had a positive effect on the mineralization of BQ. It was determined that at pH 3, FeCO3 behaved like a homogeneous catalyst by releasing Fe3+ ions; whereas, at the pH range of 5–7, it shifted to a homogeneous/heterogeneous catalyst. At pH 9, it worked solely as a heterogeneous catalyst due to the decrease of Fe ions passing into the solution. Finally, the spent catalyst did not undergo structural deformations after the EF treatment at higher pH values and could be regenerated and used several times [ABSTRACT FROM AUTHOR]

This article introduces the basic principles and characteristics of the electro-Fenton (EF) process in detail, clarifies that cathode materials and metal catalysts are important components of the EF process, focuses on the types and modification methods of cathode materials and catalysts, and analyzes working current, electrolyte pH, air volume and other parameters on the effect of EF treatment. Finally, the application of EF process in dye wastewater treatment and possible technological breakthroughs are prospected. [ABSTRACT FROM AUTHOR]

Anionic surfactant wastewater has an irreversible effect on aquatic animals and plants. In this paper, the oxidation of sodium dodecylbenzene sulfonate (SDBS) by electro-Fenton system was researched. The results demonstrated that HO2· had a weak ability to oxidize SDBS; ·OH was the primary active substance for oxidizing SDBS. The broken bond sites of SDBS molecules oxidized by the active substances were analyzed by using the concept density functional theory. The calculation results indicated that ·OH initially attacked the C3-C11 bond in the SDBS molecule, and then ·OH underwent addition reactions, forming two typical structures: aromatic sodium p-hydroxybenzene sulfonate and aliphatic linear alkanes. Phenol and sodium dodecyl sulfate (SDS) were selected to study their oxidation behaviors in the electro-Fenton system. It can reflect the oxidation process of the products after the SDBS molecule was broken. The main active substance for oxidizing phenol in the electro-Fenton cathode chamber was ·OH, but the main active substance for oxidizing SDS was HO2·. Unlike the ·OH produced by the cathode, the Pt(·OH) produced by the anode had no effect on the removal of SDBS. Nevertheless, Pt(·OH) exhibited an excellent oxidation effect on SDBS bond-breaking products. The research results clarified the mechanisms of SDBS oxidation in electro-Fenton system and the direction of regulation for the reaction path. It is believed that promoting the ·OH generated at the cathode makes SDBS bond breakage a key step in the electro-Fenton oxidation of SDBS. It provided a theoretical basis for enhancing the current efficiency of the system. [ABSTRACT FROM AUTHOR]

Water pollution and the lack of access to clean water are general global problems that result from the expansion of industrial and agricultural activities. Petroleum refinery wastewaters are considered as a major challenge to the environment and their treatment is mandatory. The present work investigated the removal of chemical oxygen demand (COD) from petroleum refinery effluents generated from the Al-Dewaniya petroleum refinery plant located in Iraq by utilizing a novel graphite-graphite electro-Fenton (EF) system. The electrochemical reactor was a tubular type with a cylindrical cathode made from porous graphite and concentric porous graphite rode acts as an anode. By adopting the response surface methodology (RSM), the impacts of different operating variables on the COD removal were investigated. The optimal conditions were a current density of 25 mA/cm2, FeSO4 concentration of 1.4 mM, and electrolysis time of 90 minutes, which resulted in the COD removal efficiency (RE%) of 99% at a specific energy consumption (SEC) of 10.34 kWh/kg COD. The results indicated that both current density and concentration of FeSO4 have a major impact on the elimination of COD, while time has a minor effect. The adequacy of the model equation was demonstrated by its high R2 value (0.987). The present work demonstrated that the graphite-graphite EF system could be considered as an effective approach for removing of COD from petroleum refinery wastewaters. [ABSTRACT FROM AUTHOR]

The electro-Fenton process (EF) has faced major challenges, including mass transfer limitations. When the targeted pollutants are present in water at very low concentrations, the degradation kinetics are slower than desired, which leads to high energy consumption. To overcome this drawback, coupled adsorption on activated carbon (AC) and the EF process can be performed. Therefore, the compounds can be preconcentrated on AC before elimination by the EF process. As such, in this study, batch experiments were conducted using low-cost granular activated carbon (GAC) packed in a stainless-steel mesh for the adsorption of caffeine. Once saturated, GAC is used as a cathode during the EF process, where the adsorption capacity is regenerated. This approach allows the regeneration of the AC for multiple cycles and the degradation of the desorbed compounds. The EF process was studied to this end, for the purposes of the removal of caffeine as a model compound. The main goals of this work are (i) to study the removal of caffeine from water in three different matrices and (ii) to regenerate GAC by using the EF process. The results reported in this study show that it is possible to achieve caffeine degradation up to 95%, 100%, and 100%, and a mineralization up to 70%, 72%, and 76% in pure water, simulated wastewater, and wastewater effluent, respectively. In the regeneration process, total elimination of the desorbed caffeine was achieved, and a regeneration efficiency of 50% was obtained for the first cycle. The results confirm the ability of the EF process to achieve regeneration of AC loaded with caffeine. [ABSTRACT FROM AUTHOR]

Iron alginate beads (Fe-Alg) were prepared, characterized and implemented for the degradation of amoxicillin (AMX) by the heterogeneous electro-Fenton process using a graphite cathode recovered from used batteries. Scanning electron microscopy (SEM) showed that (Fe-Alg) beads have a spherical shape and the results of energy dispersive spectrometric (EDS) revealed the presence of iron in (Fe-Alg). Optimization of the operating parameters showed that a complete degradation of AMX was achieved within 90 min of heterogeneous electro-Fenton treatment by operating under these conditions: initial AMX concentration: 0.0136 mM, I = 600 mA, [Na2SO4] = 50 mM, pH = 3, T = 25 °C, ω = 360 rpm. The corresponding chemical oxygen demand (COD) abatement was 50%. Increasing the contact time increased the COD abatement to 85.71%, after 150 min of heterogeneous electro-Fenton treatment. The results of the kinetic study by using nonlinear methods demonstrated that the reaction of AMX degradation obeyed to a pseudo-second-order kinetic. Iron content of 4.63% w/w was determined by the acid digestion method. After 5 cycles of use, the Alg-Fe catalyst depletion was only 8%. Biodegradability was remarkably improved after electro-Fenton pretreatment, since it increased from 0.07 initially to 0.36. The heterogeneous electro-Fenton process had efficiently eliminated AMX and it increased the biodegradability of the treated solution. HIGHLIGHTS The heterogeneous electro-Fenton process was used for the degradation of amoxicillin (AMX).; The Fe-Alg catalyst has proved its efficiency and stability.; The kinetic model of the AMX degradation obeyed to a pseudo-second-order.; The COD abatement and removal yield of AMX were 50% and 100% respectively.; The heterogeneous electro-Fenton pretreatment improved the biodegradability of the AMX from 0.07 initially to 0.36.;

[Display omitted] • Dual-functional electrocatalyst of defective cobalt-nitrogen-doped porous carbon was synthesized. • Carbon defects and graphitic nitrogen improved the selectivity and yield of H 2 O 2. • Co-doping of Co and pyridinic-N contribute to the decomposition of H 2 O 2 into ·OH. • Co 1 /Zn 1 -NPC has excellent stability and stable treatment performance in electro-Fenton. Tetracycline hydrochloride (TC) is one of the organic pollutants that can be consistently monitored in the aquatic environment and pose a great threat to the environment. The development of a bifunctional electro-Fenton (EF) catalyst capable of in situ H 2 O 2 production and decomposition to ·OH to degrade the pollutant is an efficient and green approach to deal with antibiotic pollution. The bifunctional catalysts Co, N double doped defective carbon materials were prepared by pyrolysis ball milling method using zeolite imidazolium ester skeleton structural materials (ZIFs) series materials as precursors, which showed more than 80% selectivity to H 2 O 2 and could basically remove TC within 120 min in EF system. Carbon defects and graphitic nitrogen can effectively improve the selectivity and yield of H 2 O 2 , while graphitization degree improves the charge transfer rate, the doping of Co and pyridinic-N contribute to the decomposition of H 2 O 2 into ·OH. The active species present in the Co 1 /Zn 1 -NPC/EF system is ·OH, and factors such as coexisting ions, humic acid and water quality have little effect on the efficiency of the degradation of TC in the Co 1 /Zn 1 -NPC/EF system, whereas Co 1 /Zn 1 -NPC electrocatalytic catalyst has excellent stability and stable treatment performance for a wide range of pollutants, as well as being an environmentally friendly green catalyst without metal leaching. Furthermore, the possible pathways and the toxicity hazard of TC degradation were proposed. The bifunctional electrocatalyst prepared in this research provides a novel strategy for the green and efficient treatment of pollutants in wastewater. [ABSTRACT FROM AUTHOR]

• A metal-free floating electrochemical advanced oxidation system was established. • The floating electrode can efficiently produce H 2 O 2 without aeration. • The oxygenated graphene aerogel catalyst promoted the activation H 2 O 2 to ·OH. • The primary activation sites were identified as the = O and –COOH groups. • The system exhibited wide pH application range and good practicality. Metal-free electro-Fenton (EF) are a promising technology for environmental remediation. This paper reports a novel EF modified with oxygenated graphene aerogel used as a floating electrode for efficient degradation of bisphenol A (BPA) through improved H 2 O 2 yield combined with activation of hydroxyl radical (·OH) production. Impressively, the floating configuration of the electrodes allowed oxygen from the air to diffuse naturally into the reaction interface, reducing additional aeration energy consumption. The current efficiency of the floating system for H 2 O 2 production was 40 times higher than the conventional vertical mode. The pollutant degradation trend exhibited a positive correlation with the ·OH production performance of the electrode. The modified catalyst system achieved the highest ·OH yield of 76.48 μM within 60 min, which was 2.72 times greater than that of the catalyst-free (28.10 μM) and 2.06 times higher than that of the unmodified catalyst (37.19 μM). Experiments and theoretical calculations indicated that the oxygen-containing functional groups introduced the graphene skeleton created new sites for in situ activation of electrogenerated H 2 O 2 , resulting in increased ·OH production. The primary activation sites were identified as the = O and –COOH groups, with the = O edges playing a particularly significant role. This system offers long-lasting stability and avoids secondary pollution, making it ideal for green environmental remediation compared to the traditional EF process. [ABSTRACT FROM AUTHOR]

Designing a membrane electrode with high activity and anti-scaling ability in a wide pH range is crucial to the development of flow-through electro-Fenton system. Herein, we reported a novel porous membrane composed of ultrafine FeMn bimetallic nanoparticles anchored in nitrogen-doped carbon nanofibers (FeMn/N-CNF) obtained through a facile electrospinning-carbonization process. The strong metal-support interaction (SMSI) phenomena including carbon encapsulation structure and electron transfer from metal to N-CNF, beneficial to the intrinsic activities, were successfully induced by the enhanced interfacial metal-nitrogen bonding in FeMn/N-CNF. Microstructural characterizations and leaching test revealed that the SMSI encapsulation structure could promote the formation of ultrafine FeMn nanoparticles in N-CNF during the high-temperature carbonization process and prevent leaching of active Fe/Mn metals into solution across a wide pH range. The constructed gravity-driven flow-through electro-Fenton system based on a FeMn/N-CNF cathode membrane exhibited superior performance to generate H 2 O 2 (36.23 mmol L−1 h−1) and subsequent activate H 2 O 2 decomposition to hydroxyl radicals (0.1024 min−1), achieving remarkable degradation efficiencies of 96.8%, 92.3%, and 90.3% within 60 min for Rhodamine B, Tetracycline, and Methyl Orange, respectively. Furthermore, the FeMn/N-CNF membrane filter demonstrated good pH adaptability, excellent cycle stability and anti-scaling ability during the degradation process. This work offers a viable avenue to enhance degradation performance and environmental robustness for practical water decontamination via achieving SMSI effect in carbon-supported electro-Fenton membranes. [Display omitted] • Ultrafine nanoparticles anchored in N-CNF porous membrane is simply prepared. • Strong metal-support interaction (SMSI) is existed in FeMn/N-CNF. • Gravity-driven flow-through electro-Fenton FeMn/N-CNF system is constructed. • Such system achieves efficiently degradation for various pollutants in wide pH range. • FeMn/N-CNF filter exhibits excellent anti-scaling ability and mechanical stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solvothermal method followed by calcination treatment under different temperature was facilely utilized to synthesize Fe-NiCo 2 O 4 nanosheets with different crystallinity. • The resultant Fe-NiCo 2 O 4 show similar nanosheets with porous structure. • As catalysts for OER, the Fe-NiCo 2 O 4 nanosheets obtained as 300 ℃ exhibit superior electrical conductivity and catalytic activity to the other studied Fe-NiCo 2 O 4 and RuO 2. • Additionally, the outstanding stability was observed for the optimized Fe-NiCo 2 O 4 nanosheets. Recently, the electro-Fenton (EF) process by coupling cathodic two-electron oxygen reduction reaction (2e- ORR) with anodic oxygen evolution reaction (OER) has emerged as a potentially viable technology, while the sluggish OER is the main bottleneck. As promising OER catalysts, the amorphous and crystal phases of spinel oxides display high activities and electrical conductivity, respectively. Efforts to produce amorphous/crystal spinel oxides have progressed slowly, and how an amorphous/crystal structure benefits the catalytic performances remains elusive. Herein, Fe-doped NiCo 2 O 4 (Fe-NiCo 2 O 4) was used as a model catalyst to explore the effect mechanism of crystallinity controlled by annealing temperature on OER performance. The results display that the Fe-NiCo 2 O 4 obtained at 300 ℃ shows amorphous/crystal structure, which facilitates the active site exposure and the charge transfer, leading to superior OER activity and catalytic stability. Based on the crystallinity regulation of OER catalysts, we propose an anodic optimized strategy to upgrade the EF-related processes by effectively providing O 2 produced in the anode. [ABSTRACT FROM AUTHOR]

The presence of polyethylene terephthalate (PET) microplastics (MPs) in waters has posed considerable threats to the environment and humans. In this work, a heterogeneous electro-Fenton-activated persulfate oxidation system with the FeS 2 -modified carbon felt as the cathode (abbreviated as EF-SR) was proposed for the efficient degradation of PET MPs. The results showed that i) the EF-SR system removed 91.3 ± 0.9 % of 100 mg/L PET after 12 h at the expense of trace loss (< 0.07 %) of [Fe] and that ii) dissolved organics and nanoplastics were first formed and accumulated and then quickly consumed in the EF-SR system. In addition to the destruction of the surface morphology, considerable changes in the surface structure of PET were noted after EF-SR treatment. On top of the emergence of the O-H bond, the ratio of C-O/C=O to C-C increased from 0.25 to 0.35, proving the rupture of the backbone of PET and the formation of oxygen-containing groups on the PET surface. With the verified involvement and contributions of SO 4 •- and •OH, three possible paths were proposed to describe the degradation of PET towards complete mineralization through chain cleavage and oxidation in the EF-SR system. [Display omitted] • EF-SR achieved 91.3 ± 0.9 % removal of 100 mg/L PET after 12 h at trace loss of FeS 2. • Dissolved organics and nanoplastics were formed/accumulated and quickly consumed. • Considerable changes in surface morphology and structure of PET MPs were noted. • 3 possible paths were proposed to describe PET degradation/mineralization in EF-SR. [ABSTRACT FROM AUTHOR]

A hydrophobic Cu 2 O cathode (Cu x O-L) was designed to solve the challenge of low oxidation ability in electro-Fenton (EF) for treating emerging pollutants. This fabrication process involved forming Cu(OH) 2 nanorods by oxidizing copper foam (Cu-F) with (NH 4) 2 S 2 O 8 , followed by coating them with glucose via hydrothermal treatment. Finally, a self-assembled monolayer of 1-octadecanethiol was introduced to create a low-surface-energy, functionalized Cu x O-L cathode. Results exhibited an approximately 7.9-fold increase in hydroxyl radical (·OH) generation compared to the initial Cu-F. This enhancement was attributed to two key factors: (Ⅰ) the superior O 2 -capturing ability of Cu x O-L cathode, which led to high H 2 O 2 production due to a 2 nm thick hydrophobic gas layer facilitated O 2 -capturing; (Ⅱ) a relative high concentration of Cu+ at the Cu x O-L cathode promoted the activation of H 2 O 2 into·OH. In addition, the performance of EF with the Cu x O-L cathode using sulfathiazole (STZ) as a model pollutant was evaluated. This study offers valuable insights into the design of O 2 -capturing cathodes in EF processes, particularly for treating emerging organic pollutants. [Display omitted] • Bio-inspired hydrophobic Cu 2 O cathode (Cu x O-L) was designed； • ·OH concentration on Cu x O-L cathode increased approximately 7.9-fold; • A 2-3 nm gas film enhances the cathode's O 2 capturing; • Cu+ was active site for H 2 O 2 formation, favoring its activation into·OH. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enhancing electro-Fenton performance by adjusting catalyst pore size was proposed. • Synchronized enhancement of H 2 O 2 production and Fe2+ reduction was achieved. • 0.1 mM Fe2+ was adequate to accomplish 20 mg/L sulfamethazine degradation at pH 3–7. • The energy consumption was 0.87 kWh per gram of removed total organic carbon. • Finite element simulation revealed the accelerated mass transfer on optimized pores. Electro-Fenton (EF) is efficient in decontaminating refractory pollutants but high consumption of Fe2+ as a hydrogen peroxide (H 2 O 2) activator increases its operation cost. Designing EF system with accelerated Fe2+/Fe3+ cycling is crucial for both hydroxyl radical generation and Fe2+ dosage reduction. Here, we employed pore structure tailoring engineering to optimize pore size of mesoporous hollow carbon spheres (MHCS), achieving an improved H 2 O 2 electro-synthesis and Fe2+ regeneration. MHCS with 8 nm surface pores yielded 81.33 mmol g catalyst −1h−1 H 2 O 2 and realized 51.2 % Fe2+ regeneration efficiency, enabling complete removal of sulfamethazine with a low energy consumption of just 0.87 kWh g−1 total organic carbon. Finite element simulation revealed that MHCS with 8 nm surface pores favored mass transfer, facilitating solute diffusion to the electrode's active layer for reaction. In addition, EF system maintained a degradation efficiency of 90 % after five cycles of operation and was effective in removing various types of pollutants, which implies its application potential. This work demonstrated a novel catalyst structure optimization strategy to both enhance Fe2+ regeneration and improve EF performance, offering an energy-efficient water purification solution. [ABSTRACT FROM AUTHOR]

Based on the principle of electro-Fenton (EF) reaction, this investigation was experimented to treat copper (Cu) and lead (Pb), which are lower mobile in dredged sediment in a self-made EF reactor, and simultaneously dewater it. The results of the study showed that when Fe2+ concentration was 1 mM, the initial current density was 10.4 mA/cm2, and the initial pH was neutral, after 24 h, the conversion of the stable form to the activated state of Cu and Pb were 24.77 % and 68.42 %, respectively. Further, the water content of the dredged sediment was significantly reduced from the initial 58–26 % after the EF. The mechanism experiment confirmed that ·OH and SO 4 ·- were the main factors for converting Cu and Pb forms, destroying the EPS structure in the dredged sediment and decomposing its main components, improving the dewatering property of the dredged sediment. In addition, EF treatment did not decrease microbial diversity in dredged sediments, and Flavobacterium and Bacillus , which are beneficial for agricultural production, became featured taxa after EF. This study provided a new perspective that transforms Cu and Pb into a more easily removable form with simultaneous efficient dewatering, which is more conducive to subsequent conventional treatment of the dredged sediment. • Using a novel EF reactor to treat HMs in dredged sediment and simultaneous dewatering. • Cu and Pb from oxidizable and residual states to available fraction after EF. • OH and SO 4 ·− were responsible for the transformation of Cu and Pb forms. • Reduction in water content of dredged sediment from 58.4 % to 26.3 % after EF. • Firmicutes and Actinobacteria were feature taxa after EF. [ABSTRACT FROM AUTHOR]

Electrochemical advanced oxidation processes (EAOPs) are particularly notable for their environmental friendliness, efficiency, and lack of secondary contamination. These approaches are primarily founded on the electrochemical production of powerful oxidants, exemplified by ·OH, ·O 2 -, 1O 2 and SO 4 ·−. The article commences with a thorough review of the process mechanisms of EAOPs, followed by a detailed summary of the common free radical detection methods utilized in EAOPs. Subsequently, we examine the prevalent non-active anode materials in EAOPs (BDD, SnO 2 , PbO 2), as well as the particle electrodes in solution, encompassing their preparation methods and respective performances. In addition, the application of EAOPs in the removal of organic and inorganic pollutants, desulfurization of coal and minerals, and sludge treatment was also summarized. Finally, certain limitations of EAOPs research are presented, along with some recommendations for future development. [Display omitted] • Detailed summarize the detection of free radicals in EAOPs. • Three non-active electrodes used in EAOPs were completely introduced. • EAOPs used in pollutant removal, desulfurization and sludge treatment were presented. [ABSTRACT FROM AUTHOR]

The electro-Fenton oxidation process for the degradation of organic pollutants in recalcitrant wastewater has garnered significant attention and research efforts in the field of advanced water treatment. This is primarily due to its highly effective degradation capabilities and the advantages it offers, including the avoidance of unsafe transportation and storage of hydrogen peroxide (H 2 O 2). However, challenges such as relatively high energy consumption, complex operational requirements, and limited operational stability continue to pose significant economic constraints on the widespread application of electro-Fenton technology in water purification. In this study, we employed a secondary hydrothermal method to construct a multi-layered CNT/MoS 2 /Fe 3 O 4 composite heterostructure in situ. Leveraging the synergistic effects of the introduced variable valence elements, Fe and Mo, and the interconnected multi-layered membrane structure, the CNT/MoS 2 /Fe 3 O 4 electro-Fenton membrane holds promise in a permeable filtration system. Under the conditions of a current density of 1.50 mA/cm² and an electrolyte concentration of 0.50 mol/L, the CNT/MoS 2 /Fe 3 O 4 composite membrane exhibited a degradation efficiency of over 90.00 % for 100.00 mg/L RhB within 10 minutes, and the degradation rate approached nearly 99.00 % at 60 minutes. Furthermore, the degradation efficiency for various recalcitrant organic dye wastewaters, including phenol, methyl orange, and methylene blue, could be maintained at levels ranging from 80.00 % to 97.00 %. Particularly, under optimized operating conditions, the specific energy consumption (EC) for the CNT/MoS 2 /Fe 3 O 4 membrane process was measured at 0.60±0.01 kWh/m³, showcasing exceptionally low energy consumption characteristics. In conclusion, it is expected to contribute to the reduction of the overall consumption of heterogeneous electro-Fenton oxidation systems and enhance their operational efficiency. This innovative approach represents a significant advancement in the field, offering the potential to address the economic limitations associated with electro-Fenton technology in water quality purification. [Display omitted] • In-situ interconnected CNT/MoS 2 /Fe 3 O 4 heterostructures were constructed via secondary hydrothermal method. • The CNT/MoS 2 /Fe 3 O 4 composite membrane achieved a RhB degradation rate of nearly 99.00 %. • The degradation efficiency for dyes like phenol, methyl orange and methylene blue was 80.00–97.00 %. • Optimized CNT/MoS 2 /Fe 3 O 4 membrane process had low energy consumption of only 0.60±0.01kWh/m³. [ABSTRACT FROM AUTHOR]

The removal of the bisphenol A (BPA) from sulphate-rich wastewater has been investigated using an electro-Fenton oxidation system with metal-oxide carbon nanostructured anode. The process produces highly oxidizing species, including hydroxyl radicals on the anode surface and bulk solution via an electrochemically monitored Fenton reaction. The focus of this research is the detection of BPA intermediates and the prediction of the BPA degradation mechanism during the electro-Fenton process using the SnO 2 -MWCNT nanostructured anode. In accordance to detected reactive oxygen species, BPA intermediates, and their respective peak area profiles, two primary degradation pathways can be defined. Whether direct cleavage of BPA precedes hydroxylation, oxidation, and dealkylation, or vice versa, the resulting products consist of catechols, dicatechols, quinones, aldehydes, carboxylic acids, and ultimately carbon dioxide and water. To ensure a comprehensive understanding, the impact of applied current, catalyst concentration, and treatment duration on degradation and mineralization efficiency, as well as degradation kinetics, was investigated. The degradation of BPA was found to follow pseudo-first-order reaction kinetics. The results showed that the degradation of BPA was attributed to the co-action of electro-Fenton oxidation and electrochemical oxidation. This study confirms the eco-friendly nature of the electro-Fenton process by demonstrating the toxicity of intermediaries formed during BPA treatment. • BPA degradation was studied via electro-Fenton using SnO 2 -MWCNT nanostructured anode. • BPA intermediates have been identified and two reaction pathways have been proposed. • Toxicity predictions have confirmed the formation of non-toxic intermediates. • BPA oxidation by OH∙ follows pseudo-first-order kinetics. [ABSTRACT FROM AUTHOR]

[Display omitted] • The release of Li+ were mainly triggered by the rapid attack of a large amount of OH. • Electrochemical leaching was a chemical reaction control model. • Dissolution of each metal ion was feasible in this leaching environment. In recent years, lithium-ion batteries have been increasingly used in electric and hybrid vehicles. It is anticipated that the first lithium-ion batteries will be discarded at the height of their useful lives in 2025, so developing an effective and ecologically friendly recycling process is essential. In this study, an electrochemical cathode synergism is proposed for the electro-catalyzed oxidation of lithium nickel cobalt manganese oxide powder and lithium iron phosphate powder to extract metal. The oxidation of Fe2+ and the release of Li+ (98 %) in LiFePO 4 and the leaching of Ni (92 %), Co (91 %), Mn (94 %) and Li (97 %) from its NCM523 were mainly triggered by the rapid attack of a large amount of OH during advanced oxidation. The leaching kinetic analysis showed that the leaching system for electrochemical leaching of binary and ternary cathode materials was a chemical reaction control model, and the leaching thermodynamic analysis showed that the dissolution of each metal ion was feasible in this leaching environment. The suggested recycling technique utilizes fewer chemicals and generates less waste when compared to previous recycling techniques. The method offers a fresh approach to environmentally friendly recycling for spent lithium-ion battery leaching and recycling. [ABSTRACT FROM AUTHOR]

[Display omitted] • Macroscopic ordered 3D-FeO/C electrode was constructed by 3D printing technology. • 3D-FeO/C can efficiently degrade antibiotic drug and pharmaceutical wastewater. • Confinement effect and enhanced mass transfer synergistically act on EF reaction. • Degradation mechanism of ornidazole and pharmaceutical wastewater was revealed. In this study, researchers constructed a monolithic 3D-FeO/C electrode with a macro-ordered pore structure using direct-write 3D printing technology. Experimental results showed that the 3D-FeO/C electrode possessed excellent degradation performance for ornidazole (ONZ) (complete degradation within 120 min) and pharmaceutical wastewater (51.13 % in TOC and 63.72 % in COD removal within 420 min). The detailed reaction mechanism of the EF system was revealed through characterization analysis, mass transfer simulation, and experimental results, in which the excellent EF performance is mainly due to the confinement effect of FeO active sites encapsulated in the carbon layer, as well as the enhancement of mass transfer induced by 3D printing macro-ordered structure network. In addition, the degradation pathway of ONZ, the toxicity of its degradation intermediates, and the degradation pathway of actual pharmaceutical wastewater were revealed in detail. This study proposes a new 3D printing method to enhance the mass transfer of electrode materials in EF systems, which has good potential for application to real wastewater. [ABSTRACT FROM AUTHOR]

Electrochemical oxidation (EO), electro-Fenton (EF), and photoelectro-Fenton (PEF) with a BDD anode have been comparatively assessed to remediate solutions of Red CL and/or Red WB azo dyes from real raw water. For the EO process in 50 mM Na 2 SO 4 at pH 3.0, the main oxidant was the heterogeneous •OH generated at the anode, whereas in EF and PEF, the cathodic production of H 2 O 2 and the addition of 0.50 mM Fe2+ catalyst additionally originated homogeneous •OH that enhanced the oxidation of organics. In PEF, the solution was illuminated with a 6 W UVA light. An almost total discoloration was always found operating with a 1:1 mixture of 200 mg L−1 of both dyes in 60 min, whose efficiency increased in the order of EO < EF < PEF. The HPLC analysis of the dye mixture treated by PEF disclosed that its degradation process agreed with its discoloration. A high 74% of COD was reduced due to the oxidative action of hydroxyl radicals and the photolysis of final Fe(III)-carboxylate species with UVA irradiation. The process was accompanied by an energy consumption of 0.76 kWh (g COD)−1, a value similar to the energy consumed by the applied UVA light. [Display omitted] • Remediate concentrated solutions of Red CL and/or Red WB azo dyes used in the tannery industry from real raw water. • In all these treatments, the loss of color was increased by raising the current density (j) and the dye content. • An almost total discoloration was always found operating with a 1:1 mixture of 200 mg L−1 of both dyes in 60 min. • The HPLC analysis of the dye mixture treated by PEF disclosed that its degradation process. [ABSTRACT FROM AUTHOR]

[Display omitted] • The BWBC*@Ni-F exhibited excellent H 2 O 2 accumulation of 303 mg L-1. • The DCEF system efficiently degraded contaminants in a wide pH range of 3–11. • The DCEF system displayed high TOC removal efficiency and low energy consumption. • The BCO 2 and C=O groups played a pivotal role in the activation of H 2 O 2. Electro-Fenton (EF) process stands out as an energy-efficient and highly promising advanced oxidation technology for organic contaminants degradation. However, achieving optimal heterogeneous catalytic conditions for simultaneous H 2 O 2 generation and spontaneous Fe2+ regeneration poses difficulties in conventional EF. This is due to the electric potential difference between H 2 O 2 generation and Fe2+ regeneration at a single cathode. Therefore, the boron doped biochar modified dual-cathode EF (DCEF) system was designed in this work to overcome the defect of conventional EF system, which not only demonstrated outstanding accumulation of H 2 O 2 (>300 mg L-1) but also exhibited a remarkable capability of degradation (>90 %). Furthermore, the system could also adapt to a broad pH range of 3–11. The superior doxycycline (DOX) degradation efficiency of DCEF system could be attributed to the dominant role played by C=O and BCO 2 groups in the activation of H 2 O 2 and subsequently generating reactive oxygen species (ROSs), as revealed by XPS analysis and DFT calculation. In addition, the DCEF system achieved an impressive TOC removal efficiency of 70.5 % and a minimal energy consumption (EC) of 0.32 kWh (g TOC)-1. Therefore, this work introduced a DCEF system to address the challenges of conventional EF system, which shed light on the design of wastewater treatment technology and lied the groundwork for a strategy of resource utilization. [ABSTRACT FROM AUTHOR]

• A new photovoltaic electric Fenton (PVEF) system was developed with a low energy consumption of 5.5 kWh/kg. • The performance of PVEF systems in different types of wastewater were evaluated. • The PVEF can replace the deep treatment process in wastewater treatment plants, reducing energy consumption by 803 kWh and carbon emissions by 305 t. In the current mainstream wastewater treatment technologies, electro-Fenton (EF) has been widely used as an advanced oxidation process for achieving deep degradation of organic pollutants without secondary pollution. However, the high energy consumption of EF has hindered its development to a certain extent. In this study, a photovoltaic(PV)-driven EF system is developed to incorporate photovoltaic energy into the EF system to efficiently degrade organic matter in sewage and reduce energy consumption and operating costs of sewage treatment. To fully evaluate the performance of the photovoltaic drive electro-Fenton degradation sewage (PVEF) system, we investigated the effects of system configuration, current density, and stirring speed on the degradation of methyl orange (AO7) by the PVEF system. After determining the optimal experimental conditions, we explored the treatment efficiency and feasibility of the system for three different types of pollutants. Laboratory scale experiments also confirmed the critical effects of current density and stirring speed on the energy consumption of degradation. Finally, PVEF technology replaces the advanced treatment process in the sewage treatment plant, and the energy consumption model is established based on the local dye sewage plant in Chengdu to evaluate its applicability in different regions. The experimental results show that the dual-cathode system reduced energy consumption by 24.9 % and increased degradation efficiency by 30 % compared to the conventional EF system·H 2 O 2 generated under the optimal conditions is fully utilized, resulting in a removal rate of more than 95 % in 20 min for AO7. The optimal energy efficiency condition is determined when the current density is 3 mA/cm2 and the stirring speed is 1000 rpm, which reduces the system's energy consumption. The degradation test results of different pollutants show that the system can realize the degradation of various pollutants. The simulation results of the sewage plant scale show that the PVEF system can reduce carbon emission by 305 t instead of the traditional advanced treatment process. [ABSTRACT FROM AUTHOR]

Electrochemical advanced oxidation processes (EAOPs) based on natural air diffusion electrode (NADE) promise efficient and affordable advanced oxidation water purification, but the sustainable operation of such reaction systems remains challenging due to severe cathode electrowetting. Herein, a novel floating cathode (FC) composed of a stable hydrophobic three-phase interface was established by designing a flexible catalytic layer of FC. This innovative electrode configuration could effectively prolong the service life of the cathode by mitigating the interference of H 2 bubbles from the hydrogen evolution reaction (HER), and the H 2 O 2 production rate reached 37.59 mg h−1·cm−2 and realize a long-term stable operation for 10 h. Additionally, an FC/carbon felt (CF) dual-cathode electro-Fenton system was constructed for in situ sulfamethoxazole (SMX) degradation. Efficient H 2 O 2 production on FC and Fe(III) reduction on CF were synchronously achieved, attaining excellent degradation efficiency for both SMX (ca. 100%) with 2.5 mg L−1 of Fe(Ⅱ) injection. For real wastewater, the COD removal of the FC/CF dual-cathode electro-Fenton system was stabilized at exceeding 75%. The practical application potential of the FC/CF dual-cathode electro-Fenton system was also demonstrated for the treatment of actual landfill leachate in continuous flow mode. This work provides a valuable path for constructing a sustainable dual-cathode electro-Fenton system for actual wastewater treatment. [Display omitted] • Floating cathodes facilitate sustainable electrochemical production of H 2 O 2. • The moderate loading of PTFE reinforced the anti-wettability of FC cathode. • The stable operation of FC attributed to its resistance to H 2 bubbles from HER. • Effective SMX removal was achieved in the FC/CF dual-cathode electro-Fenton system. [ABSTRACT FROM AUTHOR]

Electro-Fenton (EF) can in-situ produce H 2 O 2 and effectively activate H 2 O 2 to generate powerful reactive species for the destruction of contaminants under acidic conditions, however, the production of iron-containing sludge and requirement of low working pH significantly hinder its practical application. Herein, a novel Cu, N co-doped carbon (Cu–N@C) with metal organic framework (MOF) as a precursor was constructed and adopted for the elimination of pefloxacin (PEF) in the heterogeneous electro-Fenton (HEF) process. PEF could be almost completely removed within 1 h and total organic carbon (TOC) removal efficiency was 48.57% within 6 h. Meanwhile, Cu–N@C had good repeatability and environmental adaptability, it can still maintain excellent catalytic performance after 10 cycles, and it exhibited satisfactory remediation performance in simulated water matrix. In addition, the HEF process catalyzed by Cu–N@C also showed satisfactory degradation effect on other organic pollutants including atrazine, methylene blue, and chlorotetracycline. Under the action of impressed current, the HEF system could generate H 2 O 2 in-situ, and the active species could be generated in the redox cycle of Cu0/Cu1+/Cu2+. Electron paramagnetic resonance and quenching experiments confirmed that •OH was the dominant active species in the degradation of organic compounds. The degradation process of PEF was studied by mass spectrometry analysis of intermediate products. This study provided a simple method to prepare MOF-based electrocatalyst, which exhibits promising application potential for treatment wastewater. [Display omitted] • Cu–N@C-700 showed satisfactory reactivity to remove PEF in the HEF process. • •OH was the dominant active species in the degradation of organic pollutants. • Redox cycle of Cu0/Cu1+/Cu2+ is favorable to catalyze H 2 O 2 for •OH formation. • Cu–N@C-700 exhibited excellent applicability and stability. [ABSTRACT FROM AUTHOR]

Rational reuse of municipal sludge to produce electro-Fenton electrode can not only save resources, but also produce superior peroxide and degradation pollutants simultaneously. Herein, a novel electro-Fenton electrode derived from sludge biochar loaded on Ni foam (SBC@Ni) was constructed via high temperature pyrolysis and chemical coating for efficient H 2 O 2 evolution and pollutant degradation. Systematic experiments and density functional theory calculations (DFT calculation) explained that the production of graphite C and graphite N during high-temperature pyrolysis of municipal sludge can greatly enhance the oxygen reduction reaction of SBC@Ni electrode and promote the evolution of H 2 O 2. And the hybrid heterojunctions, such as FeP, also played a key role in electrocatalytic processes. Notably, the electrode still exhibited excellent performance after 1000 linear scans and 12 h of continuous current stimulation, which demonstrated the excellent stability of the electrode. Moreover, SBC@Ni electrode can not only effectively oxidize 4-chlorophenol through the electro-Fenton effect, but also fully mineralize organic matter, indicating promising environmental application. The free radical quenching experiment also revealed that the ·OH is the main active species for 4-CP degradation in SBC@Ni electro-Fenton system. [Display omitted] • The Ni biochar electrode effectively promoted the electro-Fenton reaction. • High-temperature pyrolysis contributed to the formation of Graphite-C/N. • DFT proved that Graphite-C/N can accelerate the 2e– ORR reaction. • Sludge biochar electrodes can efficiently and stably degrade and mineralize 4-CP. [ABSTRACT FROM AUTHOR]

• A novel sustainable electro-Fenton system is successfully constructed. • NPC-D/MoS 2 NA can simultaneously remove Cr (VI) and contaminants. • Dual-site NPC-D cathode has high selectivity of 2e− ORR for H 2 O 2 production. • Electric field-driven MoVI/MoIV conversion rapidly promotes the redox processes. • The synergistic redox mechanism of electron-Fenton system is deeply unveiled. Simultaneous removal of heavy metals and organic contaminants remains a substantial challenge in the electro-Fenton (EF) system. Herein, we propose a facile and sustainable "iron-free" EF system capable of simultaneously removing hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP). The system comprises a nitrogen-doped and carbon-deficient porous carbon (dual-site NPC-D) cathode coupled with a MoS 2 nanoarray promoter (MoS 2 NA). The NPC-D/MoS 2 NA system exhibits exceptional synergistic electrocatalytic activity, with removal rates for Cr (VI) and 4-CP that are 20.3 and 4.4 times faster, respectively, compared to the NPC-D system. Mechanistic studies show that the dual-site structure of NPC-D cathode favors the two-electron oxygen reduction pathway with a selectivity of 81 %. Furthermore, an electric field-driven uncoordinated Mo valence state conversion of MoS 2 NA enchances the generation of dynamic singlet oxygen and hydroxyl radicals. Notably, this system shows outstanding recyclability, resilience in real wastewater, and sustainability during a 3 L scale-up operation, while effectively mitigating toxicity. Overall, this study presents an effective approach for treating multiple-component wastewater and highlights the importance of structure-activity correlation in synergistic electrocatalysis. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H 2 O 2) synthesis by electrochemical two-electron oxygen reduction has garnered increasing interest as a wide range of potential applications. Gas diffusion electrodes (GDEs) can effectively promote the H 2 O 2 production efficiency by overcoming the oxygen mass transfer limitations but strongly influenced by the electrowetting process along the long-term operation. In this study, the effect of trans -electrode pressure (TEP) of GDE cathode on the electrowetting process was further elucidated. We controlled the TEP values of four types of GDEs: two Ni-based GDEs and two carbon cloth GDEs prepared by hot-pressing or brushing carbon black. SBA-15 was further used to regulate the microstructure of one Ni-based GDE. It was found that an optimal range of TEP occurred for all tested GDEs in terms of the max. concentration, the yield efficiency, the energy consumption, and the stability because TEP may change the triple-phase interface and influence the anti-electrowetting effect. The porosity of hot-pressed Ni GDE can maintain the TEP window and thus enhance the production of H 2 O 2 , likely via creating oxygen-containing functional groups and a bimodal pore structure on the electrode, revealed with several characterization techniques including SEM, CA, XPS, Raman spectra, CV and EIS. The porous Ni GDE presented an efficient and stable production of H 2 O 2 for 10 cycles: yielding H 2 O 2 at 4393.2–4602.2 mmol m−2 h−1 with current efficiencies of 94.2–98.7%. The best accumulated H 2 O 2 concentration can reach up to 3.58 ωt% H 2 O 2 at 10 h. The results provide an important reference for the industrial scaleup of electro-production of H 2 O 2 with GDEs. [Display omitted] • A comparison on working pressure windows of Ni and carbon-cloth based electrodes. • Effect of working pressure on flooding performance and H 2 O 2 production also were explored. • The trend of cell voltage, energy consumption and their cost were evaluated. • Deep in-sighting of Ni-based hot-pressing GDE electrode by XPS, Raman, CV and EIS. • Optimal H 2 O 2 production reached up to 13 g/L at 2 h and current efficiency was stable at about 98.7%. [ABSTRACT FROM AUTHOR]

Carbamazepine (CBZ) is one of the most stable pharmaceutical compounds that is commonly found in the effluents of wastewater treatment plants (WWTP). In this context, this contribution presents a comprehensive analysis of the different operating parameters of a flow-through and pilot-scale cylindrical reactor for hydrogen peroxide (H 2 O 2) generation, in which the degradation of CBZ takes place. The electrochemical system was evaluated using 8 L of electrolytes prepared with tap water in the presence of methanol as dissolved organic matter or spiked tertiary WWTP effluent, at a volumetric flow of 7 L min−1. This reactor (i) improves the mass transport due to its flow-through configuration using fibrous quasi-three-dimensional carbon felt electrodes, (ii) operates without an external oxygen supply to promote the H 2 O 2 electrosynthesis because it is incorporated by a jet aerator (iii) achieves the Fenton reaction at circumneutral pH due to Fe(II) disposition from a cation exchange resin. At first, the carbonaceous materials were electrochemically characterized by cyclic voltammetry measurements. Different operating parameters were evaluated by factorial design methodologies for H 2 O 2 generation, energetic consumption and CBZ removal. The application of a current density of 1.4 mA cm−2, in a cathode-anode-cathode arrangement immersed in a 120 mM ionic strength solution, allowed to obtain up to 6.4 mg H 2 O 2 L−1 after 40 min, consuming 0.44 kWh m−3. Later, the Fenton reaction was validated by a florescence study, and by the incorporation of 0.75 g of granular activated carbon and 5 g of Fe(II) loaded resin, CBZ abatement yields of 68 % and 32 % were obtained using a synthetic solution and a spiked tertiary WWTP effluent, respectively, and up to 28 % of the dissolved total organic carbon was removed. Finally, an analysis of the stability of the carbon felt electrodes was tackled using scanning electron microscopy and energy-dispersive X-ray spectroscopy. [Display omitted] • Electrochemical H 2 O 2 generation and CBZ degradation for real aqueous solutions. • Flow-through electrochemical reactor equipped with affordable carbon felt electrodes at pilot-scale. • Higher CBZ removal in tap water compared with CBZ spiked tertiary effluent. • The study contributes to bridge the gap between laboratory scale assays and real working conditions. [ABSTRACT FROM AUTHOR]

This presents the efficacy of a 3D-ElectroFenton (3D-EF) reactor with active perovskite/carbon black/PTFE microelectrodes for the removal of carbamazepine (CZP) present in wastewater. Incorporating particle microelectrodes in the reactor enhanced the electron transfer and improved the electrocatalytic efficiency, leading to a more effective CZP removal. The optimal operational conditions were meticulously determined, including current intensity (0.05 – 0.3 A) and particle loading (0 – 1.5 g), to optimize the process and minimize energy consumption. The findings reveal that a current intensity of 0.2 A was the most effective, achieving 90% of CZP removal in 60 min and 3.86 kWh/mg of CZP. A higher current intensity of 0.3 A significantly increased the energy consumption (6.02 kWh/mg of CZP) for a total and faster CZP removal. The 3D-EF reactor was also operated continuously with ultrapure water and real urban wastewater fortified with CZP. A remarkable 62% CZP removal after 96 h on continuous operation was achieved with urban wastewater. Physicochemical and electrochemical characterization of microelectrodes demonstrated their high mechanical integrity and chemical stability. Our study underscores the potential of a 3D-EF system as a promising advanced oxidation process to address the continuous removal of antidepressant carbamazepine as one of the more resistant micropollutants of emerging concern in wastewater treatment, offering hope for a more efficient and sustainable future. • An innovative configuration of a continuous 3D electro-Fenton (EF) reactor has been proposed. • Perovskite/Carbon Black microelectrodes enhanced the efficiency of an EF reactor. • Complete carbamazepine removal by 3D-EF process under neutral pH. • 65% carbamazepine removal in a real wastewater for 96 hours of treatment. [ABSTRACT FROM AUTHOR]

Electro-Fenton (EF) technology has been recognized as a highly promising electrochemical advanced oxidation process. Promoting effective contact between active species and contaminant is crucial in electrocatalysis. Herein, we had innovatively designed a unique nanozymes in the form of hemp-ball-like structures, consist of the uniform growth of Fe 3 O 4 nanoparticles on nitrogen-doped nano hollow carbon spheres (NHCS). This catalyst was employed in a flow-through EF system with carbon felt (CF) filters serving as the work electrode. The active sites were fully exposed through the ultradispersed Fe 3 O 4 nanoparticles, and the NHCS facilitated efficient cycling of Fe3+/Fe2+. The results showed that the generation capacity of hydroxyl radicals (·OH) was enhanced, and the oxidation flux reached 370.080 mg h−1m−2 with low energy consumption. The superiority of the hollow carrier was proved by the degradation results and COMSOL calculation for various carbon carriers. Moreover, the active catalyst exhibited adaptability in complex water matrices. This study offers a new perspective to synergize nanomaterials, EF reactions and flow-type systems. • A hemp-ball-like catalyst was fabricated with Fe 3 O 4 nanoparticle and nanoscale NHCS. • The different carbon supports was used to reveal the influence of structure. • COMSOL was used to reveal the mass transfer of the membrane interior. • NHCS-Fe 3 O 4 membrane exhibited exceptional performance and durability. • NHCS-Fe 3 O 4 membrane was high environmental adaption in the actual water. [ABSTRACT FROM AUTHOR]

The Electro-Fenton (EF) process has emerged as a promising technology for pollutant removal. However, the EF process requires the use of two catalysts: one acting as an electrocatalyst for the reduction of oxygen to H2O2 and another Fenton-type catalyst for the generation of ·OH radicals from H2O2. Thus, the search for materials with bifunctionality for both processes is required for a practical and real application of the EF process. Thus, in this work, bifunctional electrocatalysts were obtained via doping carbon microspheres with Eco-graphene, a form of graphene produced using eco-friendly methods. The incorporation of Eco-graphene offers numerous advantages to the catalysts, including enhanced conductivity, leading to more efficient electron transfer during the Electro-Fenton process. Additionally, the synthesis induced structural defects that serve as active sites, promoting the direct production of hydroxyl radicals via a 3-electron pathway. Furthermore, the spherical morphology of carbon xerogels enhances the accessibility of the reagents to the active sites. This combination of factors results in the effective degradation of Tetracycline (TTC) using metal-free catalysts in the Electro-Fenton process, achieving up to an impressive 83% degradation without requiring any other external or additional catalyst.

In this study, the electro-Fenton (EF) method was applied to remove total organic carbon (TOC) from the pesticide production wastewater containing tricyclazole (TC). Statistical Taguchi method was used to optimize the treatment performance. Analysis of variance (ANOVA) indicated that the polynomial regression model fitted experimental data with R2 of 0.969. The optimal conditions for eliminating 75.4% TOC and 93.7% TC were 0.2 mM of Fe2+, 990 mg/L of Na2SO4, 180 min of reaction time at pH 3 with 2.22 mA/cm2 of current density. The removal of TC present in the wastewater followed the first-order reaction kinetic model (R2 = 0.993); while that was the second-order kinetic model in the case of the TOC removal (R2 = 0.903). In addition, the experimental results and theory approaches (density functional theory and natural bond orbital calculations) also showed the C-N bond breaking and nitrate ions cleavage to ammonia. Acute toxicity of the pesticide wastewater after treatment (PWAT) on microcrustaceans showed that the treated wastewater still exhibited high toxicity against D. magna, with LC50 values of 3.84%, 2.68%, 2.05%, and 1.78% at 24 h, 48 h, 72 h, and 96 h, respectively. HIGHLIGHTS Electro-Fenton (EF) was employed to remove TOC and tricylazole from real pesticide wastewater.; Taguchi approach (L27) had been developed on five factors of EF on TOC removal.; ANOVA showed a well-fitted polynomial regression model with R2 of 0.969.; The nitrogen minerals reached 25.3 as explained by DFT/NBO calculations.; Cost analysis, kinetic reaction of EF process and bioassay toxicological test also evaluated.;

Development of cathode materials with high activity, stability, and wide operating pH range is crucial for electro-Fenton reactions. Herein, mesoporous sulfur-modified metal oxides were coated onto stainless steel meshes and applied as a cathode to promote in-situ generation of H2O2 for electro-Fenton processes. Different mesoporous metal oxides with and without sulfur-modification were synthesized using Fe, Ni, and Zn precursors to investigate the effect of sulfur doping. Among them, sulfur doped Fe2O3 showed the best electrocatalytic performance, and it was attributed to several factors such as large specific surface area, high-efficiency oxygen reduction reaction activity, and enhanced electron/charge transfer. The effect of operational parameters such as applied voltage, catalyst dosage, initial pH, initial concentration of phenol, and electrolyte concentration on the catalytic performance was investigated in terms of degradation efficiencies and rate constants. The results indicate that for high concentration 100 ppm phenol solution, 78% removal efficiency with a rate constant of 0.186 h−1 was achieved with sulfur-doped Fe2O3 on stainless steel mesh electrode under optimal conditions in 8 h. This cathode worked effectively in a wide pH range (3–10) due to its pH self-control ability and exhibited superior stability and reusability with insignificant deterioration in the catalytic activity. This study offers an alternative approach to fabricate electrocatalysts with low-cost sulfur-doped metal oxides for electro-Fenton systems.