Graphene Modified Electro-Fenton Catalytic Membrane for in Situ Degradation of Antibiotic Florfenicol

Electrochemical filtration for drinking water purification: A review on membrane materials, mechanisms and roles

Electrochemical filtration can not only enrich low concentrations of pollutants but also produce reactive oxygen species to interact with toxic pollutants with the assistance of a power supply, making it an effective strategy for drinking water purification. In addition, the application of electrochemical filtration facilitates the reduction of pretreatment procedures and the use of chemicals, which has outstanding potential for maximizing process simplicity and reducing operating costs, enabling the production of safe drinking water in smaller installations. In recent years, the research on electrochemical filtration has gradually increased, but there has been a lack of attention on its application in the removal of low concentrations of pollutants from low conductivity water. In this review, membrane substrates and electrocatalysts used to improve the performance of electrochemical membranes are briefly summarized. Meanwhile, the application prospects of emerging single-atom catalysts in electrochemical filtration are also presented. Thereafter, several electrochemical advanced oxidation processes coupled with membrane filtration are described, and the related working mechanisms and their advantages and shortcomings used in drinking water purification are illustrated. Finally, the roles of electrochemical filtration in drinking water purification are presented, and the main problems and future perspectives of electrochemical filtration in the removal of low concentration pollutants are discussed.

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

Iron Nanoparticle-Incorporated Laser-Induced Graphene Filters for Environmental Remediation via an In Situ Electro-Fenton Process

Laser-induced graphene (LIG) has garnered much attention due to its facile and chemically free fabrication technique. Metal nanoparticle incorporation into the LIG matrix can improve its electrical and catalytical properties for environmental application. Here, we demonstrate the fabrication of nanoscale zerovalent iron (nZVI) nanoparticle-incorporated LIG (Fe-LIG) and sulfidized-nanoscale zerovalent iron (S-nZVI) nanoparticle-incorporated LIG (SFe-LIG) surfaces. The sheets were first fabricated to investigate nanoparticle loading, successful incorporation in the LIG matrix, and electrochemical performance as electrodes. Fe-LIG and SFe-LIG sheets showed ∼3-3.5 times more charge density as compared with the control LIG sheet. The XPS and its deconvolution confirmed the presence of nZVI and S-nZVI in the Fe-LIG and SFe-LIG surfaces, which can generate in situ hydroxyl radical (•OH) via iron activation of electrogenerated hydrogen peroxide (H2O2) in short in situ electro-Fenton process. After confirmation of the successful incorporation of iron-based nanoparticles in the LIG matrix, filters were fabricated to demonstrate the application in the flow-through filtration. The Fe-LIG and SFe-LIG filters showed ∼10-30% enhanced methylene blue removal under the application of 2.5 V at ∼1000 LMH flux. The Fe-LIG and SFe-LIG filters also showed complete 6-log bacteria and virus removal at 2.5 and 5 V, respectively, while the LIG filters showed only ∼4-log removal. Such enhanced removal by the Fe-LIG and SFe-LIG filters as compared to LIG filters is attributed to the improved charge density, electrochemical activity, and in situ electro-Fenton process. The study shows the potential to develop catalytic LIG-based surfaces for various applications, including contaminant removal and microbial inactivation.

Boosted elimination of florfenicol by BiOClxBr1-x solid solutions via photocatalytic ozonation under visible light

In this work, a series of BiOClxBr1-x (BCB) solid solutions are facilely designed for visible-light-driven photocatalytic ozonation (PCO) degradation of florfenicol (FF) in water environments, which could add to the library of efficient, cost-effective and robust nanocatalysts for water purification. BCB solid solutions in the structure of 2D nanosheets are achieved involving the etching of BiOBr "micro-flowers" with HCl at different concentrations, allowing a removal ratio of FF up to 97.3 % within 1 h, superior to bare BiOBr and bare BiOCl. A strengthened synergistic effect between photocatalysis and ozonation is substantiated, where the separation of photo-induced charge transfer is accelerated, the band gap is tuned and the utilization efficiency of ozone is enhanced. This facilitates the production of reactive oxygen species identified as •OH, •O2-, and 1O2 that will attack the FF molecule for degradation based on three pathways.

New directions on membranes for removal and degradation of emerging pollutants in aqueous systems

Emerging pollutants (EPs) refer to a group of non-regulated chemical or biological substances that have been recently introduced or detected in the environment. These pollutants tend to exhibit resistance to conventional treatment methods and can persist in the environment for prolonged periods, posing potential adverse effects on ecosystems and human health. As we enter a new era of managing these pollutants, membrane-based technologies hold significant promise in mitigating impact of EPs on the environment and safeguarding human health due to their high selectivity, efficiency, cost-effectiveness and capability for simultaneous separation and degradation. Moreover, these technologies continue to evolve rapidly with the development of new membrane materials and functionalities, advanced treatment strategies, and analyses for effectively treating EPs of more recent concerns. The objective of this review is to present the latest directions and advancements in membrane-based technologies for addressing EPs. By highlighting the progress in this field, we aim to share valuable perspectives with researchers and contribute to the development of future directions in sustainable treatments for EPs.

Dechlorination Helps Defluorination: Insights into the Defluorination Mechanism of Florfenicol by S-nZVI and DFT Calculations on the Reaction Pathways

Defluorination is essential to eliminate the antibiotic resistance and detrimental effects of florfenicol (C12H14Cl2FNO4S, FF), which is achievable by sulfidated nanoscale zerovalent iron (S-nZVI), yet a comprehensive understanding of the mechanism is lacking. Herein, we used experimental data and density functional theory calculations to demonstrate four dechlorination-promoted defluorination pathways of FF, depending on S-nZVI or not. FF was defluorinated in a rapid and then slow but continuous manner, accompanying a consecutive dechlorination to deschloro (dFF) and dideschloro FF (ddFF). Unexpectedly, the predominant defluorination occurs by spontaneous hydrolysis of ddFF to form the hydrolyzed byproduct (HO-ddFF), i.e., independent of S-nZVI, which is initiated by intramolecular attack from carbonyl O to alkyl F and is thus limited for FF and dFF owing to the diminished nucleophilicity by electron-withdrawing Cl. The removal of Cl also makes the reductive defluorination of ddFF by S-nZVI amenable. The other two minor but more rapid defluorination pathways occur in synergy with the dechlorination of FF and dFF, which are mediated by the reactive carbanion intermediates and generate HO-dFF and HO-ddFF, respectively. The reliability of these dechlorination-facilitated defluorination pathways was verified by the consistency of theoretical calculations with experimental data, providing valuable insights into the degradation of fluorinated contaminants.

Degradation of phenol in wastewater through an integrated dielectric barrier discharge and Fenton/photo-Fenton process

In this study, a non-thermal dielectric barrier discharge-Fenton/photo-Fenton process was investigated to remove phenol from synthetic wastewater. The changes and optimal values of influencing parameters, including treatment time, iron concentration, phenol initial concentration, and pH, were investigated based on the central composite design (CCD) method. The presence of 0.4 mmol/L of iron in the phenol solution with a concentration of 100 mg/L increased the removal efficiency and pseudo-first-order kinetic constant compared to dielectric barrier discharge cold plasma (DBDP) alone from 0.0824 min-1 and 56.8% to 0.2078 min-1 and 86.83%, respectively. The phenol removal efficiency was reduced to 52.9%, 45.6% and 31.8% by adding tert-butyl alcohol (TBA) with concentrations of 50, 100, and 200 mg/l, respectively. After 12 min of DBDP irradiation, the pH of the sample decreased from 5.95 to 3.42, and the temperature of the sample increased from 19.3 to 37.2 degrees Celsius. The chemical oxygen demand (COD) of the sample containing 100 mg/L phenol under plasma-Fenton/photo-Fenton irradiation decreased from 241 mg/L to 161 mg/L. Phenol removal efficiency after 10 min of treatment in the presence of 0.4 mmol/L of iron with the reactor volume of 50 mL was 87%, but the efficiency decreased to 76%, 47%, and 9% by increasing the volume to 100, 200, and 400 mL, respectively. Reducing the power led to a decrease in the removal efficiency from 56.8% for 100 W power to 10.8% for 40 W. The energy efficiency for 50% removal by DBDP and plasma-Fenton/photo-Fenton systems was 5.86×10-3 kWh/mg and 1.27×10-3 kWh/mg, respectively.

Metal-free electrified membranes for contaminants oxidation: Synergy effect between membrane rejection and nanoconfinement

Electro-Fenton processes are frequently impeded by depletion of metal catalysts, unbalance between H2O2 generation and activation, and low concentration of reactive species (e.g., •OH) in the bulk solution. A metal-free electro-Fenton membrane was fabricated with nitrogen-doped carbon nanotube (N-CNT) and reduced graphene oxide (RGO). N-CNT acted as a catalyst for both H2O2 generation and activation, while the incorporated RGO served as the second catalyst for H2O2 generation and improved the performance of membrane rejection. The electrified membrane was optimized in terms of nitrogen precursors selection and composition of N-CNT and RGO to achieve optimal coupling between H2O2 generation and activation. The membrane fabricated with 67% mass of N-CNT with urea as the precursor achieved over 95% removal of the target contaminants in a single pass through the membrane with a water flux of 63 L m-2 h-1. This membrane also exhibited efficient transformation of various concentrations of contaminants (i.e., 1-10 mg L-1) over a broad range of pH (i.e., 3-9). Due to its good durability and low energy consumption, the metal-free electro-Fenton membrane holds promise for practical water treatment application. The concentration-catalytic oxidation model elucidated that the elevated contaminant concentration near the membrane surface enhanced the transformation rate by 40%. The nanoconfinement enhanced the transformation rate constant inside the membrane by a factor of 105 because of elevated •OH concentration inside the nanopores. Based on the prediction of this model, the configuration of the membrane reactor has been optimized.

Self-cleaning foulant attachment on near-infrared responsive photocatalytic membrane for continuous dynamic removing antibiotics in sewage effluent environment

Bifunctional photocatalytic nanofiltration (PNF) membrane has become a reliable frontier technique for removing refractory organic micropollutants. However, the active mitigated fouling mechanism from the microscopic perspective during its long-term operation of purifying real micro-polluted water is rarely studied. Herein, with an integrated use of QSense Explorer and confocal laser scanning microscope techniques, self-cleaning foulant attachment on an activated and customized near-infrared responsive polymeric PNF (termed as nPNF) membrane with good service performance for continuous dynamic removing antibiotics in sewage effluent environment was firstly elucidated. Time-dependent changes in dissipation oscillation frequency, sensed mass and the visualized foulant spatial distribution all indicated that there were only sporadic foulant attachment, an extremely low fouling layer thickness and irreversible fouling rate on/of the activated nPNF membrane top surface, thereby endowing it with excellent self-cleaning characteristic. This is probably because the reactive oxygen species (mainly •O2- and •OH) concurrently destroys the integrity of fouling layer and its internal adhesion structure, transforming part of the irreversible fouling on nPNF membrane surface into reversible one that is easy to wash off. These new horizons provided useful insight on the fate of selected antibiotics in the to-be-removed stage and self-cleaning foulant attachment of PNF membrane.

Electrocatalytic Deep Dehalogenation and Mineralization of Florfenicol: Synergy of Atomic Hydrogen Reduction and Hydroxyl Radical Oxidation over Bifunctional Cathode Catalyst

It is difficult to achieve deep dehalogenation or mineralization for halogenated antibiotics using traditional reduction or oxidation processes, posing the risk of microbial activity inhibition and bacterial resistance. Herein, an efficient electrocatalytic process coupling atomic hydrogen (H*) reduction with hydroxyl radical (•OH) oxidation on a bifunctional cathode catalyst is developed for the deep dehalogenation and mineralization of florfenicol (FLO). Atomically dispersed NiFe bimetallic catalyst on nitrogen-doped carbon as a bifunctional cathode catalyst can simultaneously generate H* and •OH through H2O/H+ reduction and O2 reduction, respectively. The H* performs nucleophilic hydro-dehalogenation, and the •OH performs electrophilic oxidization of the carbon skeleton. The experimental results and theoretical calculations indicate that reductive dehalogenation and oxidative mineralization processes can promote each other mutually, showing an effect of 1 + 1 > 2. 100% removal, 100% dechlorination, 70.8% defluorination, and 65.1% total organic carbon removal for FLO are achieved within 20 min (C0 = 20 mg·L-1, -0.5 V vs SCE, pH 7). The relative abundance of the FLO resistance gene can be significantly reduced in the subsequent biodegradation system. This study demonstrates that the synergy of reduction dehalogenation and oxidation degradation can achieve the deep removal of refractory halogenated organic contaminants.

Boosting Hydroxyl Radical Yield via Synergistic Activation of Electrogenerated HOCl/H2O2 in Electro-Fenton-like Degradation of Contaminants under Chloride Conditions

Hydroxyl radical production via catalytic activation of HOCl is a new type of Fenton-like process. However, metal-chlorocomplex formation under high chloride conditions could deactivate the catalyst and reduce the process efficiency. Herein, in situ electrogenerated HOCl was activated to •OH via a metal-free, B/N-codoped carbon nanofiber cathode for the first time to degrade contaminant under high chloride condition. The results show 98% degradation of rhodamine B (RhB) within 120 min (k = 0.036 min-1) under sulfate conditions, while complete degradation (k = 0.188 min-1) was obtained in only 30 min under chloride conditions. An enhanced degradation mechanism consists of an Adsorb & Shuttle process, wherein adsorption concentrates the pollutants at the cathode surface and they are subsequently oxidized by the large amount of •OH produced via activation of HOCl and H2O2 at the cathode. Density functional theory calculations verify the pyridinic N as the active site for the activation of HOCl and H2O2. The process efficiency was also evaluated by treating tetracycline and bisphenol A as well as high chloride-containing real secondary effluents from a pesticide manufacturing plant. High yields of •OH and HOCl allow continuous regeneration of the cathode for several cycles, limiting its fast deactivation, which is promising for real application.

Performance and degradation pathway of florfenicol antibiotic by nitrogen-doped biochar supported zero-valent iron and zero-valent copper: A combined experimental and DFT study

Fluorinated compounds are a class of organic substances resistant to degradation. Although zero-valent iron (Fe0) has a promising reducing capability, it still fails to degrade fluorine-containing antibiotics (i.e., florfenicol) efficiently. In this study, we applied a simple one-pot pyrolytic approach to synthesize nitrogen-doped biochar supported Fe0 and zero-valent copper (Cu0) composite (Fe/Cu@NBC) and investigated its performance on florfenicol removal. The results clearly showed that approximately 91.4% of florfenicol in the deionized water was removed by Fe/Cu@NBC within 8 h. As the reaction time was extended to 15 d, the total degradation rate of florfenicol reached 96.6%, in which the defluorination and dechlorination rates were 73.2% and 82.1%, respectively. Both experimental results and density functional theory calculation suggested that ∙OH and ·O2- triggered β-fluorine elimination, resulting in defluorination prior to dechlorination. This new finding was distinct from previous viewpoints that defluorination was more difficult to occur than dechlorination. Fe/Cu@NBC also had a favorable performance for removal of florfenicol in surface water. This study provides a new insight into the degradation mechanism and pathway of florfenicol removal in the Fe/Cu@NBC system, which can be a promising alternative for remediation of fluorinated organic compounds in the environment.

Insights into Electrochemical Dehalogenation by Non-Noble Metal Single-Atom Cobalt with High Efficiency and Low Energy Consumption

It is critical to discover a non-noble metal catalyst with high catalytic activity capable of replacing palladium in electrochemical reduction. In this work, a highly efficient single-atom Co-N/C catalyst was synthesized with metal-organic frameworks (MOFs) as a precursor for electrochemical dehalogenation. X-ray absorption spectroscopy (XAS) revealed that Co-N/C exhibited a Co-N4 configuration, which had more active sites and a faster charge-transfer rate and thus enabled the efficient removal of florfenicol (FLO) at a wide pH, achieving a rate constant 3.5 and 2.1 times that of N/C and commercial Pd/C, respectively. The defluorination and dechlorination efficiencies were 67.6 and 95.6%, respectively, with extremely low Co leaching (6 μg L-1), low energy consumption (22.7 kWh kg-1), and high turnover frequency (TOF) (0.0350 min-1), demonstrating excellent dehalogenation performance. Spiking experiments and density functional theory (DFT) verified that Co-N4 was the active site and had the lowest energy barrier for forming atomic hydrogen (H*) (ΔGH*). Capture experiments, electron paramagnetic resonance (EPR), electrochemical tests, and in situ Fourier transform infrared (FTIR) proved that H* and direct electron transfer were responsible for dehalogenation. Toxicity assessment indicated that FLO toxicity decreased significantly after dehalogenation. This work develops a non-noble metal catalyst with broad application prospects in electrocatalytic dehalogenation.

Enhancing zerovalent iron-based Fenton-like chemistry by copper sulfide: Insight into the active sites for sustainable Fe(II) supply

Zerovalent iron (ZVI)-based Fenton-like processes have been widely applied in degrading organic contaminants. However, the surface oxyhydroxide passivation layer produced during the preparation and oxidation of ZVI hinders its dissolution and Fe(III)/Fe(II) cycling, and restricts the generation of reactive oxygen species (ROS). In this study, copper sulfide (CuS) was found to effectively enhance the degradation of diverse organic pollutants in the ZVI/H₂O₂ system. Moreover, the degradation performance for the actual industrial wastewater (i.e., dinitrodiazophenol wastewater) in the ZVI/H₂O₂ system was impressively improved by 41% with CuS addition, and the COD removal efficiency could reach 97% after 2 h of treatment. Mechanism investigation revealed that the introduction of CuS accelerated the sustainable supply of Fe(II) in the ZVI/H₂O₂ system. Specifically, Cu(I) and reductive sulfur species (i.e., S^2-, S₂^2-, S_n^2- and H₂S (aq)) from CuS directly induced efficient Fe(III)/Fe(II) cycling. The iron-copper synergistic effect between Cu(II) from CuS and ZVI expedited Fe(II) generation from ZVI dissolution and Fe(III) reduction by formed Cu(I). This study not only elucidates the promotion effects of CuS on ZVI dissolution and Fe(III)/Fe(II) cycling in ZVI-based Fenton-like processes, but also provides a sustainable and high-efficiency iron-based oxidation system for removal of organic contaminants.

Preparation, performance and mechanism of metal oxide modified catalytic ceramic membranes for wastewater treatment

Catalytic ceramic membranes (CMs) integrated with different metal oxides were designed and fabricated by an impregnation-sintering method. The characterization results indicated that the metal oxides (Co₃O₄, MnO₂, Fe₂O₃ and CuO) were uniformly anchored around the Al₂O₃ particles of the membrane basal materials, which could provide a large number of active sites throughout the membrane for the activation of peroxymonosulfate (PMS). The performance of the CMs/PMS system was evaluated by filtrating a phenol solution under different operating conditions. All the four catalytic CMs showed desirable phenol removal efficiency and the performance was in order of CoCM, MnCM, FeCM and CuCM. Moreover, the low metal ion leaching and high catalytic activity even after the 6th run revealed the good stability and reusability of the catalytic CMs. Quenching experiments and electron paramagnetic resonance (EPR) measurements were conducted to discuss the mechanism of PMS activation in the CMs/PMS system. The reactive oxygen species (ROS) were supposed to be SO₄˙^- and ¹O₂ in the CoCM/PMS system, ¹O₂ and O₂˙^- in the MnCM/PMS system, SO₄˙^- and ·OH in the FeCM/PMS system, and SO₄˙^- in the CuCM/PMS system, respectively. The comparative study on the performance and mechanism of the four CMs provides a better understanding of the integrated PMS-CMs behaviors.

Source preventing mechanism of florfenicol resistance risk in water by VUV/UV/sulfite advanced reduction pretreatment

To avoid the inhibition of microbial activity and the emergence of bacterial resistance, effective abiotic pretreatment methods to eliminate the antibacterial activity of target antibiotics before the biotreatment system for antibiotic-containing wastewater are necessary. In this study, the VUV/UV/sulfite system was developed as a pretreatment technique for the source elimination of florfenicol (FLO) resistance risk. Compared with the VUV/UV/persulfate and sole VUV photolysis, the VUV/UV/sulfite system had the highest decomposition rate (0.33 min^‒1) and the highest defluorination (83.0%), resulting in the efficient elimination of FLO antibacterial activity with less than 2.0% mineralization, which would effectively retain the carbon sources for the sludge microorganisms in the subsequent biotreatment process. Furthermore, H• was confirmed to play a more important role in the elimination of FLO antibacterial activity by controlling the environmental conditions for the formation and transformation of reactive species and adding their scavengers. Based on the theoretical calculation and proposed photolytic intermediates, the elimination of FLO antibacterial activity was achieved by dechlorination, defluorination and removal of sulfomethyl groups. When the pretreated FLO-containing wastewater entered the biological treatment unit, the abundance of associated antibiotic resistance genes (ARGs) and the relative abundance of integrons were efficiently prevented by approximately 55.4% and 22.9%, respectively. These results demonstrated that the VUV/UV/sulfite system could be adopted as a promising pretreatment option for the source elimination of FLO resistance risk by target decomposition of its responsible structures before the subsequent biotreatment process.

Mechanisms of interfacial catalysis and mass transfer in a flow-through electro-peroxone process

To investigate the catalytic mechanism and mass transfer efficiency in the removal of amitriptyline using an electro-peroxide process, a CuFe₂O₄-modified carbon cloth cathode was prepared and utilized in a reaction unit. The results demonstrated a remarkable efficacy of the system, achieving 91.0% amitriptyline removal, 68.3% mineralization, 41.2% mineralization current efficiency, and 0.24 kWh/m³ energy consumption within just five minutes of treatment. The study revealed that the exposed Fe atoms of the ferrite nanoparticles, with a size of 22.7 nm and 89.7% crystallinity, functioned as mediators to bind the adsorbed O atoms. The 3d_xy, 3d_xz, and 3d²_z orbitals of Fe atoms interacted with the 2p_z orbital of O atoms of H₂O₂ and O₃ to form σ and π bonds, facilitating the adsorption-activation of H₂O₂ and O₃ into hydroxyl radicals. These hydroxyl radicals (∼ 1.15 × 10¹³ mol/L) were distributed at the cathode-solution interface and rapidly consumed along the direction of liquid flow. The flow-through cathode design improved the mass transfer of aqueous O₃ and in-situ generated H₂O₂, leading to an increased yield of hydroxyl radicals, as well as the contact time and space between hydroxyl radicals and amitriptyline. Ultimately, this resulted in a higher degradation efficiency of the system.

Electroactive membrane with the electroactive layer beneath the separation layer to eliminate the interference of humic acid in the oxidation of antibiotics

Removing harmful antibiotics is essential to reclaiming water from municipal secondary effluent. Electroactive membranes are effective in the removal of antibiotics but challenged by the abundant coexisting macromolecular organic pollutants in municipal secondary effluent. To eliminate the interference of macromolecular organic pollutants in the removal of antibiotics, we propose a novel electroactive membrane with a top polyacrylonitrile (PAN) ultrafiltration layer and a bottom electroactive layer composed of carbon nanotubes (CNTs) and polyaniline (PANi). When filtering the mixture of tetracycline (TC, a typical antibiotic) and humic acid (HA, a typical macromolecular organic pollutant), the PAN-CNT/PANi membrane performed sequential removal. It retained HA at the PAN layer (by ∼96%) and allowed TC to reach the electroactive layer where it was electrochemically oxidized (e.g., by ∼92% at 1.5 V). The TC removal of the PAN-CNT/PANi membrane was marginally affected by HA, unlike that of the control membrane with the electroactive layer on the top that showed decreased TC removal after the addition of HA (e.g., decreased by 13.2% at 1 V). The decreased TC removal of the control membrane was attributed to the attachment (but not competitive oxidation) of HA on the electroactive layer that impaired the electrochemical reactivity. The HA removal prior to TC degradation realized by the PAN-CNT/PANi membrane avoided the attachment of HA and guaranteed TC removal on the electroactive layer. Long-term filtration for 9 h revealed the stability of the PAN-CNT/PANi membrane, and its advantageous structural design was conformed in the context of real secondary effluents.

A critical review on graphene oxide membrane for industrial wastewater treatment

An important way to promote the environmental industry's goal of carbon reduction is to promote the recycling of resources. Membrane separation technology has unique advantages in resource recovery and advanced treatment of industrial wastewater. However, the great promise of traditional organic membrane is hampered by challenges associated with organic solvent tolerance, lack of oxidation resistance, and serious membrane fouling control. Moreover, the high concentrations of organic matter and inorganic salts in the membrane filtration concentrate also hinder the wider application of the membrane separation technology. The emerging cost-effective graphene oxide (GO)-based membrane with excellent resistance to organic solvents and oxidants, more hydrophilicity, lower membrane fouling, better separation performance has been expected to contribute more in industrial wastewater treatment. Herein, we provide comprehensive insights into the preparation and characteristic of GO membranes, as well as current research status and problems related to its future application in industrial wastewater treatment. Finally, concluding remarks and future perspectives have been deduced and recommended for the GO membrane separation technology application for industrial wastewater treatment, which leads to realizing sustainable wastewater recycling and a nearly "zero discharge" water treatment process.

Facilely achieved enhancement of Fenton-like reactions by constructing electric microfields

In this work, we found that the presence of non-active ZnO crystals greatly accelerated the degradation of Bisphenol A (BPA) by 3.7 folds in the peroxymonosulfate (PMS, HSO₅^-)/Co₃O₄ system. Our mechanistic study revealed that the ZnO particles would create negative electric microfields around them, which are closely related with the zeta potentials (ζ) of ZnO and affected by solution pH. According to COMSOL simulation, the electrostatic repulsion between ZnO and PMS would drive HSO₅^- toward active Co₃O₄ surface, leading to the concentration increasing of HSO₅^- around active Co₃O₄ particles, which will then improve the degradation performance. The particle size of ZnO will also affect the promoting effect greatly by COMSOL simulation. Therefore, this study for the first time reveals synergy of electric microfields for enhanced heterogeneous Fenton-like reactions, providing a low-cost and effective strategy for enhanced persulfate catalysis.

Degradation of antibiotics by electrochemical advanced oxidation processes (EAOPs): Performance, mechanisms, and perspectives

Global consumption and discharge of antibiotics have led to the rapid development and spread of bacterial antibiotic resistance. Among treatment strategies, electrochemical advanced oxidation processes (EAOPs) are gaining popularity for treating water/wastewater containing antibiotics due to their high efficiency and easiness of operation. In this review, we summarize various forms of EAOPs that contribute to antibiotic degradation, including common electrochemical oxidation (EO), electrolyte enhanced EO, electro-Fenton (EF) processes, EF-like process, and EAOPs coupling with other processes. Then we assess the performance of various EAOPs in antibiotic degradation and discuss the influence of key factors, including electrode, initial concentration and type of antibiotic, operation conditions, electrolyte, and water quality. We also review mechanisms and degradation pathways of various antibiotics degradation by EAOPs, and address the species and toxicity of intermediates produced during antibiotics treatment. Finally, we highlight challenges and critical research needs to facilitate the application of EAOPs in antibiotic treatment.

Ferrate modified carbon felt as excellent heterogeneous electro-Fenton cathode for chloramphenicol degradation

In this study, a novel and efficient heterogeneous electro-Fenton (EF) process with a potassium ferrate (K₂FeO₄) modified carbon felt (Fe-CF) cathode was developed for chloramphenicol (CAP) removal. The catalytic activity was assessed by the comparison of different systems and the effects of multiple operating parameters (K₂FeO₄ dosage, initial solution pH, applied current) and co-existing constituents. Results indicated that the Fe-CF cathode exhibited excellent performance for CAP degradation (almost 100% removal efficiency within 60 min) over a wide range of pH (pH 3-9) during heterogeneous EF ascribed to the synergistic effect of embedded iron species and porous graphitic carbon structure and effective utilization of the in-situ generated H₂O₂. Moreover, the Fe-CF cathode possessed good recyclability with low metal leaching (98.2% CAP removal efficiency after reused for 5 times) and outstanding real water application performance. The ∙OH and O₂∙^- were responsible for CAP degradation, while ∙OH played a main role. Moreover, the toxicity evaluation by E. coli growth experiments demonstrated an efficient toxicity reduction in this system. Overall, a novel heterogeneous EF functional cathode with superior performance was fabricated via a green, low-cost one-step method, which shows promising application potential for actual wastewater treatment.

A comprehensive review on reactive oxygen species (ROS) in advanced oxidation processes (AOPs)

In this account, the reactive oxygen species (ROS) were comprehensively reviewed, which were based on electro-Fenton and photo-Fenton processes and correlative membrane filtration technology. Specifically, this review focuses on the fundamental principles and applications of advanced oxidation processes (AOPs) based on a series of nanomaterials, and we compare the pros and cons of each method and point out the perspective. Further, the emerging reviews regarding AOPs rarely emphasize the involved ROS and consider the convenience of radical classification and transformation mechanism, such a review is of paramount importance to be needed. Owing to the strong oxidation ability of radical (e.g., •OH, O₂^•-, and SO₄^•-) and non-radical (e.g., ¹O₂ and H₂O₂), these ROS would attack the organic contaminants of emerging concern, thus achieving the goal of environmental remediation. Hopefully, this review can offer detailed theoretical guidance for the researchers, and we believe it able to offer the frontier knowledge of AOPs for wastewater treatment plants (WWTPs).

Effective degradation of tetracycline via recyclable cellulose nanofibrils/polyvinyl alcohol/Fe3O4 hybrid hydrogel as a photo-Fenton catalyst

In this work, the method of in-situ co-precipitation was used to prepare PVA/CNF/Fe₃O₄ hybrid hydrogel, and the relationship between its structure and performance was explored. The Fe₃O₄NPs prepared by this method were dispersed on the carrier PVA/CNF hydrogel and were easy to recover. The catalytic degradation of tetracycline was investigated using PVA/CNF/Fe₃O₄ hybrid hydrogel as photo-Fenton catalysts. The results showed that light and hydrogel carriers were pivotal factors in promoting Fe²⁺ and Fe³⁺ cycling and that the PVA/CNF/Fe₃O₄ hybrid hydrogel as catalysts were able to activate H₂O₂ to generate a large amount of oxygen radical •OH, resulting in efficient removal of tetracycline. The tetracycline degradation followed a proposed first-order kinetic model and achieved a removal rate of about 98% in 120 min at an optimum pH of 3, H₂O₂ 100 mM, catalyst 0.3 g/L, and a temperature of 25 °C.

Electroactive Ultrafiltration Membrane for Simultaneous Removal of Antibiotic, Antibiotic Resistant Bacteria, and Antibiotic Resistance Genes from Wastewater Effluent

To combat the spread of antibiotic resistance into the environment, we should adequately manage wastewater effluent treatment to achieve simultaneous removal of antibiotics, antibiotic resistant bacteria (ARB), and antibiotic resistance genes (ARGs). Herein, we fabricate a multifunctional electroactive poly(vinylidene fluoride) ultrafiltration membrane (C/PVDF) by phase inversion on conductive carbon cloth. The membrane possesses not only excellent retention toward ARB and ARGs but also exhibits high oxidation capacity as an electrode. Notably, sulfamethoxazole degradation involving hydroxylation and hydrolysis by the anode membrane is predominant, and the degradation efficiency is up to 81.5% at +4 V. Both electro-filtration processes exhibit significant ARB inactivation, anode filtration is superior to cathode filtration. Moreover, the degradation of intracellular ARGs (iARGs) located in the genome is more efficient than those located in the plasmid, and these degradation efficiencies at -2 V are higher than +2 V. The degradation efficiencies of extracellular ARGs (eARGs) are opposite and are lower than iARGs. Compared with regular filtration, the normalized flux of electroactive ultrafiltration membrane is improved by 18.0% at -2 V, 15.9% at +2 V, and 30.4% at +4 V during treating wastewater effluent, confirming its antifouling properties and feasibility for practical application.

Electrified ceramic membrane actuates non-radical mediated peroxymonosulfate activation for highly efficient water decontamination

Electrified ceramic membranes (ECMs) achieve high water decontamination efficiency mainly through implementing in situ radical-mediated oxidation in membrane filtration, whereas ECMs leveraging non-radical pathways are rarely explored. Herein, we demonstrated a Janus ECM realizing ultra-efficient micropollutant (MP) removal via electro-activating peroxymonosulfate (PMS) in a fast, flow-through single-pass electro-filtration. The Janus ECM features two separate palladium (Pd) functionalized electrocatalytic reaction zones engineered on its two sides. We confirmed that the PMS/electro-filtration system induced non-radical pathways for MP degradation, including singlet oxygenation and mediating direct electron transfer (DET) from MP to PMS. Under the design of the ECM featuring dual electrocatalytic reaction zones in the ceramic membrane intrapores, the Janus ECM showed over one-fold increase in micropollutant removal rate as 94.5% and lower electric energy consumption as 1.78 Wh g^-1 MP in the PMS electro-activation process, as compared with the conventional ECM assembly implementing only half-cell reaction. This finding manifested the Janus ECM configuration advantage for maximizing the PMS electro-activation efficiency via singlet oxygenation intensification and direct usage of cathode for DET mediation. The Janus ECM boosted the PMS electro-activation and water decontamination efficiency by enhancing the convective mass transfer and the spatial confinement effect. Our work demonstrated a high-efficiency PMS electro-activation method based on electro-filtration and maximized the non-radical mediated PMS oxidation for MP removal, expanding the ECM filtration strategies for water decontamination.

Enhanced tetracycline removal using membrane-like air-cathode with high flux and anti-fouling performance in flow-through electro-filtration system

The membrane-like air-cathodes modified with different polyaniline were prepared using phase inversion method, which possessed dual functions of interception and electrochemical degradation, and showed good conductivity (15.9 ± 0.4 to 25.7 ± 0.5 mS cm^-1) and porosity (77.0 ± 0.1 to 87.8 ± 0.1%) compared to the unmodified control one (13.2 ± 0.5 mS cm^-1, and 63.1 ± 0.7%). At tetracycline 50 mg L^-1, the cathode with 25 wt% polyaniline exhibited the highest rejection rate and final removal (71.1% and 92.9%, 35.9% and 31.4% higher than the control), the highest water flux recovery (97.9%), and the lowest attenuation of porosity and conductivity. The modified cathode also showed an autocatalytic effect on H₂O₂, an obvious ^·OH peak appeared on the electron paramagnetic resonance curves. It also had good anti-fouling performance because it exhibited a high durability (the final removal was decreased by 4.0% after 15 cycles) with a long service life of 124 periods (372 h, 15.5 d). The tetracycline (0.5 mg L^-1) removal in the river background was near 100%, and the chemical oxygen demand removal was 91.9%, supporting that it was suitable for treating antibiotics in natural water without adding agents but only for electricity consumption.

Ganzoury M, Zhang N, de Lannoy CF. Nanocomposite Polymeric Membranes for Organic Micropollutant Removal: A Critical Review

The prevalence of organic micropollutants (OMPs) and their persistence in water supplies have raised serious concerns for drinking water safety and public health. Conventional water treatment technologies, including adsorption and biological treatment, are known to be insufficient in treating OMPs and have demonstrated poor selectivity toward a wide range of OMPs. Pressure-driven membrane filtration has the potential to remove many OMPs detected in water with high selectivity as a membrane's molecular weight cutoff (MWCO), surface charge, and hydrophilicity can be easily tailored to a targeted OMP's size, charge and octanol-water partition coefficient (Kow). Over the past 10 years, polymeric (nano)composite microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) membranes have been extensively synthesized and studied for their ability to remove OMPs. This review discusses the fate and transport of emerging OMPs in water, an assessment of conventional membrane-based technologies (NF, reverse osmosis (RO), forward osmosis (FO), membrane distillation (MD) and UF membrane-based hybrid processes) for their removal, and a comparison to the state-of-the-art nanoenabled membranes with enhanced selectivity toward specific OMPs in water. Nanoenabled membranes for OMP treatment are further discussed with respect to their permeabilities, enhanced properties, limitations, and future improvements.

O- and F-doped porous carbon bifunctional catalyst derived from polyvinylidene fluoride for sulfamerazine removal in the metal-free electro-Fenton process

Heteroatom-doped carbon materials can effectively activate H₂O₂ into •OH during the metal-free electro-Fenton (EF) process. However, information on bifunctional catalysts for the simultaneous generation and activation of H₂O₂ is scarce. In this study, O- and F-doped porous carbon cathode materials (PPCs) were prepared by the direct carbonization of polyvinylidene fluoride (PVDF) for sulfamerazine (SMR) removal in a metal-free EF process. The porous structure and chemical composition of the PPCs were regulated by the carbonization temperature. PPC-6 (carbonized at 600 °C) exhibited optimal electrocatalytic performance in terms of electrochemical H₂O₂ generation and activation owing to its high specific surface area, mesoporous structure, and optimum fractions of doped O and F. Excellent performance of the 2e^- oxygen reduction reaction was found with an H₂O₂ selectivity of 93.5% and an average electron transfer number of 2.13. An H₂O₂ accumulative concentration of 103.9 mg/L and an SMR removal efficiency of 90.1% were achieved during the metal-free EF process. PPC-6 was able to stably remove SMR over five consecutive cycles, retaining 92.6% of its original performance. Quantitative structure-activity relationship analysis revealed that doped oxygen functional groups contributed substantially to H₂O₂ generation, and semi-ionic C-F bonds with high electronegativity were the cause of the activation of H₂O₂ to •OH. These findings suggest that the PVDF-derived carbonaceous catalysts are feasible and desirable for metal-free EF processes.

A critical review on classifications, characteristics, and applications of electrically conductive membranes for toxic pollutant removal from water: Comparison between composite and inorganic electrically conductive membranes

Research efforts have recently been directed at developing electrically conductive membranes (EMs) for pressure-driven membrane separation processes to remove effectively the highly toxic pollutants from water. EMs serve as both the filter and the electrode during filtration. With the assistance of a power supply, EMs can considerably improve the toxic pollutant removal efficiency and even realize chemical degradation to reduce their toxicity. Organic-inorganic composite EMs and inorganic EMs show remarkable differences in characteristics, removal mechanisms, and application situations. Understanding their differences is highly important to guide the future design of EMs for specific pollutant removal from water. However, reviews concerning the differences between composite and inorganic EMs are still lacking. In this review, we summarize the classifications, fabrication techniques, and characteristics of composite and inorganic EMs. We also elaborate on the removal mechanisms and performances of EMs toward recalcitrant organic pollutants and toxic inorganic ions in water. The comparison between composite and inorganic EMs is emphasized particularly in terms of the membrane characteristics (pore size, permeability, and electrical conductivity), application situations, and underlying removal mechanisms. Finally, the energy consumption and durability of EMs are evaluated, and future perspectives are presented.

Photoinduced carbamoylation reactions: unlocking new reactivities towards amide synthesis

The preparation of amide-containing compounds is among the most interesting and challenging topics for the synthetic community. Such relevance is given by their reactive aspects explored in the context of organic synthesis and by the direct application of these compounds as pharmaceuticals and useful materials, and their key roles in biological structures. A simple and straightforward strategy for the amide moiety installation is the use of carbamoyl radicals - this nucleophilic one-electron intermediate is prone to undergo a series of transformations, providing a range of structurally relevant derivatives. In this review, we summarize the latest advances in the field from the perspective of photoinduced protocols. To this end, their synthetic applications are organized accordingly to the nature of the radical precursor (formamides through HAT, 4-substituted-1,4-dihydropyridines, oxamic acids, and N-hydroxyphthalimido esters), the mechanistic aspects also being highlighted. The discussion also includes a recent approach proceeding via photolytic C-S cleavage of dithiocarbamate-carbamoyl intermediates. By exploring fundamental concepts, this material aims to offer an understanding of the topic, which will encourage and facilitate the design of new synthetic strategies applying the carbamoyl radical.

Catalytic Oxygen Activation over the Defective CuO Nanoparticles for Ultrafast Dehalogenation

The nucleophilic superoxide radical (O₂^•-)-based dehalogenation reaction shows great potential to degrade the toxic halogenated organic compounds (HOCs). But such an O₂^•--mediated reductive reaction often suffers from the competition of the secondary oxidative species (e.g., •OH), leading to inferior electron efficiency and possible disinfection byproduct formation. Here, an O₂^•--dominant ultrafast dehalogenation system is developed via molecular O₂ activation by the oxygen vacancy (OV)-rich CuO nanoparticles (nCuO). The nCuO delivers a remarkable dechlorination rate constant of 3.92 × 10^-2 L min^-1 m^-2 for 2,4-dichlorophenol, much higher than that of the conventional zerovalent (bi)metals. The absorbed O₂ on the nCuO surface is exclusively responsible for O₂^•- generation, and its reactivity increases with the elevated OV content because of the enhanced orbital hybridization between the O p- and Cu d-orbitals. More importantly, the ubiquitous carbonate species firmly bound to the surface OVs block the formation of the secondary oxidative species via H₂O₂ activation, assuring the dominant role of the in situ generated O₂^•- for the selective HOC dehalogenation. The carbonate-deactivated OVs of the nCuO can be feasibly recovered via air annealing for sustainable dehalogenation. This work provides a new opportunity for selective O₂^•- generation via interfacial defect engineering for dehalogenation and other environmental applications.

Cyclohexane oxidation using advanced oxidation processes with metals and metal oxides as catalysts: a review

Selective oxidation of cyclohexane has gained substantial interest in the field of research due to the prominence of its products in industrial processes. Particularly, advanced oxidation processes (AOPs) constitute a positive technology for the oxidation of cyclohexane owing to their high oxidation potentials and environmental benign properties. This review entails to address the progress made in advanced oxidation of cyclohexane over nanostructured metals and metal oxides catalysts. The main focus is directed toward the photocatalysis, Fenton oxidation and ozonation as advanced oxidation processes. Mainly, the fundamental principles, prime factors of the AOPs in conjunction with metal and metal oxide catalysts and the mechanistic insight toward the oxidation of cyclohexane are highlighted. The affirmative effects of the metals and metal oxide catalysts mainly focusing on particle size, structure and elemental composition is stressed. Lastly, the advantages and disadvantages of the AOPs and the strategic approaches to counter the disadvantages are also clearly elucidated.

Recent advances in electrocatalytic membrane for the removal of micropollutants from water and wastewater

The increasing occurrence of micropollutants in water and wastewater threatens human health and ecological security. Electrocatalytic membrane (EM), a new hybrid water treatment platform that integrates membrane separation with electrochemical technologies, has attracted extensive attention in the removal of micropollutants from water and wastewater in the past decade. Here, we systematically review the recent advances of EM for micropollutant removal from water and wastewater. The mechanisms of the EM for micropollutant removal are first introduced. Afterwards, the related membrane materials and operating conditions of the EM are summarized and analyzed. Lastly, the challenges and future prospects of the EM in research and applications are also discussed, aiming at a more efficient removal of micropollutants from water and wastewater.

The investigation of influencing factors on the degradation of sulfonamide antibiotics in iron-impregnated biochar-activated urea-hydrogen peroxide system: A QSAR study

Iron-impregnated biochar-activated urea-hydrogen peroxide (FB-activated UHP) is a potential in-situ technology for simultaneously reducing soil sulfonamide antibiotic contaminants and improving soil fertility. To better understand the degradation of sulfonamide antibiotics by FB-activated UHP, a two-dimensional quantitative structure-activity relationship (2D-QSAR) model based on quantum chemical parameters and a three-dimensional QSAR (3D-QSAR) model based on molecular force field were developed to investigate the factors influencing the removal efficiencies (Re%). The optimal 2D-QSAR model was Re%= 0.858-8.930 E-5 E_B3LYP-0.175 f(+)_x with the evaluation indices of R²= 0.732, q²= 0.571, and Q_ext²= 0.673. The given 2D-QSAR model indicated that the molecular size (E_B3LYP) and Fukui index with respect to nucleophilic attack (f(+)) were intrinsic factors influencing Re%. Three degradation pathways were subsequently proposed based on the f(+) distribution. Compared to the 2D-QSAR model, the developed 3D-QSAR model exhibited a better predictive ability, with the evaluation indices of R²= 0.989, q²= 0.696, and SEE= 0.001. The analysis of field contribution rates suggested that electrostatic field (48.2%), hydrophobic field (25.3%), and hydrogen-bond acceptor field (12.7%) were the main factors influencing Re%. These findings generated critical information for evaluating the degradation mechanisms/rules and provided theoretical bases for initially estimating the Re% of sulfonamide antibiotics undergoing FB-activated UHP process.

Heterogeneous Fenton-Like Catalysis of Electrogenerated H2O2 for Dissolved RDX Removal

New insensitive high explosives pose great challenges to conventional explosives manufacturing wastewater treatment processes and require advanced methods to effectively and efficiently mineralize these recalcitrant pollutants. Oxidation processes that utilize the fundamental techniques of Fenton chemistry optimized to overcome conventional limitations are vital to provide efficient degradation of these pollutants while maintaining cost-effectiveness and scalability. In this manner, utilizing heterogeneous catalysts and in-situ generated H2O2 to degrade IHEs is proposed. For heterogeneous catalyst optimization, varying the surface chemistry of activated carbon for use as a catalyst removes precipitation complications associated with iron species in Fenton chemistry while including removal by adsorption. Activated carbon impregnated with 5% MnO2 in the presence of H2O2 realized a high concentration of hydroxyl radical formation - 140 μM with 10 mM H2O2 - while maintaining low cost and relative ease of synthesis. This AC-Mn5 catalyst performed effectively over a wide pH range and in the presence of varying H2O2 concentrations with a sufficient effective lifetime. In-situ generation of H2O2 removes the logistical and economic constraints associated with external H2O2, with hydrophobic carbon electrodes utilizing generated gaseous O2 for 2-electron oxygen reduction reactions. In a novel flow-through reactor, gaseous O2 is generated on a titanium/mixed metal oxide anode with subsequent H2O2 electrogeneration on a hydrophobic microporous-layered carbon cloth cathode. This reactor is able to electrogenerate 2 mM H2O2 at an optimized current intensity of 150 mA and over a wide range of flow rates, influent pH values, and through multiple iterations. Coupling these two optimization methods realizes the production of highly oxidative hydroxyl radicals by Fenton-like catalysis of electrogenerated H2O2 on the surface of an MnO2-impregnated activated carbon catalyst. This method incorporates electrochemically induced oxidation of munitions in addition to removal by adsorption while maintaining cost-effectiveness and scalability. It is anticipated this platform holds great promise to eliminate analogous contaminants.

Progress of homogeneous and heterogeneous electro-Fenton treatments of antibiotics in synthetic and real wastewaters. A critical review on the period 2017-2021

Antibiotics are widely supplied over all the world to animals and humans to fight and heal bacteriological diseases. The uptake of antibiotics has largely increased the average-life expectancy of living beings. However, these recalcitrant products have been detected at low concentrations in natural waters, with potential health risks due to alterations in food chains and an increase in the resistance to bacterial infection, control of infectious diseases, and damage of the beneficial bacteria. The high stability of antibiotics at mild conditions prevents their effective removal in conventional wastewater treatment plants. A powerful advanced oxidation processes such as the electro-Fenton (EF) process is being developed as a guarantee for their destruction by ^•OH generated as strong oxidant. This review presents a critical, exhaustive, and detailed analysis on the application of EF to remediate synthetic and real wastewaters contaminated with common antibiotics, covering the period 2017-2021. Homogeneous EF and heterogeneous EF involving iron solid catalysts or iron functionalized cathodes, as well as their hybrid and sequential treatments, are exhaustively examined. Their fundamentals and characteristics are detailed, and the main results obtained for the removal of the most used antibiotic families are carefully described and discussed. The role of generated oxidizing agents is explained, and the by-products generated, and reaction sequences proposed are detailed.

H3PO4 activation mediated the iron phase transformation and enhanced the removal of bisphenol A on iron carbide-loaded activated biochar

Zero valent iron-loaded biochar (Fe⁰-BC) has shown promise for the removal of various organic pollutants, but is restricted by reduced specific surface area, low utilization efficiency and limited production of reactive oxygen species (ROS). In this study, iron carbide-loaded activated biochar (Fe₃C-AB) with a high surface area was synthesized through the pyrolysis of H₃PO₄ activated biochar with Fe(NO₃)₃, tested for removing bisphenol A (BPA) and elucidated the adsorption and degradation mechanisms. As a result, H₃PO₄ activated biochar was beneficial for the transformation of Fe⁰ to Fe₃C. Fe₃C-AB exhibited a significantly higher removal rate and removal capacity for BPA than that of Fe⁰-BC within a wide pH range of 5.0-11.0, and its performance was maintained even under extremely high salinity and different water sources. Moreover, X-ray photoelectron spectra and density functional theory calculations confirmed that hydrogen bonds were formed between the COOH groups and BPA. ¹O₂ was the major reactive species, constituting 37.0% of the removal efficiency in the degradation of BPA by Fe₃C-AB. Density functional reactivity theory showed that degradation pathway 2 of BPA was preferentially attacked by ROS. Thus, Fe₃C-AB with low cost and excellent recycling performance could be an alternative candidate for the efficient removal of contaminants.