Heterogeneous electro-Fenton System Research Articles

Endogenous iron-enriched biochar loaded nickel-foam cathode in electro-Fenton for ciprofloxacin degradation: performance, mechanism and DFT calculation

Steel mill wastewater sludge, with abundant endogenous iron resources, could be pyrolyzed into iron-enriched biochar (SBC) in one step and loaded onto nickel foam cathode (Ni-Foam) to construct a heterogeneous electro-Fenton system (SBC@Ni-Foam/EF). The purpose of this study were to optimize SBC@Ni-Foam/EF for efficient ciprofloxacin (CIP) removal, and its degradation mechanism and pathway in the presence of endogenous iron were elucidated by DFT calculation. The results showed that the highest CIP degradation efficiency (95.11 %) was achieved at a SBC pyrolysis temperature of 800 °C, an initial solution pH of 3, a Na2SO4 concentration of 0.05 mol L−1, a current density of 40 mA cm−2, and an aeration rate of 200 mL min−1. The degradation of CIP by SBC@Ni-Foam/EF was dominated by cathodic catalytic oxidation, and ·OH played a major role in the CIP degradation process. Combined with characterization and DFT calculation, the endogenous iron was dispersed in the stable Fe3O4 crystalline phase, which provided surface defects and catalytic sites for the cathode and promoted H2O2 activation to generate ·OH through iron cycling. The possible degradation pathways of CIP were proposed to include the cleavage of piperazine and quinolone rings, hydroxylation, and substitution or detachment of fluorine, etc., and the overall toxicity of the intermediates was alleviated after SBC@Ni-Foam/EF treatment. Therefore, this study was expected to achieve a win–win situation for iron-enriched sludge biomass resource utilization and CIP wastewater treatment.

Enhanced heterogeneous electro-Fenton degradation of salicylic acid by different Fe3O4 loaded carriers

Different types of materials were used as catalyst carriers to enhance the degradation of salicylic acid in the heterogeneous electro-Fenton system. During the experiments, activated carbon, carbon felt and carbon cloth were selected as carbon based materials, and sodium alginate, chitosan and polyvinyl alcohol were chosen as polymer matrix, and foam metal included zinc foam, iron foam and nickel foam (NF). The changes of surface structure and morphology of the above carriers were studied, and combined with the effects of the carriers on the degradation of salicylic acid in the electro-Fenton system. The NF was the best carrier materials for the heterogeneous electro-Fenton system, and Ni and Fe3O4 had synergistic effect in enhancing redox reactivity. With salicylic acid concentration of 100 mg/L, the temperature of 25 ℃ and the pH of 7, the NF@Fe3O4 achieved the best salicylic acid degradation performance after reaction for 2 h. The NF@Fe3O4 enhanced the performance of the electro-Fenton system, which provided a valuable reference for the application of heterogeneous catalyst carriers in the electro-Fenton system.

Improvement of heterogeneous electro-Fenton oxidation of dimethyl phthalate by embedding Fe/Co bimetallic active sites into waste wine lees biochar

Phthalates (PAEs) are frequently detected in the water environment and pose a severe threat to the ecosystem and human health. Electro-Fenton technology is regarded as an effective approach to degrade PAEs; however, the preparation of inexpensive and efficient cathode materials has restricted its further application. In this study, Fe/Co bimetallic sites were incorporated into solid waste wine lees to synthesize highly active heterogeneous catalyst, and dimethyl phthalate (DMP) was chosen as the target pollutant to investigate the activity of the catalyst. Both the degradation of DMP and the removal of total organic carbon (TOC), the performance of Fe/Co co-modified biochar (FeCo@NOPC) is superior to that of Fe (Co) alone (Fe@NOPC/Co@NOPC) and modified biochar (NOPC). Under neutral conditions. Within 5 h, the DMP removal rate reached 89 % and TOC was reduced by approximately 40 %. The mechanism study reveals that the degradation of DMP is mainly attributed to the OH generated by the cathode, and the anodic oxidation and cathode adsorption only play minor roles. Finally, the degradation path of DMP was analyzed by LC-MS technique. This study offers a novel way to utilize solid waste and reduce the cost of heterogeneous electro-Fenton system.

Fe-Ce based metal-organic framework as a novel heterogeneous catalyst accelerating redox cycle for efficient degradation of sulfamethoxazole in wide pH ranges

The electro-Fenton (EF) technology holds immense potential for wastewater treatment. However, there persist certain factors that affect its degradation efficiency, such as the restricted pH range, production of iron sludge and sluggish conversion rate between Fe2+ and Fe3+. Herein, 2,3,6,7,10,11-hexahydroxytriphenyl (HHTP) was introduced as the organic ligand to synthesize a series of efficient iron-based MOF catalysts (FexCe1-HHTP (x = 1, 2, 3, 4)) with different molar ratios for sulfamethoxazole (SMX) degradation in heterogeneous EF system. HHTP with electron-rich functional groups is beneficial to enhance performance of oxygen evolution reaction. Among these catalysts, Fe3Ce1-HHTP catalyst achieved 97.3 % degradation efficiency in 30 min and mineralization rate was 89.7 % at 1 h. The introduction of Ce promoted the transition of Fe3+ and Fe2+ in heterogeneous EF reaction. The synergistic effects between Fe3+/Fe2+ and Ce4+/Ce3+ further catalyzed the generation of hydroxyl radicals and it was proved as the main active species. The heterogeneous catalyst showed good performance in wide pH range, good stability, and high degradation efficiency to other pollutants. Three possible SMX degradation routes are suggested on basis of intermediates detected by mass spectrum analysis and theoretical calculations. The toxicity of these intermediates was assessed using Toxicity Estimation Software Tool (T.E.S.T.). This work provides valuable guidance for the design of highly efficient and stable heterogeneous EF catalyst for antibiotic degradation and expand the application potential in wastewater treatment of organic pollutants.

Heterogeneous electro-Fenton removal of polyacrylamide in aqueous solution over CoFe2O4 catalyst.

Polyacrylamide (PAM) in environmental water has become a major problem in water pollution management due to its high molecular mass, high viscosity and non-absorption by soil. CoFe2O4 with strong magnetic properties was prepared by solvent-thermal synthesis method and used as the catalyst for the removal on PAM in heterogeneous Electro-Fenton (EF) system. It showed that the removal efficiency of PAM by the heterogeneous EF system using CoFe2O4 catalyst was 92.01% at pH 3 after 120 min. Further studies indicated that ·OH was the most significant active species for the removal of PAM, and the contribution of ·O2- and SO4·- for the removal of PAM was less than 15%. The reusability test and XRD, XPS, FTIR analyses proved that the catalyst had good stability. After a repeated use for five times, the catalyst still had a high PAM removal rate and stable structure. The valence distribution and functional groups of the phase components of the catalyst did not change significantly before and after the reaction. The possible mechanism of catalyst activation of H2O2 was deduced by mechanism investigation. The CoFe2O4 is an efficient and promising catalyst for the removal of PAM wastewater.

Potential modulation strategy on bismuth vanadate-based semiconductor to enhance antibiotic degradation in heterogeneous electro-Fenton system

This work proposed the novel Co-doped bismuth vanadate bismuth/ graphite felt (Co-BiVO4/GF, Co-BVO for short) cathode with reduced metal reduction overpotential (OPMRR) for effective decomposition of antibiotic in heterogeneous electro-Fenton (EF) system. Results showed that Co doping into the BVO reduced the metal reduction overpotential and allowed the system to operate at lower cell voltages. The overpotential of cobalt reduction reaction (OPCRR) for the 3Co-BVO/GF was only 270 mV, much lower than that of bismuth reduction reaction (OPBRR) for the BVO/GF (930 mV), which allowed much higher current of cobalt reduction reaction (CRR) (15.23 mA) than that of bismuth reduction reaction (BRR) (6.51 mA) under OP, facilitating more efficient generation of H2O2 and ·OH on the 3Co-BVO/GF cathode. Moreover, the EF system with the 3Co-BVO/GF cathode achieved Levofloxacin (LEV) removal of 97.2 % within 60 min at pH 3, aeration rate of 60 mL·min−1, and voltage of −0.60 V vs. saturated calomel electrode (SCE) with LEV initial concentration of 20 mg·L−1. Density functional theory (DFT) calculations demonstrated that Co doping effectively modulated electronic structure of the BVO, accelerating electron transfer through Co-O bond and accumulation at Co active sites for reactive species production. At least 12 degradation intermediates with generally lower ecotoxicity were identified during LEV degradation, and three possible degradation routes of LEV were proposed. This study offers insights into regulating overpotential of bismuth-based cathodes for efficient pollutants elimination in EF system.

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.

Electro-Fenton degradation of pefloxacin using MOFs derived Cu, N co-doped carbon as a nanocomposite catalyst

Electro-Fenton (EF) can in-situ produce H2O2 and effectively activate H2O2 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 H2O2 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.

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.