Single Cobalt Atoms Anchored on Porous N-Doped Graphene with Dual Reaction Sites for Efficient Fenton-like Catalysis

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.

Mo doping modulates peroxymonosulfate activation of cobalt carbon nanotube-based catalysts for efficient multi-pollutants removal: Oxygen vacancies trigger the evolution of high-valence cobalt-oxo species

Formation of defective catalysts with oxygen-rich vacancies via ion doping represents an advanced strategy for enhancing catalytic activity. Cobalt oxides supported on carbon nanotubes (CNTs) were strategically designed to enhance peroxomonosulfate (PMS) through molybdenum (Mo)-doped oxygen vacancies (Vo) management to achieve the application of high-valent cobalt oxygen (Co(IV)O) dominated degradation mechanism. The first-order rate constant for tetracycline hydrochloride degradation in the CoMo/CNTs/PMS system (0.081 min-1) was twice that of the Co/CNTs system. Additionally, the system exhibited high resistance to interference and excellent pH adaptability. The system demonstrated a high removal efficiency (91.3 %-100 %) for the emerging contaminant (sodium p-perfluorous nonenoxybenzene sulfonate), as well as other organic pollutants such as carbamazepine and imidacloprid. The prepared catalyst membranes exhibited stability and effectively degraded tetracycline hydrochloride over 10 h of continuous-flow experiments, highlighting their potential for practical applications. Theoretical calculations revealed that molybdenum doping reduced the formation energy of oxygen vacancies, while these vacancies shifted the d-band center of cobalt (Co) in CoMo/CNTs upward, bringing it closer to the Fermi energy level. Furthermore, enhanced charge transfer and stronger peroxide bond stretching were observed during PMS adsorption, thus promoting the chemical reaction of PMS adsorbed on CoMo/CNTs. More significantly, the oxygen-rich vacancies in CoMo/CNTs lowered the energy barrier for Co(IV)=O generation. This study provides insights into the mechanism of ionic doping in PMS activation by metal-based catalysts, thereby expanding the application of defective catalysts in environmental remediation.

Advances in the Structure-Activity Relationship of Electrocatalytic C-N Coupling: From Nanocatalysis to Single Metal Site Catalysis

C-N coupling is crucial for constructing amides and amines and involves various fields, including medicine, chemical industries, agriculture, and energy. With the rapid development of electrocatalytic C-N coupling and the continuous improvement of catalytic performance, this field has aroused extensive research interest. A comprehensive review is urgently needed to summarize the structure-activity relationship, key challenges, and future development directions. This review provides a concise overview of the recent advancements from nanocatalysis to single metal site catalysis for electrocatalytic C-N coupling reactions. We summarize the C-N coupling mechanisms using different nitrogen sources and further analyze the influences of various active metal centers and different coordination environments on the C-N coupling performance, thereby elucidating the structure-activity relationship. Moreover, we discuss the dynamic structural evolution of active metal sites during the reaction. Finally, we present current challenges and perspectives in this field. This review aims to provide valuable insights into the development of advanced nano/single metal site catalysts for electrocatalytic C-N coupling reactions along with a deeper understanding of catalytic mechanisms.

Sonicated Carbon Nanotube Catalysts for Efficient Point-of-use Water Treatment

The rising demand for freshwater and increasing contamination of distributed water sources, such as stormwater and surface water, necessitate innovative point-of-use treatment technologies. Advanced oxidation processes (AOPs) using solid oxidants offer a promising approach for decentralized freshwater production but are often limited by nonselective radical reactions that degrade both pollutants and background water constituents. Here, sonicated carbon nanotubes (CNTs) that efficiently activate peroxymonosulfate are demonstrated, enabling selective contaminant degradation via dual nonradical pathways-singlet oxygen oxidation and direct electron transfer. Optimized sonication introduces catalytically active carbonyl (C═O) groups on CNT surfaces while preserving their graphitic structure, ensuring rapid electron transfer. This approach achieves 2,4-dichlorophenol removal, a common industrial and municipal pollutant, within 5 min at a record removal rate of 4.80 µmol g-1 s-1. Furthermore, scalable CNT catalyst synthesis and integration into flat membrane and hollow fiber filtration devices, ensuring long-term stability and efficient pollutant removal in natural river water, are demonstrated. By advancing selective CNT catalysts for AOPs, this work offers a scalable, sustainable solution for point-of-use freshwater production in real-world applications.

Oxygen-Independent Sulfate Radical and Fe2+-Modified Implants for Fast Sterilization and Osseointegration of Infectious Bone Defects

Currently, emerging dynamic therapy has gradually become a frequently used strategy for treating infectious bone defects via a rise in reactive oxygen species (ROS) levels, which can bring about oxidative harm to bacteria. However, ROS can be generated only under conditions of exogenous energy, limited by energy penetration or dependence on the existence of internal O2/H2O2. Thus, we designed Na2S2O8-decorated polyetheretherketone implants activated by Fe2+ for infected bone defects. In vitro experiments show that they generate sulfate radical (·SO4-) and hydroxyl radical (·OH) without O2/H2O2 existence, effectively killing bacteria. Additionally, the released Fe2+ enters bacteria and triggers ferroptosis-like death via lipid peroxidation. In vivo experiments show implants achieve an ideal effect of bone integration through a high-efficiency bactericidal effect and enhanced osteogenic activity. As envisioned, our proposed strategy offers a promising approach to halt refractory infection of bone tissue by autonomously catalyzing ROS storms and ferroptosis-like death, facilitating bone-defect recovery.

From Single-Atom to Dual-Atom: A Universal Principle for the Rational Design of Heterogeneous Fenton-like Catalysts

Developing efficient heterogeneous Fenton-like catalysts is the key point to accelerating the removal of organic micropollutants in the advanced oxidation process. However, a general principle guiding the reasonable design of highly efficient heterogeneous Fenton-like catalysts has not been constructed up to now. In this work, a total of 16 single-atom and 272 dual-atom transition metal/nitrogen/carbon (TM/N/C) catalysts for H2O2 dissociation were explored systematically based on high-throughput density functional theory and machine learning. It was found that H2O2 dissociation on single-atom TM/N/C exhibited a distinct volcano-type relationship between catalytic activity and •OH adsorption energy. The favorable •OH adsorption energies were in the range of -3.11 ∼ -2.20 eV. Three different descriptors, namely, energetic, electronic, and structural descriptors, were found, which can correlate the intrinsic properties of catalysts and their catalytic activity. Using adsorption energy, stability, and activation energy as the evaluation criteria, two dual-atom CoCu/N/C and CoRu/N/C catalysts were screened out from 272 candidates, which exhibited higher catalytic activity than the best single-atom TM/N/C catalyst due to the synergistic effect. This work could present a conceptually novel understanding of H2O2 dissociation on TM/N/C and inspire the structure-oriented catalyst design from the viewpoint of volcano relationship.

Electrical activation of periodate by nano-zero-valent cobalt/nitrogen-doped carbon for sulfisoxazole degradation: Insights into rapid electron transfer mechanisms

Periodate (PI) activation via three-dimensional electrochemical (E) is a promising approach for degrading sulfisoxazole (SIZ), while the scarcity of active sites significantly limits the efficient electron-transfer rate. Herein, we synthesized multiple strongly active zero-valent cobalt (Co0) nanoparticles encapsulated in nitrogen-doped carbon (NC) shells through Co-potassium chloride (KCl) doping pyrolysis of Zeolitic Imidazolate Framework-8 (ZIF-8) to induce the rapid electron transfer pathways (ETP). Specifically, molten KCl doping provides confined structures for Co0 with a diameter of 12.57 nm embedded in the NC shell, thereby expanding the active space of Co0/NC. The generated Co0/NC exhibited an enormous electrochemically active surface area (ECSA, 736.92 cm2/mg), low charge transfer resistance (Rct, 38.50 Ω), and strong adsorption energy (-6.003 eV), which together promote robust electron transfer kinetics. Capitalizing on these properties, the E-Co0/NC-PI system achieved 100% SIZ removal at a degradation rate of 1.587 min-1 under near-neutral (pH 5.00-9.00) conditions, with ultra-low energy consumption (0.011 kWh m-3, $0.125/L). This study highlights a Co0/NC-induced rapid ETP for SIZ removal, offering insights into enhanced electrical activation of PI for wastewater treatment.

CoOx/CeO2@C nanopetals derived Cobalt-Cerium Prussian blue with enhanced Dual-Enzyme mimetic activity for detection of ascorbic acid in rat brain during calm/ischemic processes

In this study, we demonstrate that a highly efficient colorimetric sensor prepared from carbon-shielded Co-Ce Prussian blue analog (PBA) nanopetals (CoOx/CeO2@C) by green chemical deposition method and thermal annealing processes for detection of ascorbic acid (AA) in cerebral microdialysis fluids. The synthesized CoOx/CeO2@C showed high dual-mimetic activity, i.e., peroxidase- and catalase-like activity, and great catalytic stability. The combination of carbon film and Co-Ce PBA nanopetals (1) greatly enhances the interfacial electron transfer rate of the nanopetals due to excellent electrical conductivity of carbon, and (2) protects nanopetals from acidic chemical environments during the catalytic process, which greatly reduces loss of the catalytic activity of the cobalt-cerium (hydroxide) oxides. Based on the peroxidase-like property of CoOx/CeO2@C nanopetals, this sensor has a good linear range from 0.1 to 150 μM with a low detection limit of 0.04 μM, i.e., improved sensitivity for AA colorimetric measurement. The developed colorimetric strategy with a green synthetic pathway, catalytic stability and wide linear range confirms the monitoring of AA in brain systems during calm/ischemic processes.

Coordination Anions Dimensionality-Engineered Dual-Atom Catalysts for Enhanced Fenton-Like Reactions: 3D Coordination Induced Spin-State Transition

Dual-atom catalysts (DACs) have shown significant application potential in Fenton-like reactions. However, effectively modulating their electronic structure and fully understanding the mechanisms driving their high catalytic activity remain challenging. Herein, we propose a coordination anions dimensionality engineering strategy to synthesize biomass-derived dual-atom FeCo-N4O1C catalysts, in which Fe and Co atoms are bridged by two-dimensional planar N atoms and a three-dimensional (3D) axial O atom. Experimental data and theoretical calculations reveal that the 3D coordination structure of FeCo-N4O1C induces the spin state of Fe undergo a transition from a low spin state to an intermediate spin state compared with single-atom Fe-N4O1C, resulting in moderate adsorption and desorption of intermediates, thus reducing the energy barriers for generating more singlet oxygen and high-valent cobalt-oxo species during peroxymonosulfate activation. The electron transfer from Co atoms to neighboring Fe atoms through N atoms and 3D axial O atoms can effectively prevent the poisoning of active species. Benefiting from the 3D coordination structure and the synergistic effects of multiple active sites, the catalyst-dose normalized reaction rate constant reaches 14.5 L min-1 g-1 under low peroxymonosulfate concentrations─an improvement of 1 ∼ 2 orders of magnitude over most reported catalysts. The practical applicability of FeCo-N4O1C is demonstrated through nearly 100% pollutant removal during 7 days of continuous operation in a membrane filtration system. This study provides deep insights into the relationship between electronic structure and catalytic performance through spin-state regulation of DACs, and introduces a promising approach for large-scale synthesis of low-cost, highly efficient DACs for Fenton-like reactions.

Enhancing 1O2 Generation Performance by Regulating C and N Coordination for Efficient Fenton-Like Catalytic Process

Singlet oxygen (1O2), a vital reactive species, exhibits excellent organic pollutant degradation selectivity in Fenton-like reactions. Recognizing and controlling the structure-activity relationship of single-atom catalysts (SACs) is essential to achieving the highly efficient and selective generation of 1O2 for various practical applications. Here, three iron single-atom catalysts with different coordination configurations (FeSAC─N4, FeSAC─N3-C1, and FeSAC─N2─C2) are prepared to modulate the selective generation of 1O2 by activating peroxymonosulfate (PMS). Replacing N coordinated to Fe atoms with C increases 1O2 selective generation thus enhancing the Fenton-like reaction activity. Specifically, FeSAC─N2─C2 presents the optimal catalytic activity, high stability, and environmental tolerance. Moreover, the 1O2 selectivity increases as the N coordination number decreases, which is in the order of FeSAC─N4 (73%) < FeSAC─N3─C1 (82%) < FeSAC─N2─C2 (90%). DFT calculations demonstrate that replacing N with C enhances the electrophilicity and electron transfer capacity, optimizes the d-band center, facilitates reactant adsorption, and reduces the energy barrier, thus facilitating 1O2 production and enhancing the Fenton-like reaction activity. This study reveals the underlying catalytic trends and mechanisms of catalyst structure-activity relationships for high selective generation of 1O2 by PMS activation, thus providing guidance for developing catalysts capable of highly selective organic pollutant degradation.

Precise manipulation of iron spin states in single-atom catalytic membranes for singlet oxygen selective production

Heterogeneous single-atom catalysts are attracting substantial attention for selectively generating singlet oxygen (1O2). However, precise manipulation of atom coordination structures remains challenging. Here, the fine coordination structure of iron single-atom carbon-nitride catalysts (Fe-CNs) was manipulated by precisely tuning the heating rate with 1 °C min-1 difference. Multiple techniques in combination with density functional theory (DFT) calculations reveal that FeN6 coordination sites with high Fe spin states promote the adsorption, electron transfer, and dissociation of peroxymonosulfate (PMS), resulting in nearly 100% selection of 1O2 generation. A lamellar single atom catalytic membrane is constructed, exhibiting high permeance, high degradation, high-salinity resistance and sustained operation stability. This work provides ideas for regulating spin states of the metal site to fabricate catalysts with selective 1O2 generation for membrane separation and environment catalysis applications.

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.

In situ self-cleaning removal of emerging organic contaminants with covalent organic framework armed with arylbiguanide

An in situ self-cleaning covalent organic framework featuring arylbiguanide arms (Aryl-BIG-COF) was first developed to remove emerging organic pollutants such as propranolol (PRO) from water. The main breakthroughs addressed the scarcity of functional active sites, the impracticality of ex situ regeneration, and the rapid recombination of electronhole pairs in the application of COFs. Owing to the directional capture ability and electronic structure regulation of the arylbiguanide arms, the adsorption capacity and photocatalytic degradation rate of the newly synthesized COF increased by nearly four and seven times, respectively. Its self-cleaning ability, driven by the photocatalytic regeneration of active sites, enabled in situ removal of PRO and sustained over 90 % removal efficiency after six cycles. Moreover, it demonstrated broad applicability for removing PRO and other emerging pollutants, such as bisphenol A (BPA), tetracycline (TC), and norfloxacin (NOR), across various water matrices with less residual toxicity. The coexisting organic matter and ions in natural water promoted the removal of PRO. The enhancement mechanism involved arylbiguanide arms narrowing the band gap and inducing local charge polarization, thereby increasing the separation efficiency of electronhole pairs. This work provides significant insights into the structural design and practical applications of COFs for purifying water.

Bimetallic-nitrogen-carbon aerogel Co/Ni-N-C derived from 2D ordered nanosheet arrays activate PMS-AOPs for effective antibiotic removal: performance, mechanism, and toxicity

In recent years, peroxymonosulfate-based advanced oxidation processes (PMS-AOPs) have garnered increasing attention for their efficacy in eliminating persistent organic pollutants. Metal-nitrogen-carbon (M-N-C) materials are frequently employed as efficient catalysts for the activation of PMS, leading to the effective production of various reactive species. In this study, a novel 3D porous cobalt/nickel bimetallic-nitrogen-carbon aerogel (Co/Ni-N-C) with well-dispersed CoNi-nanosheets that enhance electron transfer and provide a large active surface area was prepared through an in situ growth and a straightforward pyrolysis procedure of 2D cobalt/nickel metal-organic framework (CoNi-MOF) which was contained by a bamboo cellulose aerogel as a precursor. Rapid tetracycline (TC) removal (efficiency of 99.83% and mineralization rate of 69.8%) was achieved via PMS activation, facilitated by a synergistic enhancement effect of well-dispersion CoNi-nanosheet array. The evenly dispersed Co/Ni-N active sites and high Co:Ni ratio (PCo:Ni = 0.21) producing multiple reactive oxygen species (ROS) were essential in accelerating removal of contaminant. The toxicity assessment results of the intermediates further confirmed that the catalytic degradation in the Co/Ni-N-C-800/PMS system reduced the ecological toxicity of TC through dehydroxylation, demethylation, ring-opening, and deamidation. Furthermore, the Co/Ni-N-C-800/PMS system demonstrated exceptional degradation efficiency for various aromatic compounds with diverse substituents and showed good cyclic stability. These findings offer insights into the development of highly effective bimetallic-nitrogen-carbon catalytic materials.

Size-Dependent Fe-Based Catalysts for the Catalytic Transfer Hydrogenation of α,β-Unsaturated Aldehydes

Metal-based catalysts ranging from nanoparticles (NPs) to the atomic level usually exhibit varying catalytic performance. The underlying size effect is both fascinating and evident. This study thoroughly investigates the size-dependent effects of Fe-based catalysts on catalytic transfer hydrogenation (CTH) of furfural (FF) at the atomic level. Fe was precisely loaded onto N-doped porous carbon in three forms: single atoms (Fe-SAs/NC), atomic clusters (Fe-ACs/NC), and nanoparticles (Fe-NPs/NC). This was achieved through meticulous control of the iron precursor composition. Remarkably, Fe-SAs/NC exhibited exceptional catalytic efficiency, achieving an FF conversion of 91.3% and a turnover frequency (TOF) of 262.3 h-1 at 110 °C, which is 9.2 times higher than Fe-ACs/NC and an impressive 93.7 times higher than Fe-NPs/NC. The high selectivity of Fe-SAs/NC toward furfuryl alcohol was further substantiated by theoretical calculations. These calculations indicated the benefits from the η1(O)-aldehyde adsorption configuration, formed by the vertical adsorption of FF molecules on the Fe-N4 active sites. Geometrical optimization of the catalyst at the atomic scale enhances its intrinsic catalytic activity and selectivity. The proposed size effect on catalytic activity provides deeper insights into the mechanism of single-atom catalytic hydrogenation and contributes to the exploration of high-performance catalysts at the atomic level.

Rational construction of porous cobalt nanoparticle integrated nitrogen doped hollow carbon nanostructures for peptide agonist exendin-4 biosensing

In this study, we designed a point-of-care (POC) testing electrochemical biosensor using an integrated biosensing assay based on hollow-like nitrogen-doped carbon nanostructures combined with cobalt nanoparticles (Co@HNCNs, Co3O4@HNCNs, and CoP@HNCNs). These are functionalized with Anti-Exendin-4 Antibodies (Anti-Ex-4-Abs) and Bovine Serum Albumin (BSA) to create sensitive probes (Co@HNCNs/Anti-Ex-4-Abs/BSA, Co3O4@HNCNs/Anti-Ex-4-Abs/BSA, and CoP@HNCNs/Anti-Ex-4-Abs/BSA) for the ultrasensitive detection of exendin-4 (Ex-4), a peptide agonist used in the treatment of type 2 diabetes mellitus (T2DM). Among the cobalt-based carbon nanostructures, the Co3O4@HNCNs/Anti-Ex-4-Abs/BSA nanoprobe demonstrated superior ability to specifically recognize Ex-4. This was indicated by a significant decrease in the chronoamperometric (CA) i-t current response, facilitating low-level detection of Ex-4. The nanoprobe was capable of detecting Ex-4 concentrations ranging from 1.0 to 90.0 pM, with a sensitivity of 0.60 μA/pM and a limit of detection (LOD) of 0.46 pM (S/N = 3). Furthermore, the Co3O4@HNCNs/Anti-Ex-4-Abs/BSA nanoprobes demonstrated the ability to detect nanomolar levels of Ex-4 in blood serum and urine samples, achieving satisfactory recovery rates of 96-104%. The proposed electrostatic interaction chemistry approach establishes a remarkable platform for constructing a peptide agonist biosensor that is effective for detecting Ex-4 in real human serum and urine samples.

Synergistic activation of peroxymonosulfate by highly dispersed iron-based sulfur-nitrogen co-doped porous carbon for bisphenol a removal: mechanistic insights and selective oxidation

Efficient and pervasive solutions are urgently needed to mitigate pollution from emerging contaminants in aquatic environments. Activation of peroxymonosulfate (PMS) is commonly employed to remove refractory organic pollutants from water. Herein, we synthesized sulfur-nitrogen co-doped porous carbon materials loaded with highly dispersed iron species (FeSNC) using template-assisted and ligand site construction methods. The uniform doping of N, S, and Fe in the carbon substrate, along with their synergistic effects, significantly enhanced catalytic activity by creating a high degree of defects in the catalyst (I D/I G = 1.47). This enhancement facilitated efficient removal of BPA, achieving an apparent rate constant of up to 2.83 min-1, which was 30 times higher than that of SNC and 6 times higher than that of FeNC. The FeSNC/PMS system demonstrated robust catalytic stability across the pH 3-9 range, and showed minimal sensitivity to environmental factors like the aqueous matrix, with low iron ion dissolution (<0.01 mg L-1) and certain reusability. Mechanistic investigations employing quenching experiments, EPR tests, probe experiments, and electrochemical tests elucidated that the system catalyzed the degradation of BPA via two non-radical pathways: high-valent iron oxidation and singlet oxygen pathways. Additionally, the system further exhibits selective degradation of electron-rich organics (e.g., 4-chlorophenol, sulfamethoxazole, ofloxacin, etc.).

Excellent bisphenol A removal performance triggered by electron-transfer regime on cobalt phosphide embedded in nitrogen, sulfur-doped carbon/MXene

The non-radical pathway dominated by the electron transfer process (ETP) has gained considerable attention for the removal of organic contaminants in persulfate-based advanced oxidation processes. Rationally designing new catalysts with optimized composition and structural merits and further elucidating the enhanced removal mechanism are of great importance. In this work, we successfully synthesized a nitrogen-sulfur co-doped carbon encapsulated cobalt phosphide (Co2P) on both sides of MXene nanosheets (MZPC) to degrade bisphenol A (BPA) from organic wastewater. The results indicated that BPA was degraded by 98.2 % in a mere 5 min using 0.1 g L-1 of peroxymonosulfate (PMS) and 0.05 g L-1 of the optimized catalyst (MZPC-9), exhibiting an excellent pseudo-first-order kinetics rate constant (k = 1.485 min-1). Uniformly dispersed Co2P nanoparticles (approximately 9.4 nm, calculated using the Scherrer equation) on both sides of MXene exhibited enhanced binding affinity with PMS, forming the MZPC-9-PMS* metastable complexes with potent oxidative capability. The resultant MZPC-9-PMS* complexes induced the polymerization reaction of BPA and achieved 81 % total organic carbon (TOC) removal. This study offers a novel perspective on the design of metal active centers to enhance the ETP-dominated non-radical pathway for pollutant degradation.

Nanoscale-Confined Synthesis of 2D Metal Compounds for Electrochemical Applications

2D metal compounds, such as transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), and MXenes, are emerging as important electrocatalyst materials in the transition to a sustainable energy future. Aided by their high surface area, electrical conductivity, and tunable electronic properties, these materials have provided a crucial research thrust in enhancing the efficiency of green hydrogen production, fuel cells, and carbon reduction processes. Most importantly, the synthesis of nanostructured 2D compounds, while challenging, is the key to optimizing their catalytic performance. Recent advancements in this field have highlighted the potential of 2D metal compounds in revolutionizing energy conversion technologies, which entails the discovery of new material compositions, the development of novel synthetic routes, and the integration of these materials into practical energy conversion systems. This review presents an overview of the distinctive characteristics of nanoscale-confined 2D metal compounds, the challenges encountered in their synthesis, and electrochemical applications.

Single-Atom Iridium-doped Carbon Dots Nanozyme with High Peroxidase-Like Activity as Colorimetric Sensors for Multimodal Detection of Mercury Ions

Nanozyme-based colorimetric sensors are promising approaches for environmental monitoring, food safety, and medical diagnostics. However, developing novel nanozymes that exhibit high catalytic activity, good dispersion in aqueous solution, high sensitivity, selectivity, and stability is challenging. In this study, for the first time, single-atom iridium-doped carbon dot nanozymes (SA Ir-CDs) are synthesized via a simple in situ pyrolysis process. Doping carbon dots with iridium in the form of single atoms to achieve maximum atomic utilization not only enhances peroxidase (POD)-like activity to 178.81 U mg-1 but also improves the dispersibility of single-atom nanozymes in aqueous solutions over 30 days. Hence, the SA Ir-CD colorimetric platform is developed for mercury ions (Hg2+) detection and exhibited a good linear relationship from 0.01 to 10 µm and a detection limit of 4.4 nm. Notably, the changes in color can be observed not only through the naked eye but also via a smartphone, enabling convenient field and onsite monitoring without the need for sophisticated analytical equipment. In this study, an approach for fabricating single-atom metal-based carbon dot nanozymes with high POD-like activity is developed, and a new effective and easy-to-use colorimetric sensor for Hg2+ detection is constructed.

Temperature-modulated morphological changes in MIL-88B(Fe)-derived iron-based materials triggering generation of the peroxymonosulfate nonradical pathway to degrade carbamazepine: The key role of iron nanoparticles and CN

Temperature modulation of the synthesis process of MOF-derived composites is not well understood for changes in the peroxymonosulfate catalytic domain. This study synthesized a carbon-based nitrogen-doped (MN@C) MOF-derived composite catalyst derived from MIL-88B(Fe) (Materials Institute Lavoisier) by modulating temperature changes and calcination. Combined with density-functional theory calculations (DFT) analyses showed that changes in iron nanoparticles (FeNP) and CN content caused the alterations of the degradation pathways. MN@C-9 exhibited outstanding activation performance (100 % carbamazepine (CBZ) removal within 10 min). The system maintained efficient operation in different aqueous environments and a wide pH range and demonstrated efficient removal of many pollutants typical of pharmaceuticals and personal care products (PPCPs). After comprehensively analyzing the results of liquid chromatography mass spectrometry (LC-MS) and toxicity prediction, the possible degradation pathways were reasonably speculated, and the toxicity of the byproducts was greatly reduced. This study provides a potential and efficient catalyst preparation strategy for water purification.

Removal of Di (2-ethylhexyl) phthalate from groundwater by sodium persulfate activated by hollow micron zero-valent iron: Reaction mechanism and degradation path

In this study, hollow micron zero-valent iron (H-mZVI) was prepared using the ethylenediamine liquid phase reduction method. The microstructures were characterized by SEM, XRD, BET and FTIR. The results showed that H-mZVI possessed a spherical hollow structure with a particle size of approximately 1 μm. The density of H-mZVI was notably lower compared to solid micron zero-valent iron (S-mZVI). Furthermore, with an increase in ethylenediamine addition, the density initially decreased before stabilizing. Results demonstrated that the degradation efficiency of H-mZVI/PS for DEHP was 2.96 times higher than that of S-mZVI/PS. The charge density of H-mZVI/PS degradation DEHP system was higher than that of S-mZVI/PS system, and H-mZVI exhibited a fast electron migration rate and strong electron transport ability between the solution and the interface material. The degradation of DEHP by H-mZVI/PS system was carried out jointly by the surface reaction on the surface of H-mZVI particles and the homolytic reaction led by Fe2+ ions in the solution. Additionally, the contribution rate of free radicals in the degradation process of DEHP was in the order SO4-· > ·OH > 1O2. There were three degradation pathways of DEHP in H-mZVI/PS system, and the toxicity of DEHP degradation products was significantly lower than that of the parent.

Co3O4 with the Enhancement of Peroxymonosulfate Adsorption Capacity by Rare Earth Europium-Doping for High-Efficiency Organic Dye Degradation

Cobalt-based metal-organic framework (MOFs)-derived catalysts are acknowledged for their effectiveness in activating peroxymonosulfate (PMS) for the treatment of persistent pollutants. However, the limited adsorption of PMS on the catalyst surface markedly reduces its degradation efficiency. To overcome this limitation, nanoflower-like Eu2O3/Co3O4-0.3 catalysts were successfully fabricated by incorporating europium (Eu) into cobalt-based MOF via the hydrothermal and calcination techniques. The doping of Eu not only enhances the adsorption of more PMS on the catalyst's surface but also serves as an electron transfer mediator to regulate the Co2+/Co3+ redox cycle and promote the generation of oxygen vacancies (OV). The catalyst Eu2O3/Co3O4-0.3 was used to activate PMS for the degradation of rhodamine B (RhB), and it was found that the degradation rate constant (k) of the Eu2O3/Co3O4-0.3/PMS system was approximately 8 times higher than that of the Co3O4/PMS system, achieving complete degradation within 20 min. Furthermore, Eu2O3/Co3O4-0.3 exhibited excellent mineralization capacity, stability, and recyclability. Trapping experiments indicated that singlet oxygen (1O2) is the primary active species, suggesting that this material is applicable in complex aqueous environments. Density Functional Theory (DFT) calculations revealed that the adsorption energy (Eads) of PMS on the Eu2O3 surface is -4.05 eV, which is much greater than that on Co3O4 (Eads = -0.32 eV). This study provides a new method for designing nonhomogeneous catalysts to activate PMS for efficient degradation of pollutants.

MXenes Spontaneously Form Active and Selective Single-Atom Centers under Anodic Polarization Conditions

Single-atom catalysts (SACs) have emerged as a new class of materials for the development of active and selective catalysts. These materials are commonly based on anchoring a noble transition metal to some kind of carrier. In the present work, we demonstrate that MXenes─two-dimensional materials with application in energy storage and conversion─spontaneously form SAC-like sites under anodic polarization conditions, using the applied electrode potential as a probe to form catalytically active surface sites reminiscent of a SAC-like structure. Combining ab initio molecular dynamics simulations and electronic structure calculations in the density functional theory framework, we demonstrate that only the SAC-like sites rather than the basal planes of MXenes are highly active and selective for the oxygen evolution or chlorine evolution reactions, respectively. Our findings may simplify synthetic routes toward the formation of active and selective SAC-like sites and could pave the way for the development of smart materials by incorporating fundamental principles from nature into material discovery: while the pristine form of the material is inactive, the application of an electrode potential activates the material by the formation of active and selective single-atom centers.

Selective generation of hydroxyl and sulfate radicals under electric field regulation for micropollutants degradation: Mechanism and structure-activity relationship

Peroxymonosulfate (PMS) activation generates potent reactive oxygen species (ROS) such as sulfate radical (SO4·-) and hydroxyl radical (·OH), which play a key role in organic pollutant degradation. However, controlling the generation of these free radicals remains challenging. In this study, various metal (Co, Ni, and Cu)-doped nitrogen carbon compounds (NCs) were synthesized, and their performance in PMS activation under electric field regulation was explored to modulate ROS production for selective pollutant degradation. Bisphenol A (BPA), a readily degradable compound, and ibuprofen (IBU), a recalcitrant pollutant, were chosen as model pollutants to assess degradation efficiency. All catalysts achieved over 95 % BPA removal without the electric field, but the application of an electric field significantly accelerated BPA degradation, achieving complete removal within 3 min. In contrast, IBU degradation showed significant variation depending on the catalyst used and the electric field intensity, with Cu-NC demonstrating the highest performance, enhancing the degradation rate by 3.78-fold. Mechanistic studies revealed that the electric field altered the electron density on the catalyst surface, shifting ROS production from SO4·- to·OH in Co-NC systems. The findings could provide valuable insights into PMS activation under electric field regulation, offering a novel strategy for enhancing micropollutant removal through controlled ROS generation.

Nano-island-encapsulated cobalt single-atom catalysts for breaking activity-stability trade-off in Fenton-like reactions

Single-atom catalysts (SACs) have been increasingly acknowledged for their performance in sustainable Fenton-like catalysis. However, SACs face a trade-off between activity and stability in peroxymonosulfate (PMS)-based systems. Herein, we design a nano-island encapsulated single cobalt atom (CoSA/Zn.O-ZnO) catalyst to enhance the activity and stability of PMS activation for contaminant degradation via an "island-sea" synergistic effect. In this configuration, small carrier-based ZnO nanoparticles (the "islands") are utilized to confine and stabilize Co single atoms. The expansive ZnO substrate (the "sea") upholds a neutral microenvironment within the reaction system. The CoSA/Zn.O-ZnO/PMS system exhibits a remarkable selectivity in exclusively generating sulfate radicals (SO4•-), leading to a complete removal of various recalcitrant pollutants within a shorter period. Characterized by minimal leaching of active sites, robust catalytic performance, and low-toxicity decontamination, this system proves highly efficient in multiple treatment cycles and complex water matrices. The design effectively breaks the activity-stability trade-off typically associated with SACs.

Highly effective catalytic degradation of bisphenol A through activation of peroxymonosulfate by an Fe-Nx structure anchored on novel lignin-based graphitic biochar: Electron transfer mechanism

A lignin-based Fe/N co-doped carbonaceous catalyst was synthesized via freeze-drying followed by pyrolysis to activate peroxymonosulfate (PMS) for efficient degradation of bisphenol A (BPA). The Fe/N co-doped biochar exhibited a high specific surface area (364.84 m2/g), hierarchical porous structures, and abundant oxygen-containing functional groups (hydroxyl and carboxyl groups), which enhancing the dispersion of Fe3O4 nanoparticle and exposure of catalytic site. The Fe8-N10-C/PMS system achieved 100 % BPA degradation within 20 min with a corresponding first-order reaction rate constant (kobs) of 0.4056 min-1, which outperformed most reported catalysts in efficiency. Quenching and EPR analyses revealed that both free radicals (•OH, SO4•-, and O2•-) and non-radical (1O2) were rate-limiting steps, while graphitic N and Fe-Nx structures facilitated direct electron transfer from BPA to PMS in electrochemical tests. XPS results confirmed that pyrrolic N, rather than pyridinic N, played a crucial role in forming the Fe-Nx structure. Moreover, the catalyst showed excellent stability, regeneration capability, and adaptability under diverse conditions, highlighting the potential of the Fe-N-C/PMS system for practical wastewater treatment applications.

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.

Hydrothermal-mediated in-situ nitrogen doping to prepare biochar for enhancing oxygen reduction reactions in microbial fuel cells

Nitrogen-doped carbon materials are deemed promising cathode catalysts for microbial fuel cells (MFCs). The challenge lies in reducing costs and enhancing the proportion of electrocatalytically active nitrogenous functional groups. This study proposes a hydrothermal-mediated in-situ doping method to produce nitrogen-doped biochar from aquatic plants. The nitrogen atoms are anchored in the carbon structure during hydrothermal treatment. Subsequent pyrolysis converts the hydrochar into a catalyst with highly catalytically active aromatic ring structure (HC-N+PY). The as-prepared HC-N+PY electrocatalyst demonstrates superior oxygen reduction reaction activity with half-wave potentials of 0.82 V. The MFC with HC-N+PY exhibits excellent performance, with a peak power density of 1444 mW/m2. Theoretical calculations demonstrate that the synergistic effect of graphitic nitrogen and C-O groups at defect sites enhances O2 adsorption and protonation. This work highlights the potential of utilizing nitrogen-doped biochar derived from aquatic plants as an effective catalyst for enhancing the performance of microbial fuel cells.

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.

Sabatier Principle-Driven Single-Atom Coordination Engineering for Enhanced Fenton-Like Catalysis

Single-atom catalysts (SACs) are widely employed in Fenton-like catalysis, yet guidelines for their high-performance design remain elusive. The Sabatier principle provides guidance for the ideal catalyst with the highest activity. Herein, the study meticulously engineered a series of SACs featuring a broad distribution of d-band center through single-atom coordination engineering, facilitating a comprehensive exploration of the Sabatier relationship in Fenton-like catalysis. A volcanic correlation between d-band centers and catalytic activity is identified. Theoretical and experimental results show that moderate d-band center and peroxymonosulfate adsorption energy can lead to the lowest reaction barriers in the rate-determining step for generating singlet oxygen, thus enhancing catalytic efficiency toward the Sabatier optimum. As proof of concept, the Fe-N2O2/C catalyst demonstrates a degradation rate constant of 1.89 min-1, surpassing Fe-N4/C by 3.2 times and Fe-O4/C by 272 times. Moreover, Fe-N2O2/C shows exceptional tolerance to various environmental challenges, providing opportunities for achieving nearly eco-friendly pollutant degradation. The findings reveal how to use the Sabatier principle to guide the design of advanced SACs for efficient pollutant removal.

Mesoporous Atomically Dispersed Fe Catalysts with Enhanced Nonradical Pathways in Fenton-like Reactions: The Role of SiO2 Templates

Single-atom catalysts (SACs) are extensively applied in Fenton-like catalytic processes to treat water pollutants. However, the role of the porous structures of SACs supports in catalytic reactions is often overlooked despite its significant contribution to mass diffusion during the reaction. Herein, we adopted a hard-template-assisted approach to fabricate Fe-based SACs (Fe-SACs) featuring a mesoporous architecture. The SiO2 template not only adjusts the pore architecture of the support but also facilitates the conversion of active sites from nanoscale sites to single-atom sites, thereby improving the selectivity for pollutant degradation via nonradical pathways (singlet oxygen and electron transfer mechanism). The experimental results demonstrated that using large-sized SiO2 (∼200 nm) as a template leads to metal aggregation on its surface, forming Fe nanoparticles (Fe-NPs). Fe-NPs exhibit narrow pore structures that prevent peroxymonosulfate (PMS) from being activated, resulting in a slow degradation of pollutants primarily through radical pathways. In contrast, employing small-sized SiO2 (∼10 nm) as a hard template not only produces supports with mesoporous structures but also promotes the building of single-atom active sites. The prepared Fe-SACs effectively activated PMS through nonradical pathways and removed contaminants at a rate k of 0.89 min-1, 33 times faster than Fe-NPs. This template-assisted method sheds light on the synthesis of effective Fenton-like catalysts with porous structures that enhance the efficient breakdown of contaminants in wastewater.

Highly selective regulation of non-radical and radical mechanisms by Co cubic assembly catalysts for peroxymonosulfate activation

Peroxymonosulfate (PMS) activation on efficient catalysts is a promising strategy to produce sulfate radical (SO4-) and singlet oxygen (1O2) for the degradation of refractory organic pollutants. It is a great challenge to selectively generate these two reactive oxygen species, and the regulation mechanism from non-radical to radical pathway and vice versa is not well established. Here, we report a strategy to regulate the activation mechanism of PMS for the selective generation of SO4- and 1O2 with 100 % efficiency by sulfur-doped cobalt cubic assembly catalysts that was derived from the Co-Co Prussian blue analog precursor. This catalyst showed superior catalytic performance in activating PMS with normalized reaction rate increased by 87 times that of the commercial Co3O4 nanoparticles and had much lower activation energy barrier for the degradation of organic pollutant (e.g., p-chlorophenol) (18.32 kJ⋅mol-1). Experimental and theoretical calculation results revealed that S doping can regulate the electronic structure of Co active centers, which alters the direction of electron transfer between catalyst and PMS. This catalyst showed a strong tolerance to common organic compounds and anions in water, wide environmental applicability, and performed well in different real-water systems. This study provides new opportunities for the development of metal catalyst with metal-organic frameworks structure and good self-regeneration ability geared specifically towards PMS-based advanced oxidation processes applied for water remediation.

Lactobionic acid modified cobalt coordination polymer-coated peroxymonosulfate nanoparticles generate sulfate/hydroxy dual-radicals for targeted cancer therapy

Free radical therapy, based on the sulfate radical derived from peroxymonosulfate, has recently been explored as a potential cancer treatment. However, while it is promising, its successful application is restricted by several limitations including the uncontrollable generation of free radicals and the instability in aqueous medium. Herein, we prepared LCP nanoparticles by using PMS as a core, the Co-coordination polymer (Co-CP) as a coating layer, and lactobionic acid as a targeting ligand for hepatoma carcinoma cells. LCP could be activated by cobalt ions released from Co-CP, and successfully induced apoptosis and ferroptosis via the inhibition of glutathione peroxidase 4 and caused the accumulation of lipid peroxidation to enhance the efficacy of free radical therapy.

Nitrogen and magnesium codoped biochar activates periodate to remediate bensulfuron methyl-contaminated water at low temperature: Performance, mechanisms, and phytotoxicity

Bensulfuron methyl (BSM), a typical sulfonylurea herbicide, has been widely used worldwide for weed suppression and crop protection. Nevertheless, the long-term and prolonged usage led to residues in environment, resulting in the reduction of crop yields and even threatening food security. In this study, the nitrogen/magnesium codoped biochar (NMg-BC) was prepared via two-step pyrolysis method to activate periodate (PI) for BSM degradation. The results demonstrated BSM degradation rate was 87.9 % within 10 min by NMg-BC/PI system at 15 ℃. The system exhibited the favorable tolerance to environmental changes (pH, temperature, anions, and humic acids), presenting high removal efficiency of BSM. Radicals (IO3•) and non-radicals (1O2 and electron transfer) pathways contributed to the degradation of BSM, while the latter performed a crucial role in BSM degradation. Theoretical calculations further confirmed doped of N and Mg changed the electron configuration and electrostatic potential (ESP) distribution of biochar, which was beneficial to provide more active sites for PI activation. Hydroponic experiments showed that NMg-BC/PI system could effectively degrade BSM, and its residue had no significant effect on the length and weight of soybean. The study provides a promising approach for the pollutant remediation in cold regions.

Advancements on Single-Atom Catalysts-Mediated Persulfate Activation: Generating Reactive Species for Contaminants Elimination in Water

The single-atom catalyst (SAC) activated persulfate process has emerged as a highly efficient technology for eliminating refractory organic compounds in aqueous environments. This review delves into the intricacies of utilizing SACs for the effective removal of various contaminants in water. The common supports and the preparation procedures of SACs are summarized at first. The synthesis methods of SACs (i.e., wet chemical method, one-pot hydrothermal method, and high-temperature pyrolysis method) are also described. Then, a comprehensive overview of the diverse reaction mechanisms in SAC-activated persulfate systems is presented, including a radical oxidation process via sulfate or hydroxyl radicals and superoxide radicals, or a nonradical process via single oxygen, surface active complex, and high-valent metal-oxo species oxidation. The impact of key factors such as peroxides concentration, SAC dosage, reaction pH, inorganic anions, organic matter, operando stability, and real water is also delved. The removal of various pollutants (i.e., azo dyes, phenolic compounds, pharmaceuticals, and bacteria) by this process is further summarized. Finally, the challenges and perspectives in the field of water treatment utilizing SACs are discussed.

Safety Landscape of Therapeutic Nanozymes and Future Research Directions

Oxidative stress and inflammation are at the root of a multitude of diseases. Treatment of these conditions is often necessary but current standard therapies to fight excessive reactive oxygen species (ROS) and inflammation are often ineffective or complicated by substantial safety concerns. Nanozymes are emerging nanomaterials with intrinsic enzyme-like properties that hold great promise for effective cancer treatment, bacterial elimination, and anti-inflammatory/anti-oxidant therapy. While there is rapid progress in tailoring their catalytic activities as evidenced by the recent integration of single-atom catalysts (SACs) to create next-generation nanozymes with superior activity, selectivity, and stability, a better understanding and tuning of their safety profile is imperative for successful clinical translation. This review outlines the current applied safety assessment approaches and provides a comprehensive summary of the safety knowledge of therapeutic nanozymes. Overall, nanozymes so far show good in vitro and in vivo biocompatibility despite considerable differences in their composition and enzymatic activities. However, current safety investigations mostly cover a limited set of basic toxicological endpoints, which do not allow for a thorough and deep assessment. Ultimately, remaining research gaps that should be carefully addressed in future studies are highlighted, to optimize the safety profile of therapeutic nanozymes early in their pre-clinical development.

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

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

Fine Engineering of d-Orbital Vacancies of ZnN4 via High-Shell Metal and Nonmetal Single-Atoms for Efficient and Poisoning-Resistant ORR

Atomically dispersed metal-nitrogen-carbon (M-N-C) materials are active oxygen reduction reaction (ORR) catalysts. Among M-N-C catalysts, ZnN4 single-atom catalysts (SACs) due to a nearly full 3d10 electronic configuration insufficiently activate oxygen and display low ORR activity. To finely engineer d-orbital vacancies of ZnN4, we combine high-shell metal and nonmetal SAs as electronic regulators that are ZnN4Cl and carbon vacancy-hosted -Cl motifs, which show complementary electron-withdrawing capacities versus the ZnN4. Under that, the ZnN4 exhibits significantly enhanced ORR activity with a half-wave potential (E1/2) of 0.912 VRHE relative to the unmodified ZnN4 (E1/2 = 0.822 VRHE) and simultaneously robust durability (negligible activity loss after 10,000 potential cycles). Particularly, the engineered ZnN4 possesses high resistance to SCN- poisoning, which is rarely achieved among M-N-C SACs. Our works show that combining high-shell metal and nonmetal SAs can finely engineer d-orbital vacancies of metal centers to an optimal state, thereby intrinsically enhancing their catalytic performance.

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

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

Pilot-scale and large-scale Fenton-like applications with nano-metal catalysts: From catalytic modules to scale-up applications

Recently, great efforts have been made to advance the pilot-scale and engineering-scale applications of Fenton-like processes using various nano-metal catalysts (including nanosized metal-based catalysts, smaller nanocluster catalysts, and single-atom catalysts, etc.). This step is essential to facilitate the practical applications of advanced oxidation processes (AOPs) for these highly active nano-metal catalysts. Before large-scale implementation, these nano-metal catalysts must be converted into the effective catalyst modules (such as catalytic membranes, fluidized beds, or polypropylene sphere suspension systems), as it is not feasible to use suspended powder catalysts for large-scale treatment. Therefore, the pilot-scale and engineering applications of nano-metal catalysts in Fenton-like systems in recent years is exciting. In addition, the combination of life cycle assessment (LCA) and techno-economic analysis (TEA) can provide a useful support tool for engineering scale Fenton-like applications. This paper summarizes the designs and fabrications of various advanced modules based on nano-metal catalysts, analyzes the advantages and disadvantages of these catalytic modules, and further discusses their Fenton-like pilot scale or engineering applications. Concepts of future Fenton-like engineering applications of nano-metal catalysts were also discussed. In addition, current challenges and future expectations in pilot-scale or engineering applications are assessed in conjunction with LCA and TEA. These challenges require further technological advances to enable larger scale engineering applications in the future. The aim of these efforts is to increase the potential of nanoscale AOPs for practical wastewater treatment.

Promotion of Single-Electron Transfer by Low-Coordinated Co Single Atoms to Facilitate Advanced Oxidation Processes in Wastewater Treatment

Heterogeneous catalysts are fascinating for advanced oxidation processes (AOPs) in wastewater treatment to reduce cost, metal contamination, and pH operation limitations. However, they usually encounter low catalytic efficiency because of the difficult single-electron-transfer (SET) pathway during AOPs. Herein, an efficient heterogeneous catalyst for AOPs is realized through the rational regulation of N coordination around Co single-atom (SA) centers in favor of SET. As guided by calculations, low N coordination enables a high density of electronic states at the Fermi energy level of SA Co to facilitate SET activation of peroxomonosulfate (PMS). A special oxide-compounding method is further applied to decrease the N coordination of SA Co on the carbon carriers from common Co1-N3/4 to the desired Co1-N2. Co1-N2 shows a delightful activity for AOP degradation of various organic pollutants with kinetic rate and turnover frequency values up to 0.862 min-1 and 389 h-1, respectively, greatly outperforming those of Co1-N3/4. It is also superior in a wide pH operation range and has strong resistance to environmental disturbances. Detailed mechanistic investigations confirm the generation of singlet oxygen (1O2) instead of common radical O species from the SET between PMS and Co1-N2, corroborating the calculated results and accounting for the enhanced AOP activity.

Sludge-derived hydrochar modulates complete nonradical electron transfer in peroxydisulfate activation via pyrrolic-N and carbon defect: Implication for degrading electron-rich ionizable anilines compounds

Nonradical electron transfer process (ETP) is a promising pathway for pollutant degradation in peroxydisulfate-based advanced oxidation processes (PDS-AOPs). However, there is a critical bottleneck to trigger ETP by sludge-derived hydrochar due to its negatively charged surface, inferior porosity and electrical conductivity. Herein, pyrrolic-N doped and carbon defected sludge-derived hydrochar (SDHC-N) was constructed for PDS activation to degrade anilines ionizable organic compounds (IOC) through complete nonradical ETP oxidation. Degradation of anilines IOC was not only affected by the electron-donating capacity but also proton concentration in solution because of the ionizable amino group (-NH2). Diverse effects including proton favor, insusceptible and inhibition were observed. Impressively, addition of HCO3 with strong proton binding capacity boosted aniline degradation nearly 10 times. Moreover, characterizations and theoretical calculations demonstrated that pyrrolic-N increased electron density and created positively charged surface, profoundly promoting generation of SDHC-N-S2O82-* complexes. More delocalized electrons around carbon defect could enhance electron mobility. This work guides a rational design of sludge-derived hydrochar to mediate nonradical ETP oxidation, and provides insights into the impacts of proton on anilines IOC degradation.

Atomically Dispersed Cobalt Anchored on Hollow Tubular Carbon Nitride Mediates Direct Electron Transfer and Oxygen-Related Active Species Path for Activation of Permonosulfate

Atomically dispersed catalysts anchored on nitrogen-rich substrates present promising application potential for the persulfate-based advanced oxidation process. Nevertheless, efficient activation efficiency and a clear activated mechanism of persulfate remain challenging in carbon nitride-based single-atom catalysts (SACs). To these, combined with the regulation strategy of metal-ligand section and carrier's architecture, an atomically dispersed Co single-atom catalyst anchored on regular hollow tubular carbon nitride (Co/TCN SAC) herein was devised and utilized to activate permonosulfate. As a result, Co/TCN SACs show excellent catalytic performance for the degradation of common antibiotics. Combined with X-ray absorption fine structure and theory calculation, it is confirmed that superficially anchored CoO3 sites of the Co2N2O2-CoO3 unit are the catalytic active center for peroxymonosulfate (PMS) activation. The electrochemical test and in situ electron paramagnetic resonance results demonstrate radical (SO4•- and •OH) and nonradical (electron transfer process and 1O2) paths contributing to the superior catalytic performance. In addition, the catalyst exhibits high reaction efficiency and structural stability considering water quality parameters. Finally, a continuous and efficient device was operated on a laboratory scale, which exhibited satisfactory efficiency in continuously removing electron-rich antibiotics such as tetracycline. This work reveals the atomic-level modulation of cobalt atomic sites on hollow tubular carbon nitride and their structure-activity relationship with persulfate activation.

Atomically dispersed copper-zinc dual sites anchored on nitrogen-doped porous carbon toward peroxymonosulfate activation for degradation of various organic contaminants

Single-atom catalysts (SACs) have been widely studied in Fenton-like reactions, wherein their catalytic performance could be further enhanced by adjusting electronic structure and regulating coordination environment, although relevant research is rarely reported. This text elucidates fabrication of dual atom catalyst systems aimed at augmenting their catalytic efficiency. Herein, atomically dispersed copper-zinc (Cu-Zn) dual sites anchored on nitrogen (N)-doped porous carbon (NC), referred to as CuZn-NC, were synthesized using cage-encapsulated pyrolysis and host-guest strategies. The CuZn-NC catalyst exhibited high activity in activation of peroxymonosulfate (PMS) for degradation of organic pollutants. Based on synergistic effects of adjacent Cu and Zn atom pairs, CuZn-NC (PMS) system achieved 94.44 % bisphenol A (BPA) degradation in 24 min. The radical pathway predominated, and coexistence of non-radical species was demonstrated for BPA degradation in CuZn-NC/PMS system. More importantly, CuZn-NC/PMS system showed generality for degradation of various refractory contaminants. Our experiments indicate that CuZn-N sites on CuZn-NC act as active sites for bonding PMS molecules with optimal binding energy, while pyrrolic N sites are considered as adsorption sites for organic molecules. Overall, this research designs diatomic site catalysts (DACs), with promising implications for wastewater treatment.

Strong metal-support interaction (SMSI) in environmental catalysis: Mechanisms, application, regulation strategies, and breakthroughs

The strong metal-support interaction (SMSI) in supported catalysts plays a dominant role in catalytic degradation, upgrading, and remanufacturing of environmental pollutants. Previous studies have shown that SMSI is crucial in supported catalysts' activity and stability. However, for redox reactions catalyzed in environmental catalysis, the enhancement mechanism of SMSI-induced oxygen vacancy and electron transfer needs to be clarified. Additionally, the precise control of SMSI interface sites remains to be fully understood. Here we provide a systematic review of SMSI's catalytic mechanisms and control strategies in purifying gaseous pollutants, treating organic wastewater, and valorizing biomass solid waste. We explore the adsorption and activation mechanisms of SMSI in redox reactions by examining interfacial electron transfer, interfacial oxygen vacancy, and interfacial acidic sites. Furthermore, we develop a precise regulation strategy of SMSI from systematical perspectives of interface effect, crystal facet effect, size effect, guest ion doping, and modification effect. Importantly, we point out the drawbacks and breakthrough directions for SMSI regulation in environmental catalysis, including partial encapsulation strategy, size optimization strategy, interface oxygen vacancy strategy, and multi-component strategy. This review article provides the potential applications of SMSI and offers guidance for its controlled regulation in environmental catalysis.

Oxygen doping regulation of Co single atom catalysts for electro-Fenton degradation of tetracycline

Electro-Fenton is an effective process for degrading hard-to-degrade organic pollutants, such as tetracycline (TC). However, the degradation efficiency of this process is limited by the activity and stability of the cathode catalyst. Herein, a temperature gradient pyrolysis strategy and oxidation treatment is proposed to modulate the coordination environment to prepare oxygen-doped cobalt monoatomic electrocatalysts (CoNOC). The CoNOC catalysts can achieve the selectivity of 93 % for H2O2 with an electron transfer number close to 2. In the H-cell, the prepared electrocatalysts can achieve more than 100 h of H2O2 production with good stability and the yield of 1.41 mol gcatalyst-1 h-1 with an average Faraday efficiency (FE) of more than 88 %. The calculations indicate that the epoxy groups play a crucial role in modulating the oxygen reduction pathway. The O doping and unique N coordination of Co single-atom active sites (CoN(Pd)3N(Po)1O1) can effectively weaken the O2/OOH* interaction, thereby promoting the production of H2O2. Finally, the electro-Fenton system could achieve a TC degradation rate of 94.9 % for 120 min with a mineralization efficiency of 87.8 % for 180 min, which provides a reliable option for antibiotic treatment. The significant involvement of OH in the electro-Fenton process was confirmed, and the plausible mineralization pathway for TC was proposed.

Construction of portable hydrogel kits with self-ratio optical bimodal detection and smartphone imaging for on-site nitrite screening

Accurate on-site detection of nitrite in complex matrices remains a significant challenge. Herin, we construct a self-ratio optical bimodal portable kit via co-assembling NaErF4:0.5%Tm@NaYF4@NaYbF4:0.5%Tm@NaYF4 (Er:Tm@Yb:Tm) and nitrogen-doped carbon platinum nanomaterials (Pt/CN) in sodium alginate (SA) hydrogel. Pt/CN nanomaterials are synthesized by high-temperature sintering using a zinc-based zeolite imidazolium framework as a sacrificial template. The Pt/CN nanozyme possesses excellent oxidase-like activity to produce the oxidation state 3,3',5,5'-tetramethylbenzidine (oxTMB). Nitrite mediates diazotization of oxTMB to trigger the change of absorption signals, accompanying the ratio fluorescence response of the Er:Tm@Yb:Tm. Crucially, Er:Tm@Yb:Tm and Pt/CN are embedded in SA hydrogel to fabricate a portable kit with efficient and sensitive performance. An image processing algorithm is used to analyze the nitrite-induced signal change of the portable hydrogel kit, resulting in detection limits of 0.63 μM. This method has great potential for point-of-care applications due to its reliability, long-term stability, accuracy, sensitivity, and portability.

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.

Co3O4/CuO@C catalyst based on cobalt-doped HKUST-1 as an efficient peroxymonosulfate activator for pendimethalin degradation: Catalysis and mechanism

Pendimethalin (PM) is an organic pollutant (herbicide), and systematic studies on PM degradation are scarce. The efficient degradation of PM in water remains a challenge that requires to be addressed. Herein, for the first time, elemental Co was doped into HKUST-1 using a solvothermal method to generate Co3O4/CuO@C via pyrolysis. The as-prepared catalyst was used to activate peroxymonosulfate (PMS) for PM degradation, obtaining a PM degradation efficiency of 98.2 % after 30 min. The assessment of the effects of various factors on the degradation efficiency revealed that 1O2 dominated PM degradation, whereas the contribution of SO4•- was negligible. Although 3Co3O4/CuO@C exhibited a good degradation performance against other organic pollutants, its degradation performance in real water was poor. The carbon layer reduced metal-ion leaching (Co and Cu), and the synergistic interactions between Co3O4 and CuO promoted PMS activation. The roles of the components of 3Co3O4/CuO@C in PM degradation by activated PMS were investigated in the presence of CoIV and Co-OOSO3-. Two possible PM degradation pathways were systematically proposed, and the toxicity of the intermediates was analyzed. Finally, a mechanism for PM degradation by 3Co3O4/CuO@C-activated PMS was proposed.