Self-Assembly of Mn(II)-Amidoximated PAN Polymeric Beads Complex as Reusable Catalysts for Efficient and Stable Heterogeneous Electro-Fenton Oxidation

Degradation of levofloxacin using electro coagulation residuals-alginate beads as a novel heterogeneous electro-fenton composite

The presence of levofloxacin (LEV) in aqueous solutions can pose health risks to humans, have adverse effects on aquatic organisms and ecosystems, and contribute to the development of antibiotic-resistant bacteria. This study aims to investigate the feasibility of using electrocoagulation residuals (ECRs) as a heterogeneous catalyst in the electro-Fenton process for degrading LEV. By combining electrocoagulation residuals with sodium alginate, ECRs-alginate beads were synthesized as a heterogeneous electro-Fenton composite. The response surface method was employed to investigate the optimization and influence of various operating parameters such as the initial concentration of LEV (10-50 mg/L), voltage (15-35 V), pH (3-9), and catalyst dose (1-9 g/L). The successful incorporation of iron and other metals into the ECRs-alginate beads was confirmed by characterization tests such as EDX and FTIR. By conducting a batch reaction under optimal conditions (initial LEV concentration = 20 mg/L, pH = 4.5, voltage = 30V, and catalyst dose = 7 g/L), a remarkable degradation of 99% for LEV was achieved. Additionally, under these optimal conditions, a high removal efficiency of 92.3% for total organic carbon (TOC) could be attained within 120 min and these findings are remarkable compared to previous studies. The results further indicated that the degradation of levofloxacin (LEV) could be accurately quantified by utilizing the first-order kinetic reaction with a 0.03 min-1 rate constant. The synthesized beads offered notable advantages in terms of being eco-friendly, simple to use, highly efficient, and easily recoverable from the liquid medium after use.

UV-blocking and photocatalytic properties of Ag-coated cotton fabrics with Si binders for photo-degradation of recalcitrant dyes in aqueous solutions under sunlight

Textile wastewater laden with dyes has emerged as a source of water pollution. This possesses a challenge in its effective treatment using a single functional material. In respond to this technological constraint, this work presents multifunctional cotton fabrics (CFs) within a single, streamlined preparation process. This approach utilizes the adherence of Ag NPs (nanoparticles) using Si binder on the surface of CFs, resulting in Ag-coated CFs through a pad dry method. The prepared samples were characterized using scanning electron microscope-energy dispersive X-ray electroscopy (SEM-EDS), thermal gravimetric analysis (TGA), Fourier transformation infrared (FT-IR). It was found that the FT-IR spectra of Ag NPs-coated CFs had peaks appear at 3400, 2900, and 1200 cm-1, implying the stretching vibrations of O-H, C-H, and C-O, respectively. Based on the EDX analysis, the presence of C, O, and Ag related to the coated CFs were detected. After coating the CFs with varying concentrations of Ag NPs (1%, 2% and 3% (w/w)), they were used to remove dyes. Under the same concentration of 10 mg/L and optimized pH 7.5 and 2 h of reaction time, 3% (w/w) Ag-coated CFs exhibited a substantial MB degradation of 98 %, while removing 95% of methyl orange, 85% of rhodamine B, and 96% of Congo red, respectively, following 2 h of Vis exposure. Ag NPs had a strong absorption at 420 nm with 2.51 eV of energy band gap. Under UV irradiation, electrons excited and produced free radicals that promoted dyes photodegradation. The oxidation by-products included p-dihydroxybenzene and succinic acid. Spent Ag-coated CFs attained 98% of regeneration efficiency. The utilization of Ag-coated CFs as a photocatalyst facilitated treated effluents to meet the required discharge standard of lower than 1 mg/L mandated by national legislation. The integration of multifunctional CFs in the treatment system presents a new option for tackling water pollution due to dyes.

Two-dimensional manganese-iron bimetallic MOF-74 for electro-Fenton degradation of sulfamethoxazole

This study reported a novel application of Mn_0.67Fe_0.33-MOF-74 with two-dimensional (2D) morphology grown on carbon felt as a cathode for efficiently removing antibiotic sulfamethoxazole in the heterogeneous electro-Fenton system. Characterization demonstrated the successful synthesis of bimetallic MOF-74 by a simple one-step method. Electrochemical detection showed that the second metal addition and morphological change improved the electrochemical activity of the electrode and contributed to pollutant degradation. At pH 3 and 30 mA of current, the degradation efficiency of SMX reached 96% with 12.09 mg L^-1 H₂O₂ and 0.21 mM ·OH detected in the system after 90 min. During the reaction, electron transfer between ≡Fe^II/III and ≡Mn^II/III promoted divalent metal ions regeneration, which ensured the continuation of the Fenton reaction. Two-dimensional structures exposed more active sites favoring ·OH production. The pathway of sulfamethoxazole degradation and the reaction mechanisms were proposed based on the intermediates identification by LC-MS and radical capture results. High degradation rates were still observed in tap and river water, revealing the potential of Mn_0.67Fe_0.33-MOF-74@CF for practical applications. This study provides a simple MOF-based cathode synthesis method, which enhances our understanding of constructing efficient electrocatalytic cathodes based on morphological design and multi-metal strategies.

Reversible flowering of CuO nanoclusters via conversion reaction for dual-ion Li metal batteries

Dual-ion Li metal batteries based on non-flammable SO₂-in-salt inorganic electrolytes ( Li-SO₂ batteries) offer high safety and energy density. The use of cupric oxide (CuO) as a self-activating cathode material achieves a high specific capacity with cost-effective manufacturing in Li-SO₂ batteries, but its cycle retention performance deteriorates owing to the significant morphological changes of the cathode active materials. Herein, we report the catalytic effect of carbonaceous materials used in the cathode material of Li-SO₂ batteries, which act as templates to help recrystallize the active materials in the activation and conversion reactions. We found that the combination of oxidative-cyclized polyacrylonitrile (PAN) with N-doped carbonaceous materials and multi-yolk-shell CuO (MYS-CuO) nanoclusters as cathode active materials can significantly increase the specific capacity to 315.9 mAh g^- 1 (93.8% of the theoretical value) at 0.2 C, which corresponds to an energy density of 1295 Wh kg_CuO^-1, with a capacity retention of 84.46% at the 200th cycle, and the cathode exhibited an atypical blossom-like morphological change.

Mn doping improves in-situ H2O2 generation and activation in electro-Fenton process by Fe/Mn@CC cathode using high-temperature shock technique

Fe/Mn@carbon cloth (CC) was successfully fabricated through high-temperature shock (HTS) technique and used as cathode modification in heterogeneous electro-Fenton (hetero-EF) process for methylisothiazolinone (MIT) degradation. The nanocrystalline on Fe/Mn@CC electrode is doped with Fe and Mn oxides and coated with carbon layer, which could markedly enhance the electrocatalysis with high electro-chemical active area and low resistance. Fe/Mn@CC modified cathode can efficiently in-situ produce and activate H₂O₂, showing high electrocatalytic activity to MIT degradation. The 95.2% MIT degradation with in 100 min were achieved under the condition of 30 mA current, 0.75 L min^-1 aeration intensity and initial pH = 3. Based on the CV curves and stability test, the high degradation activity revealed the kinetically beneficial regeneration of Fe^II/Mn^II in Fe/Mn@CC and activation of H₂O₂. The electron transfer between Fe^II/III and Mn^II/III, together with the direct Fe^II/Mn^II regeneration on the cathode, could markedly promote the H₂O₂ utilization, and eventually lead to MIT degradation.

Multilayer Self-Assemblies for Fabricating Graphene-Supported Single-Atomic Metal via Microwave-Assisted Emulsion Micelle

Inspired by molecular self-assemblies in nature, this article reports a versatile strategy for confined encapsulation of single-atomic metal into high-quality rGO nanosheets by the microwave-assisted emulsion micelle method. Multilayer self-assembly of organometallics-surfactants micelles into the interlayer of nanosheets can not only promote microwave exfoliation and reduction of GO but also precisely control loading and distribution of single-metal atoms. With this synthetic strategy, the simultaneous trinity of exfoliation, reduction, and composition are achieved for 1 min. Experimental results and density functional theory calculations demonstrate that graphene-supported FeN₄ O₂ sites exhibit optimal binding energy toward superior selective adsorption (adsorption amount of 1975.6 mg g^-1 with separation efficiency of 97.6%) and electrocatalytic oxidation (TOFs as high as 1.31 min^-1 ). This work provides a simple and efficient avenue for the large-scale preparation of single-atomic metal composites in environmental and energy fields.

Degradation of G-Type Nerve Agent Simulant with Phase-Inverted Spherical Polymeric-MOF Catalysts

For the neutralization of chemical warfare agents (CWAs), the generation of an effective catalyst that can be handled safely and applied in personal protective equipment is required. Recently, zirconium-based metal-organic frameworks (Zr-MOFs: UiO-66 and UiO-67) have shown great promise in the degradation of CWAs, including nerve agents. Their catalytic activity is owed to the interplay of both Zr(IV) Lewis acids and Lewis basic groups in the MOF structure. The latter act as proximal bases that can interact with CWAs and improve the catalytic activity of Zr-MOFs. The powder form of MOFs, though, makes them impractical catalysts, as it is challenging to handle, regenerate, and reuse them. To address this challenge, we have synthesized three Zr-MOFs with Lewis basic amino and pyridine functionalities and shaped them in spherical polymeric beads using the phase inversion method. Using this method, we can generate beads with many polymer and MOF combinations (MOF@polymer). We controlled the MOF loading in these beads, and scanning electron microscopy images revealed that the MOF crystals are evenly distributed in the polymeric matrix, ensuring effective catalytic activity. We used these beads to degrade dimethyl p-nitrophenyl phosphate (DMNP), a simulant for the G-type nerve agent. Using ³¹P NMR, we showed that UiO-66-NH₂@PES and UiO-67-(NH₂)₂@PES PES: poly(ether sulfone) beads destruct DMNP to dimethyl phosphate (DMP) with a half-life (t_1/2) of 5.09 and 4.34 min, respectively. Beads made of hydrophobic polymers such as poly(vinylidene fluoride) (PVDF), polystyrene (PS), and Zr-MOFs with pyridine functionalities show that the quantitative hydrolysis of DMNP requires more time compared to that seen with the UiO-66-NH₂@PES beads. Our work highlights the facile shaping of MOF powders into beads that can be easily regenerated with their catalytic activity to be maintained for at least three cycles of use.

Cu-doped g-C3N4 catalyst with stable Cu0 and Cu+ for enhanced amoxicillin degradation by heterogeneous electro-Fenton process at neutral pH

The development of new heterogeneous Cu-based solid catalysts for hydroxyl radical (∙OH) generation plays a crucial role in degradation of pollutants at neutral pH circumstance. In this work, a Cu-doped graphitic carbon nitride (g-C₃N₄) complex was synthesized in one-step pyrolysis process using copper chloride dihydrate and dicyandiamide as precursors. The results reveal that after Cu doping, the bulk structure of g-C₃N₄ was destroyed with fragmentary morphology formation. Besides, Cu⁰ and Cu⁺ were successfully embedded in g-C₃N₄ sheet. Moreover, amoxicillin (AMX) removal by heterogeneous electro-Fenton process was performed to evaluate the catalytic activity of the Cu-doped g-C₃N₄. 99.1% AMX removal efficiency was obtained after 60 min electrolysis under neutral pH condition when the current density was 12 mA cm² and the catalyst dosage was 0.3 g L^-1. Both Cu⁰ and Cu⁺ were stably retained in the Cu-doped g-C₃N₄ catalyst and AMX removal efficiency reached 91.1%, even after 5 cycles, manifesting the remarkable stability of Cu-doped g-C₃N₄. Also, Cu-doped g-C₃N₄ possessed excellent catalytic activities for AMX removal in various waterbodies. According to the catalytic mechanism analysis, the ∙OH was proved to be the primary reactive species for AMX removal in heterogeneous electro-Fenton process. Based on the identification of sixteen different intermediate products, the possible degradation pathways were proposed. This work provides a simple method to synthesize a Cu-based solid catalyst containing stable Cu⁰ and Cu ⁺ for degradation of pollutants in wastewater.

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

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

Design and application of metal-organic frameworks and derivatives as heterogeneous Fenton-like catalysts for organic wastewater treatment: A review

Advanced oxidation process (AOP), with a high oxidation efficiency, fast reaction speed (relatively no secondary pollution), has become one of the core technologies of industrial wastewater and advanced drinking water treatment. Heterogeneous Fenton-like oxidation process (HFOP) is a kind of AOP, which developed rapidly in recent years in such a way to overcome the disadvantages of traditional Fenton reaction. Metal-organic frameworks (MOFs) and their derivatives become essential heterogeneous catalysts for organics mineralization due to the large specific surface area, abundant active sites, and ease of structural regulation. However, the knowledge gap on the mechanism and the fate of heterogeneous catalyst species during organics degradation activities by MOFs presents considerable impediments, particularly for a wide application and scaling up the process. This work has the potential to provide guidance and ideas for researchers and engineers in the fields of environmental remediation, environmental catalysis and functional materials. This review focuses on clarifying the critical mechanism of •OH production from MOFs and derivatives as well as its action on the organic's degradation process. The recent developments in MOF based HFOP are compared, and more attention is paid for the following aspects in this review: (1) classifies systematically progressive modification methods of MOFs by chemical and physical treatments; (2) analyzes the fate of catalytic species during treating organic wastewater; (3) proposes design ideas and principles for improving the performance of MOFs catalysts; (4) discusses the main factors influencing the catalytic properties and practical application; (5) summarizes the possible research challenges and directions for MOFs and their derivatives as catalysts applied to wastewater treatment in the future.

Bioinspired Assembly of Double Honeycomb-Like Hierarchical Capsule Confined Encapsulation with Functional Micro/Nanocrystals

Inspired by "micro/nanoreactor" effect of cellular organelle on specific biochemical reactions, a double honeycomb-like hierarchical capsule confined encapsulation with functional micro/nanocrystals is designed. The bioinspired hierarchical capsules derived from polymeric composite microspheres are successfully fabricated through a combination of selective chemical etching and pyrolysis. In situ introduction of functional guests (including organometallic molecules, tetraethoxysilane, or metal-organic frameworks (MOFs)) into internal cellular structure of microspheres is first put forward by phase inversion method. The development of selective etching creates honeycomb-like structure on the outside surface of capsule and allows sulfur to homogeneously distribute into matrix. With the novel approach, the hierarchical channels (micro-meso-macropore) of composite capsule enhance transportation of reactants and dispersion of active sites, and thus exhibit superior photocatalytic oxidation and electromagnetic absorbing. The promising strategy will be applied more generally to encapsulate different species into hierarchical capsule with tailored properties and functionalities.

A novel Electro-Fenton process characterized by aeration from inside a graphite felt electrode with enhanced electrogeneration of H2O2 and cycle of Fe3+/Fe2

A novel Electro-Fenton process characterized by aeration from inside a graphite felt electrode with enhanced generation of H₂O₂ and cycle of Fe³⁺/Fe²⁺ was proposed. The new type of Electro-Fenton process was used to degrade organic pollutants via graphite felt electrode aeration (GF-EA). The H₂O₂ concentration by GF-EA could reach 152-169 mg/L in a wide pH range (3-10), which was much higher than that achieved by graphite felt using solution aeration (GF-SA, 37-113 mg/L). For the degradation of nitrobenzene (NB), benzoic acid (BA), bisphenol A (BPA), and sulfamethoxazole (SMX) at pH 5.5, the percentage degradation by GF-EA could reach 55%, 56%, 80%, and 60% higher than those obtained by GF-SA, respectively. The solution TOC removal by GF-EA were enhanced by 29-51% relative to GF-SA. Mechanism analysis showed both OH and ferryl species were involved in the reaction system, and the amounts of OH and dissolved iron species in GF-EA group were 7.7 times and 4-8 times higher than those in GF-SA group, respectively. Besides, the mass transfer rate of GF-EA system was 5.4 times higher than that of GF-SA system. High amounts of H₂O₂, dissolved iron species and OH were attributed to the enhanced mass transfer of O₂ and the solution.

Highly efficient and stable FeIIFeIII LDH carbon felt cathode for removal of pharmaceutical ofloxacin at neutral pH

The traditional electro-Fenton (EF) has been facing major challenges including narrow suitable range of pH and non-reusability of catalyst. To overcome these drawbacks we synthesized Fe^IIFe^III-layered double hydroxide modified carbon felt (Fe^IIFe^III LDH-CF) cathode via in situ solvo-thermal process. Chemical composition and electrochemical characterization of Fe^IIFe^III LDH-CF were tested and analyzed. The apparent rate constant of decay kinetics of ofloxacin (OFC) with Fe^IIFe^III LDH-CF (0.18 min^-1) at pH 7 was more than 3 times higher than that of homogeneous EF (0.05 min^-1) at pH 3 with 0.1 mM Fe²⁺ under same current density (9.37 mA cm^-2). Also, a series of experiments including evolution of solution pH, iron leaching, OFC removal with trapping agent and quantitative detection of hydroxyl radicals (OH) were conducted, demonstrating the dominant role of OH generated by surface catalyst via ≡ Fe^II/Fe^III on LDH cathode for degradation of organics as well contributing to high efficiency and good stability at neutral pH. Besides, formation and evolution of aromatic intermediates, carboxylic acids and inorganic ions (F^-, NH₄⁺ and NO₃^-) were identified by High-Performance Liquid chromatography, Gas Chromatography-Mass Spectrometry and ionic chromatography analyses. These findings allowed proposing a plausible degradation pathway of OFC by OH generated in the heterogeneous EF process.

Supported Atomically-Precise Gold Nanoclusters for Enhanced Flow-through Electro-Fenton

Gold (Au) has been considered catalytically inert for decades, but recent reports have described the ability of Au nanoparticles to catalyze H₂O₂ decomposition in the Haber-Weiss cycle. Herein, the design and demonstration of a flow-through electro-Fenton system based on an electrochemical carbon nanotube (CNT) filter functionalized with atomically precise Au nanoclusters (AuNCs) is described. The functionality of the device was then tested for its ability to catalyze antibiotic tetracycline degradation. In the functional filters, the Au core of AuNCs served as a high-performance Fenton catalyst; while the AuNCs ligand shells enabled CNT dispersion in aqueous solution for easy processing. The hybrid filter enabled in situ H₂O₂ production and catalyzed the subsequent H₂O₂ decomposition to HO·. The catalytic function of AuNCs lies in their ability to undergo redox cycling of Au⁺/Au⁰ under an electric field. The atomically precise AuNCs catalysts demonstrated superior catalytic activity to larger nanoparticles; while the flow-through design provided convection-enhanced mass transport, which yielded a superior performance compared to a conventional batch reactor. The adsorption behavior and decomposition pathway of H₂O₂ on the filter surfaces were simulated by density functional theory calculations. The research outcomes provided atomic-level mechanistic insights into the Au-mediated Fenton reaction.

Controlled Synthesis of Manganese Oxide Nanoparticles Encaged in Hollow Mesoporous Silica Nanoreactors and Their Enhanced Dye Degradation Activity

In this study, controlled synthesis of hollow mesoporous silica nanoreactors with small manganese oxide nanoparticles in their cavities (Mn _x O _y @HMSNs) is reported, and the dye degradation performance in the presence of hydrogen peroxide over Mn _x O _y @HMSNs is investigated. Specifically, triple ligands (a compound with three dipicolinic acid groups) were used to coordinate manganese ions to form negatively charged coordination complex networks, which further combine with positively charged copolymers to obtain metal ion-containing polymer micelles. Following silica deposition onto micellar coronas and calcinations simultaneously result in hollow mesoporous silica nanoreactors and manganese oxide nanoparticles in their cavities. In this work, the influences of synthetic parameters on the structures are studied in detail. The obtained Mn _x O _y @HMSNs show greatly enhanced activity and stability for a series of dye degradations. The performance enhancement is ascribed to their unique nanostructures, where mesoporous silica walls provide protection to the inner Mn _x O _y nanoparticles and the small size of the manganese oxide nanoparticles greatly enhances the dye degradation activity.

In-situ self-assembly of robust Fe (III)-carboxyl functionalized polyacrylonitrile polymeric bead catalyst for efficient photo-Fenton oxidation of p-nitrophenol

From the view of channel confinement and functional site capture, we develop an in-situ self-assembly strategy to fabricate the carboxyl functionalized Fe-HPAN bead catalyst with highly stable and uniformly dispersed metallic sites for efficient photo-Fenton oxidation of p-nitrophenol (p-NP). BET and FTIR analysis reveal that numerous carboxyl groups and mesopores exist in Fe-HPAN beads, which acts to capture and immobilize iron ions. Catalytic results show that the degradation rate and TOC removal for p-NP were up to 99.78 and 91.68% under the optimal condition. Even at near neutral pH, the degradation rate almost keep the same and the TOC removal can still reach 73.05%. Due to the autocatalytic cycle of Fe^III/Fe^II, the apparent rate constant of Fe-HPAN (0.2247 min^-1) was 5.4 times as high as unmodified Fe-PAN (0.0415 min^-1) in the presence of H₂O₂ and visible light irradiation, which was 2-3 orders of magnitude larger than that of other reaction systems. More importantly, Fe-HPAN bead catalyst exhibited little loss of activity even after 20 cycles of re-utilization. The possible degradation pathway of p-NP was also proposed based on GC/MS analysis. The present work may provide a new perspective for the use of synthetic polymer to prepare low-cost, efficient and robust photo-Fenton oxidation catalysts.

Membrane photo-bioreactor coupled with heterogeneous Fenton fluidized bed for high salinity wastewater treatment: Pollutant removal, photosynthetic bacteria harvest and membrane anti-fouling analysis

In this study, efficient photosynthetic bacteria (PSB)-GO/PVDF membrane photo-bioreactor (MPBR) combined with heterogeneous Fenton fluidized bed was built and successfully applied for treatment of actual refractory seafood-processing wastewater with extremely high salinity. As effective pre-treatment, heterogeneous Fenton was designed for removing non-biodegradable organics and reducing iron-sludge discharge. In MPBR, GO/PVDF membrane fabricated by chemical grafting GO nanosheets was first used for salt-tolerated PSB harvest. Compared with original PVDF membrane, GO/PVDF membrane exhibited enhanced hydrophilicity, better permeability (4.4 times) and attractive flux recover rate (94%), which was attributed to remarkable reduction in hydrophobic proteins amount of extracellular polymeric substances (EPS). Importantly, COD and NH₃-N removal efficiency of MPBR with GO/PVDF membrane were kept about 95 and 98%, respectively, and average biomass productivity reached as high as 105 mg/L·d. This study provides a promising and economical way to build efficient MBR combined with new materials for high salinity hazardous wastewater treatment.