Single Iron Atom Research Articles

Catechol-Isolated Atomically Dispersed Nanocatalysts for Self-Motivated Cocatalytic Tumor Therapy.

Nanocatalytic tumor therapy based on Fenton nanocatalysts has attracted considerable attention because of its therapeutic specificity, enhanced outcomes, and high biocompatibility. Nevertheless, the rate-determining step in Fenton chemistry, which involves the transition of a high-valence metallic center (FeIII ) to a Fenton-active low-valence metallic center (FeII ), has hindered advances in nanocatalyst-based therapeutics. In this study, we constructed mesoporous single iron atomic nanocatalysts (mSAFe NCs) by employing catechols from dopamine to coordinate and isolate single iron atoms. The catechols also serve as reductive ligands, generating a field-effect-based cocatalytic system that instantly reduces FeIII species to FeII species within the mSAFe NCs. This self-motivated cocatalytic strategy enabled by mSAFe NCs accelerates the kinetics of the Fenton catalytic reaction, resulting in remarkable performance for nanocatalytic tumor therapy both in vitro and in vivo.

Single iron atom embedded in dual-size nitrogen-doped carbon framework on reduced graphene oxide: An effective catalyst for proton exchange membrane fuel cells

The commercialization of Proton Exchange Membrane Fuel Cells (PEMFCs) is hindering by the cost of noble metal catalysts. We are introducing A-FeSAC-NCDS/rGO, a novel catalyst derived from metal-organic framework through carbonization and ammonia treatment. This catalyst is incorporating single iron atoms (FeSAC) within dual-sized porous nitrogen-carbon frameworks (NCDS, 30 nm and 100 nm), supporting on reduced graphene oxide (rGO). The catalyst is providing abundant active sites, with NCDS increasing active site density and rGO enhancing material conductivity. Consequently, catalyst is exceling in the oxygen reduction reaction, boasting an onset potential of 0.807 V and a half-wave potential of 0.779 V, near benchmark Pt/C catalyst. PEMFC tests employing A-FeSAC-NCDS/rGO achieved a power density of 780.7 mWcm−2 at 1.6 A cm−2 in an H2–O2 system. In durability tests at 0.6 Acm−2 in H2-air, voltage loss was 28.68 % after 50 h. These results position the catalyst as a promising choice for PEMFC.

An Erythrocyte-Templated Iron Single-Atom Nanozyme for Wound Healing.

Iron single-atom nanozymes represent a promising artificial enzyme with superior activity owing to uniform active sites that can precisely mimic active center of nature enzymes. However, current synthetic strategies are hard to guarantee each active site at single-atom state. In this work, an erythrocyte-templated strategy by utilizing intrinsic hemin active center of hemoglobin as sing-atom source for nanozyme formation is developed. By combining cell fixation, porous salinization, and high-temperature carbonization, erythrocytes are successfully served as uniform templates to synthesize nanozymes with fully single-atom FeN4 active sites which derived from hemin of hemoglobin, resulting in an enhanced peroxidase (POD)-like activity. Interestingly, the catalytic activity of erythrocyte-templated nanozyme (ETN) shows dependence on animal species, among which murine ETN performed superior catalytic efficiency. In addition, the as-prepared ETNs display a honeycomb-like network structure, serving as a sponge to accelerate hemostasis based on the interactions with prothrombin and fibrinogen. These features enable ETN to effectively kill methicillin-resistant Staphylococcus aureus (MRSA) by combining POD-like catalysis with near-infrared (NIR) induced photothermal effect, and subsequently suitable to promote wound healing. This study provides a proof-of-concept for facile fabrication of multifunctional nanozymes with uniform single-atom active sites by utilizing intrinsic iron structure characteristics of biogenic source like erythrocytes.

Biochar-Based Single-Atom Catalyst with Fe-N3O-C Configuration for Efficient Degradation of Organic Dyes by Peroxymonosulfate Activation.

Iron single-atom catalysts (Fe SACs) hold great promise for peroxymonosulfate (PMS) activation and degradation of organic pollutants in wastewater. However, insights into crucial catalytic sites and activation mechanisms of biochar-based Fe SACs for PMS remain a challenge. Herein, cotton stalk-derived biochar-based Fe SACs (Fe SACs-BC) with an asymmetric Fe-N/O-C configuration were prepared, and their PMS activation and acid orange 7 (AO7) degradation mechanisms were investigated. The results showed that the removal efficiency of the Fe SACs-BC catalyst with Fe-N3O-C configuration for AO7 and other five investigated organic dyes reached 95-99% within 15 min. The EPR spectrums, quenching experiments, electrochemical analysis, masking experiments, XPS, and theoretical calculations indicated that degradations of organic dyes were dominated by singlet oxygen, which was generated by direct PMS conversion at the electron-deficient carbon and iron sites in the Fe-N3O-C configuration. The Fe SACs-BC/PMS exhibited high removal efficiency and strong tolerance in different water matrices with a wide pH range, various coexisting anions and interfering substances, showing great potential and applicability for efficient treatment of actual textile wastewaters.

Identification of the optimal doping position of hetero-atoms in chalcogen-doped Fe–N–C catalysts for oxygen reduction reaction

The excellent oxygen reduction reaction (ORR) activity of Fe–N–C catalysts in acidic media makes them potential for low-cost proton exchange membrane fuel cells. In recent years, it has been shown that heteroatoms (B, O, S, P, Cl, F, etc.) can be used as electron-withdrawing groups to modulate the planar structure and electron distribution of the Fe–Nx active sites to achieve simultaneous improvement of catalytic activity and stability. However, the optimal location of the heteroatoms remains unclear. Here, taking chalcogen heteroatoms (S and Se) as an example, we control the doping positions and investigate their effect on the ORR performance of the Fe–N–C catalysts. The first coordination shell of the iron single atom is identified as the optimal doping position. The optimized catalyst Fe–N3S1/NC and Fe–N3Se1/NC demonstrate improved activity and stability in both half cells and fuel cells. This work provides insights into the enhancement mechanism of heteroatom doping of single-atom catalysts.

Single atom iron as an efficient electrocatalyst for enhanced kinetics in magnesium-sulfur batteries

Magnesium-sulfur battery (MSB) with the advantages of low cost, high theoretical energy density and high security is regarding as a promising energy storage system. However, it suffers from sluggish reaction kinetics, fast capacity fading and poor cycling stability due to the shortage of compatible electrolyte and high performance cathode. Herein, Fe single atom catalyst is introduced to improve the electrochemical performance of MSB for the first time. Fe atoms are uniformly dispersed on graphene support by a facile method to prepare Fe-N-G, which is applied as an effective sulfur host. Benefited from the remarkable catalytic performance of the single-atom Fe, the produced S@ Fe-N-G exhibits a high reversible discharge specific capacity of 962 mA h g−1 at 0.1C, outstanding cycling stability of maintaining 892.7 mA h g−1 at 0.3C after 200 cycles and excellent rate capability. It is expected that this work could promote the development of more high-efficient single-atom catalysts for high performance MSB.

A dual-mode biosensor featuring single-atom Fe nanozyme for multi-pesticide detection in vegetables

The single-atom iron nanozyme (SA-Fe-NZ) exhibits high catalytic activity and excellent electron transfer efficiency in biosensors. However, the binding of bioreceptors to the surface of SA-Fe-NZ results in a decrease in the catalytic activity of the nanozyme due to its toxic effects. We utilized the toxic effects and excellent electrochemical properties of the SA-Fe-NZ to successfully construct a smartphone-assisted dual-mode biosensor. The complex formed by the binding of organophosphorus pesticides (OPs) to the aptamer exhibited toxic effects and inhibited the catalytic activity of the nanozyme, preventing the colorimetric substrate from being catalyzed. Simultaneously, the aptamers labeled with electrochemical signal molecules approached the electrode surface, causing a change in the electrochemical signal. The results demonstrated that the constructed broad-spectrum aptamer biosensor exhibited a low limit of detection of 3.55 fM and a wide linear range of 10-13-10-2 M, allowing for qualitative and quantitative detection of multiple OPs in vegetables.

Molecular Recognition Regulates Coordination Structure of Single-Atom Sites.

Coordination engineering for single-atom sites has drawn increasing attention, yet its chemical synthesis remains a tough issue, especially for tailorable coordination structures. Herein, a molecular recognition strategy is proposed to fabricate single-atom sites with regulable local coordination structures. Specifically, a heteroatom-containing ligand serves as the guest molecule to induce coordination interaction with the metal-containing host, precisely settling the heteroatoms into the local structure of single-atom sites. As a proof of concept, thiophene is selected as the guest molecule, and sulfur atoms are successfully introduced into the local coordination structure of iron single-atom sites. Ultrahigh oxygen reduction electrocatalytic activity is achieved with a half-wave potential of 0.93 V versus reversible hydrogen electrode. Furthermore, the strategy possesses excellent universality towards diversified types of single-atom sites. This work makes breakthroughs in the fabrication of single-atom sites and affords new opportunities in structural regulation at the atomic level.

Single-atom catalysts-based catalytic ROS clearance for efficient psoriasis treatment and relapse prevention via restoring ESR1

Psoriasis is a common inflammatory disease of especially high recurrence rate (90%) which is suffered by approximately 3% of the world population. The overexpression of reactive oxygen species (ROS) plays a critical role in psoriasis progress. Here we show that biomimetic iron single-atom catalysts (FeN4O2-SACs) with broad-spectrum ROS scavenging capability can be used for psoriasis treatment and relapse prevention via related gene restoration. FeN4O2-SACs demonstrate attractive multiple enzyme-mimicking activities based on atomically dispersed Fe active structures, which are analogous to those of natural antioxidant enzymes, iron superoxide dismutase, human erythrocyte catalase, and ascorbate peroxidase. Further, in vitro and in vivo experiments show that FeN4O2-SACs can effectively ameliorate psoriasis-like symptoms and prevent the relapse with augmented efficacy compared with the clinical drug calcipotriol. Mechanistically, estrogen receptor 1 (ESR1) is identified as the core protein upregulated in psoriasis treatment through RNA sequencing and bioinformatic analysis. Together, this study provides a proof of concept of psoriasis catalytic therapy (PCT) and multienzyme-inspired bionics (MIB).

Metal–Organic Framework (MOF)-Based Single-Atom Iron Catalysts for NIR-II Enhanced Catalytic-Photothermal Synergistic Antibacterial Therapy

Metal–Organic Framework (MOF)-Based Single-Atom Iron Catalysts for NIR-II Enhanced Catalytic-Photothermal Synergistic Antibacterial Therapy

Highly active, ultra-low loading single-atom iron catalysts for catalytic transfer hydrogenation

Highly effective and selective noble metal-free catalysts attract significant attention. Here, a single-atom iron catalyst is fabricated by saturated adsorption of trace iron onto zeolitic imidazolate framework-8 (ZIF-8) followed by pyrolysis. Its performance toward catalytic transfer hydrogenation of furfural is comparable to state-of-the-art catalysts and up to four orders higher than other Fe catalysts. Isotopic labeling experiments demonstrate an intermolecular hydride transfer mechanism. First principles simulations, spectroscopic calculations and experiments, and kinetic correlations reveal that the synthesis creates pyrrolic Fe(II)-plN3 as the active center whose flexibility manifested by being pulled out of the plane, enabled by defects, is crucial for collocating the reagents and allowing the chemistry to proceed. The catalyst catalyzes chemoselectively several substrates and possesses a unique trait whereby the chemistry is hindered for more acidic substrates than the hydrogen donors. This work paves the way toward noble-metal free single-atom catalysts for important chemical reactions.

Bimodal single-atom iron nanozyme biosensor for volatile amine and food freshness detection

Volatile amines (VAs) play a critical role in detecting the freshness of meat. However, the development of nondestructive, real-time, and portable techniques for monitoring VAs remains a challenge. Here, we successfully created a colorimetric-fluorescent dual-signal biosensor for meat freshness detection by using a single-atom iron nanozyme (SAFe-N-C nanozyme) and carbon quantum dots (CDs). The SAFe-N-C nanozyme with high peroxidase-like (POD-like) activity (40.22 U/mg) acts as a catalyst by facilitating the conversion of the colourless reduced state 3,3′,5,5′-tetramethylbenzidine (redTMB) to its oxidized product (oxTMB). Subsequently, the fluorescence signal of the CDs is quenched due to the inner filtering effect (IFE) between oxTMB and CDs. During food spoilage, the generation of VAs results in the reduction of oxTMB, which subsequently recovers the fluorescence of the CDs. As a result, the limits of detection (LOD) for ammonia detection are 0.9840 ppm and 0.0838 ppm within a linear range of 0.5–50 ppm. This colorimetric-fluorescent dual-signal biosensor effectively detects VAs during the spoilage of livestock and poultry meat in a nondestructive and real-time manner. This innovative work overcomes the limitation of single signal output and provides a portable and reliable method for VAs detection, proving to be a significant advancement in meat freshness assessment.

Efficient activation of peroxymonosulfate by Fe single-atom: The key role of Fe-pyrrolic nitrogen coordination in generating singlet oxygen and high-valent Fe species

Nitrogen-doped carbon matrix single-atom catalysts (SACs) for the efficient removal of organic pollutants have attracted widespread attention. However, the ligand structure and the origin of the high activity between nitrogen species and single-atoms remain elusive. Herein, nitrogen-doped carbon matrix iron single-atom catalysts (Fe/NC-SACs) that exhibit high catalytic reactivity (98.2% SMX degradation in 5 min), broad pH resistance (pH 3.0–11.1), high stability, and sustainable water treatment capacity are reported. High-valent iron (Fe IV=O) and singlet oxygen (1O2) were the reactive oxygen species observed. The electrochemical results demonstrated the generation of catalyst-PMS complexes. The DFT calculations revealed that Fe-pyrrolic N4 was the best ligand for PMS, exhibiting the highest adsorption energy, bond length variation and electron transfer capacity. The central Fe single atom and the carbon electrons adjacent to the pyrrolic N were the reactive sites of the PMS. The main source of 1O2 was the oxidation of PMS. This work provides guidance for the discovery of high-performance catalysts and provides a single-atom catalyst that can be used for practical environmental purification.

Catalytic activity and anti-passivation of single iron atoms and atomic clusters co-stabilized on carbonized waste polystyrene plastic

Catalytic activity and anti-passivation of single iron atoms and atomic clusters co-stabilized on carbonized waste polystyrene plastic

Size-matched hierarchical porous carbon materials anchoring single-atom Fe-N4 sites for PMS activation: An in-depth study of key active species and catalytic mechanisms

Single-atom catalysts are considered to be one of the most promising catalysts for AOPs. However, how to design and synthesize cost-effective and highly loaded single-atom catalysts is the bottleneck limiting its development and application. In this study, we report a highly loaded single-atom iron catalyst (Fe-SAC-BC) using waste biomass as a carbon carrier to anchor Fe-N4 sites. The catalyst showed excellent catalytic performance and stability in wastewater treatment. Unlike conventional radical oxidation, the non-radical degradation process of Fe-N4 as the active site and high-valent iron-oxygen intermediates as the key active species identified by burst and probe experiments. DFT calculations and molecular dynamics simulations were applied to the catalytic mechanism of Fe-SAC-BC, in which Fe (III)-N4 is the most likely active site and Fe (IV)-OH is the most dominant active species. This study provides new strategies and understanding for the design of novel single-atom catalysts and the mechanistic probing of the non-radical pathways of AOPs.

Lignin-based iron single-atom nanozyme for detection of organophosphorus in soil

Organophosphorus pesticides (OPs) are widely used in agriculture and their residues can pose a threat to human health. Therefore the monitoring of their residue content is necessary. In this study, a colorimetric sensing strategy was designed to detect OPs by combining nanozymes with natural enzymes. Among them, iron single-atom nanozymes (Fe-N/C) were prepared by a one-pot synthesis method by pyrolyzing alkaline lignin. Various characterization tools were used to elucidate the microstructure and reaction mechanism of the nanozymes. N in the material is mainly bound to Fe in the form of pyrrole nitrogen, catalytic H2O2 will produce OH. Fe-N/C has good peroxidase-like activity and produces signals in UV detection upon the addition of 3,3′,5,5′-tetramethylbenzidine (TMB). Combining the catalytic properties of Fe-N/C and introducing acetylcholinesterase (AChE) for the detection of OPs in soil (take chlorpyrifos for example). The product of AChE catalyzed acetylcholine (ATCh) can inhibit the color signal. In contrast, the presence of chlorpyrifos destroys the activity of AChE and restores the reaction absorbance. The amount of chlorpyrifos can be calculated by observing the changes in color. The linear range of chlorpyrifos detection based on this strategy was 0.05–10.0 μg mL−1, the detection limit was 2.11 ng mL−1. This strategy provides a sensitive method for the quantitative determination of OPs, which is important for the monitoring of OPs in the environment.

Non-heme Iron Single-Atom Nanozymes as Peroxidase Mimics for Tumor Catalytic Therapy.

Single-atom nanozymes (SAzymes) open new possibilities for the development of artificial enzymes that have catalytic activity comparable to that of natural peroxidase (POD). So far, most efforts have focused on the structural modulation of the Fe-N4 moiety to mimic the metalloprotein heme center. However, non-heme-iron POD with much higher activity, for example, HppE, has not been mimicked successfully due to its structural complexity. Herein, carbon dots (CDs)-supported SAzymes with twisted, nonplanar Fe-O3N2 active sites, highly similar to the non-heme iron center of HppE, was synthesized by exploiting disordered and subnanoscale domains in CDs. The Fe-CDs exhibit an excellent POD activity of 750 units/mg, surpassing the values of conventional SAzymes with planar Fe-N4. We further fabricated an activatable Fe-CDs-based therapeutic agent with near-infrared enhanced POD activity, a photothermal effect, and tumor-targeting ability. Our results represent a big step in the design of high-performance SAzymes and provide guidance for future applications for synergistic tumor therapy.

Facilely Tuning the First-Shell Coordination Microenvironment in Iron Single-Atom for Fenton-like Chemistry toward Highly Efficient Wastewater Purification.

Precisely identifying the atomic structures in single-atom sites and establishing authentic structure-activity relationships for single-atom catalyst (SAC) coordination are significant challenges. Here, theoretical calculations first predicted the underlying catalytic activity of Fe-NxC4-x sites with diverse first-shell coordination environments. Substituting N with C to coordinate with the central Fe atom induces an inferior Fenton-like catalytic efficiency. Then, Fe-SACs carrying three configurations (Fe-N2C2, Fe-N3C1, and Fe-N4) fabricate facilely and demonstrate that optimized coordination environments of Fe-NxC4-x significantly promote the Fenton-like catalytic activity. Specifically, the reaction rate constant increases from 0.064 to 0.318 min-1 as the coordination number of Fe-N increases from 2 to 4, slightly influencing the nonradical reaction mechanism dominated by 1O2. In-depth theoretical calculations unveil that the modulated coordination environments of Fe-SACs from Fe-N2C2 to Fe-N4 optimize the d-band electronic structures and regulate the binding strength of peroxymonosulfate on Fe-NxC4-x sites, resulting in a reduced energy barrier and enhanced Fenton-like catalytic activity. The catalytic stability and the actual hospital sewage treatment capacity also showed strong coordination dependency. This strategy of local coordination engineering offers a vivid example of modulating SACs with well-regulated coordination environments, ultimately maximizing their catalytic efficiency.

Breaking Local Charge Symmetry of Iron Single Atoms for Efficient Electrocatalytic Nitrate Reduction to Ammonia.

The electrochemical conversion of nitrate pollutants into value-added ammonia is a feasible way to achieve artificial nitrogen cycle. However, the development of electrocatalytic nitrate-to-ammonia reduction reaction (NO3-RR) has been hampered by high overpotential and low Faradaic efficiency. Here we develop an iron single-atom catalyst coordinated with nitrogen and phosphorus on hollow carbon polyhedron (denoted as Fe-N/P-C) as a NO3-RR catalyst electrode. Owing to the tuning effect of phosphorus atoms on breaking local charge symmetry of the single-Fe-atom catalyst, it facilitates the adsorption of nitrate ions and enrichment of some key reaction intermediates during the NO3-RR process. The Fe-N/P-C catalyst exhibits 90.3% ammonia Faradaic efficiency with a yield rate of 17980 μg h-1 mgcat-1, greatly outperforming the reported Fe-based catalysts. Furthermore, operando SR-FTIR spectroscopy measurements reveal the reaction pathway based on key intermediates observed under different applied potentials and reaction durations. Density functional theory calculations demonstrate that the optimized free energy of NO3-RR intermediates is ascribed to the asymmetric atomic interface configuration, which achieves the optimal electron density distribution. This work demonstrates the enhanced function of heteroatom doping on single atoms for NO3-RR, and provides an effective strategy for improving the catalytic performance of single atom catalysts in different electrochemical reactions.

Photocatalytic C–N Bond Formation with Single Iron Atoms on Sulfur-Containing Carbon Nitride

Photocatalytic C–N Bond Formation with Single Iron Atoms on Sulfur-Containing Carbon Nitride