Heterogeneous electro-Fenton System Research Articles

Cobalt based bimetallic catalysts for heterogeneous electro-Fenton adapting to vary pH for HEDP and MIT degradation

ABSTRACT Most of the materials studied as catalysts in the electro-Fenton system are variants of iron oxide or iron hydroxide. However, iron-based catalysts often exhibit weak catalytic capabilities under neutral and alkaline conditions. In this work, we synthesized three cobalt based bimetallic oxides, Co2CuOx, Co2AlOx, and Co2NiOx, using hydrothermal method and evaluated them as catalysts for the heterogeneous electro-Fenton system to remove 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) and Methylisothiazolinone [2-methyl-4-isothiazolin-3-one] (MIT). Co2NiOx has the highest catalytic degradation activity for HEDP, and Co2CuOx has the best catalytic degradation effect for MIT. Based on characterization results of the catalysts, the reasons for the differences in the pollutant removal efficiency were analysed, and the optimal pH for the three cobalt based oxides to remove HEDP and MIT was investigated. The results showed that the optimal pH values of the three cobalt based bimetallic oxides are not only influenced by the second metal type, but also by the properties of pollutants. Therefore, suitable cobalt based catalysts can be selected based on the different properties of pollutants, or the composition of cobalt based catalysts can be adjusted to meet the different pH requirements of target wastewater. The three cobalt based bimetallic oxides exhibited good degradation of HEDP and MIT under neutral conditions, which to some extent solved the problem of narrow pH range in the practical application of the electro-Fenton process.

Insight on magnetic nitrogen-doped graphene oxide composite electrode constructing heterogeneous Electro-Fenton system for treating organophosphorus pesticide wastewater

The treatment of organic phosphorus pesticide (OPP) wastewater faces challenges such as incomplete degradation and low reaction efficiency. While heterogeneous electro-Fenton (Hetero-EF) has emerged as the preferred technology for addressing these issues due to its high treatment efficiency, further optimization is still necessary. This study used a one-pot hydrothermal method to prepare magnetic nitrogen-doped graphene oxide (Fe3O4@N-GO) composite electrodes to construct a novel Hetero-EF system. Dimethoate (DIM) was chosen as the representative pollutant to investigate the effects of parameters such as current density, pH, electrode spacing, and loading amount on degradation efficiency. The results demonstrated complete degradation of DIM within 40 min. Density functional theory (DFT) calculations and intermediate product analysis revealed that the reactive sites for DIM degradation were the P=S and P=S bonds, involving both hydrolysis and •OH pathways, with a decrease in toxicity of degradation products observed. Compared to graphite electrodes, Fe3O4@N-GO composite electrodes significantly increased H2O2 production, achieving complete DIM degradation even after 5 cycles, with a phosphate conversion rate of 30–40 %. This study highlights the innovative strategy of the Hetero-EF system in its significant application value for OPP treatment.

Levofloxacin degradation in a heterogeneous electro-Fenton system with an FeOCl/MoS2 composite catalyst

To overcome the drawbacks of traditional electro-Fenton (EF) technology, such as acidic conditions (pH 3–4) and the extensive leaching of Fe ions, FeOCl/MoS2 composites were synthesized through a simple calcination method.

High-valent metal-oxo species heterogeneous activation making use of MoS2 in a novel Electro-Fenton System: pH-independent catalytic environment and nonradical generation mechanism

High-valent metal-oxo (HVMO) species emerge as promising reactive species for decontamination owing to its long and stable life expectancy. Nevertheless, it is challenging to generate HVMO using solid-phase catalysts, considering high orbital occupancy of transition metals disfavor electron migrations. Herein, we propose a universal MoS2 co-catalyst capable of inducing electronic delocalization in a layered double hydroxide composite of Co and Fe, in turn acting as a HVMO evolution booster. In this heterogeneous electro-Fenton system, the spontaneous generation of high-valent cobalt-oxo (CoIV = O) and high-valent iron-oxo (FeIV = O, FeV = O and FeVI = O) was facilitated by MoS2 configuration, accepting self-motivated electron transfer, pivotally shifting d-band centers and lowering the energy barrier by 2.81–11.62 eV. Noteworthy, HVMO production at pH 9 compensated for the sluggish Fenton’s reaction rate in alkaline, increasing over 20 % contaminant decay and shortening treatment time by ∼ 4 h even in practical aqueous matrices (tap and river water). Depending upon the pH, HVMO exhibits a distinct degradation pathway of norfloxacin (model organics), compared with other reactive oxygen species, yielding different intermediates of varying toxicity levels. This study comprehensively showcased the feasibility of activating HVMO generation by MoS2 in heterogeneous mediation, unveiled a pH-independent strategy to degrade pollutants, thereby expanding the applicability of Fenton’s technology.

Accelerated removal of sulfadiazine by heterogeneous electro-Fenton system with Pt-FeOX/graphene single-atom alloy cathodes

Heterogeneous electro-Fenton (EF) process is emerging as an attractive treatment technology for removal of sulfadiazine (SDZ), in which in situ generation of H2O2 and Fe(II) are crucial steps. In this study, Pt-FeOX/G was synthesized as a heterogeneous EF catalyst by incorporating Pt single atoms into a FeOX nanocrystal. The optimized Pt1-FeOX/G cathode exhibited an SDZ conversion of >90% within 30 min over a broad pH range (3–11). The Pt1-FeOX/G cathode under a strong alkaline medium exhibited very prominent selectivity to H2O2 via 2e− oxygen reduction reaction with a maximum H2O2 concentration of 211.93 mg L−1. The hydroxyl radicals in the cathodic chamber were mainly derived from the in situ conversion of generated H2O2 in the heterogeneous EF system. The structure-activity results of Pt-FeOX/G suggested that the SDZ removal efficiency was closely related to the decentralized morphology and electronic configuration of the Pt-FeOX microcrystalline structure. Three possible SDZ degradation pathways, dominated by S–N bond cleavage, were proposed based on the stage products. The toxicity of the major products was determined using the ecological structure-activity relationship model in conjunction with trophic aquatic organisms. This study demonstrated the feasibility of enhancing heterogeneous EF catalysis for antibiotic-polluted water using multifunctional single-atom alloy cathodes.

Enhanced electrocatalytic degradation of acid orange 7 by using double perovskite La2CoxNi1-xMnO6/nickel foam as the electro-Fenton cathodes

Adequate generation of hydrogen peroxide and its subsequent activation into reactive oxygen species (ROS) play a crucial role in the catalytic efficiency of heterogeneous electro-Fenton for the degradation of contaminants. Herein, a series of La2NiMnO6 double perovskite with Co doping (La2CoxNi1-xMnO6) were prepared by a facile sol-gel technique and applied as catalysts in heterogeneous electro-Fenton system to removal acid orange 7 (AO7). Nickel foam was chosen as the supporting substrate for the catalyst owing to its excellent physical properties to accelerate the conversion of O2 to H2O2. La2Co0.5Ni0.5MnO6 achieved 90.22 % of AO7 decomposition rate at 120 min via the heterogeneous electro-Fenton system, which was a significant improvement over the catalytic efficiency of both only NF and La2NiMnO6 electrodes. Further studies have shown that the introduction of Co could heighten the efficient redox recycling of Ni2+/Ni3+ and Mn3+/Mn4+ on the electrode surface, synergically facilitating the conversion of H2O2 to OH. Meanwhile, the three redox pairs (Ni2+/Ni3+, Mn3+/Mn4+ and Co2+/Co3+) also stimulated the production of superoxide radicals (O2−), which was also not negligible in enhancing degradation. Finally, the possible pathway and mechanism of the degradation of AO7 were proposed. This work demonstrates that La2CoxNi1-xMnO6/NF has the potential to be a satisfactory electrode for decomposition of organic dyes in aqueous solution.

Accelerating Fe(III)/Fe(II) redox cycling in heterogeneous electro-Fenton process via S/Cu-mediated electron donor-shuttle regime

In this study, we developed a Cu0.5Fe2.5S4 nanocatalyst through facile sulfidation of the Cu-MIL-88B(Fe) precursor to expedite surface Fe(III) reduction and enhance H2O2 activation in the heterogeneous electro-Fenton (HEF). The as-prepared catalyst possesses relatively large specific surface area and uniformly dispersed metal active sites. The Cu0.5Fe2.5S4-catalyzed HEF system allowed complete removal of naproxen with minimal metal leaching, surpassing that of Cu-MIL-88B(Fe) or Fe3S4. Quantitative XPS analysis, electrochemical characterization and density functional theory calculations reveal an electron donor-shuttle regime in which S2- and Cu species serve as the electron donor and shuttle, respectively. The Cu species significantly accelerate the internal electron transfer between S and Fe and mitigate the dissolution of the adjacent iron sites, securing the sustainable reducing capacity. Moreover, Cu0.5Fe2.5S4-based HEF exhibits great practicability for treatment of various organics in urban wastewater. This study opens new avenue for addressing the challenge of sluggish Fe(III)/Fe(II) cycling in HEF.

A magnetite catalysed heterogeneous solar photo electro-Fenton system enhanced with lanthanum doped bismuth ferrite photoanode for the degradation of aspirin in water

The effect of photoanode on a solar photo electro-Fenton system (SPEF) consisting of a magnetite nanoparticle catalyst impregnated carbon felt cathode is studied by coupling the SPEF system to a lanthanum-doped bismuth ferrite (La-BFO) photoanode. The resulting system, referred to as La-BFO /SPEF, was used in the degradation of acetyl salicylic acid in wastewater. The synthesised La-doped/undoped BFO photoanodes and magnetite nanoparticles were characterised with SEM, XRD and FTIR. The heterogeneous electro-Fenton system was prepared by attaching the magnetite nanoparticle to a carbon felt electrode through magnetisation. The effects of La dopant concentration in the photoanode material (doped and undoped BFO on a fluorine doped tin oxide substrate), pH values, current density and anodic oxidation contribution to the SPEF system were explored through parameters such as total organic carbon (TOC) measurements and mineralization current efficiency. A TOC removal of 68 % and 54 % was recorded for the La-doped photoanode (La-BFO/SPEF) and undoped system (BFO/SPEF) respectively, thus reflecting the contribution from the band gap tuning of the photoanode material. The predominant species in the degradation of acetyl salicylic acid were deduced by radical scavenging experiments. The coupling approach and the irradiation with visible light, enhanced the overall performance of the degradation system.

Heterogeneous electro-Fenton system using Fe-MOF as catalyst and electrocatalyst for degradation of pharmaceuticals

In recent years, heterogeneous electro-Fenton processes have gained considerable attention as an alternative to homogeneous processes. In this context, the aim of this study is the use of a commercial iron metal-organic framework (Fe-MOF), Basolite® F-300, as a base material for the design of a heterogeneous electro-Fenton treatment system for the removal of antipyrine. Initially, the catalyst was applied as powder in aqueous solution and three key parameters of the electro-Fenton process (pH, Fe-MOF concentration and current density) were evaluated and optimized by a Central Composite Design Face Centred (CCD-FC) using antipyrine removal and energy consumption as response functions. Near complete antipyrine removal (94%) was achieved under optimal conditions: pH 3, Fe-MOF 157.78 mg/L and current density 6.67 mA/cm2, obtaining an energy consumption of 0.29 W·h per mg of antipyrine removed. Later, two electrocatalysts (Fe-MOF functionalized cathodes), prepared by different Fe-MOF immobilisation approaches (composite of carbon black/polytetrafluoroethylene or by electrospinning on Ni foam), were synthesized. Their characterisation showed notable Fe-MOF incorporation into the material and favourable properties as electrocatalysts. Both Fe-MOF functionalized cathodes were evaluated in the removal of antipyrine at different pH (acidic and natural) and current density (27.78 and 55.56 mA/cm2), achieving in the best conditions removal levels around 80% in 1 h without any operational problems. In addition, several intermediates generated during the treatment were identified and their toxicity estimated. According to the obtained results, the degradation compounds have less toxicity than the parent compounds, confirming the effectiveness of the treatment.

Application of iron-intercalated graphite for modification of nickel foam cathode in heterogeneous electro-Fenton system: Bisphenol A removal from water at neutral pH

The presence of bisphenol A (BPA) in natural waters can be highly harmful due to its high persistence and adverse effects, raising concerns to remove this hazardous compound. Herein, an electro-Fenton system is proposed to eliminate BPA, wherein the iron source in the Fenton reaction is provided by its intercalation into the carbon layers of graphite. The produced heterogeneous catalyst was then coated onto the nickel foam serving as a cathode. The magnetic graphite intercalated compound (mGIC) and the modified cathode (before and after experiments) were characterized by FE-SEM, EDX, XPS, and XRD analyses. Some effective parameters, namely pH (3–9), current density (0–20 mA cm−2), and BPA concentration (0.5–20 mg L−1) were studied. At pH 3, the removal of BPA was 95.52%, and under neutral circumstances, the BPA and TOC removals were 85.70 and 58.12%, respectively at the initial BPA concentration of 10 mg L−1. The proposed system was also applied to several water sources spiked with BPA at the concentration of 5 mg L−1 under neutral pH, which exhibited considerable removal of 99.74%, 99.72%, and 92.70% for groundwater, municipal effluent wastewater, and tap water, respectively. The proposed system was applied for 15 consecutive cycles without showing significant changes in BPA removal, indicating its excellent stability and reusability. Furthermore, based on the analysis of intermediates, a possible decomposition pathway was proposed, indicating a reduction in overall toxicity. By using the proposed heterogeneous electro-Fenton system, iron waste is avoided, and operational costs of treatment can be reduced due to the absence of iron sludge production and catalyst loss.

Heterogeneous electro-Fenton system with Co/N-GO modified cathode to degrade phenolic organic pollutants: The main role of singlet oxygen

Heterogeneous electro-Fenton (hetero-EF) system has attracted much attention for the removal of refractory organic pollutants. In this study, hetero-EF for phenol degradation was constructed to use cobalt and nitrogen co-doped graphene (Co/N-GO) modified cathode. The microstructure and composition of the modified cathode material were explored using SEM, TEM, XPS, and XRD. Systematic investigation of the effects of various factors on phenol removal showed that the phenol removal rate could reach 97.00 % in the hetero-EF system by Co/N-GO within 4 h, and the substrate could be removed well in a wide pH range (3–9). The phenol removal rate was still up to 90.71 % after eight consecutive reaction cycles. Combined with the quenching test and EPR analysis, singlet oxygen (1O2) played a major role in the degradation of phenol. Further research revealed that •OH and •O2− were not only involved in oxidative degradation of pollutants, but also contributed to the production of 1O2. Meanwhile, dissolved oxygen (DO) also participated in the formation of 1O2. The study is beneficial to further develop the potential of hetero-EF system for environmental organic pollution remediation.

Accelerated electron transfer process via MOF-derived FeCo/C for enhanced degradation of antibiotic contaminants towards heterogeneous electro-Fenton system

The Fe(III) to Fe(II) process limits the rate of the electro-Fenton system. In this study, MIL-101(Fe) derived porous carbon skeleton-coated FeCo bimetallic catalyst Fe4/Co@PC-700 was prepared as a heterogeneous electro-Fenton (EF) catalytic process. The experimental results showed its good performance in catalytic removal of antibiotic contaminants, the rate constant of tetracycline (TC) degradation catalyzed by Fe4/Co@PC-700 was 8.93 times higher than that of Fe@PC-700 under the pH conditions of raw water (pH = 5.86), exhibited good removal of TC, oxytetracycline (OTC), hygromycin (CTC), chloramphenicol (CAP) and ciprofloxacin (CIP). It was shown that the introduction of Co promoted more Fe0 production, allowing the material to exhibit faster Fe(III)/Fe(II) cycling rates. 1O2 and high-priced metal oxygen species were identified as the main active species of the system, in addition to the analysis of possible degradation pathways and toxicity of intermediates of TC. Finally, the stability and adaptability of Fe4/Co@PC-700 and EF systems to different water matrices were evaluated, showing that Fe4/Co@PC-700 was easy to recover and could be applied to different water matrices. This study provides a reference for the design and system application of heterogeneous EF catalysts.

Enhanced oxidation and recovery of phosphorous from hypophosphite wastewater: Key role of heterogeneous E-Fenton system with MOFs derived hierarchical Mn-Fe@PC modified cathode

Hypophosphite has high solubility and stable chemical structure, however, the effective oxidation of hypophosphite wastewater with high purity phosphate by-product recovery remains a big challenge. In this work, hypophosphite was oxidized by heterogeneous Electro-Fenton system (hetero-EF) with Metal organic Frameworks (MOFs) derived Mn-Fe co-doped porous carbon (Mn-Fe@PC) modified cathode. The effects of cathode material, current intensity and pH value were investigated. The results indicated that the Mn-Fe@PC modified cathode performed much better on hypophosphite oxidation than Fe doped porous carbon (Fe@PC) or Mn doped porous carbon (Mn@PC) modified cathodes, and the optimal Mn/Fe doping ratio was 1: 2. In the hetero-EF system, H2PO2− (10 mM) was completely oxidized within 240 min at 10 mA/cm2 of current density and 3 of pH. The radical quenching experiments results indicated that •OH was the main active species on the oxidation of H2PO2− into H2PO4−. In addition, the actual wastewater tests confirmed the feasibility of recycling high-purity lithium iron phosphate and struvite from the phosphate solution after the oxidation of hypophosphite in hetero-EF oxidation process, which would provide a new green approach for recycling phosphorus from hypophosphite wastewater.

Efficient mineralization of coal pyrolysis wastewater in a heterogeneous electro-Fenton system using a novel Fe3O4-LaFeO3/C/GF heterojunction cathode

A bifunctional electro-Fenton (EF) cathode with Fe3O4-LaFeO3/C embedded graphite felt (GF) was synthesized through a hydrothermal process, which was used for in situ electrochemical formation of active oxygen species (ROS) for coal pyrolysis wastewater (CPW) removal. Experimental results illustrated that the mineralization efficiency of dimethylphenol (DMP) was achieved at 90.7 % within 150 min reaction. On the basis of quenching test and free radical detection, the ∙OH and ∙O2− were the detectable ROS in the hetero-EF system for DMP removal. Meanwhile, the formed oxygen vacancies (OVs) and the redox of Fe2+/Fe3+ promoted the oxygen adsorption and H2O2 activation. Density functional theory (DFT) calculations further discussed that the Fe3O4-LaFeO3 interface possessed more downward spin density of states in the conduction band, resulting in a higher total density of states (DOS) value near the Fermi level. Moreover, the Fe3O4-LaFeO3/C/GF cathode displayed good recyclability with low metal ion dissolution for 5 times (99.5 % DMP removal and 78.6 % TOC removal) and underlying actual CPW application potential (80.2 % of COD removal and 100 % of total phenol (Tph) removal). Overall, this work invented a novel and stable bifunctional cathode for the efficient removal of refractory CPW in the hetero-EF system.

Three-dimensional heterogeneous electro-Fenton system with reduced graphene oxide based particle electrode for Acyclovir removal

New pollutant pharmaceutical and personal care products (PPCPs), especially antiviral drugs, have received increasing attention not only due to their increase in usage after the outbreak of COVID-19 epidemics but also due to their adverse impacts on water ecological environment. Electro-Fenton technology is an effective method to remove PPCPs from water. Novel particle electrodes (MMT/rGO/Fe3O4) were synthesized by depositing Fe3O4 nanoparticles on reduced graphene oxide modified montmorillonite and acted as catalysts to promote oxidation performance in a three-dimensional electro-Fenton (3D-EF) system. The electrodes combined the catalytic property of Fe3O4, hydrophilicity of montmorillonite and electrical conductivity of graphene oxides, and applied for the degradation of Acyclovir (ACV) with high efficiency and ease of operation. At optimal condition, the degradation rate of ACV reached 100% within 120 min, and the applicable pH range could be 3 to 11 in the 3D-EF system. The stability and reusability of MMT/rGO/Fe3O4 particle electrodes were also studied, the removal rate of ACV remained at 92% after 10 cycles, which was just slightly lower than that of the first cycle. Potential degradation mechanisms were also proposed by methanol quenching tests and FT-ICR-MS.

In-situ cathode induction of HKUST-1-derived polyvalent copper oxides in electro-Fenton systems for effective sulfamethoxazole degradation

In this study, a graphite felt (GF) electrode material supporting a Cu-based catalyst (CuHDC-400/GF) was prepared by a hydrothermal process and subsequent heat treatment. A heterogeneous electro-Fenton (EF) system was built to investigate the degradation of sulfamethoxazole (SMX) by the composite cathode. Scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the physical and chemical properties of the composite cathode. The results show that the composite cathode CuHDC-400/GF has excellent catalytic performance, achieving 100 % removal of SMX (10 mg/L) within 45 min (aeration rate = 0.6 L min−1, current density = 5 mA cm−2, initial pH = 5.6). Furthermore, efficient removal of SMX can be achieved over a wide pH range (pH = 3–9). The electrode material can still efficiently degrade SMX after eight cycles. Compared with a heterogeneous EF system, in which the Cu catalyst was directly added to the reaction solution, using CuHDC-400/GF as the cathode realizes the in-situ catalysis of H2O2, leading to reduced catalyst consumption and enhanced electrode stability. The investigation of potential SMX degradation pathways and mechanisms revealed that the continuous production of active free radicals is facilitated by the redox cycle between CuⅠ and CuⅡ on the electrode surface, which can enable SMX degradation. Unlike the Fe-based Fenton reaction, the active superoxide radical O2– was identified as the major contributor to SMX degradation in this system, followed by the hydroxyl radical OH. The active sites for SMX degradation were predicted by density functional theory calculations. Combined with the measured mass/charge ratios, the possible degradation paths and intermediates of SMX were predicted. Furthermore, toxicity analysis shows that toxicity significantly declines after degradation. This work is expected to inspire subsequent research on heterogeneous EF cathode materials with high catalytic performance.

Two-dimensional manganese-iron bimetallic MOF-74 for electro-Fenton degradation of sulfamethoxazole

This study reported a novel application of Mn0.67Fe0.33-MOF-74 with two-dimensional (2D) morphology grown on carbon felt as a cathode for efficiently removing antibiotic sulfamethoxazole in the heterogeneous electro-Fenton system. Characterization demonstrated the successful synthesis of bimetallic MOF-74 by a simple one-step method. Electrochemical detection showed that the second metal addition and morphological change improved the electrochemical activity of the electrode and contributed to pollutant degradation. At pH 3 and 30 mA of current, the degradation efficiency of SMX reached 96% with 12.09 mg L−1 H2O2 and 0.21 mM ·OH detected in the system after 90 min. During the reaction, electron transfer between ≡FeII/III and ≡MnII/III promoted divalent metal ions regeneration, which ensured the continuation of the Fenton reaction. Two-dimensional structures exposed more active sites favoring ·OH production. The pathway of sulfamethoxazole degradation and the reaction mechanisms were proposed based on the intermediates identification by LC-MS and radical capture results. High degradation rates were still observed in tap and river water, revealing the potential of Mn0.67Fe0.33-MOF-74@CF for practical applications. This study provides a simple MOF-based cathode synthesis method, which enhances our understanding of constructing efficient electrocatalytic cathodes based on morphological design and multi-metal strategies.

Stable CuFeO/Kaolin-based catalytic particle electrode in 3D heterogeneous electro-Fenton system for orange G removal: Synthesis, performance and mechanism

Orange G is a kind of widely applied but environment-unfriendly dye. Three-dimensional heterogeneous electro-Fenton (3D/HEF), as a combination of three-dimensional electrochemical (3D/E) and heterogeneous electron-Fenton (HEF), having attracted more attentions. However, it is still insufficient in the investigation of coupling mechanism and preparation of highly stable catalytic particle electrodes. Herein, stable copper iron oxide/Kaolin catalytic particle electrodes were synthesized via a facile sol-gel method and applied in 3D/HEF for OG removal. A 40 %-CuFeO/Kaolin (450 °C, 2 h) catalytic particle electrode was optimized and a stable Fe-O-Al bond was found to form between CuFeO and Kaolin. Under optimal conditions, the removal of OG and TOC could reach 99.48 % and 58.13 % respectively within 60 min in neutral environment. From well-designed comparative experiments, various effects such as anodic oxidation, three-dimensional electrochemical oxidation were distinguished, indicating that an excellent synergism between 3D/E attributed to Kaolin and HEF due to CuFeO was the significant cause for the superiority of CuFeO/Kaolin-based 3D/HEF. Radical scavenging experiments verified both hydroxyl radical (•OH) and superoxide radical were generated with •OH dominated, which could efficiently degrade OG through such steps as desulfonation, decolorization, naphthalene opening, benzene opening. Besides, the CuFeO/Kaolin catalysts represented high stability with OG removal still maintaining 92.18 % after 8 cycles, low ion leaching and wide applicability to other dyes, manifesting a kind of fine catalytic particle electrode applied in 3D/HEF have been designed for dye removal and furthermore, providing a new idea for preparing composite catalytic particle electrode in 3D/HEF hybrid system.

Challenges and Future Roadmaps in Heterogeneous Electro-Fenton Process for Wastewater Treatment.

The efficiency of heterogeneous electro-Fenton technology on the degradation of recalcitrant organic pollutants in wastewater is glaringly obvious. This green technology can be effectively harnessed for addressing ever-increasing water-related challenges. Due to its outstanding performance, eco-friendliness, easy automation, and operability over a wide range of pH, it has garnered significant attention from different wastewater treatment research communities. This review paper briefly discusses the principal mechanism of the electro-Fenton process, the crucial properties of a highly efficient heterogeneous catalyst, the heterogeneous electro-Fenton system enabled with Fe-functionalized cathodic materials, and its essential operating parameters. Moreover, the authors comprehensively explored the major challenges that prevent the commercialization of the electro-Fenton process and propose future research pathways to countervail those disconcerting challenges. Synthesizing heterogeneous catalysts by application of advanced materials for maximizing their reusability and stability, the full realization of H2O2 activation mechanism, conduction of life-cycle assessment to explore environmental footprints and potential adverse effects of side-products, scale-up from lab-scale to industrial scale, and better reactor design, fabrication of electrodes with state-of-the-art technologies, using the electro-Fenton process for treatment of biological contaminants, application of different effective cells in the electro-Fenton process, hybridization of the electro-Fenton with other wastewater treatments technologies and full-scale analysis of economic costs are key recommendations which deserve considerable scholarly attention. Finally, it concludes that by implementing all the abovementioned gaps, the commercialization of electro-Fenton technology would be a realistic goal.

Electro-Fenton mineralization of real textile wastewater by micron-sized ZVI powder anode.

The diverse compositions and complex nature of the textile wastewater make it imperative to find an economical and suitable degradation pathway. The degradation of real textile wastewater on a novel heterogeneous electro-Fenton system was carried out with a composite anode of magnetically fixed micron ZVI coupling with a Ti/RuO2-IrO2 sheet. The influences of different variables such as mZVI dosage, H2O2 amount, applied voltage and pH value on both total organic carbon and chemical oxygen demand removal efficiencies and energy consumption were investigated. The optimized parameters were simultaneously verified by using electrochemical workstation Tafel curves and Nyquist plots. The optimal operating conditions for evaluating the wastewater treatment were H2O2 dosage of 0.10 mol·L-1, applied voltage of 5.0 V, mZVI amount of 1.0 g·L-1 and initial pH value of 3.0. The high TOC and COD removal efficiencies of 92.44 and 82.84% could be achieved simultaneously in 60 min, respectively. XRD, XPS and SEM-EDS were used to investigate the interaction between the pollutant and the mZVI. GC-MS analysis was performed on untreated and treated wastewater to determine the degradation of pollutants in dyeing wastewater during the electro-Fenton process and to effectively propose a suitable degradation mechanism for this system.