Electron delocalization triggers nonradical Fenton-like catalysis over spinel oxides

Biomass-derived in-situ carbonized ferrous sulfide for Fenton oxidation of phenol in wastewater: Mechanisms, pathways, and applications

Innovative iron-based nanoparticles (NPs) made from biomass provide sustainable solutions for environmental cleanup, integrating better environmental management with resource recycling. This study introduces biomass-derived carbon-coated iron sulfide (FeS@CMP) as an efficient Fenton catalyst for phenol oxidation, addressing challenges associated with FeS NPs in advanced oxidation processes (AOPs), for example deactivation and aggregation. Firstly, advanced characterization reveals its porous structure, high surface area, and abundant active sites, compared to carbonized biomass precursor (CMP), while FeS@CMP demonstrates superior physical and chemical stability. Secondly, FeS@CMP achieves remarkable efficiency in activating hydrogen peroxide (H2O2) for phenol removal (94.08%), which is much greater than that of CMP (40.70%). Further, mechanistic analysis identifies a synergistic electron transfer process involving multiple ROS, including •OH, SO4-•, and 1O2, driving effective phenol degradation. Thirdly, using Density Functional Theory (DFT) calculations and Liquid Chromatography-Mass Spectrometry (LC-MS), a specific degradation pathway for phenol is proposed. Finally, toxicity assessments reveal a marked decline in toxicity of degradation products and excellent reusability over multiple cycles. FeS@CMP also effectively degrades contaminants in real wastewater. This study converts waste into high-performance biomass-based catalysts, advancing sustainable development and offering an eco-friendly method for phenol removal, enhancing low-impact AOP technologies.

Amorphous Engineering Driving d-Orbital High Spin Configuration for Almost 100% 1O2-Mediated Fenton-Like Reactions

The inherent atomic disorder in amorphous materials leads to unsaturated atomic sites or dangling bonds, effectively modulating the material's electronic states and rendering it an ideal platform for the growth of single atoms. Herein, the electronic structure of isolated cobalt atoms anchored on amorphous carbon nitride (Co-ACN) is modulated through a substrate amorphization engineering, enabling the thorough removal of pazufloxacin (PZF) in 1 min with a high reaction rate constant (k1) of 3.504 min-1 by peroxymonosulfate (PMS) activation. Experiments and theoretical calculations reveal that Co-ACN exhibited a higher coordination environment (Co-N3) compared to crystalline Co-CCN (Co-N2). Meanwhile, the t2g energy level enhancement of Co 3d orbital promotes electron transition from t2g to eg, inducing more unpaired electrons and thereby driving the transition from a low-spin state (LS, t2g 6eg 1) to a high-spin state (HS, t2g 5eg 2). The HS Co-ACN optimized the d-band center, boosted the electronic transfer, and weakened the interaction between Co 3d and O 2p orbitals of HSO5 -, thereby enabling nearly 100% selective singlet oxygen (1O2) generation, whereas Co-CCN yielded coexisting reactive oxygen species (ROS). This work opens up a new paradigm for regulating the electronic structure of single-atom catalysts at the atomic scale.

Proton-coupled electron transfer controls peroxide activation initiated by a solid-water interface

Decentralized water treatment technologies, designed to align with the specific characteristics of the water source and the requirements of the user, are gaining prominence due to their cost and energy-saving advantages over traditional centralized systems. The application of chemical water treatment via heterogeneous advanced oxidation processes using peroxide (O-O) represents a potentially attractive treatment option. These processes serve to initiate redox processes at the solid-water interface. Nevertheless, the oxidation mechanism exemplified by the typical Fenton-like persulfate-based heterogeneous oxidation, in which electron transfer dominates, is almost universally accepted. Here, we present experimental results that challenge this view. At the solid-liquid interface, it is demonstrated that protons are thermodynamically coupled to electrons. In situ quantitative titration provides direct experimental evidence that the coupling ratio of protons to transferred electrons is almost 1:1. Comprehensive thermodynamic analyses further demonstrate that a net proton-coupled electron transfer occurs, with both protons and electrons entering the redox cycle. These findings will inform future developments in O-O activation technologies, enabling more efficient redox activity via the tight coupling of protons and electrons.

Constructing a Graphene-like Layered Carbocatalyst by the Dual Templating Effect for an Efficient Fenton-like Reaction

Two-dimensional (2D) carbon materials are receiving increasing attention due to their partly groundbreaking performance in catalysis and electrochemistry based on distinct physiochemical and textural properties. We focus on the challenge to directly achieve a well-developed layered morphology with a high doping level of heteroatoms as the active sites, a standard conflict of interests of high-temperature synthesis. Here, we report a dual-templating strategy to yield graphene-like layered carbon (GLC) by direct carbonization of a texturally prealigned zeolitic imidazolate framework-8 (ZIF-8). The recrystallization of ZIF-8 in an aqueous NaCl solution discloses a 2D packing mode that was retained after freeze-drying with recrystallized NaCl as an exotemplate and a space-confining nanoreactor. Further promoted by the chemical interaction of NaCl in promoting and stabilizing the carbonization process, the final product came with a well-separated layered morphology and high amounts of heteroatoms (16.6 wt % N and 7.5 wt % O). The structurally and catalytically special GLC functioned well in activating peroxymonosulfate-based Fenton-like reactions. It was shown that the reaction proceeded via nonfree-radical-mediated pathways, as reflected in significantly enhanced electron-transfer processes and ultrafast kinetics for pollutant removal. The proposed strategy is expected to afford a broader applicability for the bottom-up design of 2D carbon materials.

MnxCo3-xO4 spinel activates peroxymonosulfate for highly effective bisphenol A degradation with ultralow catalyst and persulfate usage

Persulfates-based advanced oxidation processes are highly efficient in degrading refractory organic contaminants in wastewater. However, their practical application is often limited by the extensive consumption of catalysts and oxidants. Therefore, constructing catalysts with abundant and efficient reaction interfaces is essential for improving the efficiency of persulfate activation. In this work, we develop a novel MnxCo3-xO4 spinel with highly exposed surface active sites by etching Mn-based precursors with Co ions. This process forms sufficient interface Co-O-Mn bonds, which effectively activate peroxymonosulfate (PMS) for bisphenol A (BPA) degradation. A clear structure-activity relationship is observed between the Co/Mn content ratio and the BPA degradation rate in the MnxCo3-xO4/PMS system. Notably, Mn0.1Co2.9O4 demonstrates superior PMS activation efficiency, achieving 100 % degradation of 10 mg/L BPA within 2 minutes with 0.05 g/L catalyst and 0.05 g/L persulfate usage. Experimental analyses combined with theoretical calculations identify the interface Co-O-Mn as the active site, which plays a crucial role in accelerating PMS molecule adsorption and O-O bond activation. Additionally, the spatially adjacent Co-O-Mn sites promote redox cycling for efficient interface electron transfer during the PMS activation process. Furthermore, Zebrafish toxicity studies revealed a considerable reduction in the toxicity of the BPA treatment residue in the MnxCo3-xO4/PMS system. Overall, this work presents a novel strategy for constructing spatially adjacent redox sites in dual-metal spinel materials, offering valuable insights into reducing chemical input and advancing persulfate-based environmental remediation technology.

Integration of Ag3PO4/WO3 photoanode with bifunctional CuO cathode exhibiting photocatalytic and peroxidase-mimetic properties for nanozyme-coupled photoelectrocatalytic degradation of persistent pollutant

The nanozyme-coupled photoelectrocatalytic (PEC) technology, which integrates the semiconductor photovoltaic effects with the enzyme-mimetic properties of nanomaterials, offers a promising and sustainable approach for removing organic contaminants from wastewater. In this study, a dual-photoelectrode PEC system comprising an Ag3PO4/WO3 anode and a bifunctional CuO cathode was investigated for the efficient degradation of 2,5-dichlorophenol (2,5-DCP). Under simulated solar irradiation, the Ag3PO4/WO3 photoanode demonstrated superior PEC activity for 2,5-DCP degradation and H2O2 production. The bifunctional CuO cathode significantly enhanced the degradation efficiency of 2,5-DCP, which can be attributed to its inherent photocatalytic activity and peroxidase-mimicking capability in the presence of in-situ generated H2O2. Consequently, the degradation efficiency of 2,5-DCP reached 91.2 % after 90 min of nanozyme-coupled PEC treatment. The intermediate products generated during the degradation process were identified using liquid chromatography-mass spectrometry, and a potential degradation pathway for 2,5-DCP was also proposed. This study highlights the potential of a bifunctional cathode with both photocatalytic and peroxidase-mimicking properties in the development of nanozyme-coupled PEC systems for the degradation of persistent pollutants.

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.

Promoting effect of oxygen vacancies in CuZnOx-2/peroxymonosulfate system on the p-arsanilic acid degradation and secondary arsenic species immobilization

Combining chemical oxidation and adsorption is highly desirable but challenging to remove organoarsenic compounds for water purification. Herein, we prepared a Zn-doped CuO (CuZnOx-2) catalyst by incorporating Zn atoms into the CuO lattice, which results in abundant surface oxygen vacancies (OVs) and modulates the electronic structure of Cu-OVs-Zn sites for PMS activation to degrade p-arsanilic acid (p-ASA) and adsorb the secondary arsenic species simultaneously. The elevated d-band centers for Cu upward to the Fermi level can significantly strengthen the adsorption of PMS, p-ASA, and the generated arsenic species. The OVs cause the charge redistribution to form electron-rich centers, which accelerate the electron transfer from Cu-OVs-Zn sites to adsorbed PMS, facilitating the cleavage of peroxide bond to produce SO4•-, •OH. Furthermore, the PMS adsorbed on the local environment of OVs with different configurations can directly decompose to produce 1O2 without undergoing PMS → O2•- → 1O2 or O2 → O2•- → 1O2 processes. The evolution process of the main arsenic species in solution and catalyst surface with oxidation was clarified. The ultimate removal of the total As involves 20 % As(III), 60 % As(V), and 20 % organic arsenic intermediates via forming inner-sphere complexes or electrostatic interaction. This contribution provides a brand-new perspective for the remediation of organoarsenic pollution over designing highly active catalysts.

Angstrom Confinement-Triggered Adaptive Spin State Transition of CoMn Dual Single Atoms for Efficient Singlet Oxygen Generation

To achieve high selectivity in the transformation from peroxymonosulfate to singlet oxygen, adaptive tuning of atomic spin state as the peroxymonosulfate structure varied is crucial. The angstrom confinement can effectively tune spin state, but developing an adaptive angstrom-confined atomic system is challenging. Angstrom-confined cobalt (Co) manganese (Mn) dual single atoms within flexible 2D carbon nitride interlayer are constructed to drive adaptive tuning of spin state by changing atomic coordination under angstrom confinement. The in situ characterizations and density functional theory calculations showed that medium-spin Co in Co─N4 absorbed electrons after the adsorption of peroxymonosulfate on CoMn dual single-atom sites and then cleaved O─H of peroxymonosulfate to facilitate *SO5 generation, while the introduction of *SO5 increased interlayer distance and then cleaved Co─N and Mn─N, resulting in the spin state transition from medium to high. Subsequently, the high-spin Co and Mn in Co─N2 and Mn─N2 desorbed the *O2 from *SO5, restoring the initial medium spin state. The adaptive spin state transition enhanced 38.6-fold singlet oxygen yield compared to the unconfined control. The proposed angstrom-confined diatomic strategy is applicable to serial diatomic catalysts, providing an efficient and universal design scheme for singlet oxygen-mediated selective wastewater treatment technology at the atomic level.

Unexpected chloride-triggered organics removal in the zirconium oxide activated peroxymonosulfate system

Chloride ion (Cl-) is ubiquitous in diverse water bodies, yet poses a longstanding challenge in water pollution control by hindering the efficiency of pollutant degradation. Herein, we proposed a novel concept involving the direct utilization of endogenous Cl- ions in water for rapid water purification within a non-redox zirconium oxide (ZrO2)-activated peroxymonosulfate (PMS) system. In this process, PMS was complexed on the ZrO2 surface through inner-sphere coordination, and effectively activated by the partial electron cloud deviation from Zr(IV) sites to PMS, thereby forming a metastable surface complex with an elevated redox potential. Afterwards, the coexistence of Cl- could trigger the transformation of the reactive complex into free chlorine species, thus leading to a 255.0-fold enhancement in the elimination rate of micropollutants compared with the ZrO2/PMS system. Quantitative structure-activity relationship analysis revealed that the ZrO2/PMS/Cl- system displayed strong target-dependence towards electron-rich compounds, showcasing a faster oxidation rate for pollutants with higher EHOMO energy levels. Significantly, the novel system performed robust resistance to complex water matrices, achieved low oxidant consumption for pollutant removal, and demonstrated adaptation across a broad range of Cl- concentrations (1.0-100.0 mM). Overall, our findings provide new mechanistic insights into the influence of Cl- ions on PMS activation, which refresh the understanding of the role of Cl- ions on pollutant degradation, and help to guide the treatment design for chloride-containing wastewater.

Magnesium Oxide-Supported Single Atoms with Fine-Modulated Steric Location for Polymerization Transfer Removal of Water Pollutants

Organic pollutants removal via a polymerization transfer (PT) pathway based on the use of single-atom catalysts (SACs) promises efficient water purification with minimal energy/chemical inputs. However, the precise engineering of such catalytic systems toward PT decontamination is still challenging, and the conventional SACs are plagued by low structural stability of carbon material support. Here, we adopted magnesium oxide (MgO) as a structurally stable alternative for loading single copper (Cu) atoms to drive peroxymonosulfate-based Fenton-like reactions. Through fine-tuning the Cu atom steric location from lattice-embedding to surface-loading, the system exhibited a fundamental transition in the catalytic pathways toward the PT process and drastically improved decontamination efficiency. The catalytic pathway change was mainly ascribed to a downshifted d-band center of the Cu atoms. The optimized catalyst achieved complete, rapid removal of phenolic compounds from water via nearly 100% PT pathway, accompanied by high oxidant utilization efficiency surpassing most state-of-the-art SACs. Moreover, it showed excellent structural stability and environmental robustness and was successfully used for the treatment of lake water and industrial coking wastewater. The adaptability of the spatial engineering strategy to other MgO-supported single atoms, including Fe, Co, and Ni SACs, was also demonstrated. Our work lays a foundation for further advancing SACs-based advanced oxidation technologies toward sustainable water purification applications.

High-entropy alloys catalyzing polymeric transformation of water pollutants with remarkably improved electron utilization efficiency

High-entropy alloy nanoparticles (HEA-NPs) exhibit favorable properties in catalytic processes, as their multi-metallic sites ensure both high intrinsic activity and atomic efficiency. However, controlled synthesis of uniform multi-metallic ensembles at the atomic level remains challenging. This study successfully loads HEA-NPs onto a nitrogen-doped carbon carrier (HEAs) and pioneers the application in peroxymonosulfate (PMS) activation to drive Fenton-like oxidation. The HEAs-PMS system achieves ultrafast pollutant removal across a wide pH range with strong resistance to real-world water interferences. Furthermore, the nonradical HEAs-PMS system selectively transforms phenolics into high-molecular-weight products via a polymerization pathway. The unique non-mineralization regime remarkably reduces PMS consumption and achieves a high electron utilization efficiency of up to 213.4%. Further DFT calculations and experimental analysis reveal that Fe and Co in HEA-NPs act as the primary catalytic sites to complex with PMS for activation, while Ni, Cu, and Pd serve as charge mediators to facilitate electron transfer. The resulting PMS* complexes on HEAs possess a high redox potential, which drives spatially separated phenol oxidation on nitrogen-doped graphene support to form phenoxyl radicals, subsequently triggering the formation of high-molecule polymeric products via polymerization reactions. This study offers engineered HEAs catalysts for water treatment with low oxidant consumption and emissions.

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.

Support work-function dependent Fenton-like catalytic activity of Co single atoms for selective cobalt(IV)=O generation

In Fenton-like reactions, high-valent cobalt-oxo (CoIV=O) has attracted increasing interests due to high redox potential, long lifetime, and anti-interference properties, but its generation is hindered by the electron repulsion between the electron rich oxo- and cobalt centers. Here, we demonstrate CoIV=O generation from peroxymonosulfate (PMS) activation over cobalt single-atom catalysts (Co-SACs) using in-situ Co K-edge X-ray absorption spectra, and discern that CoIV=O generation is dependent on the support work-function (WF) due to the strong electronic metal-support interaction (EMSI). Supports with a high WF value like anatase-TiO2 facilitate the binding of PMS-terminal oxo-ligand to Co sites by extracting Co-d electrons, thus decreasing the generation barrier for the critical intermediate (Co-OOSO32-). The Co atoms anchored on anatase-TiO2 (Co-TiO2) exhibited enhanced CoIV=O generation and superior activity for sulfamethoxazole (SMX) degradation during PMS activation. The normalized steady-state concentration of CoIV=O in Co-TiO2/PMS system was three orders of magnitude higher than that of free radicals, and 1.3- to 11-fold higher than that generated in other Co-SACs/PMS systems. Co-TiO2/PMS sustained efficient removal of SMX with minimal Co2+ leaching under continuous flow operation, suggesting its attractive water purification potential. Overall, these results underscore the significance of support selection for enhanced generation of high-valent metal-oxo species and efficient PMS activation in supported metal SACs.

Revealing the Overlooked Catalytic Ability of γ-Al2O3: Efficient Activation of Peroxymonosulfate for Enhanced Water Treatment

Activated alumina (γ-Al2O3) is one of the few nanomaterials manufactured at a ton-scale and successfully implemented in large-scale water treatment. Yet its role in advanced oxidation processes (AOPs) has primarily been limited to functioning as an inert carrier due to its inherently nonredox nature. This study, for the first time, presents the highly efficient capability of γ-Al2O3 to activate peroxymonosulfate (PMS) for selectively eliminating electron-rich organic pollutants in the presence of Cl-. Through experimental and theoretical analysis, we revealed that γ-Al2O3, characterized by uniquely strong Lewis acid sites, enabled robust inner-sphere complexation between PMS and Al(III) sites, triggering the oxidation of Cl- to free chlorine through a distinctive, low-energy-barrier Eley-Rideal pathway. Such a unique pathway resulted in a 42.7-fold increase in free chlorine generation, culminating in a remarkable 145.9-fold enhancement in the degradation of carbamazepine (CBZ) compared with the case without γ-Al2O3. Furthermore, this catalyst exhibited high oxidant utilization efficiency, stable performance in real-world environmental matrices, and sustained long-term activation for over 1206 bed volumes (BV) with a CBZ removal rate exceeding 90% in fixed-bed experiments. These favorable features render γ-Al2O3 an extremely promising nanomaterial for sustainable water treatment initiatives.

Revealing the essence of anion ligands in regulating amorphous MnOx to activate peracetic acid for micropollutant removal

How the anion ligands of manganese precursors affect the catalytic activity of amorphous manganese oxides (MnOx) in Fenton-like process is poorly understood. Here, five amorphous MnOx synthesized by Mn(II) precursors with different ligands were characterized and adopted to activate peracetic acid (PAA) for bisphenol A (BPA) degradation. Although > 90 % BPA removal was achieved in the five MnOx/PAA processes via both adsorption and oxidation, the oxidation kobs greatly differentiates by the ligands types with the order of MnOx-N > MnOx-S > MnOx-Cl > MnOx-AA > MnOx-OA. Ligands types would affect the specific surface area of MnOx and their ability to adsorb BPA, however which is not the decisive factor in determining the contaminant oxidation efficiency. Multiple experimental results indicate that the generation of oxygen vacancies induced by the ligands alters the Mn(III)/Mn(IV) ratio, ultimately contributing to the different efficiency of BPA oxidation driven by the direct electron transfer mechanism. Moreover, amorphous MnOx holds the promise of practical applications in catalytic PAA of various micropollutants with good stability. This study advances the fundamental understanding of ligand-regulated amorphous MnOx-catalyzed PAA process.

A new strategy integrating peroxymonosulfate oxidation and soil amendments in contaminated soil: Bensulfuron methyl degradation, soil quality improvement and maize growth promotion

Bensulfuron methyl (BSM) residues have caused serious yield reductions of sensitive crops. Chemical oxidation is an effective remediation technology, while it affects soil quality and subsequent agricultural activity, necessitating approriate improvement measures. So Fe2O3-Mn3O4 with excellent bimetallic synergistic effect was synthesized to activate peroxymonosulfate (PMS) for BSM degradation. The catalytic activity and influencing factors were systematically predetermined in water in view of soil remediation. Results showed Fe2O3-Mn3O4/PMS oxidized 99.3 % BSM within 60 min with the help of multi-reactive species and electron transfer. Meanwhile, Fe2O3-Mn3O4/PMS treatment exhibited technical feasibility in soil that 97.6 % BSM was degraded in 5 days under the low usages of Fe2O3-Mn3O4 (0.8 %) and PMS (0.15 %). Although Fe2O3-Mn3O4/PMS decreased BSM phytotoxicity and improved maize growth, a few gaps existed between the remediated group and uncontaminated group, including biomass, length, available potassium, organic matters, pH, redox potential (Eh) and sulfate content. The introductions of biochar and chitosan in remediated soils promoted growth, increased organic matters content, improved soil resistance to acidification and decreased Eh, alleviating the negative effects of Fe2O3-Mn3O4/PMS. Overall, the study provided new insights into the combination of Fe2O3-Mn3O4/PMS and biochar and chitosan in BSM-contaminated soil, achieving BSM degradation and improvements of soil quality and plant growth.

Mn─O Covalency as a Lever for Na⁺ Intercalation Kinetics: The Role of Oxygen Edge-Sharing Co Octahedral Sites in MnO₂

The strategic enhancement of manganese-oxygen (Mn─O) covalency is a promising approach to improve the intercalation kinetics of sodium ions (Na⁺) in manganese dioxide (MnO2). In this study, an augmenting Mn─O covalency in MnO2 by strategically incorporating cobalt at oxygen edge-sharing Co octahedral sites is focused on. Both experimental results and density functional theory (DFT) calculations reveal an increased electron polarization from oxygen to manganese, surpassing that directed toward cobalt, thereby facilitating enhanced electron transfer and strengthening covalency. The synthesized Co-MnO2 material exhibits outstanding electrochemical performance, demonstrating a superior specific capacitance of 388 F g-1 at 1 A g-1 and maintaining 97.21% capacity retention after 12000 cycles. Additionally, an asymmetric supercapacitor constructed using Co-MnO2 achieved a high energy density of 35 Wh kg-1 at a power density of 1000 W kg-1, underscoring the efficacy of this material in practical applications. This work highlights the critical role of transition metal-oxygen interactions in optimizing electrode materials and introduces a robust approach to enhance the functional properties of manganese oxides, thereby advancing high-performance energy storage technologies.

Unraveling the Impact of Oxygen Vacancy on Electrochemical Valorization of Polyester Over Spinel Oxides

Electrochemical upcycling of end-of-life polyethylene terephthalate (PET) using renewable electricity offers a route to generate valuable chemicals while processing plastic wastes. However, it remains a huge challenge to design an electrocatalyst with reliable structure-property relationships for PET valorization. Herein, spinel Co3O4 with rich oxygen vacancies for improved activity toward formic acid (FA) production from PET hydrolysate is reported. Experimental investigations combined with theoretical calculations reveal that incorporation of VO into Co3O4 not only promotes the generation of reactive hydroxyl species (OH*) species at adjacent tetrahedral Co2+ (Co2+ Td), but also induces an electronic structure transition from octahedral Co3+ (Co3+ Oh) to octahedral Co2+ (Co2+ Oh), which typically functions as highly-active catalytic sites for ethylene glycol (EG) chemisorption. Moreover, the enlarged Co-O covalency induced by VO facilitates the electron transfer from EG* to OH* via Co2+ Oh-O-Co2+ Td interaction and the following C─C bond cleavage via direct oxidation with a glyoxal intermediate pathway. As a result, the VO-Co3O4 catalyst exhibits a high half-cell activity for EG oxidation, with a Faradaic efficiency (91%) and productivity (1.02 mmol cm-2 h-1) of FA. Lastly, it is demonstrated that hundred gram-scale formate crystals can be produced from the real-world PET bottles via two-electrode electroreforming, with a yield of 82%.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Confronting the Mysteries of Oxidative Reactive Species in Advanced Oxidation Processes: An Elephant in the Room

Advanced oxidation processes (AOPs) are rapidly evolving but still lack well-established protocols for reliably identifying oxidative reactive species (ORSs). This Perspective presents both the radical and nonradical ORSs that have been identified or proposed, along with the extensive controversies surrounding oxidative mechanisms. Conventional identification tools, such as quenchers, probes, and spin trappers, might be inadequate for the analytical demands of systems in which multiple ORSs coexist, often yielding misleading results. Therefore, the challenges of identifying these complex, short-lived, and transient ORSs must be fully acknowledged. Refining analytical methods for ORSs is necessary, supported by rigorous experiments and innovative paradigms, particularly through kinetic analysis based on in situ spectroscopic techniques and multiple-probe strategies. To demystify these complex ORSs, future efforts should be made to develop advanced tools and strategies to enhance the mechanism understanding. In addition, integrating real-world conditions into experimental designs will establish a reliable framework in fundamental studies, providing more accurate insights and effectively guiding the design of AOPs.

A Two-Phase Hydrogenation Membrane for Contaminants Reduction at High Hydrogen Reagent Utilization Efficiency

Heterogeneous hydrogenation is surging as a promising strategy for selective removal of water pollutants, yet numerous efforts rely on catalyst design to advance catalytic activity. Herein, we enhanced the mass transfer and the utilization of hydrogen reagent through construction of a two-phase flow-through membrane reaction device (Pd/SiC-MR). Pd/SiC-MR displays high efficiency and selectivity toward removal of multiple pollutants. For instance, rapid (∼0.35 s) and exclusive hydrogenation (>99%) of carbon-chlorine bond in organohalogens were realized at high water flux (220 L/m2/h). More importantly, the two-phase Pd/SiC-MR reaction system achieved 31.4% utilization of hydrogen reagent, 1-3 orders of magnitude higher than those by classical slurry or fixed-bed reactor. The high hydrogenation performance is attributed to the close proximity of the hydrogen source, reactive hydrogen atom, and pollutant under high molecular collision frequency in membrane pores. Our study opens an approach for improved hydrogen reagent utilization while reserving the high pollutant removal efficiency through altering operating conditions, beyond complex material design limitations in hydrogenation water purification.

Revealing the Synergistic Effect of Cation and Anion Vacancies on Enhanced Fenton-Like Reaction: The Electron Density Modulation of O 2p-Co 3d Bands

Defect engineering is considered as a flexible and effective mean to improve the performance of Fenton-like reactions. Herein, a simple method is employed to synthesize Co3O4 catalysts with Co-O vacancy pairs (VP) for peroxymonosulfate (PMS) activation. Multi-scaled characterization, experimental, and simulation results jointly revealed that the cation vacancies-VCo contributed to enhanced conductivity and anion vacancies-VO provided a new active center for the 1O2 generation. Co3O4-VP can optimize the O 2p and Co 3d bands with the strong assistance of synergistic double vacancies to reduce the reaction energy barrier of the "PMS → Co(IV) = O → 1O2" pathway, ultimately triggering the stable transition of mechanism. Co3O4-VP catalysts with radical-nonradical collaborative mechanism achieve the synchronous improvement of activity and stability, and have good environmental robustness to favor water decontamination applications. This result highlights the possibility of utilizing anion and cation vacancy engineering strategies to rational design Co3O4-based materials widely used in catalytic reactions.

Performance enhancement and mechanism of electroenhanced peroxymonosulfate activation by single-atom Fe catalyst modified electrodes

Peroxymonosulfate-based electrochemical advanced oxidation processes (PMS-EAOPs) have great potential for sustainable water purification, so an in-depth understanding of its catalytic mechanism is imperative to facilitate its practical application. Herein, the performance enhancement and mechanism of electroenhanced PMS activation by single-atom Fe catalyst modified carbon felt was investigated. Compared with the anode, the cathode exhibited faster bisphenol A degradation (kcathode = 0.073 vs. kanode = 0.015 min-1), increased PMS consumption (98.8 vs. 10.3%), and an order of magnitude reduction of Fe dissolution (0.068 vs. 0.787 mg L-1). Mass transfer is a key factor limiting PMS activation, while the electrostriction of water in the hydrophobic region caused by cathode electric field (CEF) significantly increased mass transfer coefficient (km, cathode = 1.49 × 10-4 vs. km, anode = 2.68 × 10-5 m s-1). The enhanced activation of PMS is a synergistic result between electroactivation and catalyst-activation, which is controlled by the applied current density. 1O2 and direct electron transfer are the main active species and activation pathway, which achieve high degradation efficiency over pH 3 to 10. Density functional theory calculations prove CEF increases the adsorption energy, lengthens the O-O bond in PMS, and promotes charge transfer. A flow-through convection unit achieves sustainable operation with high removal efficiency (99.5% to 97.5%), low electrical energy consumption (0.15 kWh log-1 m-3), and low Fe leaching (0.81% of the total single atom Fe). This work reveals the critical role of electric fields in modulating Fenton-like catalytic activity, which may advance the development of advanced oxidation processes and other electrocatalytic applications.

Overcoming metals redox rate limitations in spinel oxide-driven Fenton-like reactions via synergistic heteroatom doping and carbon anchoring for efficient micropollutant removal

The transition metals redox rate limitations of spinel oxides during Fenton-like reactions hinder its efficient and sustainable treatment of actual wastewater. Herein, we propose to optimize the electronic structure of Co-Mn spinel oxide (CM) via sulfur doping and carbon matrix anchoring synergistically, enhancing the radicals-nonradicals Fenton-like processes for efficient water decontamination. Activating peroxymonosulfate (PMS) with optimised spinel oxide (CMSAC) achieved near-complete removal of ofloxacin (10 mg/L) within 6 min, showing 8.4 times higher efficiency than CM group. Significantly higher yields of SO4·- and high-valent metal species in CMSAC/PMS system provided exceptional resistance to co-existing anions, enabling efficient removal of various emerging contaminants in high salinity leachate. Specifically, sulfur coordination and carbon anchoring-induced oxygen vacancy synergistically improved the electronic structure and electron transfer efficiency of CMSAC, thus forming highly reactive Co sites and significantly reducing the energy barrier for Co(IV)=O generation. The reductive sulfur species facilitated the conversion of Co(III) to Co(II), thereby maintaining the stability of the catalytic activity of CMSAC. This work developed a synergistic optimization strategy to overcome the metals redox rate limitations of spinel oxides in Fenton-like reactions, providing deep mechanistic insights for designing Fenton-like catalysts suitable for practical applications.

Electron Delocalization Disentangles Activity-Selectivity Trade-Off of Transition Metal Phosphide Catalysts in Oxidative Desulfurization

Breaking the activity-selectivity trade-off has been a long-standing challenge in catalysis. Here, we proposed a nanoheterostructure engineering strategy to overcome the trade-off in metal phosphide catalysts for the oxidative desulfurization (ODS) of fuels. Experimental and theoretical results demonstrated that electron delocalization was the key driver to simultaneously achieve high activity and high selectivity for the molybdenum phosphide (MoP)/tungsten phosphide (WP) nanoheterostructure catalyst. The electron delocalization not only promoted the catalytic pathway transition from predominant radicals to singlet oxygens in H2O2 activation but also simultaneously optimized the adsorption of reactants and intermediates on Mo and W sites. The presence of such dual-enhanced active sites ideally compensated for the loss of activity due to the nonradical catalytic pathway, consequently disentangling the activity-selectivity trade-off. The resulting catalyst (MoWP2/C) unprecedentedly achieved 100% removal of thiophenic compounds from real diesel at an initial concentration of 2676 ppm of sulfur with a high turnover frequency (TOF) of 105.4 h-1 and a minimal O/S ratio of 4. This work provides fundamental insight into the structure-activity-selectivity relationships of heterogeneous catalysts and may inspire the development of high-performance catalysts for ODS and other catalytic fields.

Superoxide radicals mediated by high-spin Fe catalysis for organic wastewater treatment

Water resources are indispensable basic resources and important environmental carriers; the presence of organic contaminants in wastewater poses considerable risks to the health of both humans and ecosystems. Although the Fenton-like reactions using H2O2 as the oxidant to destroy organic pollutants are attractive, there are still challenges in improving reaction activity under neutral or even alkaline conditions. Herein, we designed a H2O2 activation pathway with O2•- as the main active species and elucidated that the spin interaction between Fe sites and coordinated O atoms effectively promotes the generation of the key intermediate Fe-*OOH. Furthermore, we successfully captured and analyzed the Fe-*OOH intermediate by in situ Raman spectroscopy. When applying FBOB to a continuous-flow reactor, CIP removal efficiency remained at around 90% within 600 min of continuous operation, achieving excellent efficiency, stability, and pH tolerance in removing pollutants.

Constructing High-Performance Cobalt-Based Environmental Catalysts from Spent Lithium-Ion Batteries: Unveiling Overlooked Roles of Copper and Aluminum from Current Collectors

Converting spent lithium-ion batteries (LIBs) cathode materials into environmental catalysts has drawn more and more attention. Herein, we fabricated a Co3O4-based catalyst from spent LiCoO2 LIBs (Co3O4-LIBs) and found that the role of Al and Cu from current collectors on its performance is nonnegligible. The density functional theory calculations confirmed that the doping of Al and/or Cu upshifts the d-band center of Co. A Fenton-like reaction based on peroxymonosulfate (PMS) activation was adopted to evaluate its activity. Interestingly, Al doping strengthened chemisorption for PMS (from -2.615 eV to -2.623 eV) and shortened Co-O bond length (from 2.540 Å to 2.344 Å) between them, whereas Cu doping reduced interfacial charge-transfer resistance (from 28.347 kΩ to 6.689 kΩ) excepting for the enhancement of the above characteristics. As expected, the degradation activity toward bisphenol A of Co3O4-LIBs (0.523 min-1) was superior to that of Co3O4 prepared from commercial CoC2O4 (0.287 min-1). Simultaneously, the reasons for improved activity were further verified by comparing activity with catalysts doped Al and/or Cu into Co3O4. This work reveals the role of elements from current collectors on the performance of functional materials from spent LIBs, which is beneficial to the sustainable utilization of spent LIBs.

Asymmetrically Coordinated Mn-S1N3 Configuration Induces Localized Electric Field-Driven Peroxymonosulfate Activation for Remarkably Efficient Generation of 1O2

Singlet oxygen (1O2) species generated in peroxymonosulfate (PMS)-based advanced oxidation processes offer opportunities to overcome the low efficiency and secondary pollution limitations of existing AOPs, but efficient production of 1O2 via tuning the coordination environment of metal active sites remains challenging due to insufficient understanding of their catalytic mechanisms. Herein, an asymmetrical configuration characterized by a manganese single atom coordinated is established with one S atom and three N atoms (denoted as Mn-S1N3), which offer a strong local electric field to promote the cleavage of O─H and S─O bonds, serving as the crucial driver of its high 1O2 production. Strikingly, an enhanced the local electric field caused by the dynamic inter-transformation of the Mn coordination structure (Mn-S1N3 ↔ Mn-N3) can further downshift the 1O2 production energy barrier. Mn-S1N3 demonstrates 100% selective product 1O2 by activation of PMS at unprecedented utilization efficiency, and efficiently oxidize electron-rich pollutants. This work provides an atomic-level understanding of the catalytic selectivity and is expected to guide the design of smart 1O2-AOPs catalysts for more selective and efficient decontamination applications.

Efficient reduction-oxidation coupling degradation of nitroaromatic compounds in continuous flow processes

Nitroaromatic compounds (NACs) with electron-withdrawing nitro (-NO2) groups are typical refractory pollutants. Despite advanced oxidation processes (AOPs) being appealing degradation technologies, inefficient ring-opening oxidation of NACs and practical large-scale applications remain challenges. Here we tackle these challenges by designing a reduction-oxidation coupling (ROC) degradation process in LaFe0.95Cu0.05O3@carbon fiber cloth (LFCO@CFC)/PMS/Vis continuous flow system. Cu doping enhances the photoelectron transfer, thus triggering the -NO2 photoreduction and breaking the barriers in the ring opening. Also, it modulates surface electronic configuration to generate radicals and non-radicals for subsequent oxidation of reduction products. Based on this, the ROC process can effectively remove and mineralize NACs under the environmental background. More importantly, the LFCO catalyst outperformed most of the recently reported catalysts with lower cost (13.72 CNY/ton) and higher processing capacity (3600 t/month). Furthermore, the high scalability, material durability, and catalytic activity of LFCO@CFC under various realistic environmental conditions prove the potential ability for large-scale applications.

Metal-organic framework derived crystalline nanocarbon for Fenton-like reaction

Nanoporous carbons with tailorable nanoscale texture and long-range ordered structure are promising candidates for energy, environmental and catalytic applications, while the current synthetic methods do not allow elaborate control of local structure. Here we report a salt-assisted strategy to obtain crystalline nanocarbon from direct carbonization of metal-organic frameworks (MOFs). The crystalline product maintains a highly ordered two-dimensional (2D) stacking mode and substantially differs from the traditional weakly ordered patterns of nanoporous carbons upon high-temperature pyrolysis. The MOF-derived crystalline nanocarbon (MCC) comes with a high level of nitrogen and oxygen terminating the 2D layers and shows an impressive performance as a carbocatalyst in Fenton-like reaction for water purification. The successful preparation of MCC illustrates the possibility to discover other crystalline heteroatom-doped carbon phases starting from correctly designed organic precursors and appropriate templating reactions.

Radiation-induced preparation of nanoscale CoO@graphene oxide for activating peroxymonosulfate to degrade emerging organic pollutants

In this study, ionizing radiation was used to induce the in-situ formation of highly dispersed nanosized cobalt oxide on the surface of graphene oxide (R-Co-GO), which was highly effective for activating PMS to degrade sulfamethoxazole (SMX). R-Co-GO had the highest catalytic activity when 150 μL cobalt chloride hexahydrate solution was used in the precursor, and the pseudo first-order kinetic constant of SMX degradation was 0.07 min-1 with high mineralization efficiency (63.1 %) and high PMS utilization efficiency. The sulfate radicals and high-valent cobalt oxo were mainly responsible for SMX degradation. Mechanism analysis showed that cobalt active site dominated in PMS activation, which was responsible for the formation of sulfate radicals and high-valent cobalt oxo; while the carbon framework contributed to the formation of singlet oxygen. The R-Co-GO-150 had good catalytic activity and stability in five cycling experiments, in which SMX was completely degraded and the concentration of dissolved Co was below 0.1 mg/L. In addition, the R-Co-GO-150/PMS system could also degrade phenol, bisphenol A, atrazine and nitrobenzene effectively, confirming its wide applicability. This study provided a facile method to uniformly disperse the metal oxides on the surface of carbon materials, and an effective system for the removal of emerging organic pollutants from the actual wastewater.

Size-Dependent Catalysis in Fenton-like Chemistry: From Nanoparticles to Single Atoms

State-of-the-art Fenton-like reactions are crucial in advanced oxidation processes (AOPs) for water purification. This review explores the latest advancements in heterogeneous metal-based catalysts within AOPs, covering nanoparticles (NPs), single-atom catalysts (SACs), and ultra-small atom clusters. A distinct connection between the physical properties of these catalysts, such as size, degree of unsaturation, electronic structure, and oxidation state, and their impacts on catalytic behavior and efficacy in Fenton-like reactions. In-depth comparative analysis of metal NPs and SACs is conducted focusing on how particle size variations and metal-support interactions affect oxidation species and pathways. The review highlights the cutting-edge characterization techniques and theoretical calculations, indispensable for deciphering the complex electronic and structural characteristics of active sites in downsized metal particles. Additionally, the review underscores innovative strategies for immobilizing these catalysts onto membrane surfaces, offering a solution to the inherent challenges of powdered catalysts. Recent advances in pilot-scale or engineering applications of Fenton-like-based devices are also summarized for the first time. The paper concludes by charting new research directions, emphasizing advanced catalyst design, precise identification of reactive oxygen species, and in-depth mechanistic studies. These efforts aim to enhance the application potential of nanotechnology-based AOPs in real-world wastewater treatment.

Nanostructured Mn@NiO composite for addressing multi-pollutant challenges in petroleum-contaminated water

Efficient catalysts play a pivotal role in advancing eco-friendly water treatment strategies, particularly in the removal of diverse organic contaminants found in water-petroleum sources. This study addresses the multifaceted challenges posed by contaminants, encompassing a spectrum of heavy metals such as As, Cd, Cr, Mn, Mo, Ni, Pb, Sb, Se, and Zn alongside pollutants like oily water (OIW), total suspended solids (TSS), chemical oxygen demand (COD), dyes, and pharmaceuticals, posing threats to both aquatic and terrestrial ecosystems. Herein, we present the synthesis of biogenically derived Mn@NiO nanocomposite (NC) photocatalysts, a sustainable methodology employing an aqueous Rosmarinus officinalis L. extract, yielding particles with a size of 36.7 nm. The catalyst demonstrates exceptional efficacy in removing heavy metals, achieving rates exceeding 99-100% within 30 min, alongside notable removal efficiencies for OIW (98%), TSS (87%), and COD (98%). Furthermore, our photodegradation experiments showed remarkable efficiencies, with 94% degradation for Rose Bengal (RB) and 96% for methylene blue (MB) within 120 min. The degradation kinetics adhere to pseudo-first-order behavior, with rate constants of 0.0227 min-1 for RB and 0.0370 min-1 for MB. Additionally, the NC exhibits significant antibiotic degradation rates of 97% for cephalexin (CEX) and 96% for amoxicillin (AMOX). The enhanced photocatalytic performance is attributed to the synergistic interplay between the Mn and NiO nanostructures, augmenting responsiveness to sunlight while mitigating electron-hole pair recombination. Notably, the catalyst demonstrates outstanding stability and reusability across multiple cycles, maintaining its stable nanostructure without compromise.

Tailoring the selective generation of oxidative organic radicals for toxic-by-product-free water decontamination

Peracetic acid (PAA) is emerging as a versatile agent for generating long-lived and selectively oxidative organic radicals (R-O•). Currently, the conventional transition metal-based activation strategies still suffer from metal ion leaching, undesirable by-products formation, and uncontrolled reactive species production. To address these challenges, we present a method employing BiOI with a unique electron structure as a PAA activator, thereby predominantly generating CH3C(O)O• radicals. The specificity of CH3C(O)O• generation ensured the superior performance of the BiOI/PAA system across a wide pH range (2.0 to 11.0), even in the presence of complex interfering substances such as humic acids, chloride ions, bicarbonate ions, and real-world water matrices. Unlike conventional catalytic oxidative methods, the BiOI/PAA system degrades sulfonamides without producing any toxic by-products. Our findings demonstrate the advantages of CH3C(O)O• in water decontamination and pave the way for the development of eco-friendly water decontaminations based on organic peroxides.

Unlocking Spin Gates of Transition Metal Oxides via Strain Stimuli to Augment Potassium Ion Storage

Transition metal oxides (TMOs) are key in electrochemical energy storage, offering cost-effectiveness and a broad potential window. However, their full potential is limited by poor understanding of their slow reaction kinetics and stability issues. This study diverges from conventional complex nano-structuring, concentrating instead on spin-related charge transfer and orbital interactions to enhance the reaction dynamics and stability of TMOs during energy storage processes. We successfully reconfigured the orbital degeneracy and spin-dependent electronic occupancy by disrupting the symmetry of magnetic cobalt (Co) sites through straightforward strain stimuli. The key to this approach lies in the unfilled Co 3d shell, which serves as a spin-dependent regulator for carrier transfer and orbital interactions within the reaction. We observed that the opening of these 'spin gates' occurs during a transition from a symmetric low-spin state to an asymmetric high-spin state, resulting in enhanced reaction kinetics and maintained structural stability. Specifically, the spin-rearranged Al-Co3O4 exhibited a specific capacitance of 1371 F g-1, which is 38 % higher than that of unaltered Co3O4. These results not only shed light on the spin effects in magnetic TMOs but also establish a new paradigm for designing electrochemical energy storage materials with improved efficiency.

Selective and ultrafast oxidation of multiple pollutants by biomorphic diatomite-based catalyst and stable catalytic Fenton-like membrane: Degradation behavior and mechanism analysis

Carbon-driven advanced oxidations show great potential in water purification, but regulating structures and properties of carbon-based catalysts to achieve ultrafast Fenton-like reactions remains challenging. Herein, a biomorphic diatomite-based catalyst (BD-C) with Si-O doping was prepared using natural diatomite as silicon source and porous template. The results showed that the metal-free BD-C catalyst exhibited ultrafast oxidation performances (0.95-2.58 min-1) towards a variety of pollutants in PMS-based Fenton-like reaction, with the Fenton-like activity of metal-free catalyst comparable to metal-based catalysts or even single-atom catalysts. Pollutants (e.g., CP, BPA, TC, and PCM) with electron-donating groups exhibited extremely low PMS decomposition with overwhelmed electron transfer process (ETP), while high PMS consumption was induced by the addition of electron-withdrawing pollutants (e.g., MNZ and ATZ), which was dominated by radical oxidation. The BD-C/PMS system also showed a high ability to resist the environmental interference. In-depth theoretical investigations demonstrated that the coordination of Si-O can lower the potential barrier of PMS activation for accelerating the generation of radicals, and also promote the electron transfer from pollutants to the BD-C/PMS complexes. In addition, BD-C was deposited onto a polytetrafluoroethylene membrane (PTFEM) with 100% of pollutants removal over 10 h, thereby revealing the promising prospects of utilizing BD-C for practical applications.

Efficient Homolytic Cleavage of H2O2 on Hydroxyl-Enriched Spinel CuFe2O4 with Dual Lewis Acid Sites

Traditional H2O2 cleavage mediated by macroscopic electron transfer (MET) not only has low utilization of H2O2, but also sacrifices the stability of catalysts. We present a non-redox hydroxyl-enriched spinel (CuFe2O4) catalyst with dual Lewis acid sites to realize the homolytic cleavage of H2O2. The results of systematic experiments, in situ characterizations, and theoretical calculations confirm that tetrahedral Cu sites with optimal Lewis acidity and strong electron delocalization can synergistically elongate the O-O bonds (1.47 Å → 1.87 Å) in collaboration with adjacent bridging hydroxyl (another Lewis acid site). As a result, the free energy of H2O2 homolytic cleavage is decreased (1.28 eV → 0.98 eV). H2O2 can be efficiently split into ⋅OH induced by hydroxyl-enriched CuFe2O4 without MET, which greatly improves the catalyst stability and the H2O2 utilization (65.2 %, nearly 2 times than traditional catalysts). The system assembled with hydroxyl-enriched CuFe2O4 and H2O2 affords exceptional performance for organic pollutant elimination. The scale-up experiment using a continuous flow reactor realizes long-term stability (up to 600 mL), confirming the tremendous potential of hydroxyl-enriched CuFe2O4 for practical applications.

Precisely constructing orbital coupling-modulated iron dinuclear site for enhanced catalytic ozonation performance

The advancement of atomically precise dinuclear heterogeneous catalysts holds great potential in achieving efficient catalytic ozonation performance and contributes to the understanding of synergy mechanisms during reaction conditions. Herein, we demonstrate a "ship-in-a-bottle and pyrolysis" strategy that utilizes Fe2(CO)9 dinuclear-cluster to precisely construct Fe2 site, consisting of two Fe1-N3 units connected by Fe-Fe bonds and firmly bonded to N-doped carbon. Systematic characterizations and theoretical modeling reveal that the Fe-Fe coordination motif markedly reduced the devotion of the antibonding state in the Fe-O bond because of the strong orbital coupling interaction of dual Fe d-d orbitals. This facilitates O-O covalent bond cleavage of O3 and enhances binding strength with reaction intermediates (atomic oxygen species; *O and *OO), thus boosting catalytic ozonation performance. As a result, Fe dinuclear site catalyst exhibits 100% ozonation efficiency for CH3SH elimination, outperforming commercial MnO2 catalysts by 1,200-fold. This research provides insights into the atomic-level structure-activity relationship of ozonation catalysts and extends the use of dinuclear catalysts in catalytic ozonation and beyond.

Heteroatom substitution enhances generation and reactivity of surface-activated peroxydisulfate complexes for catalytic fenton-like reactions

Peroxydisulfate (PDS)-based Fenton-like reactions are promising advanced oxidation processes (AOPs) to degrade recalcitrant organic water pollutants. Current research predominantly focuses on augmenting the generation of reactive species (e.g., surface-activated PDS complexes (PDS*) to improve treatment efficiency, but overlooks the potential benefits of enhancing the reactivity of these species. Here, we enhanced PDS* generation and reactivity by incorporating Zn into CuO catalyst lattice, which resulted in 99% degradation of 4-chlorophenol within only 10 min. Zn increased PDS* generation by nearly doubling PDS adsorption while maintaining similar PDS to PDS* conversion efficiency, and induced higher PDS* reactivity than the common catalyst CuO, as indicated by a 4.1-fold larger slope between adsorbed PDS and open circuit potential of a catalytic electrode. Cu-O-Zn formation upshifts the d-band center of Cu sites and lowers the energy barrier for PDS adsorption and sulfate desorption, resulting in enhanced PDS* generation and reactivity. Overall, this study informs strategies to enhance PDS* reactivity and design highly active catalysts for efficient AOPs.

Reduced Lattice Constant in Al-Doped LiMn2O4 Nanoparticles for Boosted Electrochemical Lithium Extraction

Extracting lithium selectively and efficiently from brine sources is crucial for addressing energy and environmental challenges. The electrochemical system employing LiMn2O4 (LMO) electrodes has been recognized as an effective method for lithium recovery. However, the lithium selectivity and stability of LMO need further enhancement for its practical applications. Herein, the Al-doped LMO with reduced lattice constant is successfully fabricated through a facile one-step solid-state sintering method, leading to enhanced lithium selectivity. The reduced lattice constant in Al-doped LMO is proved through spectroscopic analyses and theoretic calculations. Compared to the original LMO, the Al-doped LMO (LiAl0.05Mn1.95O4, LMO-Al0.05) exhibits highercapacitance, lower resistance, and improved stability. Moreover, the LMO-Al0.05 with reduced lattice constant can offer higher Li+ diffusion coefficient and lower intercalation energy revealed by cyclic voltammetry and multiscale simulations. When employed in hybrid capacitive deionization (CDI), the LMO-Al0.05 obtains a Li+ intercalation capacity of 21.7 mg g-1 and low energy consumption of 2.6 Wh mol-1 Li+. Importantly, the LMO-Al0.05 achieves a high Li+ extraction percentage (≈86%) with Li+/Na+ and Li+/Mg2+ selectivity of 1653.8 and 434.9, respectively, in synthetic brine. The results demonstrate that the Al-doped LMO with reduced lattice constant could be a sustainable solution for electrochemical lithium extraction.

Paint sludge derived activated carbon encapsulating with cobalt nanoparticles for non-radical activation of peroxymonosulfate

Industrial solid waste management and recycling are important to environmental sustainability. In this study, cobalt (Co) nanoparticles encapsulated in paint sludge-derived activated carbon (AC) were fabricated. The Co-AC possessed high conductivity, magnetic properties and abundant metal oxide impurities (TiAlSiOx), which was applied as multifunctional catalyst for peroxymonosulfate (PMS) activation. Compared to pure AC, the Co-AC exhibited significant enhanced performance for degradation of tetracycline hydrochloride (TCH) via PMS activation. Mechanism studies by in situ Raman spectroscopy, Fourier infrared spectroscopy, electrochemical analysis and electron paramagnetic resonance suggested that surface-bonded PMS (PMS*) and singlet oxygen (1O2) are the dominant reactive species for TCH oxidation. The non-radical species can efficiently oxidize electron-rich pollutants with high efficiency, which minimized the consumption of PMS and the catalyst. The removal percentages of TCH reached 97 % within 5 min and ∼ 99 % within 15 min in the Co-AC/PMS system. The Co active sites facilitated PMS adsorption to form the PMS* and the TiAlSiOx impurities provided abundant oxygen vacancy for generation of the 1O2. In addition, the Co-AC/PMS system achieved high efficiency and stability for oxidation of the target pollutants over a long-term continuous operation. This work not only offers a cost-effective approach for recycling industrial waste but also provides new insights into the application of waste-derived catalyst for environmental remediation.

Electronic structure modulation of iron sites with fluorine coordination enables ultra-effective H2O2 activation

Electronic structure modulation of active sites is critical important in Fenton catalysis as it offers a promising strategy for boosting H2O2 activation. However, efficient generation of hydroxyl radicals (•OH) is often limited to the unoptimized coordination environment of active sites. Herein, we report the rational design and synthesis of iron oxyfluoride (FeOF), whose iron sites strongly coordinate with the most electronegative fluorine atoms in a characteristic moiety of F-(Fe(III)O3)-F, for effective H2O2 activation with potent •OH generation. Results demonstrate that the fluorine coordination plays a pivotal role in lowering the local electron density and optimizing the electronic structures of iron sites, thus facilitating the rate-limiting H2O2 adsorption and subsequent peroxyl bond cleavage reactions. Consequently, FeOF exhibits a significant and pH-adaptive •OH yield (~450 µM) with high selectivity, which is 1 ~ 3 orders of magnitude higher than the state-of-the-art iron-based catalysts, leading to excellent degradation activities against various organic pollutants at neutral condition. This work provides fundamental insights into the function of fluorine coordination in boosting Fenton catalysis at atomic level, which may inspire the design of efficient active sites for sustainable environmental remediation.

Selective electrophilic attack towards organic micropollutants with superior Fenton-like activity by biochar-supported cobalt single-atom catalyst

The global shortage of freshwater and inadequate supply of clean water have necessitated the implementation of robust technologies for wastewater purification, and Fenton-like chemistry is a highly-promising approach. However, realizing the rapid Fenton-like chemistry for high-efficiency degradation of organic micropollutants (OMs) remains challenging. Herein, one novel system was constructed by a Co single-atom catalyst activating peroxymonosulfate (PMS), and the optimal system (SA-Co-NBC-0.2/PMS) achieved unprecedented catalytic performance towards a model OM [Iohexol (IOH)], i.e., almost 100% decay ratio in only 10 min (the observed rate constant: 0.444 min-1) with high electrophilic species 1O2 (singlet oxygen) generation. Theoretical calculations unveiled that Co-N4 sites preferred to adsorb the terminal-O of PMS (more negative adsorption energy than other O sites: -32.67 kcal/mol), promoting the oxidation of PMS to generate 1O2. Iodine (I)23 (0.1097), I24 (0.1154) and I25 (0.0898) on IOH with higher f- electrophilic values were thus identified as the main attack sites. Furthermore, 16S ribosomal RNA high-throughput sequencing and quantitative structure-activity relationship analysis illustrated the environmentally-benign property of the SA-Co-NBC-0.2 and the tapering ecological risk during IOH degradation process. Significantly, this work comprehensively checked the competence of the SA-Co-NBC-0.2/PMS system for organics abatement in practical wastewater.

Coagulation/co-catalytic membrane integrated system for fouling-resistant and efficient water purification

Low-pressure catalytic membranes allow efficient rejection of particulates and simultaneously removing organics pollutant in water, but the accumulation of dissolved organic matters (DOM) on membrane surface, which cover the catalytic sites and cause membrane fouling, challenges their stable operation in practical wastewater treatment. Here we propose a ferric salt-based coagulation/co-catalytic membrane integrated system that can effectively mitigate the detrimental effects of DOM. Ferric salt (Fe3+) serving both as a DOM coagulant to lower the membrane fouling and as a co-catalyst with the membrane-embedded MoS2 nanosheets to drive perxymonosulfate (PMS) activation and pollutant degradation. The membrane functionalized with 2H-phased MoS2 nanosheets showed improved hydrophilicity and fouling resistance relative to the blank polysulfone membrane. Attributed to the DOM coagulation and co-catalytic generation of surface-bound radicals for decontamination at membrane surface, the catalytic membrane/PMS/ Fe3+ system showed much less membrane fouling and 2.6 times higher pollutant degradation rate in wastewater treatment than the catalytic membrane alone. Our work imply a great potential of coagulation/co-catalytic membrane integrated system for water purification application.

Decoupled oxidation process enabled by atomically dispersed copper electrodes for in-situ chemical water treatment

In-situ wastewater treatment has gained popularity due to cost and energy savings tailored to water sources and user needs. However, this treatment, particularly through advanced oxidation processes (AOPs), poses ecological risks due to the need for strong oxidizing agents. Here, we present a decoupled oxidation process (DOP) using single-atom copper-modified graphite felt electrodes. This process creates a positive potential difference (ΔE ~ 0.5 V) between spatially isolated oxidants and organics and drives electron transfer-based redox reactions. The approach avoids the drawbacks of conventional AOPs, while being capable of treating various recalcitrant electron-rich organics. A floating water treatment device designed based on the DOP approach can degrade organic molecules in large bodies of water with oxidants stored separately in the device. We demonstrate that over 200 L of contaminated water can be treated with a floating device containing only 40 mL of oxidant (10 mM peroxysulphate). The modular device can be used in tandem structures on demand, maximizing water remediation per unit area. Our result provides a promising, eco-friendly method for in-situ water treatment that is unattainable with existing techniques.

Efficient treatment of actual glyphosate wastewater via non-radical Fenton-like oxidation

Compared to radical oxidative pathway, recent research revealed that non-radical oxidative pathway has higher selectivity, higher adaptability and lower oxidant requirement. In this work, we have designed and synthesized Cu2O/Cu nanowires (CuNWs), by pyrolysis of copper chloride and urea, to selectively generate high-valent copper (CuIII) upon H2O2 activation for the efficient treatment of actual glyphosate wastewater. The detailed characterizations confirmed that CuNWs nanocomposite was comprised of Cu0 and Cu2O, which possessed a nanowire-shaped structure. The electron paramagnetic resonance (EPR) analysis, in situ Raman spectra, chronoamperometry and liner sweep voltammetry (LSV) verified CuIII, which mainly contributed to glyphosate degradation, was selectively generated from CuNWs/H2O2 system. In particular, CuI is mainly oxidized by H2O2 into CuIIIvia dual-electron transfer, rather than simultaneously releasing OH• via single electron transfer. More importantly, CuNWs/H2O2 system exhibited the excellent potential in the efficient treatment of actual glyphosate wastewater, with 96.6% degradation efficiency and chemical oxygen demand (COD) dropped by 30%. This novel knowledge gained in the work helps to apply CuNWs into heterogeneous Fenton-like reaction for environmental remediation and gives new insights into non-radical pathway in H2O2 activation.

Precise coordination of high-loading Fe single atoms with sulfur boosts selective generation of nonradicals

Nonradicals are effective in selectively degrading electron-rich organic contaminants, which unfortunately suffer from unsatisfactory yield and uncontrollable composition due to the competitive generation of radicals. Herein, we precisely construct a local microenvironment of the carbon nitride-supported high-loading (~9 wt.%) Fe single-atom catalyst (Fe SAC) with sulfur via a facile supermolecular self-assembly strategy. Short-distance S coordination boosts the peroxymonosulfate (PMS) activation and selectively generates high-valent iron-oxo species (FeIV=O) along with singlet oxygen (1O2), significantly increasing the 1O2 yield, PMS utilization, and p-chlorophenol reactivity by 6.0, 3.0, and 8.4 times, respectively. The composition of nonradicals is controllable by simply changing the S content. In contrast, long-distance S coordination generates both radicals and nonradicals, and could not promote reactivity. Experimental and theoretical analyses suggest that the short-distance S upshifts the d-band center of the Fe atom, i.e., being close to the Fermi level, which changes the binding mode between the Fe atom and O site of PMS to selectively generate 1O2 and FeIV=O with a high yield. The short-distance S-coordinated Fe SAC exhibits excellent application potential in various water matrices. These findings can guide the rational design of robust SACs toward a selective and controllable generation of nonradicals with high yield and PMS utilization.

Fenton-like activity and pathway modulation via single-atom sites and pollutants comediates the electron transfer process

The studies on the origin of versatile oxidation pathways toward targeted pollutants in the single-atom catalysts (SACs)/peroxymonosulfate (PMS) systems were always associated with the coordination structures rather than the perspective of pollutant characteristics, and the analysis of mechanism commonality is lacking. In this work, a variety of single-atom catalysts (M-SACs, M: Fe, Co, and Cu) were fabricated via a pyrolysis process using lignin as the complexation agent and substrate precursor. Sixteen kinds of commonly detected pollutants in various references were selected, and their lnkobs values in M-SACs/PMS systems correlated well (R2 = 0.832 to 0.883) with their electrophilic indexes (reflecting the electron accepting/donating ability of the pollutants) as well as the energy gap (R2 = 0.801 to 0.840) between the pollutants and M-SACs/PMS complexes. Both the electron transfer process (ETP) and radical pathways can be significantly enhanced in the M-SACs/PMS systems, while radical oxidation was overwhelmed by the ETP oxidation toward the pollutants with lower electrophilic indexes. In contrast, pollutants with higher electrophilic indexes represented the weaker electron-donating capacity to the M-SACs/PMS complexes, which resulted in the weaker ETP oxidation accompanied with noticeable radical oxidation. In addition, the ETP oxidation in different M-SACs/PMS systems can be regulated via the energy gaps between the M-SACs/PMS complexes and pollutants. As a result, the Fenton-like activities in the M-SACs/PMS systems could be well modulated by the reaction pathways, which were determined by both electrophilic indexes of pollutants and single-atom sites. This work provided a strategy to establish PMS-based AOP systems with tunable oxidation capacities and pathways for high-efficiency organic decontamination.

N, S, and Cl tri-doped carbon boost the switching of radical to non-radical pathway in Fenton-like reactions: Synergism of N species and defects

Heteroatom doping represents a promising strategy for enhancing the generation of singlet oxygen (1O2) during the activation of peroxymonosulfate (PMS) using carbon-based catalysts; however, it remains a formidable challenge. In this study, we systematically controlled the structure of metal-free carbon-based materials by introducing different heteroatoms to investigate their efficacy in degrading organic pollutants in water via PMS activation. The results of reactive oxygen species detection showed that the dominant free radical in the four samples was different: CN (•SO4- and •OH), CNS (•O2-), CNCl (1O2), and CNClS (1O2). This led to the transformation of active species from free radicals to non-free radicals. The tri-doped carbons with nitrogen, sulfur, and chlorine (CNClS) exhibited exceptional performance in PMS activation and achieved a remarkable degradation efficiency of 95% within just 6 min for tetracycline. Moreover, a strong linear correlation was observed between the ratio of pyridine-N/graphite-N and ID/IG with the yield of 1O2, indicating that N species and defects play a crucial role in CNClS as they facilitate the transition from radical to non-radical pathways during PMS activation. These findings highlight the possibility that adjustable tri-heteroatom doping will expand the Fenton-like reaction for the treatment of actual wastewater.