Enhanced degradation of 2,4-dichlorophenoxyacetic acid by pre-magnetization Fe-C activated persulfate: Influential factors, mechanism and degradation pathway

Performance and mechanism of biochar@FeMg-LDH for efficient activation of persulfate for degradation of 2, 4-dichlorophenol in groundwater

Groundwater environments are complex, and traditional advanced oxidation technologies mainly based on free radicals have limitations such as poor selectivity and low interference resistance, making it difficult to efficiently degrade target pollutants in groundwater. Therefore, we developed a sludge-based biochar-supported FeMg-layered double hydroxide catalyst (BC@FeMg-LDH) for the catalytic degradation of 2, 4-dichlorophenol (2, 4-DCP) using persulfate (PDS) as an oxidant. The removal efficiency of the catalyst exceeded 95%, showing high oxidation activity in a wide pH range while being almost unaffected by reducing substances and ions in the environment. Meanwhile, under neutral conditions, the leaching of metal ions from BC@FeMg-LDH was minimal, thereby eliminating the risk of secondary pollution. According to quenching experiments and electron paramagnetic resonance spectroscopy, the main active species during BC@FeMg-LDH/PDS degradation of 2, 4-DCP is 1O2, indicating a non-radical reaction mechanism dominated by 1O2. Characterization techniques, including X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, revealed that the carbonyl (C = O) and metal hydroxyl (M-OH) groups on the material surface were the main reactive sites mediating 1O2 generation. The 1O2 generation mechanism during the reaction involved ketone-like activation of carbonyl groups on the biochar surface and complexation of hydroxyl groups on the material surface with PDS, resulting in the formation of O2·- and further generation of 1O2. 1O2 exhibited high selectivity toward electron-rich organic compounds such as 2, 4-DCP and demonstrated strong interference resistance in complex groundwater environments. Therefore, BC@FeMg-LDH holds promising applications for the remediation of organic-contaminated groundwater.

Efficient activation of peroxodisulfate by novel bionic iron-encapsulated biochar: The key roles of electron transfer pathway and reactive oxygen species evolution

In this study, a novel iron-encapsulated biochar (Fe@BC) was prepared using the biomass cultivated with an iron-containing solution. The iron in Fe@BC showed the phase change from Fe₃O₄ to α-Fe, and to CFe_15.1, with the increase of pyrolysis temperature (500-900 °C), and a graphene shell formed on the surface of Fe@BC. In addition, the signals assigned to the π-π* shake up, pyridinic N, graphitic N, and defects of Fe@BC were found to be stronger as the pyrolysis temperature increased. The F4@B9 sample, which was prepared at 900 °C, exhibited an excellent performance (98.01 %) to activate peroxydisulfate (PDS) for the degradation of 2,4-dichlorophenol. Electron paramagnetic resonanceand chemical quenching experiments revealed that reactive oxygen radicals (ROS) including sulfate radical (•SO₄^-), hydroxyl radical (•OH), superoxide radical (•O₂^-), and singlet oxygen (¹O₂) existed in the F4@B9/PDS system. Furthermore, the micro-electrolysis process facilitated the generation of •O₂^- (12.35 %) and ¹O₂ (6.49 %) compared with the pure PDS system. Density functional theory revealed that, for the F4@B9-activated PDS process, the graphene shell of F4@B9 served as catalytic active sites as well. According to the correlation analysis, the iron specie of CFe_15.1 was more favorable for the generation of ROS than α-Fe. Also, π-π* shake up, pyridinic N, graphitic N, and defects participated in the PDS activation. This study provides a new method for the preparation of high-performance catalysts from naturally grown biomass with high iron contents.

Environmental-friendly hydrochar-montmorillonite composite for efficient catalytic degradation of dicamba and alleviating its damage to crops

In recent years, carbon-based materials catalyzing peroxymonosulfate (PMS) for green degradation of persistent organic pollutants have attracted increasing attention. However, PMS activation by hydrochar composite (e.g. hydrochar-montomorillonite) has rarely been investigated. Herein, a simple preparation, low-cost and eco-friendly catalyst of hydrochar-montmorillonite composite (HC-Mt) was prepared to firstly catalyze PMS for the degradation of dicamba (DIC). The as-prepared HC-Mt showed a remarkably better catalyzing performance for PMS than pure hydrochar (HC) due to its good physicochemical characteristics and abundant oxygen-containing groups. Furthermore, the electron spin resonance (ESR) and quenching tests revealed that active species such as SO₄^-, OH and O₂^- all participated in the degradation process. DIC sites on C6, Cl 10, and O15 exhibited higher reactivity according to the density functional theory (DFT) calculation, which were easily attacked by active species. The DIC degradation mainly occurred via hydroxyl substitution, decarboxylation, oxidation and ring-cleavage and finally most of the intermediates were mineralized into CO₂ and H₂O. Finally, the phytotoxicity assessment was measured by the germination growth situation of tobacco and mung beans in the presence of DIC (with or without treatment by HC-Mt/PMS). The result showed that HC-Mt/PMS could significantly reduce the phytotoxicity of DIC to crops, suggesting that catalyzing PMS using HC-Mt was environmentally friendly. Therefore, this work did not only provide a novel catalyzing PMS strategy using hydrochar composite for wastewater treatment, but also give a new idea for herbicide phytotoxicity management.

Large-Scale Synthesis of Iron Ore@Biomass Derived ESBC to Degrade Tetracycline Hydrochloride for Heterogeneous Persulfate Activation

Iron-based catalysts are widely used in water treatment and environmental remediation due to their abundant content in nature and their ability to activate persulfate at room temperature. Here, eggshell biochar-loaded natural iron slag (IO@ESBC) was successfully synthesized to remove tetracycline hydrochloride (TCH) by activated persulfate. The morphology, structure and chemical composition of IO@ESBC were systematically characterized. The IO@ESBC/PS process showed good performance for TCH removal. The decomposition rate constant (k) for IO@ESBC was 0.011 min−1 and the degradation rate was 3690 mmol/g/h in this system. With the increase of PS concentration and IO@ESBC content, the removal rate of TCH both increased. The IO@ESBC/PS process can effectively remove TCH at pH 3–9. There are different effects on TCH removal for the reason that the addition of water matrix species (humic acid, Cl−, HCO3−, NO3− and HPO42−). The IO@ESBC/PS system for degrading TCH was mainly controlled by both the free radical pathway (SO4•−, •OH and O2•−) and non-free radical pathway (1O2). The loading of ESBC slows down the agglomeration between iron particles, and more active sites are exposed. The removal rate of TCH was still above 75% after five cycles of IO@ESBC. This interesting investigation has provided a green route for synthesis of composite driving from waste resources, expanding its further application for environmental remediations.

Enhanced removal of organic contaminants by novel iron-carbon and premagnetization: Performance and enhancement mechanism

Iron-carbon (Fe-C) microelectrolysis has attracted considerable attention in wastewater treatment due to its excellent ability to remove contaminants. Herein, novel Fe-C granules were synthesized by simple calcination method for removing organic contaminations, and a cost-effective and environmentally friendly method, namely pre-magnetization, was used to improve the micro-electrolysis performance of Fe-C. Batch experiments proved that premagnetized iron-carbon (pre-Fe-C) could significantly improve the removal of methyl orange (MO) at different Fe-C mass ratios (1:2-2:1), material dosages (1.0-2.5 g/L), initial pH values (3.0-5.0), and MO concentrations (10.0-50.0 mg/L). Electrochemical analysis showed that premagnetization could increase the current density and reduce the charge transfer resistance of the microelectrolysis system, making Fe-C more susceptible to electrochemical corrosion. Characterizations confirmed that the corrosion products of the materials included FeO, Fe₂O₃, and Fe₃O₄, and more corrosion products were formed in the pre-Fe-C system. Radical quenching experiments and electron spin resonance spectroscopy verified that ^•OH, ¹O₂, and O₂^-• were all involved in pollutant removal, and premagnetization could promote the generation of more reactive oxygen species. Overall, the pre-Fe-C process could effectively remove various organic pollutants, exhibit good adaptability to complex water environments, and hold potential for industrial applications.

Activated persulfate by iron-carbon micro electrolysis used for refractory organics degradation in wastewater: a review

With the rapid economic development, the discharge of industrial wastewater and municipal wastewater containing many refractory organic pollutants is increasing, so there is an urgent need for processes that can treat refractory organics in wastewater. Iron-carbon micro electrolysis and advanced oxidation based on persulfate radicals (SO₄^-·) have received much attention in the field of organic wastewater treatment. Iron-carbon micro electrolysis activated persulfate (Fe-C/PS) treatment of wastewater is characterized by high oxidation efficiency and no secondary pollution. This paper reviews the mechanism and process of Fe-C/PS, degradation of organics in different wastewater, and the influencing factors. In addition, the degradation efficiency and optimal reaction conditions (oxidant concentration, catalyst concentration, iron-carbon material, and pH) of Fe-C/PS in the treatment of refractory organics in wastewater are summarized. Moreover, the important factors affecting the degradation of organics by Fe-C/PS are presented. Finally, we analyzed the challenges and the prospects for the future of Fe-C/PS in application, and concluded that the main future directions are to improve the degradation efficiency and cost by synthesizing stable and efficient catalysts, optimizing process parameters, and expanding the application scope.

Enhanced degradation of 2,4-dichlorophenoxyacetic acid by electro-fenton in flow-through system using B, Co-TNT anode

A flow-through system was constructed for 2,4-dichlorophenoxyacetic acid (2,4-D) degradation for the first time using efficient boron and cobalt co-doped TiO₂ nanotubes (B, Co-TNT) as the anode and carbon black doped carbon felt (CB-CF) that had a high H₂O₂ yield as the cathode. Compared with dimensionally stable anode (DSA), whether in anodic oxidation (AO) or AO-electro-Fenton (EF) system, 2,4-D degradation in B, Co-TNT anode system was more efficient accompanying with a lower energy consumption (Ec). Different operating parameters including applied current density, initial pH and flow rate were explored, supporting that the optimal Fe²⁺ dosage was 0.5 mM while decreasing the initial pH and increasing the current intensity and flow rate were beneficial to 2,4-D removal. In this AO-EF system, the involved mechanisms for 2,4-D degradation were anodization and Fenton oxidation, possessing the comprehensive effect of ^•OH and SO₄^•- with their contribution of 92.7% and 4.8%, respectively. This flow-through AO-EF system performed a stable performance, and an efficient degradation performance with low Ec (5.8-29.5 kWh (kg TOC)^-1) was obtained for different kinds of contaminants (methylene blue, phenol, p-nitrophenol and sulfamethazine). Therefore, B, Co-TNT anode coupled with CB-CF cathode in flow-through system was effective for contaminants degradation.

Reactive oxygen species formation driven by acidophiles mediated pyrite oxidation and its potential role on 2,4-dichlorophenol transformation

Researches of reactive oxygen species (ROS) generation from pyrite oxidation and its impact on contaminants transformation has been constrained to abiotic conditions. However, pyrite oxidation by acidophiles is widespread in acidic environments. The potential role of these microorganisms on pyrite-induced ROS formation and pollutants processing is not understood well. Here, ROS production and 2,4-DCP transformation during pyrite oxidation under oxic and anoxic atmospheres by Acidithiobacillus ferrooxidans (A. ferrooxidans) were explored. 2,4-DCP removal was enhanced in biosystem. Under oxic and anoxic conditions, microbially mediated pyrite oxidation resulted in removing 93.66% and 43.77% 2,4-DCP, which were 1.14- and 1.51-fold greater than that without cells. Based on intermediates identified by LC-MS, the transformation pathway of 2,4-DCP was proposed. The trapping experiments demonstrated ROS contributed during 2,4-DCP transformation. The improving effect of A. ferrooxidans on 2,4-DCP degradation was mainly due to ROS increase. A. ferrooxidans was to promote pyrite surface renew, exposing more Fe(II) and Fe(III) sites that facilitated O₂ reduction and H₂O dissociation for ROS generation. Biogenic ROS and sulfite bio-oxidation with the free radical mechanism provided other ROS sources. ESR revealed A. ferrooxidans-pyrite interaction led to sustainable ROS production, indicating it could be a significant pathway in driving geochemical cycles of elements.

Oxidative degradation of tetracycline using peroxymonosulfate activated by cobalt-doped pomelo peel carbon composite

Tetracycline (TC) is a typical ecotoxic antibiotic, which easily causes bacterial resistance. Therefore, it is necessary to remove TC from the water environment. In recent years, advanced oxidation processes (AOPs) rely on the use of highly reactive oxidizing sulfate radical which is turning into an increasingly popular as a tool of the removal of TC. In this study, cobalt-doped pomelo peel carbon composite (Co-PPCC) was prepared by the impregnation coprecipitation method to activate peroxymonosulfate (PMS) to remove TC. SEM, BET, XRD, FTIR, XPS, TGA, and other analytical techniques indicated that a carbon composite catalyst with excellent performance has been successfully prepared. TC was removed by the synergistic effect of adsorption and catalytic degradation processes. The adsorption capacity was limited (only approximately 20% within 60 min) and tending to saturation, which indicated that the removal of TC in the Co-PPCC/PMS system was mainly due to oxidative degradation. The influence of the Co-PPCC and PMS dosage, initial TC concentration, initial pH values, and coexisting anions on the removal efficiency of TC was investigated. When the Co-PPCC catalyst dosage was 1 g/L, PMS concentration was 2 g/L, and pH value was 11, the removal efficiency of TC with a concentration of 50 mg/L reached 99% within 60 min. Free radical quenching experiment and electron paramagnetic resonance (EPR) analysis indicated that the free radical and non-radical degradation processes exist in the Co-PPCC/PMS/TC system. The main degradation products and the possible transformation pathways of TC were explored by LC-MS. In addition, after four cycles of Co-PPCC tests, the removal efficiency of TC can reach 64%. This study provides a new method to reuse abandoned pomelo peels and synthesize an economical and environmentally friendly catalyst for activating peroxymonosulfate to remove TC antibiotics in water.

Magnetized Activated Carbon Synthesized from Pomegranate Husk for Persulfate Activation and Degradation of 4-Chlorophenol from Wastewater

The compound 4-chlorophenol (4-CP) is known to be a highly toxic compound having harmful effects on human health and the environment. To date, the removal of 4-CP by advanced oxidation processes (AOPs) has attracted tremendous attentions. The persulfate-based AOPs show higher oxidation, better selectivity, wider pH range, and no secondary pollution compared to the traditional Fenton-based AOPs. Carbon materials with low cost and chemical stability are useful for the activation of persulfate (PS) to produce reactive species. Herein, we magnetized activated carbon synthesized from pomegranate husk (MPHAC). By using 4-CP as a model organic pollutant, tests of the activation of PS via MPHAC for the removal of 4-CP were performed. Batch processes were carried out to study the influence of different parameters (initial solution pH, catalyst dose, PS dose, and initial 4-CP concentration) on the adsorption of 4-CP on PHAC with ferric oxide (Fe3O4-PHAC). The results show that under the obtained optimal conditions (MPHAC dose: 1250 mg/L, PS dose: 350 mg/L, solution pH 5, an initial 4-CP concentration of 100 mg/L, and a contact time of 60 min), a 4-CP removal factor of 99.5% was reached by the developed MPHAC/PS system. In addition, it was found that reusing MPHAC in five successive cycles is feasible because the catalyst in the last cycle kept exhibiting a high potential for 4-CP absorption, indicating the economically viable procedure. Therefore, this study provides a comprehensive understanding on the degradation of 4-CP by the magnetized activated carbon persulfate system.

Insights into enhanced peroxydisulfate activation with S doped Fe@C catalyst for the rapid degradation of organic pollutants

In this study, the S modified iron-based catalyst (S-Fe@C) for activating peroxydisulfate (PDS) was fabricated by heating the S-MIL-101 (Fe) precursor at 800 °C. The resulted S-Fe@C composite mainly consisted of carbon, Fe⁰, FeS, FeS₂, and Fe₃O₄, and showed strong magnetism. Compared with Fe@C obtained from MIL-101 (Fe), the S-Fe@C exhibited much higher performance (1.5 times larger) on PDS activation and the S-Fe@C/PDS could rapidly degrade various organic pollutants in 5 min under the attack of the species of SO₄^-·, ¹O₂, electro-transfer and Fe(IV). The S element in enhancing the PDS activation mainly involved two mechanisms. Firstly, the doped S could speed up the electron transfer efficiency, resulting in a promotion on PDS decomposition; secondly, the S^2- S₂^2- or S⁰ could achieve the circulation of Fe²⁺ and Fe³⁺, leading to the formation of non-radicals Fe(IV) and ¹O₂.

A microwave radiation-enhanced Fe-C/persulfate system for the treatment of refractory organic matter from biologically treated landfill leachate

In this study, a microwave (MW) radiation enhanced Fe-C/PS system was used to treat refractory organic matter in biologically-treated landfill leachate. The effects of important influencing factors on the refractory organic matter in biologically treated landfill leachate were explored, and the main reactive oxygen species produced in the system were verified. The mechanism by which humus was degraded was investigated by analyzing effectiveness of organics removal in different systems, and comparative analysis was conducted on the Fe-C materials before and after the reaction. The results showed that degradation capacity and reaction rate of the system could be improved with an increase in the Fe-C/PS dosage and MW power, while initial acidic conditions were also conducive to the degradation of organic matter. Under the conditions of an Fe-C of 1 g L-1, PS dosage of 30 mM, MW power of 240 W, and reaction time of 10 min, the UV254, TOC, and CN removal efficiencies were 51.48%, 94.56%, and 51.59%, respectively. In the MW/Fe-C/PS system, a large amount of and a small amount of ˙OH were generated by the thermal activation of PS to remove organic matter. The removal efficiency of organic matter could be further improved via the homogeneous catalytic oxidation and heterogeneous adsorption catalytic oxidation of Fe-C materials. In addition, the MW/Fe-C/PS system was effective for removing refractory organic matter from the leachates from four typical treatment systems: DTRO, SAARB, MBR, and NF. The MW/Fe-C/PS system has the potential to be widely applied for the treatment of landfill leachate.

Iron-carbon microelectrolysis for wastewater remediation: Preparation, performance and interaction mechanisms

Rapid industrialization and urbanization have produced a lot of hazardous substances in water and wastewater, which has turned into a crucial issue to the environment and the public health. Recently, iron carbon microelectrolysis (IC-ME) has attracted extensive attention in environmental remediation due to its low costs and excellent performance. Nevertheless, there is still a lack of a more systematic review on IC-ME preparation methods, their performance, and the interaction mechanisms of IC-ME in the remediation of wastewater. Herein, this work summarizes the synthetic methods, application of IC-ME materials, and the mechanism of pollutant removal by IC-ME. A variety approaches have been applied to prepare IC-ME materials, and the preparation methods and conditions have a certain influence on the properties of IC-ME materials, thus affecting the performance of pollutant removal. The mechanisms of IC-ME for contaminants removal are very complex, including adsorption, coprecipitation, reduction, surface complexation, and oxidation. Moreover, research vacant fields and problems that existed in the application of IC-ME are proposed. At last, the problems to be addressed to adapt IC to future applications are introduced. This paper reviews and prospects IC-ME wastewater remediation technology, which provides a reference for further scientific research and engineering applications.

The radical and non-radical oxidation mechanism of electrochemically activated persulfate process on different cathodes in divided and undivided cell

Electrochemically activated persulfate (PS) employing stainless steel (SS), carbon felt (CF) and carbon black modified CF (CB-CF) as the cathode, in the divided and undivided cell, respectively, for degradation of atrazine (ATZ) was first investigated using novel B, Co-doped TiO₂ nanotubes (B, Co-TNT) anode. In undivided cell, ATZ degradation was followed the order of CF<CB-CF<SS. The main radical for ATZ removal in SS and CF system was ^•OH, while on CB-CF cathode, it was the comprehensive contribution of ^•OH and SO₄^•-. ^•OH in SS system was more inclined to free ^•OH, while in CF and CB-CF systems it was more likely to be surface ^•OH. In divided anode cell, ^•OH was responsible for ATZ degradation in all three cathodes system. However, in divided cathode cell, ^•OH played a major role for ATZ degradation in SS cathode system. In CF and CB-CF cathode systems, the ATZ degradation was the comprehensive effect of ^•OH and SO₄^•- with the contribution of ^•OH and SO₄^•- was 91.7%, 8.3%, and 96.3%, 3.6%, respectively. The quenching studies showed that non-radical oxidation occurred in anode chamber in the presence of PS. Besides, the intermediates in divided and undivided cell were detected by LC-MS, and the possible degradation pathway was proposed.

Degradation of 2,4-DCP using persulfate and iron/E-carbon micro-electrolysis coupling system

The greenhouse gas carbon dioxide (CO₂) was converted to a novel CO₂ conversion material (electrolytic carbon, EC) by molten salt electrochemical conversion, which served as the carbon source to prepare an iron-carbon composite (Fe-EC). The composite was used to activate persulfate (PS) and degrade 2,4-dichlorophenol (2,4-DCP) in an aqueous solution. The effects of several essential operating parameters such as PS dosage and pH on 2,4-DCP degradation were investigated. The removal efficiency of 2,4-DCP (20 mg L^-1) was 97.8% in the presence of Fe-EC (50 mg L^-1) and PS (1 mmol L^-1). Moreover, the average % reaction stoichiometric efficiency (RSE) (calculated for all selected times 5-60 min) was maintained at 23.07%. Electron paramagnetic resonance (EPR), classical radical scavenging experiments, and density functional theory (DFT) calculations were integrated for a mechanistic study, which disclosed that the active species in the system were identified as SO₄^⦁-, •OH, and O₂^⦁-. Moreover, the iron-carbon micro-electrolysis/PS (ICE-PS) system had a high tolerance to a wide range of pH, which would provide theoretical guidance for the treatment of organic pollutants in practical industrial wastewater.

Preparation and application of Fe/biochar (Fe-BC) catalysts in wastewater treatment: A review

The removal of organic pollutants from water environments is a challenging problem. Fe-based BC (Fe-BC) composites are promising catalysts for generating reactive oxygen species (ROS) for environmental remediation considering their low costs and excellent physicochemical surface characteristics. The synthesis methods, properties, applications, and the mechanism of Fe-BC for removing pollutants are reviewed. Various methods have been used to prepare Fe-BC composites, and the synthetic methods and conditions used affect the properties of the Fe-BC material, thereby influencing its pollutant removal performance. The mechanisms of pollutant removal by Fe-BC are intricate and include adsorption, degradation and reduction. Fe loading on BC could improve the performance of BC by affecting its surface area, surface functional groups and electron transfer rate. Moreover, research gaps and uncertainties that exist in the use of Fe-BC were identified. Finally, the problems that need to be solved to make Fe-BC suitable for future applications are described.

Perdisulfate-assisted advanced oxidation of 2,4-dichlorophenol by bio-inspired iron encapsulated biochar catalyst

To improve advanced oxidation processes (AOPs), bio-inspired iron-encapsulated biochar (bio-inspired Fe⨀BC) catalysts with superior performance were prepared from iron-rich biomass of Iris sibirica L. using a pyrolysis method under anaerobic condition. The obtained compounds were used as catalysts to activate perdisulfate (PDS) and then degradate 2,4-dichlorophenol (2,4-DCP), and synthetic iron-laden biochar (synthetic Fe-BC) was used for comparison. The highest removal rate of 2,4-DCP was 98.35%, with 37.03% of this being distinguished as the contribution of micro-electrolysis, greater than the contribution of adsorption (32.81%) or advanced oxidation (28.51%). The high performance of micro-electrolysis could be attributable to the formation of Fe (Iron, syn) and austenite (CFe_15.1) with strong electron carrier at 700 °C. During micro-electrolysis, Fe²⁺ and electrons were gradually released and then used as essential active components to enhance the AOPs. The slow-releasing Fe²⁺ (K = 0.0048) also inhibited the overconsumption of PDS (K = -0.00056). Furthermore, the electrons donated from Fe⨀BC-4 were able to activate PDS directly. The electrons were enriched by the porous structure of Fe⨀BC-4, and the formation of the COFe bond in the π-electron system could also accelerate the electron transfer to activate PDS. Similar reactive oxygen species (ROS) were identified during the micro-electrolysis and AOPs, leading to similar degradation pathways. The higher does concentration of O₂^- generated during micro-electrolysis than during the AOPs also led to a greater dechlorination effect.

Ultrasonic coupling with electrical current to effective activation of Persulfate for 2, 4 Dichlorophenoxyacetic acid herbicide degradation: modeling, synergistic effect, and a by-product study

In this research work, we investigated the ability of the oxidative degradation of 2, 4-Dichlorophenoxy acetic acid herbicide via ultrasonic-assisted in electro-activation of the persulfate system in the presence of nano-zero valent iron. The effect of experimental parameters such as pH value [4-8], electrical current (0.5-1 A), persulfate concentration (0.25-0.5 mg.l-1), nano zero-valent iron dose (0.05-0.1 mg.l-1), and initial organic pollutant concentration (50-100 mg.l-1) on the ultrasonic-electropersulfate process performance was assessed via central composite design. The combination of ultrasonic waves with the electrochemical process to activation of persulfate showed better efficiency into 2, 4-Dichlorophenoxy acetic acid herbicide degradation compared to their implementation in individual and binary systems. Following optimal conditions (pH = 5.62, 0.80 A applied electrical current, 0.39 mg/L persulfate concentration, 0.07 mg/L nano-zero valent iron, and 50 mg/L 2,4-Dichlorophenoxy acetic acid concentration in 40 min reaction), nearly 91% removal was done. Moreover, the complete removal of 2, 4-Dichlorophenoxy acetic acid, 92% COD, and 88% TOC removal was achieved by this process near 140 min reaction. The scavenging experiment confirmed the role of free oxidizing species in the degradation of 2, 4-Dichlorophenoxy acetic acid during the process. Approximately 50% improved 2, 4-Dichlorophenoxy acetic acid removal in the process against the inclusive efficiency of single mechanisms. The obtained results were fitted to the pseudo-first-order kinetic model with a high correlation coefficient (R2 = 0.96). Five important intermediate products of 2, 4-D oxidation were 2, 4-dichlorophenol (2, 4-DCP), 2, 6-dichlorophenol (2, 6-DCP), 4, 6 dichlororesorcinol (4, 6-DCR), 2-chlorohydroquinone (2-CHQ), and 2-chloro-1, 4-benzoquinone (2-CBQ). In the end, can be employed as a satisfactory advanced oxidation process in high mineralization of 2, 4-D and refractory organic pollutants.

Enhancement of Fe-C micro-electrolysis in water by magnetic field: Mechanism, influential factors and application effectiveness

Fe-C micro-electrolysis system has been widely used in filters, or as an advanced treatment process in some water treatment plants to treat various wastewater. In this study, Fe-C micro-electrolysis process was enhanced by an economical and environmentally friendly method, applied magnetic field. Batch kinetic experiments and scanning electron micrographs demonstrated a more effective micro-electrolysis and more severely corroded on the surface of Fe-C after applying a magnetic field at pH 3.0. An applied magnetic field reduced the charge-transfer resistance and increased the current density in micro-electrolysis system and Fe-C became more prone to electrochemical corrosion. Corrosion products were proved to be Fe²⁺, Fe₃O₄, and C-O, moreover, the formation of them were also increased in the presence of a magnetic field. Base on that, some influential factors like magnetic field flux intensity, Fe-C particle size, pH, Fe-C dosage and its reusability were investigated in this paper. Since Fe²⁺ release was accelerated in micro-electrolysis system by an applied magnetic field, combination of various advanced oxidation processes were designed to explore the application effectiveness of the system. The degradation rate of target contaminant was significantly improved in the presence of a magnetic field, suggesting it could be a reliable method for wastewater treatment.

Enhanced visible-light photoactivities of porous LaFeO3 by synchronously doping Ni2+ and coupling TS-1 for CO2 reduction and 2,4,6-trinitrophenol degradation

TOC showing the enhanced visible-light photoactivities of porous LaFeO3 by synchronously doping with Ni2+ and coupling with TS-1 for CO2 reduction and 2,4,6-trinitrophenol degradation.

Kinetic and mechanism study of UV/pre-magnetized-Fe0/oxalate for removing sulfamethazine

In this study, UV irradiated photochemical reactions of oxalate (Ox) with premagnetized-Fe⁰ (pre- Fe⁰) as the catalyst was used to degrade sulfamethazine (SMT). Magnetic field promoted the release of iron ion from Fe⁰ thus enhanced SMT and Ox removal in UV/pre- Fe⁰/Ox process. X-ray photoelectron spectroscopy demonstrated that the presence of UV and Ox promoted the transformation of Fe³⁺ to Fe²⁺ on Fe⁰, which enhanced the surface bound •OH (•OH_surf) generation. Ox inhibited the formation of iron (hydro)xides and enhanced the hydroxylation of Fe⁰ surface. •OH_surf was mainly responsible for SMT removal (44%), while UV direct photolysis and •OH in the solution both caused around 28% SMT removal. The process with Ox exhibited much higher efficiency in SMT degradation than that added with H₃PO₄, citric acid and ethylenediaminetetraacetic acid, which greatly expanded the chelate-modified Fenton processes and their treatment efficiency.

The bio-chemical cycle of iron and the function induced by ZVI addition in anaerobic digestion: A review

Zero-valent iron (ZVI) is known to be an additive in facilitating waste treatment and improving biogas production in anaerobic digestion (AD) systems. This review concentrates on the chemical cycle of iron as well as the function of the iron cycle in the removal of four kinds of pollutants: organic carbon, nitrogen, sulphur and phosphorus, which are commonly encountered in waste treatment. In recent studies, the addition of ZVI to an AD system promoted the in-situ production of CH₄ from CO₂, enabling carbon capture through biotechnology. Additionally, using iron-carbon microbial electrolytic cells in AD systems in order to accelerate electron transport, as well as specific pollutant degradation mechanisms, are illustrated in the present study. Particularly, the main factors affecting the removal efficiency of contaminants in a ZVI-AD system such as pH, VFA/ Alkalinity (ALK), oxidation-reduction potential and particle size are reviewed. According to the above characteristics, combined with technical model and economic analyses, an AD system based on ZVI was considered to be an economical, efficient and carbon-neutral pollutant treatment technology. Accordingly, Iron-based AD is suggested to be a promising and sustainable approach orientated to a circular economy, which may be applied to many waste treatments fields.

High-efficiency degradation of organic pollutants with Fe, N co-doped biochar catalysts via persulfate activation

In this study, the Fe, N co-doped biochar (Fe-N-BC) was prepared by pyrolyzing wheat straw, urea and iron salts and used to activate persulfate (peroxydisulfate, PS) for organic contaminant degradation. Iron oxide doping not only introduced magnetism into the biochar for easy separation, but also influenced its catalytic ability for PS activation. In the Fe-N-BC/PS system, almost all acid orange (AO7) was removed within 90 min with an apparent rate constant (k_obs) of 0.114 min^-1, which was almost 37 times larger than that of pure N-BC (0.003 min^-1). Factors influencing the removal of AO7 were investigated, including PS concentration, catalyst dosage, and initial pH. The Fe-N-BC/PS system had high removal efficiencies for various organic contaminants and showed high resistance to inorganic anions in aquatic environments. The radical quenching studies, electron paramagnetic resonance (EPR) measurements, and electrochemical analyses verified that the mechanism of AO7 degradation in the Fe-N-BC/PS system included both radical and non-radical pathways involving the generation of OH, SO₄^-, O₂^-, ¹O₂, and electron transfer. Additionally, persistent free radicals (PFRs) on the catalysts also related to their catalytic efficiencies. These results demonstrated that the Fe-N-BC/PS system had the potential for wastewater treatment applications.

A comparative study on the treatment of 2,4-dinitrotoluene contaminated groundwater in the combined system: efficiencies, intermediates and mechanisms

In this study, scrap irons (SI)/granular activated carbons (GAC) micro-electrolysis treatment and persulfate-releasing materials (PRM) treatment were employed to construct the combination reduction and oxidation system to treat 2,4-dinitrotoluene (2,4-DNT) contaminated groundwater. The 2,4-DNT treatment efficiencies in the PRM pre-treatment before SI/GAC micro-electrolysis treatment (FM-1 = PRM + SI/GAC) and SI/GAC micro-electrolysis pre-treatment before the PRM treatment (FM-3 = SI/GAC + PRM) were investigated in two separated columns. As control groups, the separated SI and GAC instead of the SI/GAC mixture were used in another two separated columns (FM-2 = PRM + SI + GAC; FM-4 = SI + GAC + PRM). The highest treatment efficiencies of 2,4-DNT in the FM-1 and FM-3 systems reached 79% and 93% during 5 PV, respectively. We found that the filling position of SI, GAC and PRM significantly affected the variations of pH, oxidation-reduction potential, Fe²⁺ and S₂O₈^2- concentrations in the combined systems. These results indicated that the SI/GAC micro-electrolysis pre-treatment of 2,4-DNT before the PRM treatment (FM-3) is more beneficial. The fifteen main intermediates in the combined system were identified by the detection of liquid chromatograph mass spectrometer. Furthermore, the possible treatment pathways of 2.4-DNT were proposed on the basis of identified intermediates. The treatment mechanisms in the FM-1 and FM-3 systems were proposed with the reduction mechanism in the SI/GAC micro-electrolysis system and the oxidation mechanism in the PRM treatment. Therefore, the combination of the reduction pre-treatment with the SI/GAC micro-electrolysis system and the oxidation post-treatment with persulfate can effectively treat the nitroaromatic compounds contaminated groundwater.

Chemical removal and selectivity reduction of nitrate from water by (nano) zero-valent iron/activated carbon micro-electrolysis

The processes of (n)ZVI/AC（（nano）zero valent iron/activated carbon）micro-electrolysis were applied for nitrate removal from groundwater, aiming to reduce nitrate to N₂, an environmentally friendly end product. (n)ZVI was utilized and combined with selected commercial AC to form the micro-electrolysis. Effect of different operational parameters, including reductant dosage, (n)ZVI/AC ratios, and reaction pH, on nitrate and TN removal were cleared. The results showed that nZVI presents higher reaction activities than ZVI in micro-electrolysis. With the increase of the (n)ZVI/AC mass ration from 1:2 to 2:1, the TN removal increased from 16.8% to 38.9%, then declined with the further increase of the ratio. The nitrate removal was negatively correlated with the initial pH of the solution. Compared to ZVI particles, even with a lower dosage, nZVI presented 100% nitrate removal at acidic and neutral pH conditions, and TN removal could maintain higher than 35% with pH lower than 9.0. A kinetic model was also established to explain the pathways of nitrate removal, and the results indicated that AC not only enriched nitrate as an adsorbent but also present highly potential in catalytic converting nitrate to N₂. The technique presented great potentials in removing nitrate from water and a promising application prospect.

Zero-valent iron/activated carbon microelectrolysis to activate peroxydisulfate for efficient degradation of chlortetracycline in aqueous solution

Tetracycline antibiotics are widely used in human and veterinary medicine; however, their gradual increase in the aquatic environment poses a serious threat to human health and ecosystems. The reactivity of peroxydisulfate (PDS) in the degradation of chlortetracycline (CTC) in aqueous solution using a zero-valent iron/activated carbon (AC) microelectrolysis method (Fe⁰–AC/PDS) was investigated by batch experiments. The results showed that the effects of different systems were as follows: Fe⁰–AC/PDS > Fe⁰/PDS > AC/PDS > Fe⁰–AC > AC > Fe⁰ > PDS. In the Fe⁰–AC/PDS system, the degradation efficiency of CTC could reach 88% under the following optimal experimental conditions: Fe⁰ dose of 0.4 g L⁻¹, PDS dose of 2 g L⁻¹, pH of 3 and initial CTC concentration of 50 mg L⁻¹. The presence of Cl⁻, HCO₃⁻ and H₂PO₄⁻ inhibited the degradation of CTC, while humic acid accelerated the degradation rate of CTC. The mineralization of CTC was evaluated from the TOC, with a value of 31.44% in 7 h. Free radical identification experiments showed that SO₄⁻˙ and O₂⁻˙ were involved in the degradation of CTC. The iron and carbon materials had good reusability, and the degradation rate of CTC was still approximately 70% after four cycles. Finally, the possible mechanism for the degradation of CTC by the Fe⁰–AC/PDS systems was discussed. Based on the above conclusions, Fe⁰–AC microelectrolysis is a new heterogeneous catalytic method for green and efficient activation of PDS and demonstrates potential applicability in the treatment of wastewater.

The microelectrolysis system composed of zero-valent iron and activated carbon can effectively activate persulfate to produce SO₄⁻˙ and O₂⁻˙, which have excellent capacity for degradation of chlortetracycline hydrochloride.

Ferrous metal-organic frameworks with stronger coordinatively unsaturated metal sites for persulfate activation to effectively degrade dibutyl phthalate in wastewater

In the advanced oxidation system (AOPs) of persulfate (PS) activated by iron-based metal-organic frameworks (MOFs), aim at solving the problem on the treatment difficulty of wastewater with low concentration persistent organic pollutants (POPs), a new type of ferrous metal-organic frameworks (Fe(Ⅱ)-MOFs) with stronger coordinatively unsaturated metal sites (CUS) was successfully synthesized by different methods. The catalytic performance of Fe(Ⅱ)-MOFs was were obtained by the experiment of degrading dibutyl phthalate (DBP) through persulfate activation. It was found that the degradation efficiency of 0.018 mmol L^-1 DBP was 86.73% under the conditions of 0.40 g L^-1 and 2.70 mmol L^-1 persulfate at a wide pH range. At the same time, the crystal structure and surface morphology of Fe(Ⅱ)-MOFs did not change significantly after reaction and it could still maintain the removal rate of 75.44% of the target pollutants in the fifth cycle. Furthermore, in the consideration of iron valence state of MOFs before and after reaction, and combined with the analysis of electrochemical properties, the possible mechanism of PS activation was proposed, namely the metastable electron layer inside ferrous ions produced the internal power to accelerate the electron transfer in CUS, leading to improve the activity of the catalyst.

Highly Efficient Utilization of Nano-Fe(0) Embedded in Mesoporous Carbon for Activation of Peroxydisulfate

Nanoscale zerovalent iron (nZVI) particles have received much attention in environmental science and technology due to their unique electronic and chemical properties. However, the aggregation and oxidation of nZVI brings much difficulty in practical application of environmental remediation. In this study, we reported a composite nano-Fe(0)/mesoporous carbon by a chelation-assisted coassembly and carbothermal reduction strategy. Nano-Fe(0) particles with surface iron oxide (Fe₂O₃·FeO) were wrapped with graphitic layers which were uniformly dispersed in mesoporous carbon frameworks. The unique structure made the nano-Fe(0) particles stable in air for more than 20 days. It was used as a peroxydisulfate (PDS) activator for the oxidation treatment of 2,4,6-trichlorophenol (TCP). The TOF value of MCFe for TCP degradation is nearly 3 times higher than those of FeSO₄ and Fe₂O₃·FeO and nearly 2 times than that of commercial nZVI. The reactive oxygen species (ROS) including •SO₄^-, HO•, and •O₂^-, ¹O₂ are efficiently generated by PDS activation with MCFe. The PDS activation process by nano-Fe(0) particles was intrinsically induced by the ferrous ions (Fe(II)) continuously generated at the solid/aqueous interface. Namely, the nano-Fe(0) particles were highly efficiently utilized in sulfate radical-based advanced oxidation processes (SR-AOP). The porous structure also assists the absorption and transfer of TCP during the degradation process.

Applying bio-electric field of microbial fuel cell-upflow anaerobic sludge blanket reactor catalyzed blast furnace dusting ash for promoting anaerobic digestion

In this study, a novel manner of bio-electric field (BEF) which generated by upflow anaerobic sludge blanket (UASB)-microbial fuel cell (MFC) integrated system facilitated iron-carbon micro-electrolysis in blast furnace dusting ash (BFDA) was proposed for the reinforcement of anaerobic digestion in UASB. The responses of COD removal efficiency and biogas production with (0.1-0.4 V) BEF catalyzed 5 g BFDA(R_{MFC-5gBFDA-UASB}) were much higher than the other tests, and maximum reached 86% and 240 ml/d respectively. Ultra-fast acidogenesis was achieved with 0.3 V BEF supplied to BFDA and the time shortened 94 h compared controlled (R_UASB) with R_{MFC-5gBFDA-UASB}. With the electrochemical and microbial community analysis, the redox ability and direct interspecies electron transfer accumulated with BEF catalyzed. The abundance of Firmicutes which could generate bio-hydrogen was highest in R_{MFC-5gBFDA-UASB} (44.58%) compared to R_UASB (31.36%) and R_5gBFDA-UASB (40.04%). In addition, the structure and morphology variation of BFDA revealed that the synergistic effects of BEF stimulated iron-carbon micro-electrolysis for electron transferring and enhanced the activities of methanogens and acetogens with high relative abundance to biotransform organic compounds, as well as adsorption and precipitation of iron oxides (hematite and magnetite) promoting anaerobic digestion. The MFC-BFDA-UASB integrated system provides a promising and cost-effective way to enhance anaerobic digestion and recycled functionalized waste effectively.

Efficient degradation of Orange G with persulfate activated by recyclable FeMoO4

In this study, FeMoO₄ was applied to activate persulfate (PS, S₂O₈^2-) for azo dye Orange G (OG) degradation. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption isotherms. FeMoO₄ showed excellent efficiency in activating PS for OG removal. More than 95% could be removed after 40 min under reaction conditions of 4 mM PS, 0.3 g L^-1 FeMoO₄ and 0.2 mM OG. The effect of different parameters (PS doses, FeMoO₄ doses and pH) were evaluated. The results showed that acid condition provided higher efficiency and overdosing FeMoO₄ and PS presented a scavenging effect. Major intermediates were identified and possible degradation pathway was proposed. Recycle tests presented that FeMoO₄ had excellent recyclable stability in activating PS for OG removal. Sulfate radicals and hydroxyl radicals all occurred in the oxidation reactions and the former came first. The oxidation reaction was involved in the translation of Fe²⁺/Fe³⁺ occurred on the surface layer. This study revealed that the FeMoO₄/PS system is a very promising method for degrading organic contaminants in the environment.