Singlet oxygen mediated iron-based Fenton-like catalysis under nanoconfinement

Multifunctional nanozymatic biosensors: Awareness, regulation and pathogenic bacteria detection

It is estimated that approximately 700,000 fatalities occur annually due to infections attributed to various pathogens, which are capable of dissemination via multiple environmental vectors, including air, water, and soil. Consequently, there is an urgent need to enhance and refine rapid detection technologies for pathogens to prevent and control the spread of associated diseases. This review focuses on applying nanozymes in constructing biosensors, particularly their advancement in detecting pathogenic bacteria. Nanozymes, which are nanomaterials exhibiting enzyme-like activity, combine unique magnetic, optical, and electronic properties with structural diversity. This blend of characteristics makes them highly appealing for use in biocatalytic applications. Moreover, their nanoscale dimensions facilitate effective contact with pathogenic bacteria, leading to efficient detection and antibacterial effects. This article briefly summarizes the development, classification, and strategies for regulating the catalytic activity of nanozymes. It primarily focuses on recent advancements in constructing biosensors that utilize nanozymes as probes for sensitively detecting pathogenic bacteria. The discussion covers the development of various optical and electrochemical biosensors, including colorimetric, fluorescence, surface-enhanced Raman scattering (SERS), and electrochemical methods. These approaches provide a reliable solution for the sensitive detection of pathogenic bacteria. Finally, the challenges and future development directions of nanozymes in pathogen detection are discussed.

Oxygen vacancies-mediated the peracetic acid activation to selectively generate 1O2 for water decontamination

As a pre-oxidation unit, developing non-radical pathway-dominant advanced oxidation processes (AOPs) with remarkably-efficient oxidation, superior environmental robustness, and ecological safety is essential in actual water pollution control. Herein, using Co3O4 as an example, we present an oxygen vacancies (OVs)-mediated peracetic acid (PAA) activation process, thereby predominantly generating singlet oxygen (1O2) for degrading contaminants. In-situ monitoring of PAA activation by OVs-rich Co3O4 (Co3O4-OVs) reveals that surface oxygen-containing intermediates (e.g., *OH and *O) are the precursors of 1O2. Theoretical calculations show that the selective adsorption of terminal oxygen atoms (ATO) in PAA serves as an activity descriptor for 1O2 generation. OVs can induce electron redistribution, triggering the ATO-dominated PAA adsorption to form the Co3O4-OVs-PAA* complex, followed by O-O bond breakage to yield *OH. Concurrently, OVs modulate the Co d-band center, lowering the energy barrier for 1O2 formation. The system enables ultra-fast catalytic performance (kobs = 1.17 min-1) for degrading sulfamethoxazole, outperforming pristine Co3O4 by 11.64-fold. The high-selectivity towards non-radical pathway endows the Co3O4-OVs/PAA system with remarkable stability in complex environment backgrounds and continuous-flow microreactor. This work not only provides a broad perspective on the modulation of non-radical pathways via defect engineering, but also advances the development of PAA-based AOPs for water decontamination.

Selective ·OH generation in Fenton-like reaction by dual sulfur coordination of iron organic frameworks

Traditional Fenton-like reaction simultaneously generates hydroxyl radical (·OH) and superoxide radical (·O2-) through Fe(Ⅲ)/Fe(Ⅱ) cycle, while ·OH with higher oxidation capacity is commonly consumed by ·O2-. Therefore, selective generation of ·OH but not ·O2- in Fenton-like reaction is highly desirable, but still remains challenging since it is hard to bypass Fe cycle process. This work constructed dual S coordination of Fe organic frameworks, i.e. S-Fe-MOFs, using ligand with mercaptan groups (-SH), which achieving 93.89 % selectivity of ·OH generation in Fenton-like reaction, much higher than that of Fe-MOFs without S-Fe coordination (48.65 %). Benefiting from selectivity of ·OH generation, Fenton-like activity of S-Fe-MOFs up to 0.36 min-1 using bisphenol A (BPA) as a probe, was 75 times than that of Fe-MOFs (0.0048 min-1). Dual S coordination could give rise to a symmetrical "push-pull" effect on OO bond of H2O2 by changing adsorption configuration from "end-on" to "side on" type that two O atoms in H2O2 adsorbed together on Fe sites, and thus resulting in one H2O2 split directly two ·OH. Differ from traditional ·OH generation pathway, this process not only bypasses electron transfer between Fe(Ⅱ)/Fe(Ⅲ) cycle but also avoids the electron loss of catalyst, endowing S-Fe-MOFs excellent stability in Fenton-like reaction. S-Fe-MOFs on fix-bed reactor maintained high efficiency towards BPA degradation in 12 h continuous flow in real water environment. This work provides new insight into designing catalyst to overcome the limitation of traditional Fenton-like reaction.

A nature-inspired metal-free electrocatalyst towards efficient electron transfer and robust cascade oxygen reduction for wastewater treatment

The pressing demand for removing high-risk emerging contaminants from wastewater calls for tailored treatment strategies, for which heterogeneous electrocatalysis induced by cascade oxygen reduction reaction (ORR) holds considerable potential. This process, however, suffers from poor interfacial electron transfer and discounted performance in non-acidic conditions. Inspired by the electron respiration chain of cells, a metal-free, quinone-based catalyst (PBth-BQ) was innovatively designed and synthesized. With excellent redox reversibility over 50 cycles and no risk of metal leaching, it boosted the direct electron transfer by 110 % compared to the bare graphite substrate and facilitated cascade ORR to generate ·OH for effective contaminant abatement in the pH range of 3-13. Among them, pH 8 demonstrated the best performance, which is suitable for wastewater treatment. In particular, PBth-BQ performed well as both anodic and cathodic electrodes in azithromycin mineralization with different oxygen donors, verified by the in-situ mass spectrum. Considering the abundance of quinone-like structures in oxidized carbon materials, this biomimetic design may inspire the further exploration of cheap and efficient electrocatalysts for wastewater treatment.

Ferrihydrite/B, N co-doped biochar composites enhancing tetracycline degradation: The crucial role of boron incorporation in Fe(III) reduction and oxygen activation

Harnessing the redox potential of biochar to activate airborne O2 for contaminant removal is challenging. In this study, ferrihydrite (Fh) modified the boron (B), nitrogen (N) co-doped biochars (BCs) composites (Fh/B(n)NC) were developed for enhancing the degradation of a model pollutant, tetracycline (TC), merely by airborne O2. Fh/B(3)NC showed excellent O2 activation activity for efficient TC degradation with a apparent TC degradation rate of 5.54, 6.88, and 22.15 times that of B(3)NC, Fh, and raw BCs, respectively, where 1O2 and H2O2 were identified as the dominant ROS for TC degradation. The B incorporation into the carbon lattice of Fh/B(3)NC promoted the generation of electron donors, sp2 C and the reductive B species, hence boosting Fe(III) reduction and 1O2 generation. O2 adsorption was enhanced due to the positively charged adsorption sites (C-B+and NC+). And 1O2 was generated via Fe(II) catalyzed low-efficient successive one-electron transfer (O2 → O2·- → 1O2, H2O2), as well as biochar catalyzed high-efficient two-electron transfer (O2 → H2O2 → 1O2) that does not involve .O2- as the intermediate. Moreover, Fh/B, N co-doped biochar showed a wide pH range, remarkable anti-interference capabilities, and effective detoxification. These findings shed new light on the development of environmentally benign BCs materials capable of degradading organic pollutants.

Efficient three-dimensional electrochemical degradation of alizarin red by CeO2-MnO2/NF particle electrode synergized with ozone

In this study, nickel foam-loaded Mn and Ce bimetallic oxide composites were successfully synthesized as particle electrodes by a hydrothermal method and synergized with ozone for the efficient degradation of alizarin red (AR), a typical anthraquinone dye. The effects of common factors on the degradation rate of alizarin red were investigated. The optimal experimental conditions were derived as applied voltage = 3.5 V, initial pH = 5.5, NaCl concentration of 4.5 g/L, and initial dye concentration of 20 mg/L. The particle electrode had a high cyclic stability after five cycles. The active sites of the dye molecular structure were analyzed in combination with the Fukui function, and the degradation pathway of alizarin red was proposed on this basis. By comparing the degradation effect of alizarin red under three different systems of O3, 3DER and 3DER-O3, it was confirmed that the three-dimensional electrode has a good synergistic effect in conjunction with ozone. Finally, the degradation mechanism of alizarin red under the CeO2-MnO2/NF synergistic ozone system was derived, in which the single linear oxygen (1O2) played a major role in the degradation process.

Combat against antibiotic resistance genes during photo-treatment of magnetic Zr-MOFs@Layered double hydroxide heterojunction: Conjugative transfer risk mitigating and bacterial inactivation

The dissemination of antimicrobial resistance (AMR) in wastewater treatment poses a severe threat to the global ecological environment. This study explored the effectiveness of photocatalysis in inactivating antibiotic resistant bacteria (ARB) and quantitatively clarified the inhibiting rate of the transfer of antibiotics resistance genes (ARGs). Herein, the magnetic heterojunction as UiO-66-NH2@CuFe LDH-Fe3O4 (UN-66@LDH-Fe) effectively facilitated the electron-hole separation and accelerated the photogenerated charge transfer, thereby guaranteeing the stable practical application in aeration tanks. Notably, the internal electric field of heterogeneous photocatalyst resulted in significant increase of ARGs inactivation, achieving 5.63 log of ARB, 3.66 log of tetA and 3.57 log of Ampr genes were photodegraded under optimal reaction conditions within 6 h. Based on the complex microbial and molecular mechanism of multiple-ARB communities inactivation in photo-treatment, the photogenerated reactive oxygen species (ROSs, ·OH and ·O2-) effectively destroyed bacterial membrane protein, thereby the intracellular ROSs and redox cycles further induced oxidative stress, attributing to the abundance reduction of ARGs and their host bacteria. Moreover, long-term (7 days) continuous operation preliminarily verified the practical potential in reducing AMR spread and developing wastewater treatment efficacy. Overall, this study presented an advantageous synergistic strategy for mitigating the AMR-associated environmental risk in wastewater treatment.

Simultaneous removal of cadmium and tetracycline from aqueous solutions by oxalic acid and pyrite co-modified biochar: Performance and mechanism

The remediation of combined contamination with heavy metals and antibiotics in soil and aqueous environments represents an ongoing challenge. In this study, a novel highly functionalized biochar-based composite (FeS2@OA-BC) was synthesised by combining oxalic acid (OA) pre-treatment with ball-milling of FeS2 for the simultaneous removal of cadmium (Cd2+) and tetracycline (TC) from aqueous solutions. FeS2@OA-BC demonstrated exceptional performance in simultaneously removing 74.7 % of Cd2+ and 95.8 % of TC from the binary systems, meanwhile the degradation rate of TC reached up to 64.8 %. Moreover, no significant competitive or promoting effects between Cd2+ and TC removal were observed by FeS2@OA-BC in binary systems. The adsorption of Cd2+ was primarily governed by three mechanisms: complexation with functional groups, Cd-π conjugation and cation exchange. Meanwhile, TC degradation relied on reactive oxygen species (ROS), where hydroxyl radicals (•OH) and hydrogen peroxide (H2O2) played dominant roles, with singlet oxygen (1O2) contributing minimally. The co-modification of OA and FeS2 synergistically introduces abundant exogenous defect sulphur vacancies (SVs), enhancing molecular oxygen activation and stimulating more ROS for TC degradation, as well as promoting more functional groups as adsorption sites for Cd2+ complexation. This therefore ultimately led to the reinforcement of the concurrent removal of Cd2+and TC. Overall, FeS2@OA-BC shows great promise for addressing combined pollution involving heavy metals and antibiotics in environmental systems.

Carbonized nitrogen-containing conjugated microporous polymers: Versatile platforms for high-performance carbon catalytic membranes and their angstrom-confined activation mechanism on peroxymonosulfate

Engineering high-performance N-doped carbon catalysts for peroxymonosulfate (PMS) activation and elucidating their activation mechanism are crucial for the degradation of emerging pollutants. In this study, we propose a novel self-template carbonization strategy (NSCS) based on a N-containing conjugated microporous polymer (NCMP, poly(triphenylamine)) to fabricate high-performance N-doped porous carbon catalysts. Owing to the unique N-mediated catalytic sites within the confined micropores of the NCMP precursor, the NSCS approach enables the investigation of reactive oxygen species evolution and their formation mechanisms as carbonization temperature increases from 200 to 1400 °C. The catalyst carbonized at 1000 °C exhibited high degradation activity (k = 0.170 min-1), driven primarily by O2•- and 1O2, with minor contributions from •OH and SO4•-. Additionally, a PMS self-decomposition and ¹O2 generation mechanism within angstrom-confined spaces was identified. A self-supported carbon catalytic membrane was fabricated from CPTPA-1000 (CPTPA-CNT) due to its high conjugation and thermal stability. This membrane demonstrated efficient removal of organic pollutant (k = 123.54 min-1, 220.3 L m-2 h-1 bar-1, 120 h, 99.4 %), outperforming the carbonized CNT membrane (k = 19.54 min-1, 67.5 L m-2 h-1 bar-1, 120 h, 14.8 %). This work paves an avenue for the design of high-performance carbon-based membranes and gives new insights into the 1O2 generation mechanism in N-doped carbon catalysts.

Hydrothermal reduction and phase transformation of Fe(III) minerals induced by rice straw to improve the heterogeneous Fenton degradation of metolachlor

Heterogeneous Fenton technology is effective in degrading residual pesticides in soil, but the reduction of Fe(III) in the mineral structure presents a bottleneck. This study combined rice straw with Schwertmannite (Sch), ferrihydrite (Fh), and magnetite (Mag) via a hydrothermal process to obtain iron oxides-hydrothermal carbon composites (Sch@HTC, Fh@HTC, and Mag@HTC). Poor-crystallized Sch and Fh, which were more capable of accepting electrons compared to well-crystallized Mag, exhibited obvious phase transformation to highly active Fe(II)-mineral (humboldtine) via the combination of oxalic acid, an intermediate product, with reduced Fe(II), while Mag was hard to achieve. After hydrothermal treatment, all composites showed enhanced catalytic activity, which increased with the degree of phase transformation. Especially, Sch@HTC demonstrated the highest catalytic activity, degrading 85 % of metolachlor in soil within 24 hours, 2-10 times faster than the others. Surprisingly, the solid-phase Fe(II) in soil increased slightly after the Fenton reaction. Moreover, the in-situ fluorescence intensity of HO• in soil was continuously enhanced, and the effective utilization of H2O2 to HO• was improved. These results confirmed that HTC could provide electrons to Fe(III) during the hydrothermal process, facilitating the Fe(III)/Fe(II) redox cycle and sustaining reactive Fe(II), thus overcoming key challenges in heterogeneous Fenton catalysis.

Enhanced activation of peroxide to generate singlet oxygen via boron-doped Cu single-atom catalysts for efficient water treatment

The development of advanced oxidation processes (AOPs) for environmental remediation has spurred a growing interest in catalysts that selectively generate non-radical species such as singlet oxygen (1O2). However, the precise engineering of catalytic sites to enhance targeted 1O2 production remains a formidable challenge. This study reports a B-doped graphitic carbon nitride-supported Cu single-atom catalyst (CuBCN) that significantly enhances H2O2 activation for efficient 1O2 production. Through comprehensive experimental and theoretical analysis, revealing that B doping modulates the electronic properties at the Cu active sites. This modification reduces the electron density around Cu, increasing the Cu(II) fraction essential for the formation and subsequent oxidation of ·OOH intermediates. Additionally, B influences the d-band center of Cu, optimizing the adsorption energy of ·OOH, which in turn facilitates selective 1O2 production. The CuBCN/H2O2 system exhibits exceptional Fenton-like performance, producing 1O2 as the principal active species, even in challenging water conditions characterized by high pH, high ionic strength, and high concentrations of humic substances. This work not only highlights the potential of tailored single-atom catalysts in pollution control but also offers significant insights for designing catalysts for efficient H2O2 activation.

Rapid charge transfer and O3 selective catalysis induced by B-doped nanoconfined reactor realized complete Cu-EDTA decomplexation: Significant role of BC3 conformation

Nanoconfinement strategy that overcomes the defects of conventional heterogeneous catalysts in electron and mass transport provides a new outlet to enhance REDOX processes. Nonetheless, limitations in the activity and selectivity of effective catalytic sites are still the drawbacks of nanoconfined catalysts. In this study, a B-doped carbon nanotubes-confined-FexOy catalyst (B500Fe200@CNTs-L) coupled with a dielectric barrier discharge (DBD) plasma system (DBD/B500Fe200@CNTs-L) was developed for Cu-EDTA removal. The DBD/B500Fe200@CNTs-L system realized 100% Cu-EDTA decomplexation within 3 min, which was 3.6 times kinetically faster than without B doping. The system emphasized extensive pH adaptability, maintaining 100% Cu-EDTA removal at a pH of 3-9. B doping increased the selectivity to O3 and promoted active species generation, in which •OH and O2•- prominently contributed to Cu-EDTA decomplexation, as well as FeIV=O. The strong electronic activity induced by BC3 conformation enhanced charge transfer, regulating the positive charge and d-band center of central Fe atoms to decline the energy barriers of H2O2 and O3 adsorption and active species formation. Moreover, this system emphasized the superior catalytic stability under different matrix water (Cl⁻, CO₃²⁻, NO₃⁻, SO₄²⁻, and PO₄³⁻).

Nanoconfinement-mediated non-radical enhanced pollutant degradation on Fe single-atom electrocatalyst

Heterogeneous electro-Fenton (EF) technology is an efficient approach for antibiotics degradation, but the effective mineralization of pollutants in complex actual water remains challenging due to the susceptibility of hydroxyl radical (∙OH) to environmental influences. Herein, a Fe-single atom anchored porous hollow carbon sphere (FexHCS) material with nano-confinement structure was designed for simultaneously catalyzing H2O2 to produce ∙OH and 1O2. Benefiting from oxidation of ∙OH and selective reaction of alkyl group with 1O2, the kinetic constant (k) of the FexHCS-based EF system achieves 4.13 h-1, which is 3.7 times higher than that of the traditional Fenton (1.13 h-1) under the same conditions for ofloxacin (OFL) degradation. The mineralization efficiency of OFL by FexHCS-based EF reaches 72.7 %, exceeding most of the previously reported catalysts within 1 h. The COD value of actual pharmaceutical wastewater is reduced from 801 mg L-1 to 49 mg L-1 after 5 h of treatment, and the energy consumption for wastewater treatment is calculated to be 15.9 kW h kg-1 COD-1. This work demonstrates the attractive advantages of 1O2 enhanced electro-Fenton performance in complex actual water and provides new insights into developing novel electrocatalysts for wastewater treatment.

Enhancing 1O2 Production with Biomimetic Pt Catalysts through Electronic Structure Modification

Singlet oxygen (1O2) is an excellent reactive oxygen species in the biomedical disinfection field; however, efficient and selective generation of 1O2 remains challenging. Herein, we design bioinspired Pt@UiO-66-X catalysts (X = -NH2, -H, -Br), with Pt nanoparticles as active centers and metal-organic framework (MOF) nanocavities as biomimetic binding pockets, to form a tailored electronic microenvironment for enhancing 1O2 generation. The results demonstrate that the electron-withdrawing functionalized Pt@UiO-66-Br can significantly improve the production efficiency of 1O2, which is 1.5 and 2.5 times higher than those of Pt@UiO-66 and Pt@UiO-66-NH2, respectively. Ab initio calculations reveal that electron-withdrawing functional groups can reduce the local electron density of Pt, thereby leading to a decrease in antibonding-orbital occupancy in Pt-Oads and subsequently facilitating the formation of *OO. Importantly, the Pt@UiO-66-Br catalyst shows good antibacterial properties both in vitro and in vivo. This work provides a promising prospect for the rational design of high-performance biomimetic catalysts for antibacterial application.

Regulation of Surface Terminal Hydroxyl Coverage of FeOCl Catalyst via Crystal Facet Protection for Enhanced H2O2 Activation

The unique Fe coordination environment in the FeOCl catalyst confers superior reducible electronic properties, rendering them attractive Fenton-like active sites. DFT calculations reveal that the U-shaped coordinated Fe sites formed with 50% terminal hydroxyl coverage exhibit the best H2O2 activation performance, which allows the adsorbed H2O2 to form a ·OH directly with much lower activation energy. Herein, a crystal facet protection strategy induced by rapid high-temperature annealing is developed to synthesize FeOCl with high exposure of Fe atoms while regulating the surface hydroxyl coverage. The dominant expression of the (021) facet resulted in an optimized surface terminal hydroxyl coverage of 58.3%, increasing the intrinsic activity of FeOCl by 4.3 times. The d-band center of FeOCl with optimized terminal hydroxyl coverage is closer to the Fermi level, thus exhibiting higher affinity for H2O2, and the increased amount of U-shaped coordinated Fe sites enables sufficient ·OH generation for enhanced decontamination performance. Since the terminal hydroxyl groups can be consumed by Ca2+ and Mg2+ through coprecipitation, preremoving the hardness of actual wastewater is indispensable in the application of the FeOCl/H2O2 system. Our finding provides a new way to improve the intrinsic activity of FeOCl catalyst, which is helpful for its application in other environmental remediations.

Self-Activated Heterogeneous Fenton Process for Accelerated Degradation of Aromatic Pollutants over Copper Oxide Catalysts

Metal-based heterogeneous catalysts have been commonly adopted for Fenton-like oxidation of organic pollutants, but generally suffer from inadequate activity in practical water treatment applications due to surface passivation by accumulated pollutants and sluggish redox cycling of active metal. Here, we observed an unusual phenomenon of pollutant-induced activity enhancement for copper oxide (CuO) in H2O2 activation and phenol degradation, which is in sharp contrast to considerable activity decay of Fe2O3 catalyst. The CuO was found to stabilize and activate phenol via ligand-to-metal charge transfer route, generating surface-bound phenoxyl radicals for further mediating the H2O2 activation and enabling a rapid regeneration of low-valent Cu. Based on this principle, a Fe-Cu bimetal oxides catalyst was elaborated to further augment the catalyst-phenol interaction towards self-activated Fenton oxidation. The optimal catalyst achieved 14-time faster pollutant degradation rate and 2 order-of-magnitude higher H2O2 utilization efficiency than the Fe2O3 control. It also demonstrated good adaptability to degradation of diverse substituted benzenes and maintained stable performance for treatment of real lake water during 100-day continuous operation. Our work implies that the catalyst-pollutant interaction may be rationally leveraged and modulated to create highly efficient and stable heterogeneous catalytic systems, thus further unlocking their potential for sustainable water purification application.

Synchronization Strategy for Activity and Stability in Fenton-Like Single-Atom Catalysis

Single-atom catalysts (SACs) have garnered significant attention in the applications of environmental remediation based on Fenton-like systems. Current research on Fenton-like single-atom catalysis often emphasizes catalytic activity and mechanism regulation, while paying limited attention to the simultaneous enhancement of both activity and stability-a critical factor for the practical and scale-up applications of SACs. This review systematically summarizes recent advances in synchronization strategies for improving the activity and stability of Fenton-like single-atom catalysis, with a focus on the design principles and mechanisms of four key strategies: coordination engineering, confinement effects, carrier substitution, and catalytic module design. To the best of knowledge, this represents the first comprehensive review of Fenton-like single-atom catalysis from the perspective of concurrent optimization of activity and stability. Additionally, the auxiliary role of machine learning and lifecycle assessment (LCA) is evaluated in advancing these synchronization strategies. By investigating the interplay among different support materials, coordination configurations, and reaction environments, as well as enlarged modules, key factors governing the stability/activity of SACs are highlighted, and future directions are proposed for developing next-generation catalysts with high efficiency and long-term durability for practical environmental remediation.

Chemistry for water treatment under nanoconfinement

The global freshwater crisis, exacerbated by escalating pollution, poses a significant threat to human health. Addressing this challenge required innovative strategies to develop highly efficient and process-adaptable materials for water decontamination. In this regard, nanomaterials with confinement structures have emerged as a promising solution, outperforming traditional nanomaterials in terms of efficiency, selectivity, stability, and process adaptability, thereby serving as an ideal platform for designing novel functional materials for sustainable water treatment. This Review focuses on recent advancements and employment of nanoconfinement effects in various water treatment processes, emphasizing the fundamental chemistry underlying nanoconfinement effects. Also, the existing knowledge gaps related to nanoconfinement effects and future prospects for expanding their applications in diverse water treatment scenarios are discussed.

One Heterogeneous Catalyst Drives Two Selective Fenton-like Reaction Modes for Sustainable Water Decontamination

Heterogeneous Fenton-like reactions based on nonradical reactive oxygen species (ROS) are desirable for selective water decontamination, and different pollutants coexisting in real scenarios necessitate a rational combination of multiple ROS for efficient and sustainable decontamination. However, the general one-catalyst-for-one-ROS strategy toward selective ROS generation inevitably renders the combinational process lengthy and cost ineffective. Herein, we developed a new approach to enable the separate but selective generation of two distinct ROS in one catalyst via peroxymonosulfate activation. The unique catalyst is comprised of a graphitic layer bottom-wrapped Fe@Fe3C encapsulated inside nitrogen-doped carbon nanotubes. The Fe3C shell facilitates selective formation of surface-bound FeIV═O with up to 96.0% selectivity, and the applied electric field could switch ROS generation toward free 1O2 with 90.5% selectivity, as enabled by C atoms adjacent to graphite N. One dual-site catalyst enables both high cumulative concentration for FeIV═O and 1O2 up to 16605 and 7674 μM at 30 min, respectively. Based on such a simple electricity on/off switch mode, a tandem process operated in one unit was proposed to efficiently degrade mixed pollutants of distinct adsorption properties. This study presents a simple but very effective strategy to modulate selective ROS generation that simplifies tandem Fenton-like systems for sustainable water decontamination.

Confining Hollow CoSn(OH)6 Cubes Inside Polydopamine Nanotubes To Significantly Promote Fenton-like Catalysis for Water Treatment

Tubular nanoreactors, which exhibit a distinctive void-confinement effect, have become intriguing for their prospective applications in catalysis. However, rationally constructing these structures remains a formidable challenge, particularly in realizing a significantly synergistic catalytic enhancement. In this study, we present a reliable template polymerization-guided synthetic strategy, creating hollow CoSn(OH)6 cubes inside polydopamine (PDA) nanotubes (CoSn(OH)6@PDA NTs). This sample functions as a potent peroxymonosulfate (PMS) activator for toxic contaminant oxidation. Diverse reactive oxygen species produced within the nanotubes significantly enhance this efficiency. The exceptional catalytic property results from the rich active sites of CoSn(OH)6 and the distinct nanotubular structure, which concentrates reactants and benefits the mass transfer process. This research opens possibilities for developing high-performance and robust catalysts with spatial confinement effects, advancing water treatment technology.

ZIF-Derived Catalyst with Co-Co/Co-N Dual Active Sites for Boosting Mixed Pathway Decontamination in Fenton-like Catalysis

Pollutant degradation via radical-nonradical mixed pathways offers opportunities to break the reactivity-stability trade-off in heterogeneous Fenton-like catalysis for water treatment; however, a precise catalyst design to enforce such mixed pathways remains challenging. Herein, by using bimetallic ZIFs as the precursor, we fabricated a cobalt (Co)-based catalyst (Co0.75Zn0.25-NC) with dual active sites for peroxymonosulfate (PMS) activation, where the Co-Co site and Co-N site preferentially catalyze the sulfate radicals and single oxygen generation, respectively. The system exhibited superior pollutant degradation activity, especially for the lectron-rich pollutants like tetracycline, high PMS utilization efficiency, negligible interference by the complicated water matrix, and good adaptation to broad pH and water quality conditions. A stable operation of the corresponding catalytic ceramic membrane was also demonstrated, achieving ∼70% pollutant removal during the long-term continuous-flow operation. This work offers valuable references to guide the Fenton-like catalyst design toward sustainable and low-carbon water purification applications.

MoS2/CoMoO4 composite heterogeneous catalyst towards enhanced activation of peroxymonosulfate for the efficient degradation of tetracycline hydrochloride

In this research, a composite catalyst of MoS2-modified CoMoO4 (MoS2/CoMoO4) was effectively synthesized and utilized to activate peroxymonosulfate (PMS) for the removal of tetracycline hydrochloride (TCH) in water. It was found that the MoS2/CoMoO4/PMS system possessed a greater ability to eliminate TCH compared with CoMoO4/PMS system. The experimental results demonstrated that the 0.6-MoS2/CoMoO4/PMS system eliminated 92.1% TCH (15 mg/L) and removed 50.3% TOC within 30 min under the conditions of 40 mg/L 0.6-MoS2/CoMoO4 and 0.5 mM PMS. The main active substances produced by MoS2/CoMoO4 activated PMS were sulfate radicals (SO4•-), hydroxyl radicals (•OH), singlet oxygen (1O2), and superoxide radicals (O2•-), as determined by scavenging experiments and EPR analyses. Probable catalytic mechanism of 0.6-MoS2/CoMoO4 for activating PMS was proposed from two aspects: one is the synergy of Co3+/Co2+ and Mo6+/Mo4+ cycles in 0.6-MoS2/CoMoO4/PMS system; on the other hand, the low valence molybdenum and sulfur promoted the Co3+/Co2+ redox recycle during PMS activation. After four reuses, the removal performance of TCH still reached 85.1%, and the crystal structure and the element compositions of the catalyst did not alter, implying that 0.6-MoS2/CoMoO4 composite had good reusability. Thus,0.6-MoS2/CoMoO4 composite has broad application prospects in removing organic contaminants.

Singlet oxygen presenting a higher detoxification potential on enrofloxacin than sulfate and hydroxyl radicals

With the aid of radical and non-radical reactive species (RS), advanced oxidation processes can efficiently degrade emerging organic contaminants including antibiotics but may generate toxic transformation products (TPs). However, the detoxification capacity of popular RS has not been well elucidated. This study compared the detoxification of enrofloxacin (ENR) with three RS-dominated systems: 1O2, SO4•-+•OH, •OH. The toxicity of ENR TPs generated from those systems was evaluated with multiple methods. It was found that the 1O2-dominated system detoxified ENR more effectively than the other systems in terms of microbial respiratory inhibition, developmental toxicity in zebrafish embryos, and three typical molecular biomarkers, including reactive oxygen species (ROS), and lactate dehydrogenase (LDH), and glutathione S-transferase (GST). Based on their chemical structures of ENR TPs projected with UPLC-QTOF-MS/MS, the toxicity prediction tool (T.E.S.T) revealed that the 1O2-dominated system led to more harmless TPs than the others. The results of this study underscore the great potential of 1O2-dominated system in the detoxification of organic contaminants.

Accelerated arsenic decontamination using graphene oxide-supported metal-organic framework nanoconfined membrane for sustainable performance

Developing highly efficient bimetallic metal-organic frameworks (MOFs) as catalysts for Fenton-like reactions holds significant promise for decontamination processes. Although MOFs with excellent decontamination capabilities are achievable, ensuring their long-term stability, especially in the organoarsenic harmless treatment, remains a formidable challenge. Herein, we proposed a unique nanoconfinement strategy using graphene oxide (GO)-supported Prussian blue analogs (PBA) as catalytic membrane, which modulated the peroxymonosulfate (PMS) activation in p-arsanilic acid (p-ASA) degradation from traditional radical pathways to a synergy of both radical and non-radical pathways. This dual-pathway activation with sulfate radicals (SO4•-) and singlet oxygen (1O2) was a significant advancement, ensuring the exceptionally high reactivity and stability for over 80 h of continuous membrane operation. The PBA@GO membrane achieved a degradation rate constant of 0.79 ms-1, with an increase of four orders of magnitude compared to the nonconfined PBA@GO composites, while ensuring comprehensive arsenic removal ensuring comprehensive arsenic removal and demonstrating remarkably efficient total organic carbon elimination (92.2 % versus 57.6 % in 20 min). The PBA@GO membrane also showed excellent resistance towards inorganic ions, humic acid, and complex water matrices. This facile and universal strategy paves the way for the fabrication of MOFs-based catalytic membranes for optimizing performance in arsenic pollution treatment.

Ultrafast Water Purification by Template-Free Nanoconfined Catalysts Derived from Municipal Sludge

Nanoconfinement at the interface of heterogeneous Fenton-like catalysts offers promising avenues for advancing oxidation processes in water purification. Herein, we introduce a template-free strategy for synthesizing nanoconfined catalysts from municipal sludge (S-NCCs), specifically engineered to optimize reactive oxygen species (ROS) generation and utilization for rapid pollutant degradation. Using selective hydrofluoric acid corrosion, we create an architecture that confines atomically dispersed Fe centers within a micro-mesoporous carbon matrix in situ. This method maximizes the utilization of silicon and aluminum content from sludge, prevents metal agglomeration, and precisely regulates the chemical environment of Fe active sites. As a result, the S-NCCs promote a transition from nonradical to hybrid radical/nonradical reaction mechanisms, significantly enhancing ROS efficiency, stability, and pollutant degradation rates. These catalysts demonstrate exceptional pollutant removal performance, achieving a 261-fold increase in degradation efficiency for compounds such as phenol and sulfamethoxazole compared to unconfined analogs, outperforming most state-of-the-art Fenton-like systems. Our findings highlight the transformative potential of nanoconfined catalysis in environmental applications, providing an effective and scalable solution for sustainable water purification.

Novel millimeter-sized honeycomb-like Fe/Fe3C@HBC from waste cotton textiles towards rapid degradation of ofloxacin via activation of H2O2

Although multiphase catalysts with large sizes exhibit excellent recyclability and low toxicity in heterogeneous Fenton reactions, their reactivity, reusability and storage stability for degradation of organic contaminants still need improvement, which is essential for treating complex wastewater and ensuring environmental sustainability. In this study, the waste cotton textiles were firstly used as the carbon source to generate a novel millimeter-sized catalyst (Fe/Fe3C@HBC) with a honeycomb-like structure, which could effectively activate H2O2 to realize rapid removal of ofloxacin (OFL) (100% in 10 min). It achieved remarkable removal performance across a broad temperature range (4-40 °C) and high-concentration OFL. It even demonstrated excellent removal towards other typical contaminants (Tetracycline, Ciprofloxacin, Methylene Blue, Rhodamine B, Malachite Green), showing outstanding storage stability, physical structural stability, reusability and separation characteristics. Whereafter, its removal mechanism was also explored, showing that it was entirely dependent on the degradation by the reactive oxygen species (ROS), including •OH, O2•- and 1O2, as well as the persistent free radicals from the catalyst. Moreover, the honeycomb-like structure promoted the effective utilization of H2O2, facilitated the generation of •OH and expedited the accumulation of OFL on the catalyst surface. Fe/Fe3C (inside of the catalytic instead of in the reaction solution) was essential for the degradation. Finally, the OFL degradation pathways and toxicity predictions were also proposed. Overall, this innovation supports cleaner water resources and enhances public health, demonstrating a significant step forward in environmental remediation technologies.

Spatial Profiling of Multiple Enzymatic Activities at Single Tissue Sections via Fenton-Promoted Electrochemiluminescence

Profiling multiple enzymatic activities in tissue is crucial for understanding complex metabolic and signaling networks, yet remains a challenge with existing optical microscopies. Here, we developed a Fenton-promoted luminol electrochemiluminescence (ECL) imaging method to achieve the spatial mapping of multiple enzymatic activities within a single tissue section. This method quantitatively visualizes individual enzymatic activity by combining the enzymatic conversion of substrates with the chemical confinement of the locally produced hydrogen peroxide. To achieve high-resolution spatial imaging by limiting the diffusion (∼500 μm) of hydrogen peroxide, iron oxide nanoparticles were coated on the tissue surface to initiate the Fenton process, locally converting hydrogen peroxide into short-lived hydroxyl radicals with a nanometer-scale diffusion range. The Fenton-promoted ECL emission is confined at the enzymatic conversion sites, offering unprecedented spatial visualization of four tumor-associated oxidases within a single tissue section. Colocalization revealed a synergistic effect between lysyl oxidase and quiescin sulfhydryl oxidase on post-translational modifications of tumor extracellular matrix proteins, along with a previously undiscovered interaction with amiloride-sensitive amine oxidase, which could not be distinguished based on expressions or single enzymatic activity alone. This approach offers a novel activity-based protein profiling tool at the tissue level, providing new data for future enzynomic research and multimodal imaging.

Nanoconfined catalytic macrostructures for advanced water remediation: From basic understanding to future application strategies

In recent years, nanoconfined catalytic macrostructures applied to advanced oxidation processes (AOPs) have been rapidly developed, effectively solving the problems of traditional heterogeneous AOPs, such as mass transfer limitation, limited diffusion of short-lived reactive oxygen species (ROS), and aggregation/leaching of catalysts. Compared with the traditional heterogeneous AOPs systems, the nanoconfined catalytic macrostructures have unique interactions between the oxidants, catalysts, ROS and micropollutants, which could significantly increase the yield and mass transfer of ROS. At present, there is a lack of comprehensive reviews on the nanoconfined catalytic macrostructures from basic theory to application performances and future development strategies. This study reviewed the preparation routines of various nanoconfined catalytic macrostructures, assessed their structural differences, catalytic properties and nanoconfined catalytic mechanisms via integrated density functional theory (DFT) and molecular dynamics (MD) stimulations. We also proposed the future strategies for nanoconfined catalytic macrostructures in combination with the machine learning, which could provide key information on the feasibility of the technology and future research directions. This review aims to enhance scholarly interest in the application of nanoconfined macrostructures in the AOPs fields, anticipating significant technical feasibilities for scale-up AOPs application of nanoconfinement.

Electron transfer tuning for persulfate activation via the radical and non-radical pathways with biochar mediator

Electron mediator-based in-situ chemical oxidation (ISCO) offers a novel strategy for groundwater remediation due to diverse reaction pathways. However, distinguishing and further tuning the reaction pathway remains challenging. Herein, biochar as an electron mediator targeted active peroxysulphate (PDS) via the radical or non-radical pathway. Exemplified by the triazin pesticides removal, the complex radical (•OH and SO4•-) and non-radical active species (electron transfer oxidation) were generated and identified in different biochar/PDS systems. The electron transfer process between biochar and PDS was significantly distinguished via an innovatively in-situ visualization of radical pathway, and the electron transfer oxidation non-radical pathway is directly unveiled via a galvanic cell experiment combined with LC-MS analyses. The electron transfer mechanism was revealed via establishing the quantitative structure-activity relationships between biochar and ln kobs. The redox capacity of biochar was assessed as a key for tuning the atrazine degradation by non-radical pathway, and the surface carbon-centered persistent free radicals (PFRs) were identified as key electron donors for triggering the radical pathway. This study gives new insights into the electron transfer mechanism during tuning radical and non-radical activation pathways and the enhanced utilization of oxidants in ISCO technology.

Mechanistic insights into carbonate radical-driven reactions: Selectivity and the hydrogen atom abstraction route

Carbonate radical (CO3•) is inevitably produced in advanced oxidation processes (AOPs) when addressing real-world aqueous environments, yet it often goes unnoticed due to its relatively lower reactivity. In this study, we emphasized the pivotal role of CO3• in targeting the elimination of contaminants by contrasting it with conventional reactive oxygen species (ROSs) and assessing the removal of sulfamethazine (SMT). Similar to singlet oxygen (1O2), CO3• shows a preference for electron-rich organic compounds. In addition, hydrogen atom abstraction (HAA) was determined as the primary pathway in CO3•-driven reactions, with a lower free energy barrier (∆G‡) compared to the addition process, while single electron transfer (SET) was found to be thermodynamically unfavorable in all selected aromatics with varying substituents, using DFT calculations. The H atoms within amino groups (NH2 and NH) were shown to be the most susceptible to abstraction by CO3•, which is more facile than hydroxyl radical (•OH) due to the shorter NH bond cleavage length. Finally, the degradation intermediates of SMT by CO3• were identified, with SO2 extraction, the cleavage of SN and CN bonds, and nitration/nitrosation of NH2 groups being the main degradation pathways. The results from this study are expected to set the stage for the large-scale utilization of CO3• and advance our understanding of its reaction characteristics.

Photodegradation of Chlorinated Persistent Organic Pollutants (Cl-POPs) in Pearl River Suspended Particulate Matter-Water Systems: Kinetics, Quantitative Structure-Activity Relationship (QSAR) Development, and Mechanism

Chlorinated persistent organic pollutants (Cl-POPs) are highly hydrophobic and are easily adsorbed to solid particulate matter after being released into the water column, thus affecting the transformation process and environmental fate. This study investigated the photodegradation behavior of 16 Cl-POPs in the Pearl River suspended particulate matter (SPM)-water system. The photodegradation rates of polychlorinated biphenyls (PCBs) were generally higher than those of dioxins and increased with substitution numbers of Cl atoms. A QSAR model correlating photodegradation rate constants of Cl-POPs and their structural parameters was established by using multiple linear regression (MLR) analysis and machine learning. The model results showed that soil-water partition coefficient (KOC), morgan fingerprint (mf_1747), and nucleophilicity index (NI) were the main factors affecting the photodegradation of Cl-POPs, confirming that the photodegradation of Cl-POPs with higher hydrophobicity and larger nucleophilic reactivity proceeded faster. According to the quenching experiment and theoretical calculation results, •O2- in the hydrophobic region contributed more to the strongly hydrophobic Cl-POPs, while the contribution of •OH was mainly concentrated in the weakly hydrophobic Cl-POPs. This study provided valuable insights into photolysis-related environmental persistence and fate of Cl-POPs in the SPM-water system.

Carbonaceous materials in structural dimensions for advanced oxidation processes

Carbonaceous materials have attracted extensive research and application interests in water treatment owing to their advantageous structural and physicochemical properties. Despite the significant interest and ongoing debates on the mechanisms through which carbonaceous materials facilitate advanced oxidation processes (AOPs), a systematic summary of carbon materials across all dimensions (0D-3D nanocarbon to bulk carbon) in various AOP systems remains absent. Addressing this gap, the current review presents a comprehensive analysis of various carbon/oxidant systems, exploring carbon quantum dots (0D), nanodiamonds (0D), carbon nanotubes (1D), graphene derivatives (2D), nanoporous carbon (3D), and biochar (bulk 3D), across different oxidant systems: persulfates (peroxymonosulfate/peroxydisulfate), ozone, hydrogen peroxide, and high-valent metals (Mn(VII)/Fe(VI)). Our discussion is anchored on the identification of active sites and elucidation of catalytic mechanisms, spanning both radical and nonradical pathways. By dissecting catalysis-related factors such as sp2/sp3 C, defects, and surface functional groups that include heteroatoms and oxygen groups in different carbon configurations, this review aims to provide a holistic understanding of the catalytic nature of different dimensional carbonaceous materials in AOPs. Furthermore, we address current challenges and underscore the potential for optimizing and innovating water treatment methodologies through the strategic application of carbon-based catalysts. Finally, prospects for future investigations and the associated bottlenecks are proposed.

Confined iron-based nanomaterials for water decontamination: Fundamentals, applications, and challenges

Nanotechnology-enabled water treatment is the most attractive approach to realizing advanced purification of contaminated waters that challenge the efficacy of traditional water treatment technologies. Confining nanomaterials inside porous scaffolds or substrates is one of the most effective strategies to push nano-enabled water treatment technologies forward from laboratory to field application. As flourishingly reported, confinement effects induce significantly improved decontamination efficiency, such as enhanced adsorption capacity, reaction kinetics, stability, and selectivity. In this review, first we provide an overview of the general fundamentals of nanoconfinement effects and their implications in environmental remediation. Next, we review confined Fe-based nanomaterials, such as different polymorphs of iron-oxides, oxyhydroxides, zero-valent iron, and single-atom iron as representative materials towards their applications in nanoconfinement systems for water decontamination. Finally, we propose future studies based on the missing scientific fundamentals regarding nanoconfinement effects and challenges for translating unique and promising nanoconfinement observations to engineering applications of confined nanomaterials-driven water treatment technologies.

Bagasse modification of red mud for efficient photocatalytic degradation of real dye wastewater: An utilization attempt for massive waste

The high concentration of metal compounds found in red mud (RM) can serve as cost-effective raw materials for photo Fenton catalysts in the treatment of organic dye wastewater. In this study, RM was modified with bagasse using a hydrothermal method to prepare a photo-Fenton catalyst. The degradation efficiency of Rhodamine (RhB) solution under different conditions was evaluated. In a reactive system with a catalyst concentration of 1 g/L, RhB concentration of 20 mg/L, reaction pH of 6.1 and H2O2 concentration of 0.0485 mol/L, the degradation rate of RhB reached 86.88% after 110 min of reaction. RhB exhibited a consistently high degradation rate across 6 experimental cycles. Toxicity experiments confirmed that the concentration of heavy metal ions in the liquid phase fell within national standards. Real dye wastewater was tested under natural sunlight, with results indicating a 64.31% reduction in COD(Chemical Oxygen Demand) and a 47.63% decrease in TOC(Total Organic Carbon) after 220 min of treatment. The biodegradability of dye wastewater had also been significantly improved. These findings strongly support the green and sustainable development of the printing and dyeing industry, which also offer important solutions for the utilization of massive industrial solid waste and agricultural solid waste.

Mechanism insights into customized 2D nanoconfined catalyst via peroxymonosulfate activation for efficient sulfamethoxazole degradation: Key roles of electronic structure and non-radical pathway

The technology to solve the problem of the efficient pollutant removal in peroxymonosulfate (PMS) activation was the ultimate goal. There was an urgent need to achieving higher catalytic activity and oxidation efficiency. Herein, we present a MgAl-based layered double hydroxide assembled as a 2D confined catalyst (MgAl-Co-LDH) with Co metal in chelated form (Co-EDTA) for highly efficient PMS activation degrading sulfamethoxazole (SMX). Co-EDTA as an active site enlarged the interlayer height of MgAl-LDH to form a nanoconfined space. The confinement interlayer structure acted as a mediator for electron transfer, which improved the effective collision of active sites with PMS and SMX. The confined catalyst had a rate constant of 0.2262 min-1, which was much superior to the non-confined catalyst by 8.76 times. A series of experiments proved that the reactive species transformed the radical pathway into singlet oxygen (1O2). The density functional theory calculations proved that the capability of PMS cleavage was optimized and modulated the electronic structure of MgAl-Co-LDH, which enhanced the reactivity of the D-band center electrons of Co-active sites. This study offered a method to investigate the catalytic degradation mechanisms of confined catalysts used in wastewater treatment.

Expanding the pH range of Fenton-like reactions for pollutant degradation: The impact of acidic microenvironments

Heterogeneous Fenton reactions offer the opportunities to overcome iron sludge accumulation and limited recyclability of existing homogeneous Fenton process, but the sharp attenuation in their reactivity at near-neutral and even higher pH conditions, still remains a formidable challenge. In this work, we report a versatile and robust approach to create a local acidic microenvironment on BiOI with graphene oxide bonding, enabling the heterogeneous Fenton (BiOI@rGO/H2O2) system to sustainably degrade organic pollutants over a wide pH range (3.0-10.0). Notably, BiOI@rGO exhibits a superior catalytic activity (∼100 % removal) and robust durability (over ten cycles) in degrading bisphenol A and tetracycline, even in real wastewater scenarios. Furthermore, immobilizing the BiOI@rGO on carbon felt to establish a continuous flow-through device achieves a stable treatment performance with a degradation efficiency exceeding 98 % for micropollutants over a continuous operation. This work provides a paradigm for constructing an acidic microenvironment on the catalyst to surmount the pH limitations of the heterogeneous Fenton reactions for advanced water purification.

Oxidative Polymerization in Water Treatment: Chemical Fundamentals and Future Perspectives

For several decades, the methodology of complete destruction of organic pollutants via oxidation, i.e., mineralization, has been rooted in real water treatment applications. Nevertheless, this industrially accepted protocol is far from sustainable because of the excessive input of chemicals and/or energy as well as the unregulated carbon emission. Recently, there have been emerging studies on the removal of organic pollutants via a completely different pathway, i.e., polymerization, meaning that the target pollutants undergo oxidative polymerization reactions to generate polymeric products. These studies have collectively shown that compared to the conventional mineralization pathway, the polymerization pathway allows more efficient removal of target pollutants, largely reduced input of chemicals, and suppressed carbon emission. In this review, we aim to provide a comprehensive examination of the fundamentals of the oxidative polymerization process, current state-of-the-art strategies for regulation of the polymerization pathway from both kinetic and thermodynamic perspectives, and resource recovery of the formed polymeric products. In the end, the limitations of the polymerization process for pollutant removal are discussed, with perspectives for future studies. Hopefully, this review could not only provide critical insight for the advancement of polymerization-oriented technologies for removal of more organic pollutants in a greener manner but also stimulate more paradigm innovations for low-carbon water treatment.

Efficient generation of singlet oxygen (1O2) by CoP/Ni2P@NF for degradation of sulfamerazine through a heterogeneous electro-Fenton process at circumneutral pH

In electro-Fenton (EF), the development of a catalytic material with wide pH application range and high interference resistance is more suitable for practical wastewater treatment. In this study, the nanoneedle-shaped CoP/Ni2P heterostructure loaded onto a nickel foam substrate (CoP/Ni2P@NF) was successfully fabricated, which was used as a cathode material for heterogeneous electro-Fenton (Hetero-EF) to degrade sulfamerazine (SMR) at circumneutral pH. The SMR degradation efficiency within 90 min went to 100% and 87% at initial pH of 6.8 and 11, respectively. Experiments and theoretical calculations demonstrated that the heterostructure of CoP/Ni2P redistributed the interfacial charge and accelerated the electron transfer, resulting in different two-electron oxygen reduction (2e-ORR) selectivity and activity than CoP and Ni2P. The ion interference and complex water quality experiment exhibited that the degradation performance remained almost unchanged, showing better anti-interference ability and complex water quality applications. Through quenching experiments and EPR tests, it is confirmed that singlet oxygen (1O2) was the major reactive oxygen species (ROS) and 1O2 was converted from hydroxyl radical (·OH) adsorbed on the catalyst surface. This study provides an efficient catalyst for the application of Hetero-EF to remove organic compounds in complex water at circumneutral pH.

Atomically Dispersed Fe-Mo Catalysts Mediate Fenton-Like Reaction to Efficiently Degrade Chlorophenol Pollutants Through Synergistic Oxidation and Dechlorination Reactions

Chlorophenols are difficult to degrade and mineralize by traditional advanced oxidation processes due to the strong electronegativity of chlorine. Here, a dual-site atomically dispersed catalyst (FeMoNC) is reported, which Fe/Mo supported on mesoporous nitrogen-doped carbon is prepared through high-temperature migration. The FeMoNC exhibits a high dechlorination rate of 93.3% within 1 min. Theoretical calculation suggested that the doping of high-valence Mo6+ as the electron reservoir, promoted electronic delocalization at Fe sites, thereby enhancing the adsorption and dissociation of peroxymonosulfate (PMS), subsequent generation of Fe (IV) = O and singlet oxygen (1O2) species. An interesting finding is that Mo sites can adsorb chlorine sites in 4-chlorophenol (4-CP) and induce C─Cl bond fracture. Thus, the FeMoNC/PMS system has high catalytic performance due to the synergistic effects of Mo-induced dechlorination and non-radical species (Fe(IV) = O and 1O2) as the degradation pathways, the degradation efficiency of 99.1% of 4-CP within 5 min without significant performance decline after 168 h ≈15,120-bed volumes. These findings can advance mechanistic understanding of PMS activation at the molecular level and guide the rational design of efficient eco-friendly single-atom catalysts (SACs) catalysts with bimetallic atomic sites.

Cobalt(II) Aqua Complex-Mediated Hydrogen Peroxide Activation: Possible Roles of HOOOH and Co(II)-OOOH Intermediates in Singlet Oxygen Generation

Density functional theory (DFT) calculations indicate that [CoII(H2O)6]2+ reacts with two H2O2 molecules to form [(H2O)4CoII(OOH)(H2O2)]+ reactant complexes, which decompose through three distinct pathways depending on the relative orientation between the coordinated -OOH and H2O2 ligands. The reactive intermediates produced via these activation pathways include hydroperoxyl (•OOH)/superoxide (O2•-) radicals, singlet oxygen (1O2), and Co(III) species [(H2O)5CoIII(O)]+, [(H2O)4CoIII(OH)2]+, and [(H2O)5CoIII(OH)]2+. The Co(III) species display from moderate to strong oxidizing abilities that have long been overlooked. Remarkably, our DFT calculations reveal the possible formation of hydrogen trioxide (HOOOH) and Co(II)-OOOH intermediates during [(H2O)4CoII(OOH)(H2O2)]+ decomposition and that the hydrolysis of these transient species is a route to 1O2 production. Because two of the three activation pathways do not involve changes in the oxidation state of the Co center, they may apply to other systems comprising redox-inert metal ions.

Incidental iron oxide nanoclusters drive confined Fenton-like detoxification of solid wastes towards sustainable resource recovery

The unique properties of nanomaterials offer vast opportunities to advance sustainable processes. Incidental nanoparticles (INPs) represent a significant part of nanomaterials, yet their potential for sustainable applications remains largely untapped. Herein, we developed a simple strategy to harness INPs to upgrade the waste-to-resource paradigm, significantly reducing the energy consumption and greenhouse gas emissions. Using the recycling of fly ash from municipal solid waste incineration (MSWI) as a proof of concept, we reveal that incidental iron oxide nanoclusters confined inside the residual carbon trigger Fenton-like catalysis by contacting H2O2 at circumneutral pH (5.0-7.0). This approach efficiently detoxifies the adsorbed dioxins under ambient conditions, which otherwise relies on energy-intensive thermal methods in the developed recovery paradigms. Collective evidence underlines that the uniform distribution of iron oxide nanoclusters within dioxin-enriched nanopores enhances the collision between the generated active oxidants and dioxins, resulting in a substantially higher detoxification efficiency than the Fe(II)-induced bulk Fenton reaction. Efficient and cost-effective detoxification of MSWI fly ash at 278‒288 K at pilot scale, combined with the satisfactory removal of adsorbed chemicals in other solid wastes unlocks the great potential of incidental nanoparticles in upgrading the process of solid waste utilization and other sustainable applications.

Boosting singlet oxygen generation for salinity wastewater treatment through co-activation of oxygen and peroxymonosulfate in photoelectrochemical process

High concentrations of inorganic ions in saline wastewater pose adverse effects on hydroxyl radical (HO•)-dominated technologies. Here, we report a unique strategy for boosting singlet oxygen (1O2) generation via coactivation of oxygen and peroxymonosulfate (PMS) by regulating the electron transfer regime in the photoelectrochemical process. The Fe-N bridge in atomic Fe-modified graphitic carbon nitride (denoted SA-FeCN) favors the construction of electron-defective Fe and electron-rich N vacancies (Nvs) to accelerate directional electron transfer. The produced intermediate (HSO4-O···Fe-Nvs···O-O) as a chemical channel accelerates the directional electron transfer from PMS to further reduce O2 to form activated products (SO5 •-, O2 •-), thereby transforming O2 into 1O2. An optimized 1O2 generation rate of 39.4 μmol L - 1 s - 1 is obtained, which is 15.7-945.0 times higher than that in traditional advanced oxidation processes. Fast kinetics are achieved for removing various phenolic pollutants in a nonradical oxidation pathway, which is less susceptible to the coexistence of natural organic matter and inorganic ions. The COD removal for coal wastewater and complex industrial wastewater in real scenarios is found to reach a value of 90%-96% in 3 h. This work provides a new direction for boosting the 1O2 generation rate, especially for the selective degradation of target electron-rich contaminants in saline wastewater.

Sustainable production of 2,5-diformylfuran via peroxymonosulfate-triggered mild catalytic oxidation of lignocellulosic biomass

The relentless depletion of fossil fuels accentuates the urgent necessity for the sustainable synthesis of chemicals from renewable biomass. 5-Hydroxymethylfurfural (HMF), extracted from lignocellulosic biomass, emerges as a beacon of hope for conversion into value-added chemicals. However, the inherent susceptibility of its unsaturated aldehyde groups to excessive oxidation often culminates in undesired reactions, compromising both the yield and specificity of the desired products. Here, we introduce a holistic methodology for the cost-effective and ecologically responsible generation of 2,5-diformylfuran (DFF), through the heterogeneously catalyzed oxidation of HMF utilizing peroxymonosulfate (PMS) under benign conditions. This strategy, characterized by the meticulous enhancement of surface ketone groups via a mixed-salt-assisted co-pyrolysis technique, achieves an unparalleled selective activation of PMS, engendering singlet oxygen to catalyze the oxidation of HMF into DFF with a selectivity surpassing 80%. Life-cycle assessments underscore a negligible impact on human health, ecosystems, and natural resources, endorsing the holistic utilization of biomass. This integration of pyrolysis for the creation of functional carbonaceous materials within biomass conversion processes significantly enhances sustainability and economic viability, while paving green pathways for selective biomass oxidation and the production of high-value chemicals.

Low-peroxide-consumption fenton-like systems: The future of advanced oxidation processes

Conventional heterogeneous Fenton-like systems employing different peroxides have been developed for water/wastewater remediation. However, a large population of peroxides consumed during various Fenton-like systems with low utilization efficiency and associated secondary contamination have become the bottlenecks for their actual applications. Recent strategies for lowering the peroxide consumptions to develop economic Fenton-like systems are primarily devoted to the effective radical generation and subsequent high-efficiency radical utilization through catalysts/systems engineering, leveraging emerging nonradical oxidation pathways with higher selectivity and longer life of the reactive intermediate, as well as reactor designs for promoting the mass transfer and peroxides decomposition to improve the yield of radicals/nonradicals. However, a comparative review summarizing the mechanisms and pathways of these strategies has not yet been published. In this review, we endeavor to showcase the designated systems achieving the reduction of peroxides while ensuring high catalytic activity from the perspective of the above strategic mechanisms. An in-depth understanding of these aspects will help elucidate the key mechanisms for achieving economic peroxide consumption. Finally, the existing problems of these strategies are put forward, and new ideas and research directions for lowering peroxide consumption are proposed to promote the application of various Fenton-like systems in actual wastewater purification.

Shell-induced enhancement of Fenton-like catalytic performance towards advanced oxidation processes: Concept, mechanism, and properties

Fenton-like advanced oxidation processes (AOPs) are commonly used to eliminate recalcitrant organic pollutants as they produce highly reactive oxygen species through the reactions between the catalysts and oxidants. Recently, considerable attention has been directed towards shell-structured Fenton-like catalysts that offer high stability, maximum utilization of active sites, and exceptional catalytic performance. In this review, we have introduced the concept of several typical shell-forming architectures (e.g., hollow structure, core-shell structure, yolk-shell structure, particle-in-tube structure, and multi-shelled structure), elucidating their role in promoting Fenton-like reaction catalysis through the nanoconfinement mechanism. In each aspect, the correlation between the shell-induced effects and the Fenton-like catalytic performance is highlighted. Finally, future challenges and opportunities for the development of shell-structured Fenton-like catalysts towards AOPs are presented, offering bright practical application prospects.

Multistage Generation Mechanisms of Reactive Oxygen Species and Reactive Chlorine Species in a Synergistic System of Anodic Oxidation Coupled with in Situ Free Chlorine and H2O2 Production

Electro-oxidation (EO) is an efficient approach to removing refractory organics in wastewater. However, the interference from chlorine ions (Cl-) can generate reactive chlorine species (RCS), potentially leading to the production of undesirable chlorinated byproducts. A novel approach involving the cathodic oxygen reduction reaction (ORR) for in situ H2O2 production has emerged as a promising strategy to counteract this issue. This study systematically investigated the dynamics and transformation of RCS and reactive oxygen species (ROS) in an ORR/chloride-containing EO (EO-Cl) system, elucidating their respective roles in organic removal and chlorinated byproduct minimization. Distinct generation rates and patterns were observed for free chlorine and H2O2 in the ORR/EO-Cl system. The rapid generation of free chlorine at the anode quickly reached a dynamic equilibrium, which contrasted with the moderate, continuous cathodic production of H2O2, resulting in considerable H2O2 accumulation over time. This difference established kinetics-driven ROS and RCS formation and distribution, influencing the subsequent organic degradation process. Three distinct stages were identified in the degradation process. In stage I, free chlorine was the primary species, along with reactive species including Cl2•-, 1O2, ClO•, HO•, and Cl•. In stage II, the gradual accumulation of H2O2 consumed free chlorine, favoring the formation of 1O2 and HO•. In stage III, excessive H2O2 quenched the free radicals. Insights into these multistage mechanisms reveal that the rapid degradation of chlorinated byproducts by 1O2 and HO• occurs in stage II of the ORR/EO-Cl system.

Selective elimination of organic pollutants and analysis of effects and novel mechanisms of aged microplastics on wavelength-dependent UV-LED/H2O2 system

The selective removal of organic pollutants and potential impact of aged microplastics (MPs) as emerging pollutants in wavelength-dependent UV-LED/H2O2 system are not fully understood. This study found that cefalexin (CFX) degradation efficiency in UV-LED alone system was highly correlated with its UV molar absorbance (R2=0.994), while in UV-LED/H2O2 system, it was correlated with ·OH yield (R2=0.991) across various wavelengths. Quantitative structure-activity relationship (QSAR) analysis showed selective degradation of six pollutants based on their e--donating capabilities (R2=0.748-0.916). The coexistence of aged MPs, introducing C-O/C=O groups and rearranging their surface e-, potentially affected the elimination efficiency of CFX. Aged polystyrene (PS) decreased the degradation efficiency of CFX by shorting the O-O bond length (lO-O) in H2O2 and capturing e- from H2O2, whereas aged polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) had negligible effects as the lO-O elongation balanced the e--donating effect of H2O2. Additionally, phenol released from aged PS, with strong nucleophilicity, competing with CFX for ·OH, further decreasing CFX degradation efficiency. This study provides valuable insights into organic pollutant selective removal and reveals a novel inhibitory mechanism of aged PS on the performance of UV-LED/H2O2 technology.

DFT Study on the Mechanism of As(III) Oxidation in the Presence of Fe(II) and O2

In natural aquatic environments, the fate of arsenic (As) is significantly influenced by redox processes involving iron (Fe) species. Understanding the mechanisms governing As transformation in the presence of Fe species is crucial for comprehending its environmental impact and advancing remediation strategies. In this work, the oxidation of As(III) in oxygenated Fe(II) solutions was investigated. Density functional theory (DFT) methods were employed to explore the reaction of Fe(II) with 3O2 and subsequent As(III) oxidation by reactive species generated from Fe(II) oxidation. Electron paramagnetic resonance analysis was utilized to confirm the formation of reactive species in the solution. Based on these results, it is concluded that 1O2, ·O2H, and Fe(IV) are the critical oxidants responsible for As(III) oxidation in oxygenated Fe(II) solutions under circumneutral conditions. 1O2 readily oxidizes As(III) by forming an arsenic superoxide AsO5H3. Interaction of As(III) with ·O2H or Fe(IV) leads to As(IV), which is further oxidized to As(V) by 3O2, Fe(III), and Fe(IV).

Uncovering the Size-Dependent Thermal Solid Transformation of Akaganéite

Investigating the structural evolution and phase transformation of iron oxides is crucial for gaining a deeper understanding of geological changes on diverse planets and preparing oxide materials suitable for industrial applications. In this study, in-situ heating techniques are employed in conjunction with transmission electron microscopy (TEM) observations and ex-situ characterization to thoroughly analyze the thermal solid-phase transformation of akaganéite 1D nanostructures with varying diameters. These findings offer compelling evidence for a size-dependent morphology evolution in akaganéite 1D nanostructures, which can be attributed to the transformation from akaganéite to maghemite (γ-Fe2O3) and subsequent crystal growth. Specifically, it is observed that akaganéite nanorods with a diameter of ∼50 nm transformed into hollow polycrystalline maghemite nanorods, which demonstrated remarkable stability without arresting crystal growth under continuous heating. In contrast, smaller akaganéite nanoneedles or nanowires with a diameter ranging from 20 to 8 nm displayed a propensity for forming single-crystal nanoneedles or nanowires through phase transformation and densification. By manipulating the size of the precursors, a straightforward method is developed for the synthesis of single-crystal and polycrystalline maghemite nanowires through solid-phase transformation. These significant findings provide new insights into the size-dependent structural evolution and phase transformation of iron oxides at the nanoscale.

Regulating the Electronic Structure of Cu Single-Atom Catalysts toward Enhanced Electro-Fenton Degradation of Organic Contaminants via 1O2 and •OH

Heterogeneous electro-Fenton degradation with 1O2 and •OH generated from O2 reduction is cost-effective for the removal of refractory organic pollutants from wastewater. As 1O2 is more tolerant to background constituents such as salt ions and a high pH value than •OH, tuning the production of 1O2 and •OH is important for efficient electro-Fenton degradation. However, it remains a great challenge to selectively produce 1O2 and improve the species yield. Herein, the electronic structure of atomically dispersed Cu-N4 sites was regulated by doping electron-deficient B into porous hollow carbon microspheres (CuBN-HCMs), which improved *O2 adsorption and significantly enhanced 1O2 selectivity in electro-Fenton degradation. Its 1O2 yield was 2.3 times higher than that of a Cu single-atom catalyst without B doping. Meanwhile, •OH was simultaneously generated as a minor species. The CuBN-HCMs were efficient for the electro-Fenton degradation of phenol, sulfamethoxazole, and bisphenol A with a high mineralization efficiency. Its kinetic constants showed insignificant changes under various anions and a wide pH range of 1-9. More importantly, it was energy-efficient for treating actual coking wastewater with a low energy consumption of 19.0 kWh kgCOD-1. The superior performance of the CuBN-HCMs was contributed from 1O2 and •OH and its high 1O2 selectivity.