Metal Coordination Complex Derived Fe7S8 Particles Embedded in N-doped Carbon Framework with Regulated Porous Structure Enabling High-Rate and Durable Sodium Storage.

Iron sulfides with high theoretical capacity confront the challenges of low rate capability and severe capacity fading for sodium storage, which are mainly caused by poor electron/ion transport kinetics and drastic volume fluctuations during cycling. Herein, to mitigate these obstacles, a multi-step synthetic tactic involving solvothermal, carbonization, and subsequent sulfurization is put forward for the construction of wire-like structure by confining Fe7S8 particles in porous N-doped carbon framework (denoted as Fe7S8/PNC) using zinc iron nitrilotriacetate as template. By partially substituting Fe3+ with Zn2+ in the metal coordination complex, the porous structure of coordination complex derived carbon framework can be regulated through pore structure engineering of Zn nanodroplets. The desired porous and robust core/shell structure can not only afford favorable electron/Na+ transport paths and additional active sites for Na+ storage, but also provide reinforced structural integrity of interior Fe7S8 particles by retarding the pulverization and buffering the mechanical stress against volume fluctuations. As anode for sodium-ion batteries, the optimal Fe7S8/PNC delivers a high reversible capacity (743 mAh g-1 at 0.1 A g-1), superior rate capability (553 mAh g-1 at 10 A g-1), and long-term cycling stability (602 mAh g-1 at 5 A g-1 with 98.5% retention after 1000 cycles).

Acetylcholine triggered enzymatic cascade reaction based on Fe7S8 nanoflakes catalysis for organophosphorus pesticides visual detection.

BACKGROUND: Organophosphorus pesticides (OPs) play important roles in the natural environment, agricultural fields, and biological prevention. The development of OPs detection has gradually become an effective strategy to avoid the dangers of pesticides abuse and solve the severe environmental and health problems in humans. Although conventional assays for OPs analysis such as the bulky instrument required analytical methods have been well-developed, it still remains the limitation of inconvenient, inefficient and lab-dependence analysis in real samples. Hence, there is an urgent demand to develop efficient detection methods for OPs analysis in real scenarios. RESULTS: Here, by virtue of the highly efficient catalytic performance in Fe7S8 nanoflakes (Fe7S8 NFs), we propose an OPs detection method that rationally integrated Fe7S8 NFs into the acetylcholine (ACh) triggered enzymatic cascade reaction (ATECR) for proceeding better detection performances. In this method, OPs serve as the enzyme inhibitors for inhibiting ATECR among ACh, acetylcholinesterase (AChE), and choline oxidase (CHO), then reduce the generation of H2O2 to suppress the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) that catalyzed by Fe7S8 NFs. Benefiting from the integration of Fe7S8 NFs and ATECR, it enables a sensitive detection for OPs (e.g. dimethoate). The proposed method has presented good linear ranges of OPs detection ranging from 0.1 to 10 µg mL-1. Compared to the other methods, the comparable limits of detection (LOD) of OPs are as low as 0.05 µg mL-1. SIGNIFICANCE: Furthermore, the proposed method has also achieved a favorable visual detection performance of revealing OPs analysis in real samples. The visual signals of OPs can be transformed into RGB values and gathered by using smartphones, indicating the great potential in simple, sensitive, instrument-free and on-site analysis of pesticide residues in environmental monitoring and biosecurity research.

Spatially Confined Fe7S8 Nanoparticles Anchored on a Porous Nitrogen-Doped Carbon Nanosheet Skeleton for High-Rate and Durable Sodium Storage.

Iron sulfides are widely explored as anodes of sodium-ion batteries (SIBs) owing to high theoretical capacities and low cost, but their practical application is still impeded by poor rate capability and fast capacity decay. Herein, for the first time, we construct highly dispersed Fe7S8 nanoparticles anchored on a porous N-doped carbon nanosheet (CN) skeleton (denoted as Fe7S8/NC) with high conductivity and numerous active sites via facile ion adsorption and thermal evaporation combined procedures coupled with a gas sulfurization treatment. Nanoscale design coupled with a conductive carbon skeleton can simultaneously mitigate the above obstacles to obtain enhanced structural stability and faster electrode reaction kinetics. With the aid of density functional theory (DFT) calculations, the synergistic interaction between CNs and Fe7S8 can not only ensure enhanced Na+ adsorption ability but also promote the charge transfer kinetics of the Fe7S8/NC electrode. Accordingly, the designed Fe7S8/NC electrode exhibits remarkable electrochemical performance with superior high-rate capability (451.4 mAh g-1 at 6 A g-1) and excellent long-term cycling stability (508.5 mAh g-1 over 1000 cycles at 4 A g-1) due to effectively alleviated volumetric variation, accelerated charge transfer kinetics, and strengthened structural integrity. Our work provides a feasible and effective design strategy toward the low-cost and scalable production of high-performance metal sulfide anode materials for SIBs.

Realizing Ultrafast and Robust Sodium-Ion Storage of Iron Sulfide Enabled by Heteroatomic Doping and Regulable Interface Engineering.

Fe-based sulfides are a promising type of anode material for sodium-ion batteries (SIBs) due to their high theoretical capacities and affordability. However, these materials often suffer from issues such as capacity deterioration and poor conductivity during practical application. To address these challenges, an N-doped Fe7S8 anode with an N, S co-doped porous carbon framework (PPF-800) was synthesized using a template-assisted method. When serving as an anode for SIBs, it delivers a robust and ultrafast sodium storage performance, with a discharge capacity of 489 mAh g-1 after 500 cycles at 5 A g-1 and 371 mAh g-1 after 1000 cycles at 30 A g-1 in the ether-based electrolyte. This impressive performance is attributed to the combined influence of heteroatomic doping and adjustable interface engineering. The N, S co-doped carbon framework embedded with Fe7S8 nanoparticles effectively addresses the issues of volumetric expansion, reduces the impact of sodium polysulfides, improves intrinsic conductivity, and stimulates the dominant pseudocapacitive contribution (90.3% at 2 mV s-1). Moreover, the formation of a stable solid electrolyte interface (SEI) film by the effect of uniform pore structure in ether-based electrolyte produces a lower transfer resistance during the charge-discharge process, thereby boosting the rate performance of the electrode material. This work expands a facile strategy to optimize the electrochemical performance of other metal sulfides.

Boosting electron transport process over multiple channels induced by S-doped carbon and Fe7S8 NPs interface toward high-efficiency antibiotics removal.

The enhancement of electron transport process on multiple channels of C-Fe and C-S-Fe bonds between dual-reaction centres was investigated for stimulating the antibiotics degradation in Fenton-like processes. Herein, multiple channels structure of sulfur-doped carbon coupled Fe7S8 cluster through C-Fe bond and C-S-Fe bond was constructed through density functional theory (DFT), and S-doped carbon framework coated Fe7S8 nanoparticles (Fe7S8/SC) Fenton-like catalyst was prepared through hydrothermal and subsequent sulfuration process. The DFT calculations revealed that electrons are thermodynamically transferred from carbon to iron along both C-Fe and C-S-Fe bonds. The optimized Fe7S8/SC catalyst exhibited desirable catalytic property for Fenton-like degradation for various antibiotics, the removal of amoxicillin, norfloxacin, and tetracycline hydrochloride reach 98.9%, 97.8%, and 99.3% respectively within 40 min under neutral pH, and catalyst also demonstrated excellent cycle stability after five runs. The excellent degradation effect of antibiotics by Fenton-like catalyst was attributed to the intensified electron transport process by multiple electron transfer channels between dual reaction centres, making FeII easier to regenerate. This study spreads a new route for the enhancement of electron transport process in Fenton-like catalysts by constructing multiple channels.

Iron-sulphur transformation control for enhancing Cr(VI) removal in flake and nanoscale porous pyrrhotite (Fe7S8) added wastewater.

Hexavalent chromium (Cr(VI)) contaminated wastewater should be addressed efficiently in the environmental field. In previous applications, nano iron sulfides amendment has not been well controlled for iron-sulfur transformation. In this study, the novel flake and nanoscale porous pyrrhotite (Fe7S8) (FNPP) amendment was synthesized. The iron-sulphur transformation of FNPP was controlled and optimized for enhancing Cr(VI) removal. The specific surface area and average pore diameter of the FNPP amendment reached 115.7 m2/g and 2.1 nm. The maximum adsorption capacity of total chromium reached 66.3 mg/g. The optimized iron-sulphur transformation condition was an initial FNPP and Cr(VI) molar ratio of 8, pH at 5.6, in which the Cr(VI) removal reached 96.5% and all producing S2- was utterly consumed. It is confirmed that S2- fast induced Fe3+/Fe2+ circulation and FNPP has a speedier adsorption rate for Cr(III) than Cr(VI). Fe2+ and S2- mediated the Cr(VI) reduction to Cr(III), thus, much faster Cr(VI) removal was achieved. High efficiency removal mechanism of Cr(VI) was combined with surface adsorption/reduction and solution reduction/precipitation. The research demonstrated that controlling and optimizing the iron-sulphur transformation of Fe7S8 amendment can significantly enhance Cr(VI) removal.

Controllable Synthesis Quadratic-Dependent Unsaturated Magnetoresistance of Two-Dimensional Nonlayered Fe7S8 with Robust Environmental Stability.

Two-dimensional (2D) iron chalcogenides (FeX, X = S, Se, Te) are emerging as an appealing class of materials for a wide range of research topics, including electronics, spintronics, and catalysis. However, the controlled syntheses and intrinsic property explorations of such fascinating materials still remain daunting challenges, especially for 2D nonlayered Fe7S8 with mixed-valence states and high conductivity. Herein, we design a general and temperature-mediated chemical vapor deposition (CVD) approach to synthesize ultrathin and large-domain Fe7S8 nanosheets on mica substrates, with the thickness down to ∼4.4 nm (2 unit-cell). Significantly, we uncover a quadratic-dependent unsaturated magnetoresistance (MR) with out-of-plane anisotropy in 2D Fe7S8, thanks to its ultrahigh crystalline quality and high conductivity (∼2.7 × 105 S m-1 at room temperature and ∼1.7 × 106 S m-1 at 2 K). More interestingly, the CVD-synthesized 2D Fe7S8 nanosheets maintain robust environmental stability for more than 8 months. These results hereby lay solid foundations for synthesizing 2D nonlayered iron chalcogenides with mixed-valence states and exploring fascinating quantum phenomena.

MOF-Derived Fe7 S8 Nanoparticles/N-Doped Carbon Nanofibers as an Ultra-Stable Anode for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have aroused wide concern due to their potential applications in large-scale energy-storage systems. In this work, a hybrid of Fe7 S8 nanoparticles/N-doped carbon nanofibers (Fe7 S8 /N-CNFs) is designed and synthesized via electrospinning. As an anode for SIBs, Fe7 S8 /N-CNFs exhibit a high reversible capacity of 649.9 mAh g-1 at 0.2 A g-1 after 100 cycles, and superior cycling stability for 2000 cycles at 1 A g-1 with only 0.00302% capacity decay per cycle. Such excellent performance originates from: i) Fe7 S8 nanoparticles (average diameter of 17 nm), which shorten the Na+ diffusion distance; ii) the unique 3D N-CNFs, which enhance the conductivity, alleviate the self-agglomeration and large volume change of Fe7 S8 nanoparticles, and offer numerous active sites for Na+ adsorption and paths for electrolyte diffusion. The fascinating structure and superior electrochemical properties of Fe7 S8 /N-CNFs shed light on developing high-performance SIBs anode materials.

Magnetic structure and exchange interactions in pyrrhotite end member minerals: hexagonal FeS and monoclinic Fe7S8.

Iron mono-sulphides, or pyrrhotites, are minerals present in the Earth's crust and mantle as well as major magnetic constituents of several classes of meteorites, thus are of interest to a wide range of disciplines including geology, geophysics, geochemistry, and material science. Despite displaying diverse magnetic properties as a result of iron vacancy ordering, the underlying exchange mechanism has not been quantified. This study presents an examination of the electronic and magnetic properties for the two pyrrhotite group end members, hexagonal FeS and monoclinic Fe7S8(4C superstructure) by means of density functional theory coupled with a Heisenberg magnetic model. The easy magnetization axes of FeS and Fe7S8are found to be positioned along the crystallographicc-direction and at an angle of 56° to thec-direction, respectively. The magnetic anisotropy energy in Fe7S8is greatly increased as a consequence of the vacancy framework when compared to FeS. The main magnetic interaction, in both compounds, is found to be the isotropic exchange interaction favouring antiferromagnetic alignment between nearest-neighbouring spins. The origin of the exchange interaction is elucidated further following the Goodenough-Kanamori-Anderson rules. The antisymmetric spin exchange is found to have a minor effect in both compounds. The theoretical findings presented in this work thus help to further resolve some of the ambiguities in the magnetic features of pyrrhotites.

Confining Pyrrhotite Fe7 S8 in Carbon Nanotubes Covalently Bonded onto 3D Few-Layer Graphene Boosts Potassium-Ion Storage and Full-Cell Applications.

The pyrrhotite Fe7 S8 with mixed Fe-valence possesses high theoretical capacity, high conductivity, low discharge/charge voltage plateaus, and superior redox reversibility but suffers from structural degradation upon (de)potassiation process due to severe volume variations. Herein, to conquer this issue, a novel hierarchical architecture of confining nano-Fe7 S8 in carbon nanotubes covalently bonded onto 3D few-layer graphene (Fe7 S8 @CNT@3DFG) is designed for potassium storage. Notably, CNTs could successfully grow on the surface of 3DFG via a tip-growth model under the catalytic effect of Fe3 C. Such structure enables the hierarchical confinement of 0D nano-Fe7 S8 to 1D CNTs and further 1D CNTs to 3DFG, effectively buffering the volume variations, prohibiting the agglomeration of Fe7 S8 nanograins, and boosting the ionic/electronic transportation through the stable and conductive CNTs-grafted 3DFG framework. The as-prepared Fe7 S8 @CNT@3DFG electrode delivers an exceptional rate capability (502 mAh g-1 at 50 mA g-1 with 277 mAh g-1 at 1000 mA g-1 ) and an excellent long-term cyclic stability up to 1300 cycles. Besides, the in-situ XRD and ex-situ XPS/HRTEM results first elucidate the highly reversible potassium-storage mechanism of Fe7 S8 . Furthermore, the designed potassium full-cell employing Fe7 S8 @CNT@3DFG anode and potassium Prussian blue (KPB) cathode delivers a promising energy density of ≈120 Wh kg-1 , demonstrating great application prospects.

Single-crystalline Fe7S8/Fe3O4 coated zero-valent iron synthesized with vacuum chemical vapor deposition technique: Enhanced reductive, oxidative and photocatalytic activity for water purification.

Well-defined core/shell type single crystalline Fe7S8/Fe3O4 coated α-Fe hybrids (Fe7S8/Fe3O4@Fe) are synthesized with vacuum chemical vapor deposition (CVD) technique. The CVD process triggers conversion of naturally formed Fe3O4 layer on the surface of commercial Fe nanoparticles from amorphous into single crystalline phase. The Fe7S8/Fe3O4 coat promotes the surface affinity of dissolved oxygen and targets and rapidly transfers electrons from the Fe core to targets, which decreases water splitting on Fe7S8/Fe3O4@Fe surface and endows Fe7S8/Fe3O4@Fe with ultra-strong reducibility and improved oxidative ability under different conditions. Different with the sulfurized ZVI prepared with hydrothermal or solvothermal method, the increase of reaction solution pH is retarded due to the relieved water splitting instead of releasing H+ via oxidation of S2-/S22- on the Fe7S8 coat. The cooperation of Fe7S8 with Fe3O4 and α-Fe not only improves the anti-oxidation ability of Fe7S8 coating but also broadens its band gap. By using Fe7S8/Fe3O4@Fe nanohybrids as photocatalysts, light irradiation accelerates the degradation of organic pollutants combined with enhanced mineralization efficiency. The Fe7S8/Fe3O4@Fe exhibits good performance when it is utilized to treat the influent from a municipal sewage treatment plant upon air aeration or under visible light and solar light irradiation.

A Robust Strategy for Engineering Fe7S8/C Hybrid Nanocages Reinforced by Defect-Rich MoS2 Nanosheets for Superior Potassium-Ion Storage.

Metal sulfides have attracted tremendous research interest for developing high-performance electrodes for potassium-ion batteries (PIBs) for their high theoretical capacities. Nevertheless, the practical application of metal sulfides in PIBs is still unaddressed due to their intrinsic shortcomings of low conductivity and severe volume changes during the potassiation/depotassiation process. Herein, robust Fe7S8/C hybrid nanocages reinforced by defect-rich MoS2 nanosheets (Fe7S8/C@d-MoS2) were designed, which possess abundant multichannel and active sites for potassium-ion transportation and storage. Kinetic analysis and theoretical calculation verify that the introduction of defect-rich MoS2 nanosheets dramatically promotes the potassium-ion diffusion coefficient. The ex-situ measurements revealed the potassium-ion storage mechanism in the Fe7S8/C@d-MoS2 composite. Benefitting from the tailored structural design, the Fe7S8/C@d-MoS2 hybrid nanocages show high reversible capacity, exceptional rate property, and superior cyclability.

In-situ synthesis of Fe7S8 nanocrystals decorated on N, S-codoped carbon nanotubes as anode material for high-performance lithium-ion batteries.

Fe7S8 has emerged as an attractive anode material for lithium-ion batteries (LIBs) due to its outstanding features such as low cost, high theoretical capacity, as well as environmental benignity. However, the rapid capacity fading derived from the tremendous volume change during the charging/discharging process hinders its practical application. Nanostructure engineering and the combination with carbonaceous material are essential to address this issue. In this work, Fe7S8 nanocrystals decorated on N, S-codoped carbon nanotubes (Fe7S8-NSC) were synthesized through a facile one-step pyrolysis of Fe-containing polypyrrole (PPy) nanotubes with sulphur powders under nitrogen atmosphere. When evaluated as anode of LIBs, Fe7S8-NSC demonstrates excellent cycling stability (718.8 mAh g-1 at 100 mA g-1 after 100 cycles) and superior rate ability (290.8 mAh g-1 at 2000 mA g-1). Moreover, Fe7S8-NSC shows a typical specific capacity recovery phenomenon, an extraordinary capacity of 744.4 mAh g-1 at 2000 mA g-1 after 1000 cycles can be achieved, which outperforms most of the Fe7S8-based anode materials reported before. The Fe7S8-NSC should be a promising anode material for high-performance LIBs.

Surface Modification of Fe7 S8 /C Anode via Ultrathin Amorphous TiO2 Layer for Enhanced Sodium Storage Performance.

Iron sulfides with high theoretical capacity and low cost have attracted extensive attention as anode materials for sodium ion batteries. However, the inferior electrical conductivity and devastating volume change and interface instability have largely hindered their practical electrochemical properties. Here, ultrathin amorphous TiO2 layer is constructed on the surface of a metal-organic framework derived porous Fe7 S8 /C electrode via a facile atomic layer deposition strategy. By virtue of the porous structure and enhanced conductivity of the Fe7 S8 /C, the electroactive TiO2 layer is expected to effectively improve the electrode interface stability and structure integrity of the electrode. As a result, the TiO2 -modified Fe7 S8 /C anode exhibits significant performance improvement for sodium-ion batteries. The optimal TiO2 -modified Fe7 S8 /C electrode delivers reversible capacity of 423.3 mA h g-1 after 200 cycles with high capacity retention of 75.3% at 0.2 C. Meanwhile, the TiO2 coating is conducive to construct favorable solid electrolyte interphase, leading to much enhanced initial Coulombic efficiency from 66.9% to 72.3%. The remarkable improvement suggests that the interphase modification holds great promise for high-performance metal sulfide-based anode materials for sodium-ion batteries.

Porous pyrrhotite Fe7S8 nanowire/SiOx/nitrogen-doped carbon matrix for high-performance Li-ion-battery anodes.

Iron sulfides, known as attractive anode materials for rechargeable lithium-ion batteries, have been extensively studied. Nevertheless, low electrical conductivity and huge volume expansion of iron sulfides hinder its practical applications. Herein, a novel method was developed to synthesize ternary porous Fe7S8 nanowires/SiOx/nitrogen-doped carbon matrix by facile hydrothermal method and subsequent sulfidation derived from bamboo leaves. The SiOx/nitrogen-doped carbon matrix can ensure the growth of nanowires, maintain the structural stability, improve the conductivity and provide improved capacity of Fe7S8. The 3D matrix structure and porous properties of Fe7S8 nanowires effectively relieve the volume change upon the insertion/extraction of Li+. The Fe7S8/SiOx/nitrogen-doped carbon anode exhibited a superior discharge capacity of 1060.2 mA h g-1 at 200 mA g-1 along with good long cycling performance of 415.8 mA h g-1 at the 1000th cycle at 5 A g-1. The facile strategy for preparing ternary Fe7S8 composites with superb LIB electrochemical performances demonstrates a great potential in electrochemical energy storage.

High-Performance Flexible Freestanding Anode with Hierarchical 3D Carbon-Networks/Fe7 S8 /Graphene for Applicable Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have gained tremendous interest for grid scale energy storage system and power energy batteries. However, the current researches of anode for SIBs still face the critical issues of low areal capacity, limited cycle life, and low initial coulombic efficiency for practical application perspective. To solve this issue, a kind of hierarchical 3D carbon-networks/Fe7 S8 /graphene (CFG) is designed and synthesized as freestanding anode, which is constructed with Fe7 S8 microparticles well-welded on 3D-crosslinked carbon-networks and embedded in highly conductive graphene film, via a facile and scalable synthetic method. The as-prepared freestanding electrode CFG represents high areal capacity (2.12 mAh cm-2 at 0.25 mA cm-2 ) and excellent cycle stability of 5000 cycles (0.0095% capacity decay per cycle). The assembled all-flexible sodium-ion battery delivers remarkable performance (high areal capacity of 1.42 mAh cm-2 at 0.3 mA cm-2 and superior energy density of 144 Wh kg-1 ), which are very close to the requirement of practical application. This work not only enlightens the material design and electrode engineering, but also provides a new kind of freestanding high energy density anode with great potential application prospective for SIBs.

Removal of Arsenic from water using synthetic Fe7S8 nanoparticles.

In the present study, pyrrhotite was used to remove arsenite and arsenate from aqueous solutions. The Fe7S8 was synthesized using a solvothermal synthetic method and it was characterized using XRD and SEM micrographs. Furthermore, the particle size for the nanomaterial Fe7S8 was determined to be 29.86 ± 0.87 nm using Scherer's equation. During the pH profile studies, the optimum pH for the binding of As (III) and As (V) was determined to be pH 4. Batch isotherm studies were performed to determine the binding capacity of As(III) and As(V), which was determined to be 14.3 mg/g and 31.3 mg/g respectively for 25°C. The thermodynamic studies indicated that the ΔG for the sorption of As(III) and As(V) ranged from -115.5 to -0.96 kJ/mol, indicating a spontaneous process was occurring. The enthalpy indicated that an exothermic reaction was occurring during the adsorption in which the ΔH was -53.69 kJ/mol and -32.51 kJ/mol for As(III) and As(V) respectively. In addition, ΔS values for the reaction had negative values of -160.46 J/K and -99.77 J/K for the adsorption of As(III) and As(V) respectively which indicated that the reaction was spontaneous at low temperatures. Furthermore, the sorption for As(III) and As(V) was determined to follow the second order kinetics adsorption model.

Colloidal synthesis of ternary AgFeS2 nanocrystals and their transformation to Ag2S-Fe7S8 heterodimers.

Ternary-/hetero-nanocrystals: a facile one-pot colloidal route for controlled synthesis of ternary AgFeS2 nanocrystals, which have a band gap of 1.21 eV, is presented for the first time. Such ternary AgFeS2 nanocrystals can transform to Ag2 S-Fe7 S8 heterodimers by internal thermal reaction at elevated temperature, providing a new route to synthesize semiconductor hetero-nanostructures.