Critical Review on the Mechanisms of Fe2+ Regeneration in the Electro-Fenton Process: Fundamentals and Boosting Strategies

Lewis acid sites-regulated microscopic interface on graphite felt surface for enhanced heterogeneous electro-Fenton process: Formation of confinement effect and generation of singlet oxygen

The short lifetime and limited diffusion capability of hydroxyl radicals (•OH) restrict the further development of heterogeneous electro-Fenton (Hetero-EF) technology. In contrast, singlet oxygen (1O2) demonstrates many advantages over •OH. In the present work, a porous confined graphite felt (PCGF) was prepared through in-situ etching of nickel oxide (NiOx) and used as the cathode for Hetero-EF, aiming at constructing a 1O2-dominated Hetero-EF system to enhance its degradation performance for various antibiotic pollutants in wastewater. The in-situ etching of NiOx introduced abundant Lewis acid sites within the porous architecture of PCGF, enabling the modulation of electrode's interfacial properties and selective adsorption of Lewis basic substances, thereby generating a characteristic "confinement effect". This enhanced interfacial interaction achieved 50.23 % adsorptive removal of oxytetracycline within 30 min without external power supply, facilitating the enrichment of pollutants at the cathode interface. Meanwhile, the "confinement effect" significantly enhanced the utilization efficiency of reactive oxygen species and the selectivity of 1O2. The PCGF electrode demonstrated excellent degradation performance across a wide range of pH and exhibited strong anti-interference capability. The results from radical quenching experiments and density functional theory calculations revealed that the generation of 1O2 proceeded through multiple routes involving hydrogen peroxide, •OH, and superoxide anions. The present study presents a novel strategy for advancing the development of 1O2-dominated Hetero-EF systems for treating antibiotic-containing wastewaters.

A novel approach based on PEM electrolysis technology for iron recovery from acid mine drainage: performance and mechanism

Acid mine drainage (AMD) resulting from mining activities poses a significant global environmental challenge. Iron is the most concentrated pollutant in AMD, which impedes the treatment process of lime neutralization and generates substantial sludge. To achieve efficient removal and resource recovery of iron, a proton exchange membrane (PEM) electrolysis system was developed. Under optimal operating conditions of 15 g/L sulfate concentration and 60 mA current intensity, the system removal efficiency achieved a 100 % for Fe, As, Cu, Mn, Zn, and Cr within 290 min. The Fe was converted into Fe3O4, which displayed a high purity of 99 %, a particle size of 297 ± 1.6 nm, and a saturation magnetization of 54.2 emu/g. Electron paramagnetic resonance (EPR) and radical quenching experiments identified hydroxyl radicals (·OH) as the primary species driving the Fe2+ oxidation process, which significantly contributed to the efficient removal of Fe. During the initial stage of electrolysis, Fe2+ was partially oxidized to Fe3+ by ·OH and H2O2 produced by oxygen reduction reaction, subsequently hydrolyzing to form γ-FeOOH. As the pH increased, which was attributed to the hydrogen evolution reaction, additional Fe2+ hydrolyzed to generate green rust. In the later electrolysis stages, remaining Fe2+, green rust, and γ-FeOOH underwent electron transfer reactions, dissolving and recrystallizing to Fe3O4. In the treatment of real AMD, the system achieved 100 % removal efficiencies for Fe2+ and Mn2+, yielding Fe3O4 as the electrolysis product. Economic analysis indicated that the cost of the technology was only 0.52 $/m3, demonstrating its potential for large-scale application.

Size-optimized Prussian blue and oxygen-doped carbon nanotubes encapsulation: A catalyst in electro-Fenton for antibiotic degradation

The Electro-Fenton (EF) process has been identified as a potentially effective solution for the treatment of antibiotic wastewater. However, challenges related to catalyst activity and stability persist as significant obstacles. In this study, we developed a bifunctional catalyst that has demonstrated stability in practical applications. A systematic investigation was conducted into the influence of Prussian Blue (PB) particle size (350-950 nm) on Fe3+/Fe2+ conversion efficiency, and it was identified that 592 nm PB was optimal, achieving the highest conversion rate of 0.162 min-1. To further enhance Fe3+/Fe2+ cycling, PB was encapsulated within oxidized carbon nanotubes (OCNT), forming an interconnected OCNT/PB catalyst that exhibited a remarkable 204.8 % synergistic enhancement. The superior performance of the catalyst can be attributed to three key factors: (i) The presence of dual active sites for the oxygen reduction reaction (ORR) and Fenton reaction, separated by an atomic-scale distance of 2.352 Å, facilitating both hydrogen peroxide (H2O2) generation and its subsequent activation into reactive radicals. (ii) OCNT functioning as an electron-transfer bridge between the cathode and PB, effectively overcoming PB's inherent low conductivity. (iii) Fe complexation on the PB surface with oxygen-containing functional groups, which significantly accelerates Fe3+/Fe2+ redox cycling. Quantitatively, the coupling of ORR and Fenton sites accounts for 46.6 % of the catalytic activity, the electron-transfer bridge contributes 21.8 %, and Fe complexation enhances activity by 31.5 %. This study offers novel insights into the design of high-performance EF catalysts and presents an innovative strategy for the efficient degradation of organic pollutants in water.

Selective and iron-independent ferroptosis in cancer cells induced by manipulation of mitochondrial fatty acid oxidation

Despite the promise of ferroptosis in cancer therapy, selectively inducing robust ferroptosis in cancer cells remains a significant challenge. In this study, manipulation of fatty acids β-oxidation (FAO) by combination of mild photodynamic therapy (PDT) and inhibition of triglycerides (TGs) synthesis was found to induce robust and iron-independent ferroptosis in cancer cells with dysregulated lipid metabolism for the first time. To achieve that, TGs synthesis inhibitor of xanthohumol (Xan) and FAO initiator of tetrakis (4-carboxyphenyl) porphyrin (TCPP) were co-delivered by a nanoplexes composed of pH-responsive amphiphilic lipopeptide C18-pHis10 and DSPE-PEG2000. TCPP was found to rapidly increase the intracellular ROS under laser irradiation without inducing antioxidant response and apoptosis, activating the AMPK in cancer cells and accelerating mitochondrial FAO. Xan fueled the mitochondrial FAO with substrates by suppressing the conversion of fatty acids (FAs) to TGs. This also led to augmented intracellular polyunsaturated fatty acids (PUFAs) and PUFAs-phospholipids levels, increasing the intrinsic susceptibility of cancer cells to lipid peroxidization. As a result, the excessive ROS generated from the sustained mitochondrial FAO caused remarkably lipid peroxidation and ultimately ferroptosis. Collectively, our study provides a new approach to selectively induce iron-independent ferroptosis in cancer cells by taking advantage of dysregulated lipid metabolism.

Efficient antibiotic tetracycline degradation and toxicity abatement via the perovskite-type CaFexNi1-xO3 assisted heterogeneous electro-Fenton system

As one of the emerging contaminants, antibiotics are posing a great threat to the human health and environment, which requires effective treatment methods. Heterogeneous electro-Fenton is a promising technique for organic contaminant elimination, but preparation of an appropriate heterogeneous electro-Fenton catalyst still remains challenging. In this work, the feasibility of perovskite-type CaFexNi1-xO3 as heterogeneous electro-Fenton catalyst for tetracycline (TC) removal and toxicity abatement has been explored. It was found that, among the examined CaFexNi1-xO3 catalysts with different Ni doping amount, CaFe3/4Ni1/4O3 exhibited the best performance, achieving 92.1 % TC removal within 30 min without pH adjustment in the presence of 0.05 M Na2SO4 electrolyte. Choosing Cl--containing electrolyte enabled further improvement towards TC elimination. In addition, the CaFe3/4Ni1/4O3 based heterogeneous electro-Fenton system presented other advantages including good recyclability and universal applicability, and significant toxicity reduction (verified via both ECOSAR simulation and soybean germination test). The TC degradation pathways were elucidated through identification of intermediate products and DFT calculations. Mechanism investigations revealed that there existed a strong synergy between Fe and Ni, and ·OH and ·O2- played the primary roles in the system while 1O2 played an auxiliary role. This study presented a promising heterogeneous electro-Fenton catalyst for degradation of antibiotics such as tetracycline.

Anode-Cathode Synergistic Filter Activating Peroxymonosulfate at Multiple Active Sites for Highly Efficient and Economical Water Purification

Developing an efficient dual-electrode system for peroxymonosulfate (PMS) activation is essential to expand the scope for wastewater treatment and solve issues of low treatment capacity, poor mineralization, and high energy consumption. This study proposed an oxygen vacancy-mediated LaCoO3-modified Ti4O7 (LCVTO) anode membrane and in situ grown nanocarbon-modified carbon felt (C/CF) cathode to coactivate PMS, achieving 100% sulfamethoxazole (SMX) elimination in 37.3 s. The rate constant (k = 15.84 min-1) was 12 and 21 times higher than those of the anode and cathode processes, with energy consumption reduced to just 7.9% and 4.6%, respectively. This filter supports either high-flux pollutant removal (1061 L/m2·h) or deep mineralization (89%) at 212.22 L/m2·h. In situ electrochemical infrared spectroscopy and density functional theory calculations revealed the reaction mechanism of multiple active sites, with the anode (Co and Vo) supplying •OH, SO4•-, and 1O2 and the nanocarbon on the cathode contributing additional 1O2. This process demonstrated excellent pH adaptability (4-14) for SMX removal, outstanding reusability, and continuous operation capability. Its resilience to wastewater matrix interference enables the efficient and economical treatment of both high-conductivity mariculture wastewater and low-conductivity municipal sewage with remarkably low electric energy (0.08-0.16 kWh/kg of COD). This approach offers promising prospects for addressing water pollution challenges across industrial and environmental contexts.

Degradation of antibiotics and profiling of transformation products upon peracetic acid-mediated treatment of electrochlorinated groundwater in a flow-through reactor

Preventing the formation of hazardous chlorinated transformation products (Cl-TPs) when applying the electrochemical advanced oxidation processes (EAOPs) is a major challenge for ensuring their broader scale-up. In this context, the addition of peracetic acid (PAA) can potentially contribute to reduce the risk of Cl-TPs, but the associated transformation pathways remain insufficiently understood. Here, PAA-mediated electrochlorination process was found to reduce typical Cl-TPs (e.g., chloroform below 60 μg L-1) by 26.9 %∼80.8 %. Under optimized conditions, an innovative PAA-based treatment in a single-pass flow-through electrochemical reactor achieves the removal of four mixed antibiotics with low specific energy consumption (5.3 Wh mmol-1). The antibiotics concentration in the effluent remained below the detection limit within 10 operation cycles. In addition, reductions in Cl-TPs were achieved in both simulated and actual groundwater, meeting the 2022 Chinese drinking water quality standards. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that PAA-based electrochlorination preferentially removed highly unsaturated heavy byproducts (O/C < 0.3, MW >400 Da), and the CHOCl formulae number decreased by 59 %. The transformation pathways of Cl-TPs were mainly identified as decarbonylation, dihydroxylation, and hydrogenation. Moreover, the possible halogenation pathways number showed a significant decrease of 77.9 %. These findings provide deeper insights into the degradation mechanisms and Cl-TPs minimization during PAA-mediated electrochemical antibiotic degradation, shedding light on the transformation processes in diverse environmental scenarios.

Strategy for enhanced soil lead passivation and mitigating lead toxicity to plants by biochar-based microbial agents

In the study, bone char (BC) backed biochemical composite coupling with phosphate-solubilizing bacteria (CFB1-P) was prepared to explore the passivation performance of lead (Pb) in soil and the mitigation effect on plant growth under Pb stress by measuring change of soil Pb speciation, plant growth parameters and physiological and biochemical indexes. After 30 d of remediation, addition of 1 % CFB1-P could effectively reduce 55.43 % of Pb labile fractions and converted them into Fe-Mn oxide and residual forms. Meanwhile, the bioavailability of Pb was not significantly affected by wetting-drying and freezing-thawing after 20 times cycles (the DTPA-Pb content only increased 6.91-7.35 mg/kg), which proved that the CFB1-P had an excellent prospect of passivating Pb. Moreover, the CFB1-P effectively increased soil fertility and improved soil enzyme activity. The application of CFB1-P could reshape the soil microbial community by recruiting beneficial microorganisms (Bacillus, Sulfurifustis, and Gaiella), which contributed to the improvement of Pb-contaminated soil quality. Furthermore, the fresh weight, photosynthetic pigment concentration, stems and roots length of cucumber seedings were significantly increased. Pb in the cucumber seedings and antioxidant enzyme activities of cucumber seedings were prominently decreased. Therefore, the study can offer a preferable comprehending for the advance of sustainable high-efficiency materials which microbial agent based on functional biochar remediated Pb-polluted soil.

Carbon quantum dots as efficient cocatalysts in Fenton-like processes: Preparation optimization and mechanistic insights

Carbon quantum dots (CQDs) are promising cocatalysts in Fenton-like technologies, leveraging hydrogen peroxide and boosting Fe2 + generation and thereby expediting the advanced oxidation process. Although several studies have shown that the preparation affects the cocatalytic performance of the resulting CQDs, the precise correlation between the preparation and the cocatalytic efficiency is unclear. Here, we combine the batch experiments with the theoretical calculations to systematically explore how the parameters in electrochemical exfoliation preparation affect the cocatalytic performance of the as-prepared CQDs. The results show that adjusting parameters like voltage, electrolyte concentration, and electrolysis duration can precisely regulate the surface functional groups of CQDs, which in turn affects the cocatalytic performance. A linear positive correlation is identified between the surface carboxyl content and the pseudo-first-order rate constant (kobs) in Fenton-like reactions, with the highest carboxyl content (18.26 mmol/g) found in C@C3-30V-24H that induces the optimum catalytic performance to the C@C3-30V-24H-Fe3+/H2O2 system for phenol removal (97.75 % versus 21.17 % in Fe3+/H2O2 system at pH 3). DFT calculations reveal that phenolic compounds with electron-donating groups are more readily oxidized and that those with lower LUMO levels demonstrate higher kobs. This study underscores the crucial role of CQDs preparation on their cocatalytic performance in Fenton-like reactions.

Performance enhancement and mechanism of tetracycline removal by visible light-driven photo bio-electro-fenton system with CoFe-LDH/g-C3N4 cathode

Bio-electro-Fenton (BEF) technology has shown significant advantages in the treatment of antibiotic wastewater. However, the strict pH application range (2-3) still limits the practical application of BEF. To overcome the limitation of pH on traditional BEF, CoFe-LDH/g-C3N4 composite catalyst was synthesized by hydrothermal method and applied to the BEF cathode to construct a photo-BEF (PBEF) system. The performance of the PBEF system under visible light was investigated with tetracycline hydrochloride (TC) as the target pollutant. The results showed that the PBEF system could extend the pH application range to 3-11 and could maintain more than 80 % of TC removal. The highest removal efficiency of TC by PBEF reached 94.98 % at pH 5, and the highest TOC removal could achieve 70.09 %, indicating that the PBEF can effectively remove TC. Meanwhile, PBEF also showed good universality, anti-interference and stability. In addition, to explore the mechanism of TC degradation by PBEF, the quenching experiments and electron spin resonance (ESR) tests were used to identify and evaluate the contribution of the reactive oxygen species in TC removal. And the results showed that e- and •OH played the major role in TC removal. Density functional theory (DFT) calculations were used to analyze the active sites of TC molecules, and three possible degradation pathways of TC were proposed. Moreover, the toxicity of TC degradation by PBEF was effectively reduced. This study proposes a new way to broaden the application range of pH by PBEF and provides a novel alternative for antibiotics removal from wastewater.

Roles of oxygen vacancies in layered double hydroxides-based catalysts for wastewater remediation: fundamentals and prospects

Wastewater globally is a significant concern for environmental health and for the sustainable management of water resources. Catalysed based advanced oxidation processes (AOP), as a relatively low operation cost and high removal efficiency of pollutants method, has a promising potential to treat the wastewater. Among the numerous catalysts, Layered Double Hydroxides (LDHs) stands out for lamellar structure, high charge density, and tuneable properties. Meanwhile, oxygen vacancies engineering could modulate the electronic properties of materials and create active centres to regulate the poor charge transfer capability of LDHs. In this regard, this review is focused on how to create and confirm the oxygen vacancies, as well as the applications of the wastewater treatment from different AOPs. It starts with the synthesized of oxygen vacancies via chemical reduction method, plasma etching method, hydrothermal treatment method, ion doping strategy. Followed by the description of characterization methods, including EPR, XPS, XAS, Raman. Finally, the role of oxygen vacancies in LDHs for contaminant removal across various systems, including photocatalysis, electrocatalysis, Fenton reactions, and sulfate radical-based processes, was thoroughly examined and analyzed.

Tumor microenvironment triggered iron-based metal organic frameworks for magnetic resonance imaging and photodynamic-enhanced ferroptosis therapy

Photodynamic therapy (PDT) primarily relies on the generation of reactive oxygen species (ROS) to eliminate tumor cells. However, the elevated levels of glutathione (GSH) within tumor cells can limit the efficacy of PDT, posing a challenge to achieve complete tumor eradication. Herein, a porous iron-based metal-organic frameworks (PEG-Fe-MOFs) nanoplatform was developed for the combined application of PDT and ferroptosis in cancer treatment. The coordination between tetrakis (4-carboxyphenyl) porphyrin (TCPP) and ferric (Fe3+) enabled PEG-modified Fe-MOFs (PEG-Fe-MOFs) to deliver excellent T1-weighted magnetic resonance (MR) imaging performance in physiological environments. Within the tumor microenvironment (TME), PEG-Fe-MOFs gradually degraded to release TCPP, which could be utilized for fluorescence imaging. Moreover, Fe2+ enhanced intracellular ROS levels via the Fenton reaction, generating hydroxyl radicals that further amplified ROS production. This synergistic effect comprising increased ROS levels and GSH depletion augmented the efficacy of PDT while simultaneously inducing robust ferroptosis in tumor cells, thereby maximizing therapeutic outcomes. Both in vitro and in vivo experiments have demonstrated the superior T1 weighted MR and fluorescence imaging capabilities of PEG-Fe-MOFs, along with its potent synergistic therapeutic effects on tumors. These results highlighted the potential of this nanoplatform for combining PDT and ferroptosis in cancer treatment.

Reverse-engineered Electro-Fenton for the selective synthesis of oxalic or oxamic acid through the degradation of acetaminophen: A novel green electrocatalytic refinery approach

The Electro-Fenton process (EF) has been conventionally applied to efficiently degrade refractory and/or toxic pollutants. However, in this work, EF was used as a reverse engineering tool to selectively synthesize highly value-added products (oxalic or oxamic acid) through the degradation of the model pollutant acetaminophen, a widely used analgesic and antipyretic drug. It was found that the production of either oxalic or oxamic acid is dictated by the applied current density. Hence, oxalic acid is favored at low current densities trough a mechanism dominated by homogeneous •OH radical oxidation, while oxamic acid is the majoritarian product at high current densities where electron transfer at the anode surface becomes an important mechanism in combination with •OH oxidation. Under optimal reaction conditions (0.71 mA cm-2 and 100 mg l-1 of initial total organic carbon (TOC) concentration), up to 227.1 ± 26.3 mg l-1 of oxalic acid were produced, with high yield and selectivity of 54.9 ± 5.1 % and 94.7 ± 9.9 %, respectively (the TOC removal was 42.0 ± 2.4 %). In the case of oxamic acid, the highest concentration of 33.8 ± 2.1 mg l-1 was produced at 2.13 mA cm-2 and an initial TOC concentration of 50 mg l-1, which represented a yield of 18.7 ± 0.3 % and 60.9 ± 9.3 % selectivity (71.1 ± 4.4 % of TOC removal). It is worth noting that at low current density when oxalic acid is favored, the selectivity for both products was 100 %, meaning that those were the only products remaining in the solution, with oxalic acid as the major product (94.7 ± 9.9 % with initial TOC of 100 mg l-1, and 98.7 ± 0.9 % with initial TOC of 50 mg l-1). This is a pioneer work on EF applications to the field of wastewater valorization/refining through the recovery of value-added products within a circular economy.

Stability challenges of transition metal-modified cathodes for electro-Fenton process: A mini-review

Electro-Fenton (EF) process with transition-metal (TM) modified cathode has been regarded as a green and promising technology for wastewater treatment. Recently, breakthroughs in boosting catalyst activity for both two-electron oxygen reduction reaction (2e- ORR) and Fenton's reaction have gained intensive attention. However, achieving long-term stability of catalysts remains challenging, but is decisive for large-scale applications. This minireview provides fundamental understanding on the activity-stability correlation and the deactivation mechanisms of TM-based catalysts in EF systems, focusing on physical and chemical evolution, metal dissolution, catalyst detachment and structure collapse during long-term electrolysis. Subsequently, ongoing efforts from catalyst design to electrode engineering to stabilize the metal active sites are highlighted. Finally, the challenges and future perspectives in developing active and durable TM-modified cathodes are discussed, serving as a roadmap towards the large-scale application of EF process for wastewater treatment.

Voltammetric methodology for the quality control and monitoring of sulfamethoxazole removal from water

Sulfamethoxazole is an antibiotic that is among the drugs most frequently found in waters around the world because of its habitual consumption and its high chemical stability that prevents it from being eliminated from the environment. In this study, an electroanalytical methodology based on differential pulse voltammetry is developed for the analysis of sulfamethoxazole at trace levels in water. After the optimization of the instrumental parameters a linear range from 6.59 to 96.27 μM was found with limits of detection and quantification of 1.98 and 6.59 μM, respectively, with an RSD below 6 %. Moreover, several validation studies involving different pH values, water samples and instrumentation-techniques were performed in order to ensure the robustness of the method. For this purpose, the peak area was used as quantitative variable since it is not affected by the pH of the medium even if there is any modification of this parameter during the experiments. Furthermore, the effect of other drug such as trimethoprim on the analytical signal of sulfamethoxazole was also evaluated. Once the method was developed it was tested on the quality control of Soltrim®, obtaining recoveries between 98 and 102 %. Lastly, the voltammetric method was applied for the in situ monitoring of sulfamethoxazole's removal from water samples, specifically by anodic oxidation and electro-Fenton treatments. While the former was coupled to an adsorption process, the latter was carried out with different iron sources including commercial medicines that can be found in wastewater. The problem of significant variation in pH during the treatment was solved by working with the peak area, and so obtaining valid and reliable kinetic data. Although anodic oxidation proved to be faster considering the calculated kobs, electro-Fenton turned out to be more efficient in eliminating the drug, achieving the disappearance of its analytical signal in only 30 min of treatment.

Leveraging Iron in the Electrolyte to Improve Oxygen Evolution Reaction Performance: Fundamentals, Strategies, and Perspectives

Electrochemical water splitting is a pivotal technology for storing intermittent electricity from renewable sources into hydrogen fuel. However, its overall energy efficiency is impeded by the sluggish oxygen evolution reaction (OER) at the anode. In the quest to design high-performance anode catalysts for driving the OER under non-acidic conditions, iron (Fe) has emerged as a crucial element. Although the profound impact of adventitious electrolyte Fen+ species on OER catalysis had been reported forty years ago, recent interest in tailoring the electrode-electrolyte interface has spurred studies on the controlled introduction of Fe ions into the electrolyte to improve OER performance. During the catalytic process, scenarios where the rate of Fen+ deposition on a specific host material outruns that of dissolution pave the way for establishing highly efficient and dynamically stable electrochemical interfaces for long-term steady operation. This review systematically summarizes recent endeavors devoted to elucidating the behaviors of in situ Fe(aq.) incorporation, the role of incorporated Fe sites in the OER, and critical factors influencing the interplay between the electrode surface and Fe ions in the electrolyte environment. Finally, unexplored issues related to comprehensively understanding and leveraging the dynamic exchange of Fen+ at the interface for improved OER catalysis are summarized.

Nitrogen-doped porous hydrochar for enhanced chromium(VI) and bisphenol A scavenging: Synergistic effect of chemical activation and hydrothermal doping

Nitrogen-doped porous hydrochar (NPHC) was successfully synthesized by hydrothermal carbonization and activation with KHCO3, which was employed for scavenging hexavalent chromium (Cr(VI)) and bisphenol A (BPA) in contaminated water. N doping increased the unique active sites such as amino and molecular N in NPHC for adsorbing contaminants, and enhanced the activation effect. Compared to original (HC) and N-doped hydrochar (NHC), the SBET of material improved from 3.99 m2/g and 4.71 m2/g to 1176.77 m2/g. Meanwhile, NPHC exhibited more superior adsorption capacity for Cr(VI) (323.25 mg/g) and BPA (545.34 mg/g) than that of porous hydrochar (213.17 and 343.67 mg/g). Moreover, NPHC possessed pH-dependence and presented more excellent tolerance for interfering ions and regeneration performance. Notably, the Cr(VI) capture by NPHC was dominated via pore filling, electrostatic interaction, reduction, and complexation, while π-π stacking, H-bond interaction, and hydrophobic action were relevant to the binding mechanism of BPA. Overall, the proposed functionalization strategy for biochar was conducive to enhance the remediation of water bodies.

Nitrogen metabolic responses of non-rhizosphere and rhizosphere microbial communities in constructed wetlands under nanoplastics disturbance

Constructed wetlands (CWs) serve as crucial sinks for nanoplastics, making them a significant research hotspot regarding the impacts of nanoplastics on the nitrogen metabolism within microbial communities. However, there has been a lack of comparative analysis between rhizosphere and non-rhizosphere microbial communities under nanoplastics disturbance. This study analyzes the nitrogen metabolic responses of these microbial communities in CWs following repeated nanoplastics disturbance. Results indicated that repeated nanoplastics disturbances led to a 17.72 % decrease in the relative abundance of nitrifying bacteria in rhizosphere microbial community, while the relative abundance of Polaromonas increased by 5.24 % in non-rhizosphere community. Microbial network revealed that rhizosphere microbial community primarily contributed to nitrogen metabolism by forming a tightly connected network. In contrast, non-rhizosphere microbes dominated nitrogen cycling by promoting energy and information exchange among microbes. Furthermore, rhizosphere and non-rhizosphere microbial communities exhibited distinct resistance and adaptation to nanoplastics disturbance. Rhizosphere microbes responded by activating antioxidant systems, whereas non-rhizosphere microbes could develop adaptive growth and metabolism, using nanoplastics as a carbon source. The adaptation strategies of non-rhizosphere community proved more advantageous for coping with persistent nanoplastics disturbance. This study comprehensively investigated the differences of nitrogen metabolism between rhizosphere and non-rhizosphere microorganisms in CWs under nanoplastics disturbance.

Nano zero-valent iron with a self-forming Co-catalytic surface for enhanced Fenton-like reactions

Fenton reactions, commonly employed in environmental remediation, decompose H₂O₂ using Fe2⁺ to generate free radicals. However, the efficiency is often limited by the slow conversion of Fe³⁺ to Fe2⁺. In this study, we synthesize zero-valent iron nanoparticles (nZVI) via a green, plant extract-mediated reduction method, resulting in nZVI coated with a reductive polyphenolic layer that enhances Fe³⁺/Fe2⁺ cycling. Supported on bamboo-derived biochar (BBC) via in situ reduction, the nZVI showe improved dispersibility and recovery during catalytic processes. Characterizations by SEM, TEM, FTIR, XRD, and XPS together confirm the successful synthesis of the nZVI/BBC composite. We evaluate the catalytic performance by degrading Eriochrome Black T (EBT) dye in the presence of H₂O₂. Under optimal conditions (35 °C, pH 3), the nZVI/BBC catalyst achieves over 90% degradation of EBT within 10 min. The dual function of the surface-functionalized nZVI as both iron source and co-catalyst significantly improves the reaction efficiency, offering a promising approach for environmental remediation.

Reshape Iron Nanoparticles Using a Zinc Oxide Nanowire Array for High Efficiency and Stable Electrocatalytic Nitrogen Fixation

As a type of century-old catalyst, the use of iron-based materials runs through the Haber-Bosch process and electrochemical synthesis of ammonia because of its excellent capability, low cost, and abundant reserves. How to continuously improve its catalytic activity and stability for electrochemical nitrogen fixation has always been a goal pursued by scientific researchers. Herein, we develop a free-standing iron-based catalyst, i.e., the iron nanoparticles with zinc oxide nanowire array support (Fe/ZnO NA), which exhibits a high ammonia yield of ∼54.81 μg h-1 mgcat.-1 and a Faradaic efficiency (FE) of ∼9.56% in a 0.5 M potassium hydroxide solution, along with good reusability and durability. Its electrocatalytic ability is superior to that of commercial Fe materials and most reported Fe-based catalysts, thus showing great competitiveness. This is because the ZnO NA not only supplies stable support for the homogeneous dispersion of Fe nanoparticles but also provides a very beneficial synergy to their catalytic activity. The work renews traditional iron-based catalysts and is thus of great significance for promoting the industrialization of electrochemical ammonia synthesis.

Comediating Adsorption and Electron Transfer via Dual-Active Site Catalyst Construction for Improving the Treatment of Extraction Wastewater

Solvent extraction is widely applied, while extraction wastewater treatment remains a huge challenge because of the stability of extractants. Heterogeneous Fenton-like catalysis is a promising method, but the short half-life of hydroxyl radicals (⋅OH) generated by hydrogen peroxide (H2O2) activation results in unsatisfactory ⋅OH utilization and organics removal. Herein, an efficient strategy for treating extraction wastewater based on comediating adsorption and electron transfer by fluorine and nitrogen co-doped carbon (FNC) catalyst with dual-active site was developed. Specially, N sites adsorb organics and F sites activate H2O2, shortening the migration distance of ⋅OH. Theoretical calculation and di(2-ethylhexyl) phosphoric acid (D2EHPA) extraction wastewater degradation experiment showed that F site with electron acquisition can transfer electrons provided by electron-rich D2EHPA enriched at N sites to H2O2, facilitating the continuous generation of ⋅OH through lowering the energy barrier for H2O2 activation. As a result, 96.49 % D2EHPA in simulated wastewater and 90.26 % total organic carbon in real extraction wastewater were removed. Moreover, FNC catalyst exhibited excellent reusability and ionic adaptability, and can be extended to the removal of various extractants. The proposed dual-active site catalyst provides an effective strategy for Fenton-like reaction to treat refractory extraction wastewater, promoting sustainable development of solvent extraction industry.

Heterogeneous catalysts for electro-Fenton degradation of cytostatic drug cytarabine

In the present work, a reduced graphene oxide (rGO) modified-Fe3O4 doped bifunctional carbon felt cathode (rGO-Fe3O4/CF) that is capable of generating and converting H2O2 into hydroxyl radicals (•OH) on-site was fabricated, thus removing the need for an external catalyst. In addition, an rGO-modified cathode (rGO/CF) with high H2O2 production efficiency and a heterogeneous Fenton catalyst (CNT-Fe3O4) with magnetic properties were fabricated. The study examined the degradation and mineralization of the cytostatic drug cytarabine (CYT) using two HEF configurations: (i) a bifunctional cathode rGO-Fe3O4/CF and (ii) a combination of the rGO/CF cathode with CNT-Fe3O4 catalyst. The effects of parameters such as catalyst concentration, initial pH, and applied current were studied. HPLC and ion chromatography analyses were used to identify carboxylic acids and inorganic end-products, respectively. The results show that 0.1 mM CYT was completely degraded within 18 min at an applied current of 300 mA in the HEF system with the rGO-Fe3O4/CF bifunctional cathode. Total organic carbon (TOC) analysis revealed that the bifunctional cathode system achieved 98.2% mineralization of CYT after 4 h of treatment at 300 mA. Using the rGO/CF cathode and CNT-Fe3O4 catalyst cell, total degradation of 0.1 mM CYT occurred within 7 min, and nearly total mineralization (97.3% TOC removal) was achieved at 300 mA after 4 h.

Tuning the thermodynamic and kinetic performance of Fenton process - effects of dissolved anions/gases and temperature

Inorganic anions such as chloride (Cl-), nitrate (NO 3 - ), sulfate (SO 4 2 - ), carbonate (CO 3 2 - ), bicarbonate (HCO 3 - ), dihydrogen phosphate (H 2 PO 4 - ), fluoride (F-) are ubiquitous in water matrices, play a significant role in the degradation of organic pollutants by Fenton process. In the present study, the performance of Fenton process in the presence of these anions was studied using phenol as a model compound along with the underlying mechanism and their tolerance limit. The presence of these anions affects the rate constant of the Fenton process and decreases in the following order, ClO 4 - -NO 3 - -SO 4 2 - -Cl- > HCO 3 -  > CO 3 2 -  > H 2 PO 4 -  > F-. Among the anions studied, H 2 PO 4 - and F- ions inhibit the oxidation process at a low concentration of 50 mg/L. The chloride ion inhibits the reaction at high concentrations above 1000 mg/L by a factor of 1.1 times for every 500 mg/L. An increase in temperature from 293 to 323 K increases the rate constant of the Fenton process for the phenolic compounds studied (phenol, 2-chlorophenol, 2-nitrophenol and 2-methylphenol) by 1.3-1.5. The energy of activation (Ea), enthalpy of activation (ΔHa) and entropy of activation (ΔSa) for the degradation of phenolic compounds were found to be 6.68-10.14 kJ/mol; 4.16-7.56 kJ/mol and -273.36 to -264.30 JK-1mol-1.

Activation potential decreasing of iron oxide/graphite felt cathode by introducing Mn in electrochemical Fenton-like reactions

In electrochemical advanced oxidation processes (EAOPs), energy consumption cannot be ignored. In this work, Mn-Fe oxide/graphite felt (GF) cathodes were synthesized by in situ reduction and low temperature calcination. The obtained Mn-Fe oxide/GF was used as cathodes to activate peroxymonosulfate (PMS) for atrazine (ATZ) degradation in the EAOPs system. The minimal activation potential (ηmin) of PMS was used to evaluate the activity of the cathodes, and it was found that the introduction of Mn element can effectively reduce the ηmin of PMS on the Fe oxide/GF cathode. The energy consumption by optimized Mn-Fe oxide/GF can be decreased to ∼85.1% in the EAOPs system compared to that without Mn. In addition, the introducing of Mn can also enhance the activity and stability of the catalyst with decreased Fe leaching. Quenching experiments and electron paramagnetic resonance (EPR) test indicated that the EAOPs system could generate several reactive oxygen species (ROSs), including •OH, SO4•-, O2•- and 1O2. This work decreases the potential by introducing Mn and provides a method to reduce the energy consumption in EAOPs.

Effective removal of Cr(VI) from water by ball milling sulfur-modified micron zero-valent iron：Influencing factors and removal mechanism

To address the issues of ZVI's susceptibility to oxidation and aggregation, ball milling and Na2S·9H2O modification were employed on ZVI to enhance its efficiency in removing Cr(VI) from effluent. The characterization results expressed that S-mZVIbm had mesoporous and macroporous structures, enabling successful capture of Cr(VI). Moreover, S-mZVIbm had the highest adsorption capacity for Cr(VI) (350.04 mg/g) at pH = 2.00 and reached kinetic equilibrium within 420 min. Furthermore, the adsorption of Cr(VI) by S-mZVIbm conformed to the Avrami-fractional-order model, demonstrated that the adsorption process indicated a complex multi-adsorption process. Meanwhile, the adsorption also fit to Langmuir and Sips models, suggesting monolayer-level adsorption with heterogeneous sites located on S-mZVIbm. The S-mZVIbm could enhance Cr(VI) adsorption through various synergistic mechanisms, such as electrostatic interaction, chemical precipitation, surface complexation, and reduction. Overall, this research presented an innovative perspective for the modification of ZVI, and S-mZVIbm could be widely applied in the practical remediation of wastewater containing Cr(VI).

Connecting the dots: Involvement of methyltransferase-like 3, N6-methyladenosine modification, and ferroptosis in the pathogenesis of intracerebral hemorrhage pathogenesis

Intracerebral hemorrhage is a profoundly detrimental acute cerebrovascular condition with a low overall survival rate and a high post-onset disability rate. Secondary brain injury that ensues post-ICH is the primary contributor to fatality and disability. Hence, the mitigation of brain injury during intracerebral hemorrhage progression has emerged as a crucial aspect of clinical management. N6-methyladenosine is the most pervasive, abundant, and conserved internal co-transcriptional modification of eukaryotic ribonucleic acid and is predominantly expressed in the nervous system. Methyltransferase-like 3 is a key regulatory protein that is strongly associated with the development of the nervous system and numerous neurological diseases. Ferroptosis, a form of iron-associated cell death, is a typical manifestation of neuronal apoptosis in neurological diseases and plays an important role in secondary brain damage following intracerebral hemorrhage. Therefore, this review aimed to elucidate the connection between m6A modification (particularly methyltransferase-like 3) and ferroptosis in the context of intracerebral hemorrhage to provide new insights for future intracerebral hemorrhage management approaches.

Bimetallic FeCu-MOF derivatives as heterogeneous catalysts with enhanced stability for electro-Fenton degradation of lisinopril

A bimetallic FeCu/NC core-shell catalyst, consisting in nanoparticles where zero-valent Fe and Cu atoms, slightly oxidized on their surface, are encapsulated by carbon has been successfully prepared by modifying the synthesis route of MIL(Fe)-88B. FeCu/NC possessed well-balanced textural and electrochemical properties. According to voltammetric responses, in-situ Fe(III) reduction to Fe(II) by low-valent Cu was feasible, whereas the high double-layer capacitance confirmed the presence of a great number of electroactive sites that was essential for continuous H2O2 activation to •OH via Fenton's reaction. Electrochemical impedance and distribution of relaxation times (DRT) analysis informed about the strong leaching resistance of FeCu/NC. To validate the promising features of this catalyst, the advanced oxidation of the antihypertensive lisinopril (LSN) was investigated for the first time. The heterogeneous electro-Fenton (HEF) treatment of 16.1 mg L-1 LSN solutions was carried out in a DSA/air-diffusion cell. At pH 3, complete degradation was achieved within 6 min using only 0.05 g L-1 FeCu/NC; at near-neutral pH, 100 % removal was also feasible even in actual urban wastewater, requiring 60-75 min. The FeCu/NC catalyst demonstrated high stability, still maintaining 86.5 % of degradation efficiency after 5 cycles and undergoing low iron leaching. It outperformed the monometallic (Fe/NC and Cu/NC) catalysts, which is explained by the Cu(0)/Cu(I)-catalyzed Fe(II) regeneration mechanism that maintains the Fenton's cycle. LC-MS/MS analysis allowed the identification of two main primary LSN by-products. It can then be concluded that the FeCu/NC-based HEF process merits to be further scaled up for wastewater treatment.

Coordination engineering of heterogeneous high-valent Fe(IV)-oxo for safe removal of pollutants via powerful Fenton-like reactions

Coordination engineering of high-valent Fe(IV)-oxo (FeIV=O) is expected to break the activity-selectivity trade-off of traditional reactive oxygen species, while attempts to regulate the oxidation behaviors of heterogeneous FeIV=O remain unexplored. Here, by coordination engineering of Fe-Nx single-atom catalysts (Fe-Nx SACs), we propose a feasible approach to regulate the oxidation behaviors of heterogeneous FeIV=O. The developed Fe-N2 SACs/peroxymonosulfate (PMS) system delivers boosted performance for FeIV=O generation, and thereby can selectively remove a range of pollutants within tens of seconds. In-situ spectra and theoretical simulations suggest that low-coordination Fe-Nx SACs favor the generation of FeIV=O via PMS activation as providing more electrons to facilitate the desorption of the key *SO4H intermediate. Due to their disparate attacking sites to sulfamethoxazole (SMX) molecules, Fe-N2 SACs mediated FeIV=O (FeIVN2=O) oxidize SMX to small molecules with less toxicity, while FeIVN4=O produces series of more toxic azo compounds through N-N coupling with more complex oxidation pathways.

Challenges and opportunities for large-scale applications of the electro-Fenton process

As an electrochemical advanced oxidation process, the electro-Fenton (EF) process has gained significant importance in the treatment of wastewater and persistent organic pollutants in recent years. As recently reported in a bibliometric analysis, the number of scientific publications on EF have increased exponentially since 2002, reaching nearly 500 articles published in 2022 (Deng et al., 2022). The influence of the main operating parameters has been thoroughly investigated for optimization purposes, such as type of electrode materials, reactor design, current density, and type and concentration of catalyst. Even though most of the studies have been conducted at a laboratory scale, focusing on fundamental aspects and their applications to degrade specific pollutants and treat real wastewater, important large-scale attempts have also been made. This review presents and discusses the most recent advances of the EF process with special emphasis on the aspects more closely related to future implementations at the large scale, such as applications to treat real effluents (industrial and municipal wastewaters) and soil remediation, development of large-scale reactors, costs and effectiveness evaluation, and life cycle assessment. Opportunities and perspectives related to the heterogeneous EF process for real applications are also discussed. This review article aims to be a critical and exhaustive overview of the most recent developments for large-scale applications, which seeks to arouse the interest of a large scientific community and boost the development of EF systems in real environments.

How many organic small molecules might be used to treat COVID-19? From natural products to synthetic agents

A large scale of pandemic coronavirus disease (COVID-19) in the past five years motivates a great deal of endeavors donating to the exploration on therapeutic drugs against COVID-19 as well as other diseases caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Herein is an overview on the organic small molecules that are potentially employed to treat COVID-19 and other SARS-CoV-2-related diseases. These organic small molecules are accessed from both natural resources and synthetic strategies. Notably, typical natural products presented herein consist of polyphenols, lignans, alkaloids, terpenoids, and peptides, which exert an advantage for the further discovery of novel anti-COVID-19 drugs from plant herbs. On the other hand, synthetic prodrugs are composed of a series of inhibitors towards RNA-dependent RNA polymerase (RdRp), main protease (Mpro), 3-chymotrypsin-like cysteine protease (3CLpro), spike protein, papain-like protease (PLpro) of the SARS-CoV-2 as well as the angiotensin-converting enzyme 2 (ACE2) in the host cells. Synthetic strategies are worth taken into consideration because they are beneficial for designing novel anti-COVID-19 drugs in the coming investigations. Although examples collected herein are just a drop in the bucket, developments of organic small molecules against coronavirus infections are believed to pave a promising way for the discovery of multi-targeted therapeutic drugs against not only COVID-19 but also other virus-mediated diseases.

Preparation of functionalized porous chitin carbon to enhance the H2O2 production and Fe3+ reduction properties of Electro-Fenton cathodes for efficient degradation of RhB

The performance of Electro-Fenton (EF) cathode materials is primarily assessed by H2O2 yield and Fe3+ reduction efficiency. This study explores the impact of pore structure in chitin-based porous carbon on EF cathode effectiveness. We fabricated mesoporous carbon (CPC-700-2) and microporous carbon (ZPC-700-3) using template and activation methods, retaining nitrogen from the precursors. CPC-700-2, with mesopores (3-5 nm), enhanced O2 diffusion and oxygen reduction, producing up to 778 mg/L of H2O2 in 90 min. ZPC-700-3, with a specific surface area of 1059.83 m2/g, facilitated electron transport and ion diffusion, achieving a Fe2+/Fe3+ conversion rate of 79.9%. EF systems employing CPC-700-2 or ZPC-700-3 as the cathode exhibited superior degradation performance, achieving 99% degradation of Rhodamine B, efficient degradation, and noticeable decolorization. This study provides a reference for the preparation of functionalized carbon cathode materials for efficient H2O2 production and effective Fe3+ reduction in EF systems.

Progress and challenges in the use of electrochemical oxidation and reduction processes for heavy metals removal and recovery from wastewaters

Heavy metals-laden industrial wastewater represents both a threat to ecosystems and human health and, in some instances, a potential source of valuable metals however the presence of organic ligands that bind the metals in heavy metal complexes (HMCs) renders metal removal (and, where appropriate, recovery) difficult. Electrochemical-based oxidation and reduction processes represent a potentially promising means of degrading the organic ligands and reducing their ability to retain the metals in solution. In this state-of-the-art review, we provide a comprehensive overview of the current status on use of electrochemical redox technologies for organic ligand degradation and subsequent heavy metal removal and recovery from industrial wastewaters. The principles and degradation mechanism of common organic ligands by various types of electrochemical redox technologies are discussed in this review and consideration given to recent progress in electrode materials synthesis, cell architecture, and operation of electrochemical redox systems. Furthermore, we highlight the current challenges in application of electrochemical redox technologies for treatment of HMC-containing wastewaters including (i) limited understanding of the chemical composition of industrial wastewaters, (ii) constrained mass transfer process affecting the direct/indirect electron transfer, (iii) absence of approaches to convert recovered metal into high-value-added products, and (iv) restricted semi-or full-industrial-scale application of these technologies. Potential strategies for improvement are accordingly provided to guide efforts in addressing these challenges in future research.

Influence of interelectrode distances in electrocoagulation: is there any possibility and advantages to operate at micro-distances with low-conductivity effluents?

It has been proposed for the first time to investigate the possibility to implement micro-inter-electrode distances in electrocoagulation (EC) in order to improve both the treatment and energy efficiencies compared to conventional EC cells with centimetric distances. The study has been performed in a microfluidic monopolar flow-by filter-press cell for the treatment of simulated and real low-conductivity (0.5-1 mS cm-1) laundry wastewaters. The influences of interelectrode distance (delec) (100-10,000 μm), applied current density (japp) (10-200 mA cm-2), and types of anode materials (iron, aluminium and stainless steel) have been studied. The removal of representative organic pollutant (i.e., paracetamol at 15 mg L-1) as well as of total organic carbon (TOC) content (312 mg-C L-1) from actual wastewater was noticed, including at micro-distances. Optimal treatment capacities were obtained with delec of 0.5 mm (57% TOC removed), 3 mm (58% TOC removed) and 10 mm (41% TOC removed) and with japp of 70 mA cm-2, 40 mA cm-2 and 20 mA cm-2 respectively, using stainless steel anode. It led to reduced energy requirement at micro-distances (16 kWh g-TOC-1 at 500 μm) compared to millimetric gap (19 kWh g-TOC-1 at 3 mm, 40 kWh g-TOC-1 at 10 mm). Contrastingly, more sludge was generated with micrometric distance (172 g-sludge g-TOC-1 at 500 μm) compared to larger gaps (95 g-sludge g-TOC-1 at 3 mm, 87 g-sludge g-TOC-1 at 10 mm) due to higher optimal japp at low distances. The efficiency was maximal with an aluminium electrode, but this anode remained inapplicable with micro-distances using the current reactor design, given the high sludge production between the cathode and anode.

Repurposing waste-iron electrocoagulated algal biomass as effective heterogenous (bio)electro-fenton catalyst for phthalate removal from wastewater

The presence of refractory micropollutants in natural waters poses significant environmental and health risks. Preferably, advanced oxidation techniques like electro-Fenton (EF) and bio-electro-Fenton (BEF) are used to mitigate micropollutants; nevertheless, their field-scale implementation is limited by prohibitive catalyst cost. As an alternative, waste-iron electrocoagulated algal biomass (A-BC/Fe) was explored as a heterogeneous Fenton catalyst to eliminate dimethyl phthalate (DMP) from wastewater. The Fenton-conducive morphological, chemical, and electrochemical properties of the A-BC/Fe catalyst were revealed by detailed characterisation. In EF treatment, 10 mg/L of DMP was completely degraded within 15 min at pH of 7.0, 50 mM Na2SO4, and cathode potential of - 1.4 V vs. Ag/AgCl. Moreover, the EF system achieved 87.80 ± 2.10% and 96.14 ± 1.10% of DMP removal from secondary and tertiary treated municipal sewage, respectively. The A-BC/Fe catalyst-driven EF process disintegrated DMP into benign non-toxic by-products and showed stable performance over eight batch cycles with only a 1.71% decline in DMP removal efficiency. Further, the A-BC/Fe-catalysed BEF system eliminated 94.81 ± 1.90% of DMP in 4 h while achieving a maximum power density of 124.03 ± 5.64 mW/m2. This investigation underscores the potential of repurposing electrocoagulated algal biomass as a sustainable heterogenous catalyst for micropollutant remediation.

Bio-inspired Cu2O cathode for O2 capturing and oxidation boosting in electro-Fenton for sulfathiazole decay

A hydrophobic Cu2O cathode (CuxO-L) was designed to solve the challenge of low oxidation ability in electro-Fenton (EF) for treating emerging pollutants. This fabrication process involved forming Cu(OH)2 nanorods by oxidizing copper foam (Cu-F) with (NH4)2S2O8, followed by coating them with glucose via hydrothermal treatment. Finally, a self-assembled monolayer of 1-octadecanethiol was introduced to create a low-surface-energy, functionalized CuxO-L cathode. Results exhibited an approximately 7.9-fold increase in hydroxyl radical (·OH) generation compared to the initial Cu-F. This enhancement was attributed to two key factors: (Ⅰ) the superior O2-capturing ability of CuxO-L cathode, which led to high H2O2 production due to a 2 nm thick hydrophobic gas layer facilitated O2-capturing; (Ⅱ) a relative high concentration of Cu+ at the CuxO-L cathode promoted the activation of H2O2 into·OH. In addition, the performance of EF with the CuxO-L cathode using sulfathiazole (STZ) as a model pollutant was evaluated. This study offers valuable insights into the design of O2-capturing cathodes in EF processes, particularly for treating emerging organic pollutants.

Valorizing waste activated sludge incineration ash to S-doped Fe2+@Zeolite 4A catalyst for the treatment of emerging contaminants exemplified by sulfamethoxazole

The global attention towards waste management and valorization has led to significant interest in recovering valuable components from sludge incineration ash (SIA) for the synthesis of functional environmental materials. In this study, the SIA was converted to an S-doped Fe2+-zeolite type catalyst (FZA) for the treatment of emerging contaminants (ECs), exemplified by sulfamethoxazole (SMX). Results demonstrate that FZA effectively catalyzed the activation of peracetic acid (PAA), achieving a remarkable degradation of 99.8% under optimized conditions. Mechanistic investigations reveal that the FZA/PAA system can generate ·OH, 1O2, O2·－, and Fe(Ⅳ), with ·OH playing a dominant role in ECs degradation. Additionally, the doped S facilitated electrochemical performance, Fe2+ regeneration and fixation in FZA. Practical application elucidated that the FZA/PAA system can work in complex environments to degrade various ECs without generating high-toxicity ingredients. Overall, valorizing SIA to FZA provides dual achievement in waste management and ECs removal.

In Situ Production of Hydroxyl Radicals via Three-Electron Oxygen Reduction: Opportunities for Water Treatment

The electro-Fenton (EF) process is an advanced oxidation technology with significant potential; however, it is limited by two steps: generation and activation of H2O2. In contrast to the production of H2O2 via the electrochemical two-electron oxygen reduction reaction (ORR), the electrochemical three-electron (3e-) ORR can directly activate molecular oxygen to yield the hydroxyl radical (⋅OH), thus breaking through the conceptual and operational limitations of the traditional EF reaction. Therefore, the 3e- ORR is a vital process for efficiently producing ⋅OH in situ, thus charting a new path toward the development of green water-treatment technologies. This review summarizes the characteristics and mechanisms of the 3e- ORR, focusing on the basic principles and latest progress in the in situ generation and efficient utilization of ⋅OH through the modulation of the reaction pathway, shedding light on the rational design of 3e- ORR catalysts, mechanistic exploration, and practical applications for water treatment. Finally, the future developments and challenges of efficient, stable, and large-scale utilization of ⋅OH are discussed based on achieving optimal 3e- ORR regulation and the potential to combine it with other technologies.

The recent development of innovative photoelectro-Fenton processes for the effective and cost-effective remediation of organic pollutants in waters

Wastewaters with toxic and recalcitrant organic contaminants are poorly remediated in conventional wastewater treatment plants. So, powerful processes need to be developed to destroy such organic pollutants to preserve the quality of the aquatic environment. This critical and comprehensive review presents the recent innovative development of photoelectro-Fenton (PEF) covering the period 2019-September 2024. This emerging photo-assisted Fenton-based electrochemical advanced oxidation process (EAOP) is an efficient and cost-effective treatment for water remediation. It possesses a great oxidation power because the in-situ generated hydroxyl radical as oxidant is combined with the photolysis of the organic by-products under UV or sunlight irradiation. The review is initiated by a brief description of the characteristics of the PEF process to stand out in the role of generated oxidizing agents. Further, the homogeneous PEF. PEF-like, solar PEF (SPEF), and SPEF-like processes with iron catalysts are discussed, taking examples of their application to the removal and mineralization of solutions of industrial chemicals, herbicides, dyes, pharmaceuticals, and direct real wastewaters. Novel heterogeneous PEF treatments of such pollutants with solid iron catalysts or functionalized cathodes are analyzed. Finally, novel hybrid processes including PEF/photocatalysis and PEF/photoelectrocatalysis, followed by novel and potent sequential processes like electrocoagulation-PEF and persulfate-PEF, are discussed. Throughout the manuscript, special attention was made to the total operating cost of PEF, which is more expensive than conventional electro-Fenton due to the high electric cost of the UV lamp, pointing to consider the much more cost-effective SPEF as a preferable alternative in practice.

Interfacial Anion-Induced Dispersion of Active Species for Efficient Electrochemical Baeyer-Villiger Oxidation

Degradable polymers are an effective solution for white plastic pollution. Polycaprolactone is a type of degradable plastic with desirable mechanical and biocompatible properties, and its monomer, ε-caprolactone (ε-CL), is often synthesized by Baeyer-Villiger (B-V) oxidation that demands peroxyacids with low safety and low atom-efficiency. Herein, we devised an electrochemical B-V oxidation system simply driven by H2O2 for the efficient production of ε-CL. This system involves two steps with the direct oxidation of H2O2 into •OOH radicals at the electrode surface and the indirect oxidation of cyclohexanone by the generated reactive oxygen species. The modulation of the interfacial ionic environment by amphipathic sulfonimide anions [e.g., bis(trifluoromethane)sulfonimide (TFSI-)] is highly critical. It enables the efficient B-V oxidation into ε-caprolactone with ∼100% selectivity and 68.4% yield at a potential of 1.28 V vs RHE, much lower than the potentials applied for electrochemical B-V oxidation systems using water as the O sources. On hydrophilic electrodes with the action of sulfonimide anions, hydrophilic H2O2 can be enriched within the double layer for direct oxidation while hydrophobic cyclohexanone can be simultaneously accumulated for rapidly reacting with the reactive oxygen species. This work not only enriches the electrified method of the ancient B-V oxidation by using only H2O2 toward monomer production of biodegradable plastics but also emphasizes the critical role of the interfacial ionic environment for electrosynthesis systems that may extend the scope of activity optimization.

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.

Abdominal multi-organ iron content and the risk of Parkinson's disease: a Mendelian randomization study

Background

To evaluate the causal relationship between abdominal multi-organ iron content and PD risk using publicly available genome-wide association study (GWAS) data.

Methods

We conducted MR analysis to assess the effects of iron content in various abdominal organs on PD risk, followed by reverse analysis. Additionally, MVMR analysis evaluated the independent effects of organ-specific iron content on PD. We utilized genetic variation data from the UK Biobank, including liver iron content (n = 32,858), spleen iron content (n = 35,324), and pancreas iron content (n = 25,617), as well as summary-level data for Parkinson's disease from the FinnGen (n = 218,473) and two other large GWAS datasets of European populations (First dataset n = 480,018; Second dataset n = 2,829). The primary MR analysis used the inverse variance-weighted (IVW) method, confirmed by MR-Egger and weighted median methods. Sensitivity analysis was performed to address potential pleiotropy and heterogeneity. Observational cohort results were validated through replication cohort analysis, followed by meta-analysis.

Results

IVW analysis revealed a causal relationship between increased liver iron content and elevated risk of PD (OR = 1.27; 95% CI: 1.05-1.53; p = 0.015). No significant causal relationship was observed between spleen (OR = 1.00; 95% CI: 0.76-1.32; p = 0.983) and pancreatic (OR = 0.93; 95% CI: 0.72-1.20; p = 0.573) iron content and increased risk of PD. Meta-analysis of GWAS data for PD from three different sources using the random-effects IVW method showed a statistically significant causal relationship between liver iron content and the occurrence of PD (OR = 1.17, 95% CI: 1.01-1.35; p = 0.012).

Conclusion

This study presents evidence from Mendelian randomization (MR) analysis indicating a significant causal link between increased liver iron content and a higher risk of Parkinson's disease (PD). These findings suggest that interventions targeting body iron metabolism, particularly liver iron levels, may be effective in preventing PD.

Sustainable electro-Fenton simultaneous reduction of Cr (VI) and degradation of organic pollutants via dual-site porous carbon cathode driving uncoordinated molybdenum sites conversion

Simultaneous removal of heavy metals and organic contaminants remains a substantial challenge in the electro-Fenton (EF) system. Herein, we propose a facile and sustainable "iron-free" EF system capable of simultaneously removing hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP). The system comprises a nitrogen-doped and carbon-deficient porous carbon (dual-site NPC-D) cathode coupled with a MoS2 nanoarray promoter (MoS2 NA). The NPC-D/MoS2 NA system exhibits exceptional synergistic electrocatalytic activity, with removal rates for Cr (VI) and 4-CP that are 20.3 and 4.4 times faster, respectively, compared to the NPC-D system. Mechanistic studies show that the dual-site structure of NPC-D cathode favors the two-electron oxygen reduction pathway with a selectivity of 81 %. Furthermore, an electric field-driven uncoordinated Mo valence state conversion of MoS2 NA enchances the generation of dynamic singlet oxygen and hydroxyl radicals. Notably, this system shows outstanding recyclability, resilience in real wastewater, and sustainability during a 3 L scale-up operation, while effectively mitigating toxicity. Overall, this study presents an effective approach for treating multiple-component wastewater and highlights the importance of structure-activity correlation in synergistic electrocatalysis.

Overlooked Impacts of Alcohols in Electro-H2O2 and Fenton Chemistry

Alcohols are promising fuels for direct alcohol fuel cells and are common scavengers to identify reactive oxygen species (ROS) in electro-Fenton (EF) systems. However, the side impacts of alcohols on oxygen reduction reactions and ROS generation are controversial due to the complex interactions between electrodes and alcohol-containing electrolytes. Herein, we employed synchrotron-Fourier-transform infrared spectroscopy and electron paramagnetic resonance technologies to directly observe the changes of chemical species and electrochemical properties on the electrode surface. Our studies suggested that alcohols exhibited different limiting degrees on proton (H+) mass transfer toward the catalytic surface, following an order of methanol < ethanol < isopropanol < tert-butyl alcohol (TBA). In addition, the formation of hydrophobic TBA clusters at high concentrations (>400 mM) resulted in a significant reduction in ionic conductivity and an elevation in charge transfer resistance, which impedes H+ mass transfer and raises the energy barrier for 2e- oxygen reduction reaction processes. Moreover, the organic radical •CH2(CH3)2CH2OH produced by the interaction of Fe3+ and •OH with the alcohol in the EF system serves as a crucial intermediate in facilitating H2O2 regeneration, which complicates the quenching effect of alcohols on •OH identification. Therefore, it is recommended that methanol should be used as the scavenger instead of TBA and the concentration should be less than 400 mM in EF systems.

Degradation of thiocyanate by Fe/Cu/C microelectrolysis: Role of pre-magnetization and enhancement mechanism

Thiocyanate (SCN-), a non-volatile inorganic pollutant, is commonly found in various types of industrial wastewater, which is resistant to hydrolysis and has the potential to be toxic to organisms. Premagnetized iron-copper-carbon ternary micro-electrolytic filler (pre-Fe/Cu/C) was prepared to degrade SCN-. Pre-Fe/Cu/C exhibited the most significant enhancement effect on SCN- removal when magnetized for 5 min with an intensity of 100 mT, and the SCN- removal rate was the highest at an initial pH of 3.0 and an aeration rate of 1.6 L/min. The electrochemical corrosion and electron transfer in the pre-Fe/Cu/C system were confirmed through SEM, XPS, FTIR, XRD, and electrochemical tests. This resulted in the formation of more corrosion products and multiple cycles of Fe2+/Fe3+ and Cu0/Cu+/Cu2+. Additionally, density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) were utilized to illustrate the oxygen adsorption properties of the materials and the participation of reactive oxygen species (1O2, ·O2-, and ·OH) in SCN- removal. The degradation products of SCN- were identified as SO42-, HCO3-, NH4+, and N2. This study introduced the use of permanent magnets for the first time to enhance Fe/Cu/C ternary micro-electrolytic fillers, offering a cost-effective, versatile, and stable approach that effectively effectively enhanced the degradation of SCN-.

Integrating electro-Fenton and microalgae for the sustainable management of real food processing wastewater

The present study demonstrates, for the first time, the feasibility of a two-step process consisting of Electro-Fenton (EF) followed by microalgae to treat highly loaded real food processing wastewater along with resource recovery. In the first step, EF with a carbon felt cathode and Ti/RuO2-IrO2 anode was applied at different current densities (3.16 mA cm-2, 4.74 mA cm-2 and 6.32 mA cm-2) to decrease the amount of organic matter and turbidity and enhance biodegradability. In the second step, the EF effluents were submitted to microalgal treatment for 15 days using a mixed culture dominated by Scenedesmus sp., Chlorosarcinopsis sp., and Coelastrum sp. Results showed that current density impacted the amount of COD removed by EF, achieving the highest COD removal of 77.5% at 6.32 mA cm-2 with >95% and 74.3% of TSS and PO43- removal, respectively. With respect to microalgae, the highest COD removal of 85% was obtained by the culture in the EF effluent treated at 6.32 mA cm-2. Remarkably, not only 85% of the remaining organic matter was removed by microalgae, but also the totality of inorganic N and P compounds, as well as 65% of the Fe catalyst that was left after EF. The removal of inorganic species also demonstrates the high complementarity of both processes, since EF does not have the capacity to remove such compounds, while microalgae do not grow in the raw wastewater. Furthermore, a maximum of 0.8 g L-1 of biomass was produced after cultivation, with an accumulation of 32.2% of carbohydrates and 25.9% of lipids. The implementation of the two processes represents a promising sustainable approach for the management of industrial effluents, incorporating EF in a water and nutrient recycling system to produce biomass that could be valorized into clean fuels.

Antibiotic Degradation via Fenton Process Assisted by a 3-Electron Oxygen Reduction Reaction Pathway Catalyzed by Bio-Carbon-Manganese Composites

Bio-carbon-manganese composites obtained from olive mill wastewater were successfully prepared using manganese acetate as the manganese source and olive wastewater as the carbon precursor. The samples were characterized chemically and texturally by N2 and CO2 adsorption at 77 K and 273 K, respectively, by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. Electrochemical characterization was carried out by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The samples were evaluated in the electro-Fenton degradation of tetracycline in a typical three-electrode system under natural conditions of pH and temperature (6.5 and 25 °C). The results show that the catalysts have a high catalytic power capable of degrading tetracycline (about 70%) by a three-electron oxygen reduction pathway in which hydroxyl radicals are generated in situ, thus eliminating the need for two catalysts (ORR and Fenton).

Geochemical fractionation of iron in paper industry and municipal landfill soils: Ecological and health risks insights

Industrial processes and municipal wastes largely contribute to the fluctuations in iron (Fe) content in soils. Fe, when present in unfavorable amount, causes harmful effects on human, flora, and fauna. The present study is an attempt to evaluate the composition of Fe in surface soils from paper mill and municipal landfill sites and assess their potential ecological and human health risks. Geochemical fractionation was conducted to explore the chemical bonding of Fe across different fractions, i.e., water-soluble (F1) to residual (F6). Different contamination factors and pollution indices were evaluated to comprehend Fe contamination extent across the study area. Results indicated the preference for less mobile forms in the paper mill and landfill, with 26.66% and 43.46% of Fe associated with the Fe-Mn oxide bound fraction (F4), and 57.22% and 24.78% in the residual fraction (F6). Maximum mobility factor (MF) of 30.65% was observed in the paper mill, and 80.37% in the landfill. The enrichment factor (EF) varied within the range of 20 < EF < 40, signifying a high level of enrichment in the soil. The individual contamination factor (ICF) ranged from 0 to >6, highlighting low to high contamination. Adults were found to be more vulnerable towards Fe associated health risks compared to children. The Hazard Quotient (HQ) index showed the highest risk potential pathways as dermal contact > ingestion > inhalation. The study offers insights into potential Fe contamination risks in comparable environments, underscoring the crucial role of thorough soil assessments in shaping land use and waste management policies.

All-in-one continuous electrochemical monitoring of 2-phenylphenol removal from water by electro-Fenton treatment

The biggest allure of heterogeneous electro-Fenton (HEF) processes largely fails on its high efficiency for the degradation of a plethora of hazardous compounds present in water, but still challenging to search for good and cost-effective electrocatalyst. In this work, carbon black (CB) and oxidised carbon black (CBox) materials were investigated as cathodes in the electrochemical production of hydrogen peroxide involved in HEF reaction for the degradation of 2-phenylphenol (2PP) as a target pollutant. The electrodes were fabricated by employing carbon cloth as support, and the highest H2O2 production yields were obtained for the CBox, pointing out the beneficial effect of the hydrophilic character of the electrode and oxygen-type functionalization of the carbonaceous surface. HEF degradation of 2PP was explored at -0.7 V vs. Ag/AgCl exhibiting the best conversion rates and degradation grade (total organic carbon) for the CBox-based cathode. In addition, the incorporation of an electrochemical sensor of 2PP in line with the HEF reactor was accomplished by the use of screen-printed electrodes (SPE) in order to monitor the pollutant degradation. The electrochemical sensor performance was evaluated from the oxidation of 2PP in the presence of Fe2+ ions by using square wave voltammetry (SWV) technique. The best electrochemical sensor performance was based on SPE modified with Meldola Blue showing a high sensitivity, low detection limit (0.12 ppm) and wide linear range (0.5-21 ppm) with good reproducibility (RSD 2.3 %). The all-in-one electrochemical station has been successfully tested for the degradation and quantification of 2PP, obtaining good recoveries analysing spiked waters from different water matrices origins.

Oxygen-containing functional groups in Fe3O4@three-dimensional graphene nanocomposites for enhancing H2O2 production and orientation to 1O2 in electro-Fenton

In electro-Fenton (EF), development of a bifunctional electrocatalyst to realize simultaneous H2O2 generation and activation efficiently for generating reactive species remains a challenge. In particular, a nonradical-mediated EF is more favorable for actual wastewater remediation, and deserves more attention. In this study, three-dimensional graphene loaded with Fe3O4 nanoparticles (Fe3O4@3D-GNs) with abundant oxygen-containing functional groups (OFGs) was synchronously synthesized using a NaCl-template method and served as a cathode to establish a highly efficient and selective EF process for contaminant degradation. The amounts of OFGs can be effectively modulated via the pyrolysis temperature to regulate the 2e- oxygen reduction reaction activity and reactive oxygen species (ROS) production. The optimized Fe3O4@3D-GNs synthesized at 750 °C (Fe3O4@3D-GNs-750) with the highest -C-O-C and -C꞊O group ratios exhibited the maximum H2O2 and 1O2 yields during electrocatalysis, thus showing remarkable versatility for eliminating organic contaminants from surface water bodies. Experiments and theoretical calculations have demonstrated the dominant role of -C-O-C in generating H2O2 and the positive influence of -C꞊O sites on the production of 1O2. Moreover, the surface-bound Fe(II) favors the generation of surface-bound •OH, which steers a more favorable oxidative conversion of H2O2 to 1O2. Fe3O4@3D-GNs were proven to be less pH-dependent, low-energy, stable, and recyclable for practical applications in wastewater purification. This study provides an innovative strategy to engineer active sites to achieve the selective electrocatalysis for eliminating pollution and reveals a novel perspective for 1O2-generation mechanism in the Fenton reaction.

MoS2-mediated active hydrogen modulation to boost Fe2+ regeneration in solar-driven electro-Fenton process

The sluggish kinetics of Fe2+ regeneration seriously hinders the performance of Fenton process. However, the conventional Fenton system excessively stifle hydrogen-producing reactions, ignoring the significance of active hydrogen (H*) in Fe3+ reduction. Herein, a strategy of H* modulation is developed by decorating molybdenum disulfide (MoS2) on a graphite felt (GF) cathode to boost Fe2+ regeneration in solar-driven electro-Fenton (SEF) process. With MoS2 regulation, moderately dispersed MoS2 on GF can serve as a bifunctional cathode, where the H* and hydrogen peroxide (H2O2) are simultaneously generated through H+ reduction and O2 reduction, respectively. The in-situ generated H2O2 can trigger Fenton reactions with Fe2+, while the H* with robust reducing potential can significantly expedite Fe3+ reduction, consequently enhancing the HO• production. Both DFT calculations and EPR experiments confirm that H* can be activated via MoS2 decoration. The results show that Fe2+ concentration in the MoS2 @GF-SEF system remains at 15.74 mg/L (56.21%) after 6 h, which is 17.89 times that of the GF-SEF system. Moreover, the HO• content and organics degradation rate in the MoS2 @GF-SEF are 3.61 and 5.30 times those of the GF-SEF, respectively. This study provides a practical cathode strategy of H* modulation to enhance HO• production and electro-Fenton process. ENVIRONMENTAL IMPLICATION: Boosting Fe2+ regeneration is of great value for the Electro-Fenton process. Herein, report a strategy to achieve this goal based on a MoS2 @GF cathode. Remarkably, the MoS2 @GF system exhibits exceptional efficiency for both various refractory organic compounds with environmentally hazardous effects and sterilization aspects, which can also work over a wide range of pH values (3-11). Specially, this system is driven only by solar energy. These characteristics make the electro-Fenton system more suitable for practical wastewater treatment.