Abstract ：

Valorization of iron-rich metallurgical slags in the construction of Fenton-like catalysts has an appealing potential from the perspective of sustainable development. For the first time, copper smelting slag (CSS) was utilized as the precursor to synthesize hollow sea urchin-like Fe–Cu nanoreactors (Cu1.5Fe1Si) to activate peroxymonosulfate (PMS) for chlortetracycline hydrochloride (CTC) degradation. The hyper-channels and nano-sized cavities were formed in the catalysts owing to the induction and modification of Cu, not only promoting the in-situ growth of silicates and the formation of cavities due to the etching of SiO2 microspheres, but also resulting the generation of nanotubes through the distortion and rotation of the nanosheets. It was found that 100 % CTC degradation rate can be achieved within 10 min for Cu1.5Fe1Si, 75 times higher than that of Cu0Fe1Si (0.0024 up to 0.18 M−1‧min−1). The unique nanoconfined microenvironment structure could enrich reactants in the catalyst cavities, prolong the residence time of molecules, and increase the utilization efficiency of active species. Density functional theory (DFT) calculations show that Cu1.5Fe1Si has strong adsorption energy and excellent electron transport capacity for PMS, and Fe-Fe sites are mainly responsible for the activation of PMS, while Cu assists in accelerating the Fe(II)/Fe(Ⅲ) cycle and promotes the catalytic efficiency. The excellent mineralization rate (83.32 % within 10 min) and efficient treatment of CTC in consecutive trials corroborated the high activity and stability of the Cu1.5Fe1Si. This work provides a new idea for the rational design of solid waste-based eco-friendly functional materials, aiming at consolidating their practical application in advanced wastewater treatment. © 2024 Elsevier Inc.

Keyword ：

Organoclay Waste utilization Plastic bottles Microspheres Bioremediation Fly ash Manganese nodules Effluent treatment Copper smelting Reactor refueling Silica Slags

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Abstract ：

The preparation of stable and high-efficiency heterogeneous electro-Fenton cathodes for the treatment of pollutants is important for environmental remediation. Herein, a novel N-doped MOF-derived Fe/Co bimetallic catalyst was in-situ grown on graphite felt (GF) surface to yield a composite cathode Fe/CoNHDC-400@GF for use in electro-Fenton process. The introduction of cobalt accelerated electron transfer due to existing polyvalent metals. The synergistic effect between Co-0, Co-II, Co-III, Fe-II, and Fe. enabled the continuous generation of reactive oxygen species ((OH)-O-center dot and O-center dot(2)-). Under near-neutral conditions (pH=6.5), complete removal of 10 mg L-1 chloroquine phosphate (CQP) was achieved within 60 min. Additionally, efficient removal was also achievable over a wide pH range (pH=3-11). The mechanistic investigations indicated (OH)-O-center dot as a major active oxygen species for CQP degradation. A combination of the experimental results with density functional theory calculations (DFT) clarified the degradation pathway and intermediate products of CQP. Moreover, the toxicity of degradation products significantly reduced. Overall, valuable insights on preparing composite cathodes grown in-situ for efficient removal of refractory pollutants from wastewater during the heterogeneous electro-Fenton process were provided, useful for future consideration.

Keyword ：

Heterogeneous electro-Fenton process In-situ catalysis Chloroquine phosphate Polyvalent metals synergistic effect

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Abstract ：

Electro-Fenton (EF) process stands out as an energy-efficient and highly promising advanced oxidation technology for organic contaminants degradation. However, achieving optimal heterogeneous catalytic conditions for simultaneous H2O2 generation and spontaneous Fe2+ regeneration poses difficulties in conventional EF. This is due to the electric potential difference between H2O2 generation and Fe2+ regeneration at a single cathode. Therefore, the boron doped biochar modified dual-cathode EF (DCEF) system was designed in this work to overcome the defect of conventional EF system, which not only demonstrated outstanding accumulation of H2O2 (>300 mg L-1) but also exhibited a remarkable capability of degradation (>90 %). Furthermore, the system could also adapt to a broad pH range of 3-11. The superior doxycycline (DOX) degradation efficiency of DCEF system could be attributed to the dominant role played by C=O and BCO2 groups in the activation of H2O2 and subsequently generating reactive oxygen species (ROSs), as revealed by XPS analysis and DFT calculation. In addition, the DCEF system achieved an impressive TOC removal efficiency of 70.5 % and a minimal energy consumption (EC) of 0.32 kWh (g TOC)(-1). Therefore, this work introduced a DCEF system to address the challenges of conventional EF system, which shed light on the design of wastewater treatment technology and lied the groundwork for a strategy of resource utilization.

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Electro-Fenton Dual -cathode Biochar Boron doping Dual active sites

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Abstract ：

Cu-based nanocatalysts have received much attention for their high efficiency and environmental friendliness in heterogeneous electro-Fenton (hetero-EF) technology. However, designing catalysts posses high stability and efficient pollutant degradation performance remains challenging. In this work, a novel binder-free copper foam (CF)-supported CuxO nanorod array electrode was prepared by solvothermal and calcination methods and used for the degradation of sulfamethoxazole (SMX). The hetero-EF system with CuxO NRs/CF-300 C as cathode achieved 100 % SMX degradation in 90 min. Experimental and theoretical calculations showed that the coexistence of Cu-0, Cu+, and Cu(2+ )in Cu-based catalysts promotes the generation of & sdot;O-2(-) and facilitates redox cycling of Cu species (Cu+/Cu2+), thus enhancing SMX degradation efficiency. In addition, CuxO NRs/CF-300 C expanded the pH range (3-11) and exhibited remarkable stability, making it an excellent synthetic electrode material with production potential. This discovery successfully overcame the low and unstable Cu+ activation capacity and the short lifetime of reactive oxygen species in conventional heterogeneous reactions. This work provides a practical approach for developing reliable Cu-based nanocatalysts and facilitating the degradation of organic contaminants.

Keyword ：

Active oxygen species Heterogeneous electro-Fenton Sulfamethoxazole Copper -based nanocatalysts Synergistic effect

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Abstract ：

Developing eco-friendly, economical, and efficient catalytic systems for pollutant removal has become an imperative orientation in water treatment. Conversion of municipal sludge into multifunctional biochar has been considered as a feasible strategy for dual applicability in water treatment and sludge management. Herein, municipal biological and ferric sludge were recycled to synthesize an iron-based biochar (Fe4SBC1-800) with great magnetic separation performance (Ms = 29.96 emu g  1). The mixed sludge-derived biochar (Fe4SBC1-800) engaged as an efficient catalyst of peroxymonosulfate (PMS), which efficiently promoted the pollutants elimination including typical azo dye and several antibiotics and anti-inflammatory drugs. The enhanced degradation performance primarily originated from the formation of reactive radicals and non-radical species. The respective and synergetic mechanisms of biochar and supported iron species on PMS activation were verified based on experimental results and theoretical computations. The carboxyl groups served as the major active sites of biochar that donated electrons to PMS for center dot OH and SO4 center dot  formation. The supported FeO species further boosted the activation capability: (i) the enhanced formation of radicals and FeIV = O via heterogeneous Fenton-like reactions; (ii) the promoted oxygen reduction for O2 center dot  formation by promoting electron transfer from PMS to the FeO species through high sp2-hybridized biochar. Overall, this study innovatively proposed a sustainable and efficient activation system for PMS by iron-based magnetic biochar, which systematically probed the activation mechanism and reconsidered the role of the supported iron species in the iron-based biochar/PMS system.

Keyword ：

Electron transfer Carboxyl group Iron Magnetic biochar Peroxymonosulfate

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Abstract ：

Electro-Fenton (EF) process, featuring in-situ hydrogen peroxide (H2O2) production, has received increasing attention for its efficacy in degrading organic pollutants. However, challenges such as low oxygen utilization efficiency and high energy consumption persist. In this study, a novel Carbon Black-loaded Carbon Felt (CB-CF) electrode using the electrophoretic deposition (EPD) technique was prepared to boost the efficiency of H2O2 production. Various aeration patterns and aeration gas were systematically introduced to assess the oxygen utilization pathway and improve oxygen utilization efficiency. The CB-CF cathode, forming an efficient triphase interface, coupled with the side-oxygen mode, demonstrates rapid H2O2 production (48.82 mg/h) at a remarkably low energy consumption (14.46kWh & sdot;kg- 1) with the current density of 15 mA/cm2. The fabricated CB-CF exhibited exceptional performance, achieving over 90% degradation efficiency of Fulvic Acid (FA) within 60 minutes in the EF system. Stability experiments underscored the impact of current density and hydrophobicity on the electrode but revealed that PTFE recoating effectively preserves stability. Furthermore, the straightforward and efficient electrode preparation process, combined with the favorable electrochemical properties of CBCF, positions it as a promising candidate for large-scale applications in H2O2 electro-synthesis and environmental remediation.

Keyword ：

Electrophoretic deposition Oxygen utilization efficiency Three-phase interface In-situ H 2 O 2 production Side-Aeration Electro-Fenton

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In this study, an electro-Fenton gas diffusion electrode featuring air self-respiration was fabricated by incorporating carbon nanotubes, carbon nitride, and polytetrafluoroethylene onto graphite felt. The fabrication process involved a synergistic approach of ultrasonic impregnation and vacuum filtration, establishing a gas-liquid-solid tri-phase interface both on the surface and within the electrode. This preparation method facilitates autonomous air intake, diffusing it to the tri-phase reaction interface, thereby eliminating the necessity for aeration and reducing operational costs. The optimal electrode preparation conditions were determined through Box-Behnken Design response surface experiments, leading to the enhancement of H2O2 production conditions. Under the optimized conditions, H2O2 accumulation reached 45.83 mg L-1 cm(-2)h(-1), surpassing the performance achieved with conventional ultrasonic impregnation and vacuum filtration methods. Furthermore, the performance of self-breathing and the impact factors are explored. Finally, the electrode's efficacy was demonstrated through the degradation of phenol and bisphenol A with concentrations of 100 mg L-1 exhibiting degradation rates of 92 % and 95 %, respectively, within 60 min.

Keyword ：

Gas diffusion electrode H2O2 production Electro-Fenton Self-breathing

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Abstract ：

Non-metallic atom doping is a good strategy to promote the cathode performance in the electro-Fenton process. Therefore, a mixed-valence copper (I and II) phosphate (Cu2PO4) catalyst on P-doped etched graphite felt (EGF), with a strip-groove rough surface, was prepared in this study. The P-doped Cu2PO4/EGF electrode completely removed sulfamethoxazole (SMX) from contaminated water within 90 min over a wide pH range of 5.6-9 and removed 99.6% of SMX at pH 11. Quenching experiments showed that the main reactive oxygen species (ROS) was center dot O-2(-). According to density functional theory calculations, the adsorption reaction energy (EP = 2.149) of P atoms doped on the EGF surface was lower than that of pyrrolic nitrogen atoms (EN = 0.434), indicating that they were more conducive to oxygen adsorption. Finally, we investigated the mechanism of P-doped Cu2PO4/ EGF adsorption and the catalytic production of center dot O-2(-) from O-2. Four main degradation pathways were identified based on the intermediates identified during degradation. Toxicity analysis of the intermediates showed that electro-Fenton degradation reduced the ecotoxicity of SMX. The enhanced electrocatalytic activity obtained by P doping of heterogeneous catalysts provides a new method for preparing efficient and stable composite electrodes for pollutant degradation.

Keyword ：

Superoxide anion radical Phosphorus doped electrode Degradation pathways Cu2PO4 Etched graphite felt

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Herein, a single-atom catalyst (SAC) featuring Fe-N-5 sites (FeNC) with optimized electronic structures was constructed and applied to activate peroxymonosulfate (PMS) for wastewater purification. The high-coordinated Fe-N-5 sites was obtained by creating a high-nitrogen gas environment around fully exposed Fe atomic sites on chitosan surface during pyrolysis. The FeNC/PMS system demonstrated excellent decontamination capability, superior anti-pH interference ability, while also exceptional durability in a continuous-flow catalytic filtration reactor. Experiments and density functional theory calculations unveiled that Fe-N-5 site was the active center. Meaningfully, neighboring carbonyl groups narrowed the gap between d-band center of Fe 3d and Fermi level, which increased the adsorption energy of PMS on Fe-N-5 sites, thus lowering the energy barrier for singlet oxygen generation. This study brings a vivid electronic structure optimization strategy for enhancing the catalytic activity of Fe SAC as well as guiding the selection of desirable catalysts for wastewater purification by Fenton-like chemistry.

Keyword ：

Electronic structure optimization High-coordinated M-N-x sites Density functional theory Fenton-like reaction Single-atom catalysts

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The inefficient electron transfer and Fe(III)/Fe(II) cycle remain significant obstacles in the electro-fenton process. Herein, a nitrogen-doped graphite felt (NGF)-supported CoFe/CoFe2O4 heterostructure is synthesized that achieves highly efficient interfacial electron transfer and stable Co/Fe redox cycle. Theoretical calculations demonstrate that the CoFe/CoFe2O4 heterointerfaces induce local charge redistribution benefiting from the electronic communication between electron acceptor (CoFe2O4) and electron donor (CoFe). Analysis of the Fermi level indicates that the introduction of CoFe alloy enhances the electron density of the catalyst. The CoFe/ CoFe2O4@NGF cathode can remove bisphenol A (BPA) completely in 90 min, and the pseudo-first-order kinetic constant (0.0625 min(-1)) is 23 times higher than the GF system. Notably, the CoFe/CoFe2O4@NGF electrode maintains excellent catalytic capability and stability within a broad pH range (3-11). The construction of the CoFe/CoFe2O4 heterostructure reduces the adsorption energy of oxygen, which ultimately increases the yield of reactive oxygen species (ROS). Quenching experiments revealed that hydroxyl radical (center dot OH) played a dominant role in the degradation of BPA, and significantly reduced the biotoxicity of intermediate products. This work offers a dependable approach for developing bimetallic catalysts with high catalytic activity.

Keyword ：

Heterogeneous electro-Fenton Heterointerface Electron transfer Bimetallic catalyst

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