Iron Sites Research Articles

Theory-driven design of local spin-state modulation at atomically dispersed iron sites for enhanced CO2 electroreduction

Herein, density functional theory (DFT) was used to guide the systematic design of highly efficient single-atom electrocatalysts to improve the kinetics of the CO2 reduction reaction (CO2RR). We present a novel class of catalysts that exhibit magnetic-proximity-induced exchange splitting (spin polarization). The design of these catalysts involved the precise modulation of d-shell energy levels at metallic sites and the subsequent alteration of the atomic/molecular orbitals of the adsorbed intermediates. To validate the effectiveness of our design strategy, we introduced neighboring nitrogen (N) doping near the Fe-N4 coordination environment, demonstrating the successful manipulation of the local spin state of the active sites. The results of the theoretical calculations align with the experimental results, with remarkable selectivity exceeding 90 % at low potentials (<-0.5 V vs. RHE) and sustained electrocatalytic activity for over 24 h. In situ characterization further revealed that a modulated local spin state led to a decrease in the occupation of the Fe 3d spin-down electronic states below the Fermi level. Concurrently, electrons migrated to the frontier antibonding orbitals of *COOH. This dual effect resulted in a lower reaction energy (ΔG), representing a thermodynamic benefit, and accelerated proton transfer to *COOH, representing a kinetic benefit, collectively enhancing the electrocatalytic process.

Improving the adsorption properties of low surface area hardwood biochar for the removal of Fe+ and PO₄3- from aqueous solution.

Biochar produced from wood residues may provide a new method and material for managing the environment, particularly in terms of carbon sequestration and contaminant remediation. Additionally, biochar produced from wood residues is free of chemical fertilizers, likewise in rice straw, wheat straw, corn straw, etc. This study investigated the removal of iron from aqueous solutions by a novel low-cost and eco-friendly biochar made from hardwood trees and modified by adding MgCl2 for effective phosphate removal. Optimal adsorption conditions were determined through studies of adsorption time, pH, and adsorbent dosage. Batch equilibrium isotherm and kinetic experiments and pre/post-adsorption characterizations using FESEM-EDS, XRD, and FTIR suggested that the presence of carboxyl group elements and colloidal and nano-sized MgO (periclase) particles on the biochar surface were the main adsorption sites for aqueous iron and phosphate respectively. In this study, the HW and MgO-HW biochar showed excellent Dubinin-Radushkevich isotherm (D-R) maximum adsorption capacities of 289.45 and 828.82mg/g for iron and phosphate. The kinetic study for iron and phosphate adsorption was described well by pseudo second-order model and pseudo second-order model respectively. The HW biochar and the prepared MgO-HW biochar exhibited commendable iron adsorption (98.25%) performance at 10 pH units and phosphate (96.22%) at pH 6 respectively. Thus, this research reveals a waste-to-wealth strategy by converting hardwood waste into mineral-biomass biochar with excellent Fe and P adsorption capabilities and environmental adaptability.

Mesoporous carbon spheres modified with atomically dispersed iron sites for efficient electromagnetic wave absorption

Carbon materials have obtained some achievements in electromagnetic wave (EMW) absorption owing to their excellent electrical conductivity and low density. However, poor impedance matching and high electrical conductivity limit their EMW absorption properties. Metal single atoms absorbers have garnered considerable attention in EMW absorption, largely due to the high metal availability and special coordination structure, but the modulation of the EMW absorption properties still needs to be improved. Herein, atomically dispersed Fe sites embedded into the N-doped mesoporous carbon spheres (Fe–SAs/NC) were synthesized through a facile coordination-assisted polymerization assembly strategy without acid leaching treatment. Benefitting from abundant mesoporous structure, the Fe–SAs/NC displays large specific surface area (339 m2 g−1) and optimized impedance matching, which results in an effective reduction of the absorber density. The homogeneously dispersed Fe single atoms (Fe–SAs) on the carbon skeleton lead to the improvement in conduction and dipole polarization losses of Fe–SAs/NC, which endows Fe–SAs/NC with exceptional EMW absorption properties. Experimental results indicate that Fe–SAs/NC displays desirable EMW absorption properties with the minimal reflection loss of −52.5 dB at 2.8 mm and the effective absorption bandwidth of 4.8 GHz. The study provides valuable insights for the development of carbon materials modified with atomically dispersed metal sites to achieve high-efficient EMW absorbers.

Ball milling of pyrite in air to significantly promote the Fenton reaction: A mechanistic study

Natural pyrite (FeS2) has been widely used as heterogenous Fenton catalyst due to the unique iron supplying and ferrous regeneration performance, however, natural pyrite has poor catalytic activity due to the low surface reactivity. Ball milling is commonly used to modify pyrite, but the mechanism has not been thoroughly studied. In our work, by optimizing the ball milling conditions, the catalytic efficiency of modified pyrite is increased by 60 times compared to natural pyrite, and the ball milled pyrite Fenton system was able to degrade dyes and a series of antibiotics within 30 min. Compared to ball milling in nitrogen and vacuum, ball milling in air increased the proportion of S2− and active iron sites on the surface of pyrite, which assisted and accelerated the regeneration of ferrous and enhanced the iron supplying performance. This work explored the mechanisms of ball milling to modify the properties of pyrite, reported a green and efficient ball milled pyrite Fenton system, and provided a new insight in regulating ball milling conditions for mechanochemical modification.

Atomically dispersed iron sites from eco-friendly microbial mycelium as highly efficient hydrogenation catalyst

Iron, one of the most abundant elements on earth and an essential element for living organisms, plays a crucial role in our daily metabolism. In the field of catalysis, the development of high-performance catalysts based on less toxic iron element is also of significant importance for green chemistry and a sustainable future. To construct Fe-based heterogeneous catalysts with excellent hydrogenation performance, precise modulation of the atomic coordination structure is a key strategy for enhancing catalytic activity. In this study, we present an in-situ coating method for applying a zeolitic imidazolate framework (ZIF) onto the surface of fungal hyphae. The asymmetric coordination structure of Fe1-N3P1 was precisely tailored by utilizing the phosphorus source from the fungus and the nitrogen source in the ZIFs. Detailed characterizations and density functional theory calculations revealed that the incorporation of ZIFs not only increased the specific surface area of catalysts, but also facilitated the dispersion of Fe2P nanoparticles into the Fe1-N3P1 center, making the lowest reaction energy barrier and resulting in the best performance for nitrobenzene hydrogenation when compared to the Fe2P nanoparticles and clusters. This research introduces a novel design concept for constructing asymmetric monoatomic configuration based on the inherent characteristics of natural microorganisms and the exogenous porous coordination polymers.

N-coordinated iron sites dispersed in porous carbon frameworks to activate peroxymonosulfate for efficient sulfisoxazole degradation and real hospital wastewater decontamination

Herein, an N-coordinated Fe site dispersed in porous carbon frameworks (Fe-NC) fabricated from zeolitic imidazolate frameworks encapsulated with iron acetylacetonate (Fe(acac)3 @ZIFs) was employed to activate peroxymonosulfate (PMS) for the attenuation of sulfisoxazole (SIZ) and treating real hospital wastewater. The constructed Fe-NC/PMS system exhibited good catalytic stability for SIZ degradation, maintaining excellent degradation performance over multiple cycles with virtually no leaching. The quenching experiments, electron paramagnetic resonance (EPR) capture analyses, and semi-quantitative measurements showed that singlet oxygen (1O2) and high-valent metal-oxo species were mainly responsible for SIZ degradation by Fe-NC/PMS. Significantly, ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS/MS) was used to trace 134 pharmaceutical contaminants in real hospital wastewater. Effective degradation was achieved for 87 % of the pharmaceutical contaminants by the Fe-NC/PMS process. Seventy-four pharmaceutical contaminants were eliminated. Taken together, this work successfully established the Fe-NC/PMS technology using the developed iron-based materials and explored its application to real hospital wastewater treatment, providing an eco-friendly and effective strategy for treating wastewater.

Bioinspired Homonuclear Diatomic Iron Active Site Regulation for Efficient Antifouling Osmotic Energy Conversion.

Membrane-based reverse electrodialysis is globally recognized as a promising technology for harnessing osmotic energy. However, its practical application is greatly restricted by the poor anti-fouling ability of existing membrane materials. Inspired by the structural and functional models of natural cytochrome c oxidases (CcO), the first use of atomically precise homonuclear diatomic iron composites as high-performance osmotic energy conversion membranes with excellent anti-fouling ability is demonstrated. Through rational tuning of the atomic configuration of the diatomic iron sites, the oxidase-like activity can be precisely tailored, leading to the augmentation of ion throughput and anti-fouling capacity. Composite membranes featuring direct Fe-Fe motif configurations embedded within cellulose nanofibers (CNF/Fe-DACs-P) surpass state-of-the-art CNF-based membranes with power densities of ca. 6.7Wm-2 and a 44.5-fold enhancement in antimicrobial performance. Combined, experimental characterization and density functional theory simulations reveal that homonuclear diatomic iron sites with metal-metal interactions can achieve ideally balanced adsorption and desorption of intermediates, thus realizing superior oxidase-like activity, enhanced ionic flux, and excellent antibacterial activity.

Photocatalytic degradation of the remazol red ultra RGB dye using SrFe12O19-Fe3O4 magnetic oxides dispersed in silica: Effect of reduction temperature

Dyes are the most frequently discarded industrial wastes in aquatic ecosystems, among which Remazol Red ultra RGB stands out. In this context, magnetic iron-based catalyst dispersed in silica were prepared by Pechini route as an alternative for the photodegradation of Remazol Red Ultra RGB. The XRD and Mössbauer spectroscopy results indicated the formation of a magnetic material that, after reduction treatment with H2, forms a magnetite phase combined with Sr hexaferrite dispersed in amorphous silica. The TPR-H2 profiles indicated the reduction of Fe3+ to Fe2+ within the considered temperature range, the amount of Fe2+ increased with rising temperature. The SEM images showed sponge-like morphology for the samples. The EDS spectra and mapping confirmed a high uniformity in the distribution of active iron species in the silica. The magnetic measurements showed a lower magnetic signal for the sample reduced at 600 °C, due to the lower magnetic moment of Fe2+ formed after the reduction. The diffuse reflectance spectra showed a main absorption region between 500 and 200 nm and the estimated band-gap values were of 1.4 and 1.9 eV for the reduced sample and the fresh oxide, respectively. The surface charge was obtained via zeta potential, demonstrating good stability under pH changes and reaching a negative potential in the pH range from 2 to 6. The photocatalytic tests showed that the samples with higher content of Fe2+ demonstrated a greater photocatalytic degradation of the Remazol Red Ultra RGB dye, reaching 100 % degradation in 1 h for the solid reduced at 600 °C. A plausible mechanism for the photodegradation of Remazol Red Ultra RGB was proposed, considering the different elementary steps involving the participation of iron sites and the formation of oxidant radicals.

Exploring the Frontiers of Heterometallic Systems: the {FeW5} Octahedral Cluster Complex.

This research presents the first examples of heterometallic octahedral cluster complexes incorporating both 5d and 3d metals, specifically, tungsten and iron. The key compound, (TBA)2[FeW5Br14] (TBA = tetrabutylammonium), exhibits selective ligand substitution reactions at the iron site when exposed to various solvents. Several {FeW5}-type anions, namely, [FeW5Br14]2-, [FeW5Br13(L)]- (L = H2O, DMSO, CH3CN), and [(FeW5Br13)2O]4-, were revealed and characterized by single-crystal X-ray diffraction analysis. The redox properties of [FeW5Br14]2- were studied and compared with those of [W6Br14]2-. Density functional theory calculations demonstrated that the bonding between Fe and W atoms is fundamentally different from the bonding between 4d (Mo-Mo) or 5d (W-W) metals in isotypic {M6} clusters.

A structural and functional model for alkene dioxygenases

In this article, we report sterically-controlled iron sites based on non-chelating bulky imidazole ligands. Adding 6 equiv. of 1,2-dimethylimidazole (1,2-Me2Im) to Fe(OTf)2⋅2CH3CN affords the first example of a 5-coordinate imidazole‑iron complex ([Fe(1,2-Me2Im)5](OTf)2, 1). The structure is distorted square pyramidal (τ5 = 0.41). When an iPr group is substituted for the methyl group at the 2-position on the imidazole (2-iPr-1-MeIm), the 14-electron complex ([Fe(2-iPr-1-MeIm)4](OTf)2, 2) is obtained. This complex exhibits slightly distorted tetrahedral geometry (τ'4 = 0.93) with four N-donors and serves as a 4-His iron structural model complex for carotenoid cleavage dioxygenases (CCD). The electronic structure of 1 and 2 were characterized by Mössbauer spectroscopy. Reactions of 1 and 2 with model olefin substrates (1-R-4-(1-methoxyprop-1-en-2-yl)benzene; R = Me or Br) in the presence of oxygen result in olefin cleavage yielding ketone and aldehyde products, although 2 yields more products than 1. Support for a proposed reaction mechanism for 2 is offered from Density Functional Theory (DFT) calculations.

A bioinspired Fe/Mo bimetallic nitride catalyst for efficient electrochemical ammonia synthesis and Zn-nitrate battery

The electrocatalytic nitrate reduction reaction to ammonia (NRA) offers a promising alternative to traditional ammonia synthesis methods. In nature, enzymes containing molybdenum and iron sites catalyze the reduction of nitrate and nitrite ions. Drawing inspiration from these enzymes, we synthesized a carbon-coated nano-octahedra of FeMo-based nitride (FeMoN@C NO) by pyrolyzing phosphomolybdic acid hydrate (POM) doped Fe-NH2-MIL-101 to catalyze NRA. Experimental results demonstrate that in an alkaline environment, FeMoN@C NO exhibits a suitable hydrogen evolution reaction (HER) capacity, and the protons or hydroxyls produced effectively facilitate the hydrogenation reaction in the ammonia synthesis process. Additionally, the introduction of Mo increases the number of active sites and effectively reduces the thermodynamic barrier in NRA, thereby enhancing the rate of ammonia synthesis. As a result, FeMoN@C NO displays outstanding NH3 Faradaic efficiency (FE) of 98.2 % and an NH3 yield of 434.16 µmol/h cm−2. Building upon the excellent electrocatalytic properties of FeMoN@C NO, a new Zn-nitrate battery system is assembled in this work, which exhibits an outstanding peak power density of 3.23 mW cm−2 and an FE of 91.58 % for NH3 production. This work provides a new perspective for designing enzyme-mimicking nitrate reduction catalysts and broadens the application of Zn-based batteries.

Tuning FeO covalency boosts catalytic ozonation over spinel oxide for chemical industrial wastewater decontamination

AbstractHeterogeneous catalytic ozonation (HCO) emerges as a promising chemical industrial wastewater treatment solution, offering enhanced ozone utilization and reduced secondary pollutants. However, challenges in scaling HCO arise from a limited understanding of the catalytic mechanisms of metal oxides, particularly in generating active ozone sites. Here, we demonstrated the improvement of catalytic ozonation efficiency by enhancing the covalent bonding between FeO in Fe/Co spinel oxides. This alteration exploits the stronger electron‐donating capacity of Fe (II), enhancing FeOM bonds and electron enrichment at iron sites, leading to a significant reduction in the activation energy for ozone. Pilot experiments demonstrated a 75.3% COD removal efficiency and a threefold increase in ozone utilization efficiency compared to pure ozone system for chemical industrial wastewater treatment. This study not only advances our understanding of spinel oxides in ozone catalysis but also opens new avenues for practical HCO applications in water treatment.

Fabrication and magnetic performance of rare-earth dysprosium doped Ca-Mg hexaferrite nanoparticles

In this research, dysprosium-substituted M-type Ca-Mg hexaferrites are successfully fabricated via sol–gel combustion technique, employing a nominal composition of Ca0.5Mg0.5Fe12-xDyxO19 (x = 0.0, 0.04, 0.08, 0.12, and 0.15). Analysis of XRD patterns reveals exclusive peaks corresponding to the M-type hexaferrite, with no indications of additional phases, underscoring the high purity and crystalline integrity of the synthesized material. The Rietveld refinement is used to evaluate lattice parameters ’a’ and ’c’ along with the cell volume ’V ’ using the distinct iron sites. Notably, a discernible upward trend in both lattice constants and cell volume emerged with the gradual introduction of dysprosium Dy+3 ion. Hexaferrite phase formation was also confirmed through the ‘c/a’ ratio which lies below the critical value of 3.98. Synthesized samples shows a composite surface morphology with adherent clusters of small crystals and well-formed individual crystals. VSM analysis suggests, remarkable results, particularly at the x = 0.15 doping level, which exhibits the highest magnetic parameters, including Ms = 32.13 emu g−1, Mr = 20.34 emu g−1, and Hc = 1.418 kOe. These results suggest that the synthesized samples hold promise as suitable contenders for optimizing recording media, offering the potential for improved data storage performance.

Oxygen-enriched Fe-N-C electrocatalyst for efficient oxygen reduction reaction

The cathode's oxygen reduction reaction (ORR) plays a crucial role in a variety of fuel cells. Developing affordable and efficient non-precious electrocatalysts for the ORR poses a major hurdle in the realm of electrochemical energy technologies. This work presents a transition metal-based catalyst, Fe-ONC, in which Fe is loaded in an oxygen-enriched nitrogen-doped carbon (NC) material. Oxygen enrichment of the catalyst was achieved by a pre-oxidation strategy. The XPS analysis reveals that Fe-ONC exhibits a higher abundance of oxidized species. The Fe of Fe-ONC exists in the form of Fe3O4 particles and Fe-Nx, respectively, which are uniformly distributed in the NC. The even spread of iron sites and the plentiful presence of oxygen-rich species are key factors in the superior ORR efficiency of Fe-ONC. Fe-ONC's half-wave potential (E1/2) in an alkaline environment (0.1 M KOH) stands at 0.891 V, markedly surpassing the standard commercial Pt/C value (0.840 V). Additionally, Fe-ONC demonstrated enhanced longevity and resistance to ethanol in comparison to commercially available Pt/C. Fe-ONC's outstanding efficacy highlights its potential as an alternative to precious metal catalysts. The document outlines a plan for creating ORR catalytic materials that are sustainable, economical, and efficient.

Challenges and Opportunities in Preparing Fe-N-C Layers Supported on Non-Carbon Supports

Global energy demand will be continuously rising in the foreseeable future. To mitigate the results of climate change it is necessary to reduce the emittance of greenhouse gases. One promising approach is to switch to hydrogen as energy carrier and use proton exchange membrane fuel cells (PEMFCs) to efficiently convert H2 into electric power. Here, hydrogen and oxygen/air are used to directly generate electrical energy with only water as byproduct. Both reactions need to happen efficiently at the same time. The oxygen reduction reaction (ORR), however, is a very sluggish four-electron-reaction and needs efficient catalysts.The state-of-the-art ORR catalyst in PEMFC is platinum but that is a very scarce and expensive metal. Hence, it is important to switch to precious-metal-group (PGM) free catalysts. In recent years, bio inspired iron-based FeNC catalysts have been shown to approach ORR activities that are competitive with those of platinum, even though they need a higher catalyst loading than Pt to reach the desired high current densities.1–3 Those catalysts feature single Fe atoms surrounded by four N atoms in graphitic carbon. The drawback of those materials is their lower stability compared to PGM materials. In a nutshell, the carbon matrix oxidizes during operation in PEMFCs, changing the morphology of the catalytic center and rendering it less active, or inactive, depending on the carbon oxidation extent. Direct demetallation phenomena are also possible, leaving a N4 cavity without metal cation center. It was shown recently by Wu et al.4 that it is possible to raise durability by adding an additional carbon layer on the catalyst. One alternative approach to reduce those degradations is to interface Fe-N4 sites with a carbon-free support. The targeted support material must be immune to corrosion in acid and withstand the typical ORR electrochemical potentials. It also has to be electrically conductive to facilitate electron transfers, both locally and on long scale.In this work, conductive ceramic metal oxide materials (Ta doped SnO2, TTO) was investigated as a possible alternative catalyst supports. This material is resistant to acid and can withstand prolonged potentials at operating conditions in PEMFCs.5 During the synthesis of the FeNC catalysts, high temperatures are generally applied. Such treatments can be detrimental to the conductivity of ceramics due to metal aggregation (in case of doped materials) and may also lead to morphological changes as well as the reduction of the ceramics to metallic materials. A robust method to synthesize FeNC catalysts is by mixing the separate Fe, N and C precursors and using optimized thermal treatment. In this study, the effect of the pyrolysis conditions as well as the ratio of FeNC precursors to TTO was investigated with various characterization methods, e.g. X-ray absorption spectroscopy, Mossbauer spectroscopy, and high resolution TEM. The characterization techniques confirm the presence of single atom Fe as well as different Sn species that might contribute to the activity. The resulting materials were electrochemically characterized with rotating disc electrode techniques and in PEM fuel cells for their ORR-activity and durability. It was shown that the activity of materials with a high FeNC precursor content relative to TTO can outperform a reference FeNC synthesized similarly but without TTO, in both RDE (Figure) and PEMFC.The presentation will report in detail the effects of pyrolysis conditions and FeNC precursor/TTO content on the structure, activity and stability of materials.(1) Mehmood, A. et al. High Loading of Single Atomic Iron Sites in Fe–NC Oxygen Reduction Catalysts for Proton Exchange Membrane Fuel Cells. Nat. Catal. 2022, 5 (4), 311–323. https://doi.org/10.1038/s41929-022-00772-9.(2) Gasteiger, H. A.; Marković, N. M. Just a Dream—or Future Reality? Science 2009, 324 (5923), 48–49. https://doi.org/10.1126/science.1172083.(3) Zion, N. et al.. Electrocatalysis of Oxygen Reduction Reaction in a Polymer Electrolyte Fuel Cell with a Covalent Framework of Iron Phthalocyanine Aerogel. ACS Appl. Energy Mater. 2022, 5 (7), 7997–8003. https://doi.org/10.1021/acsaem.2c00375.(4) Liu, S.et al. Atomically Dispersed Iron Sites with a Nitrogen–Carbon Coating as Highly Active and Durable Oxygen Reduction Catalysts for Fuel Cells. Nat. Energy 2022, 7 (7), 652–663. https://doi.org/10.1038/s41560-022-01062-1.(5) Jiménez-Morales, et al. Strong Interaction between Platinum Nanoparticles and Tantalum-Doped Tin Oxide Nanofibers and Its Activation and Stabilization Effects for Oxygen Reduction Reaction. ACS Catal. 2020, 10 (18), 10399–10411. https://doi.org/10.1021/acscatal.0c02220. Figure 1

Lejja archaeological site, Southeastern Nigeria and its potential for archaeological science research

In 2017/2018, two seasons of archaeological surveys were undertaken in Lejja, southeastern Nigeria. The aim of the archaeological field work was to systematically sample the area to locate archaeological sites, scatters of artefacts, features; and to characterize and record these findings. A particular objective was to identify sites with different typological or chronological characteristics and to then select representative examples for further investigation and excavations. This paper thus focuses for the first time; on the general knowledge of the archaeological signatures in addition to iron working that abound at the Lejja site from an archaeological perspective. We aimed to identify sites with evidence of iron production and sites with other characteristics of human habitation to compare inter-site variation. Using ethnoarchaeological studies, archaeological surveys and excavations, sixteen new sites were identified stretching from iron smelting sites to domestic/habitation sites and ancestral sites. We utilized both a systematic transect and an opportunistic approach to locate and map the archaeological sites encountered. The focus of the study was on thirteen key villages in Lejja southeastern Nigeria. Analysis of data shows that there seem to be distinct areas on the landscape for habitation and metal working respectively. However, it is unclear as yet what this distinction represents in terms of social organization, particularly whether they represent one community with different activity sites or two communities with distinct identities or indeed a more complex temporal and spatial patterning.

Mössbauer analysis of (FeNiCrSiB) amorphous alloy ribbons

The fabrication of iron-based amorphous alloys was executed through the utilization of the melt-spinning technique, followed by a characterization employing X-ray diffraction (XRD), scanning electron microscopes (SEM) and transmission Mössbauer spectroscopy (MS). The studies were performed on Fe76-xNixCr4Si8B12 (where x = 0, 4, 12, and 30) metallic glasses in the form of ribbons. Mössbauer spectroscopy enables the exploration of the localized surroundings of iron (Fe) atoms within the glassy state, revealing alterations in the amorphous structure attributed to variations in the addition of Nickel (Ni). The broad lines in the Mössbauer spectra of ferromagnetic amorphous ribbons are a result of the distribution of non-equivalent iron sites and interatomic distances. The line intensity ratio suggests a preferential orientation of iron moments within the ribbon plane. The results derived from Mössbauer analysis indicate that the amorphous alloys feature bimodal distributions of the hyperfine fields. Changes in the nickel content within the alloys impact the disorder in the as-cast state and concurrently influence parameters such as the average hyperfine field <Hhyp>, the average radius R of the first coordination shell, and the number of nearest neighbor Fe atoms.

Imaging Single Prussian Blue Nanoparticles with Extraordinary Low-Spin Iron Capacity.

In attempts to obtain high-capacity Prussian blue nanomaterials, current efforts are predominantly focused on the particle-ensemble-level understanding of their structure-activity relationships. Complementarily, it would be insightful to screen out extraordinary individuals from the nanoparticle population. Using a simple and efficient technique of bright-field microscopy, this work enables, for the first time, quantitative characterization of the overall two-redox-center electrochemistry of single Prussian blue nanoparticles many at a time. Quantitative optical voltammograms with little interference from solvent breakdown and non-Faradaic electrode charging/discharging are extracted for each single nanoparticle, revealing clear heterogeneity among them. On this basis, the microscopic method allows a detailed comparative analysis between the two redox-active sites. It is found that while the synthesized nanoparticles show a similar specific capacity of the high-spin (HS-Fe) sites with STD/mean = 30%, most individual nanoparticles exhibit monodispersedly small capacities of the low-spin iron (LS-Fe) sites, only about of the HS-Fe capacity. Most importantly, it is discovered that there is always a small fraction (∼8%) of the single nanoparticles showing an impressively tripled LS-Fe capacity. Facilitated by optical imaging, the discovery of this easily overlooked extraordinary subpopulation confers alternative opportunities for targeted efforts for material chemists to improve synthesis and material design based on these unusual individuals, which in turn implies the general significance of nanoparticle screening.

A tandem activity-based sensing and labeling strategy reveals antioxidant response element regulation of labile iron pools

Iron is an essential element for life owing to its ability to participate in a diverse array of oxidation-reduction reactions. However, misregulation of iron-dependent redox cycling can also produce oxidative stress, contributing to cell growth, proliferation, and death pathways underlying aging, cancer, neurodegeneration, and metabolic diseases. Fluorescent probes that selectively monitor loosely bound Fe(II) ions, termed the labile iron pool, are potentially powerful tools for studies of this metal nutrient; however, the dynamic spatiotemporal nature and potent fluorescence quenching capacity of these bioavailable metal stores pose challenges for their detection. Here, we report a tandem activity-based sensing and labeling strategy that enables imaging of labile iron pools in live cells through enhancement in cellular retention. Iron green-1 fluoromethyl (IG1-FM) reacts selectively with Fe(II) using an endoperoxide trigger to release a quinone methide dye for subsequent attachment to proximal biological nucleophiles, providing a permanent fluorescent stain at sites of elevated labile iron. IG1-FM imaging reveals that degradation of the major iron storage protein ferritin through ferritinophagy expands the labile iron pool, while activation of nuclear factor-erythroid 2-related factor 2 (NRF2) antioxidant response elements (AREs) depletes it. We further show that lung cancer cells with heightened NRF2 activation, and thus lower basal labile iron, have reduced viability when treated with an iron chelator. By connecting labile iron pools and NRF2-ARE activity to a druggable metal-dependent vulnerability in cancer, this work provides a starting point for broader investigations into the roles of transition metal and antioxidant signaling pathways in health and disease.

Enhanced tetracycline hydrochloride degradation at near neutral conditions with FeOx modified Bi4TaO8Cl catalyst: Coupling the photocatalytic and Fenton oxidation

The efficient regeneration of Fe2+ active sites in heterogeneous catalysts is of great significance for the photo-Fenton progress. Herein, amorphous FeOx as one efficient cocatalyst was anchored on the Bi4TaO8Cl nanosheets to boost the activation of H2O2 and the separation of photogenerated carriers. The surface-exposed FeOx can produce Fe2+ active sites by extracting the photogenerated electrons from Bi4TaO8Cl. As a result, the redox cycle of Fe3+/Fe2+ was built and the carriers were separated to boost the continuous photo-Fenton degradation. As a result, H2O2 are continuously activated through the cycle of Fe3+/Fe2+. The coupling of photocatalysis and the Fenton reaction enhances the TC-H degradation performance and suppress the loss-activation of iron sites. The optimized FeOx/Bi4TaO8Cl sample exhibited the highest degradation ratio of about 83.5 % in 20 min, which was nearly 4 times that of the pure Bi4TaO8Cl. In addition, the better performance of FeOx/Bi4TaO8Cl catalyst under near-neutral conditions also sheds new insights about the design of efficient photo-Fenton catalysts that can work under mild conditions.