Nitrogen moieties -dominated Co-N-doped nanoparticle-modified cathodes in heterogeneous-electro-Fenton-like system for catalytic decontamination of EDTA-Ni(II)

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

Electro-Fenton (EF) can in-situ produce H2O2 and effectively activate H2O2 to generate powerful reactive species for the destruction of contaminants under acidic conditions, however, the production of iron-containing sludge and requirement of low working pH significantly hinder its practical application. Herein, a novel Cu, N co-doped carbon (Cu-N@C) with metal organic framework (MOF) as a precursor was constructed and adopted for the elimination of pefloxacin (PEF) in the heterogeneous electro-Fenton (HEF) process. PEF could be almost completely removed within 1 h and total organic carbon (TOC) removal efficiency was 48.57% within 6 h. Meanwhile, Cu-N@C had good repeatability and environmental adaptability, it can still maintain excellent catalytic performance after 10 cycles, and it exhibited satisfactory remediation performance in simulated water matrix. In addition, the HEF process catalyzed by Cu-N@C also showed satisfactory degradation effect on other organic pollutants including atrazine, methylene blue, and chlorotetracycline. Under the action of impressed current, the HEF system could generate H2O2 in-situ, and the active species could be generated in the redox cycle of Cu0/Cu1+/Cu2+. Electron paramagnetic resonance and quenching experiments confirmed that •OH was the dominant active species in the degradation of organic compounds. The degradation process of PEF was studied by mass spectrometry analysis of intermediate products. This study provided a simple method to prepare MOF-based electrocatalyst, which exhibits promising application potential for treatment wastewater.

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

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

Treatment of electroplating industry wastewater: a review on the various techniques

Water pollution by recalcitrant compounds is an increasingly important problem due to the continuous introduction of new chemicals into the environment. Choosing appropriate measures and developing successful strategies for eliminating hazardous wastewater contaminants from industrial processes is currently a primary goal. Electroplating industry wastewater involves highly toxic cyanide (CN), heavy metal ions, oils and greases, organic solvents, and the complicated composition of effluents and may also contain biological oxygen demand (BOD), chemical oxygen demand (COD), SS, DS, TS, and turbidity. The availability of these metal ions in electroplating industry wastewater makes the water so toxic and corrosive. Because these heavy metals are harmful to living things, they must be removed to prevent them from being absorbed by plants, animals, and humans. As a result, exposure to electroplating wastewater can induce necrosis and nephritis in humans and lung cancer, digestive system cancer, anemia, hepatitis, and maxillary sinus cancer with prolonged exposure. For the safe discharge of electroplating industry effluents, appropriate wastewater treatment has to be provided. This article examines and assesses new approaches such as coagulation and flocculation, chemical precipitation, ion exchange, membrane filtration, adsorption, electrochemical treatment, and advanced oxidation process (AOP) for treating the electroplating industry wastewater. On the other hand, these physicochemical approaches have significant drawbacks, including a high initial investment and operating cost due to costly chemical reagents, the production of metal complexes sludge that needs additional treatment, and a long recovery process. At the same time, advanced techniques such as electrochemical treatment can remove various kinds of organic and inorganic contaminants such as BOD, COD, and heavy metals. The electrochemical treatment process has several advantages over traditional technologies, including complete removal of persistent organic pollutants, environmental friendliness, ease of integration with other conventional technologies, less sludge production, high separation, and shorter residence time. The effectiveness of the electrochemical treatment process depends on various parameters, including pH, electrode material, operation time, electrode gap, and current density. This review mainly emphasizes the removal of heavy metals and another pollutant such as CN from electroplating discharge. This paper will be helpful in the selection of efficient techniques for treatment based on the quantity and characteristics of the effluent produced.

Novel strategies and advancement in reducing heavy metals from the contaminated environment

The most contemporary ecological issues are the dumping of unprocessed factories' effluent. As a result, there is an increasing demand for creative, practical, environmentally acceptable, and inexpensive methodologies to remediate inorganic metals (Hg, Cr, Pb, and Cd) liquidated into the atmosphere, protecting ecosystems. Latest innovations in biological metals have driven natural treatment as a viable substitute for traditional approaches in this area. To eliminate pesticide remains from soil/water sites, technologies such as oxidation, burning, adsorption, and microbial degradation have been established. Bioremediation is a more cost-effective and ecologically responsible means of removing heavy metals than conventional alternatives. As a result, microorganisms have emerged as a necessary component of methyl breakdown and detoxification via metabolic reactions and hereditary characteristics. The utmost operative variant for confiscating substantial metals commencing contaminated soil was A. niger, which had a maximum bioaccumulation efficiency of 98% (Cd) and 43% (Cr). Biosensor bacteria are both environmentally sustainable and cost-effective. As a result, microbes have a range of metal absorption processes that allow them to have higher metal biosorption capabilities. Additionally, the biosorption potential of bacterium, fungus, biofilm, and algae, inherently handled microorganisms that immobilized microbial cells for the elimination of heavy metals, was reviewed in this study. Furthermore, we discuss some of the challenges and opportunities associated with producing effective heavy metal removal techniques, such as those that employ different types of nanoparticles.

Electro-activating non-radical 1O2/H* via single atom manganese modified cathode: The indispensable role of metal active site Mn

As an alternative to noble-metal Pt based catalysts, metal-based single atomic catalytic (SACs) exhibited excellent atom efficiency and catalytic activity via exposing abundant single atomic active centers. Here, we synthesized the monatomic Mn ligands anchored on porous N, P, S- co-doped carbon framework (Mn content over 4.5 wt%) (denoted as Mn-SAC@PZS). The single atomic Mn exhibited super mass activity (11.58 m² g^-1) and kinetic current (1.122×10³ µA) with a much lower Tafel slope (4.25 mV dec^-1) at 0.792 V (vs. SCE). XANES and EXAFS revealed that the mononuclear Mn were inclined to coordinate with N and S rather than P to form the R space of Mn, in which the first coordination shells backscattered with Mn-N and Mn-S. RRDE revealed that one-electron ORR pathway (72 ~ 100%) dominated at the potential of 0.5 ~ 0.7 V, oxygen molecule was absorbed/activated on site Mn* to form O* intermediate, then further activated to ¹O₂ via one-electron ORR pathway, while H* was electro activated by non-metallic active sites (i.e. pyri-N, sp-N, -PN and SO). In addition, the Mn-SAC@PZS was capable of highly selectively capturing and effectively degrading CIP in the presence of HA. Fast and complete removal of CIP was achieved within 30 min in the Mn-SAC@PZS-EFLP system, and the apparent rate constant (k) was up to 0.25 min^-1. The energy consumption value was 0.453 kWh m^-3, much lower than non-single atomic catalyst MnxOy@PZS (0.655 kWh m^-3), which was comparable with the state-of-the-art advanced oxidation processes. These findings provided new insights into the maximum release of the atomic activity of the catalyst, and provides a possible way to selectively remove aromatics from multiple pollutants in complex water system.

Fate of metal-EDTA complexes during ferrihydrite aging: Interaction of metal-EDTA and iron oxides

The widespread presence of ferrihydrite in the environment makes many contaminants including metal-EDTA complexes being adsorbed on it. However, the fate of metal-EDTA complexes during the transformation of ferrihydrite was poorly understood. Understanding the migration and speciation changes of metal-EDTA adsorbed on ferrihydrite during the transformation was helpful to predict its fate in some natural and engineering environments. In this work, the interaction of the two metal-EDTA complexes (Ni(II)-EDTA and Ca(II)-EDTA) and ferrihydrite during the 9-day transformation of ferrihydrite at different pH values was studied. The results showed that part of EDTA complexing metals changed to non-complexed metals during the ferrihydrite transformation, which was due to the fact that metal in the metal-EDTA exchanged with Fe(III) on ferrihydrite. Besides, different speciation of metal ions migrated during the transformation of ferrihydrite. Meanwhile, Fe(III)-EDTA formed in this process, and the exchange of metal in Ca(II)-EDTA with Fe(III) in ferrihydrite was faster than that of Ni(II)-EDTA. Besides, the presence of metal-EDTA affected the transformation rate of ferrihydrite under neutral and alkaline condition, and metal-EDTA accelerated the dissolution of ferrihydrite to form goethite. Therefore, ferrihydrite and metal-EDTA influenced each other during the transformation of ferrihydrite. The results of this work revealed that the process of metal-EDTA dissolving ferrihydrite not only included the dissociation of metal-EDTA, but also involved the migration of metal ions and affected the transformation of ferrihydrite.

A critical review on metal complexes removal from water using methods based on Fenton-like reactions: Analysis and comparison of methods and mechanisms

Metals mainly exist in the form of complexes in urban wastewater, fresh water and even drinking water, which are difficult to remove and further harm human health. Fenton-like reaction has been used for the removal of metal complexes. Effective removal of metal complexes using Fenton-like reaction requires the removal of both metals and organic ligands, meanwhile, the fate of metals and organic pollutions must be clearly understood. Thus, this review summarizes the relevant research on metal complex removal from using Fenton-like reactions in the past ten years, with the detailed removal approaches and mechanisms analyzed. Electro-, photo-, microwave/ultrasound-Fenton reactions or the synergistic Fenton reaction have been shown to exhibit excellent metal complex treatment capabilities. Furthermore, various catalysts, such as transition metals, bimetals and metal-free catalytic systems can expand the potential applications of Fenton-like reactions. Novel Fenton reaction methods without the addition of metals or H₂O₂, with construction of a dual active center catalyst, or with the introduction of other free radicals, are all worthy of further investigation. Due to increasing levels of environmental metal and organic pollutions remediation requirements, more research is required for the development of economical and efficient novel Fenton-like processes.

Enhanced electro-Fenton catalytic performance with in-situ grown Ce/Fe@NPC-GF as self-standing cathode: Fabrication, influence factors and mechanism

Heterogeneous electro-Fenton (E-F) is considered as an attractive technique for efficient removal of refractory organic pollutants in wastewater. The regeneration of Fe^II and catalyst reusability are key issues for effective and sustainable degradation. Developing binder-free iron phase/carbon composite cathode is a feasible strategy. In this work, the stable Ce/Fe-nanoporous carbon modified graphite felt electrode (Ce/Fe@NPC-GF) was fabricated using in situ solvothermal method and subsequent carbonization treatment, which worked as the cathode in a heterogeneous electro-Fenton system to degrade sulfamethoxazole. The electrocatalytic activity was significantly improved with doping of Ce. It was found that mesoporous Ce/Fe@NPC-GF cathode demonstrated high oxygen reduction activity and low resistance. The co-existence of Fe^Ⅱ/Fe^Ⅲ and Ce^Ⅲ/Ce^Ⅳ redox couples enhanced remarkably interfacial electron transfer, promoting in-situ H₂O₂ generation and decomposition, sequentially boosting the production of reactive radicals (·OH and ·O₂^-). Under 20 mA and pH 3, Sulfamethoxazole (SMX) was basically degraded in 120 min, and the removal rate was satisfactory in wide pH (2-6). After 8 cycles, the electrode could still maintain high stability and outstanding catalytic capacity. This work displayed a novel in-situ preparation method of composite cathode with excellent catalytic performance in E-F system, which offered inspiration for developing efficient heterogeneous electro-Fenton cathode material.

Prompting direct single electron transfer to produce non-radical 1O2/H* by electro-activating peroxydisulfate process with core-shell cathode

A novel heteroatomic N, P and S co-doped core-shell material (MnFe₃O₄@PZS) was synthesized by a simple polycondensation hydro-thermal method, and used as the cathode to cooperate with electron-catalysis to activate persulfate (S₂O₈^2-) (E-MnFe₃O₄@PZS-PDS) for tetracycline (TTC) degradation. Radical scavenger studies demonstrated that non-radicals including atomic H* and singlet oxygen (¹O₂) rather than sulfate and hydroxyl radicals were the crucial reactive oxygen species (ROS). Electrochemical analysis indicated that Mn doping could promote electro-catalytic process via diverting pathway from four/two-electron to one-electron to generate non-radical H*/¹O₂ at the cathode, including one-electron oxygen reduction reaction (1e-ORR) (O₂→¹O₂), and one-electron hydrogen reduction reaction (1e-HRR) (H₂O+e^-→H^∗), as evidenced by the lowest onset potential (0.072 V) together with electron transfer number (n = 1.65). Besides, the regeneration/reduction of Fe^Ⅱ/Ⅲ/Mn^Ⅱ/Ⅲ/Ⅳ and persulfate will not cause excessive consumption of electron and chemicals due to that could directly get the electron individually from the cathode and anode, and finally TTC could be completely degraded with low energy consumption (0.655 kWh m^-3). This study provides new insights into the direct single electron activating PDS to produce non-radical H*/¹O₂ via core-shell catalytic MnFe₃O₄@PZS, and displays a promising application in wastewater treatment.

A novel core-shell Fe@Co nanoparticles uniformly modified graphite felt cathode (Fe@Co/GF) for efficient bio-electro-Fenton degradation of phenolic compounds

In this study, a core-shell Fe@Co nanoparticles uniformly modified graphite felt (Fe@Co/GF) was fabricated as the cathode by one-pot self-assembly strategy for the degradation of vanillic acid (VA), syringic acid (SA), and 4-hydroxybenzoic acid (HBA) in the Bio-Electro-Fenton (BEF) system. The Fe@Co/GF cathode showed dual advantages with excellent electrochemical performance and catalytic reactivity not only due to the high electron transfer efficiency but also the synergistic redox cycles between Fe and Co species, both of which significantly enhanced the in situ generation of H₂O₂ and hydroxyl radicals (OH) to 152.40 μmol/L and 138.48 μmol/L, respectively. In this case, the degradation rates of VA, SA, and HBA reached 100, 94.32, and 100%, respectively, within 22 h. Representatively, VA was degraded and ultimately mineralized via demethylation, decarboxylation and ring-opening reactions. This work provided a promising approach for eliminating typical recalcitrant organic pollutants generated by the pre-treatment of lignocellulose resources.

Cobalt-doped hydroxyapatite nanoparticles as a new eco-friendly catalyst of luminol-H2O2 based chemiluminescence reaction: Study of key factors, improvement the activity and analytical application

In this study, a novel catalyst based on hydroxyapatite doped by cobalt for chemiluminescence reaction of luminol oxidation by H₂O₂ was suggested for the first time. The catalyst nanoparticles were synthesized by a hydrothermal method and characterized by various methods including density functional theory calculations. The impact of nanoparticles sizes, surface composition, contact efficiency and crystallinity on chemiluminescence intensity were investigated. The maximum chemiluminescence intensity was obtained for polycrystalline nanoparticles. This phenomenon was studied in detail and applied for chemiluminescence analysis for the first time. The chemiluminescence determination of sulfonamides as model analytes was considered. The sensing was based on sulfonamides-dependent quenching of the chemiluminescence intensity in the presence of novel catalyst existed as an aqueous suspension.