Structure Of FeN Research Articles

Cyclic catalytic Fe-N doped composite particle electrodes derived from gasification fine slag for non-selective mineralization of organic wastewater

As a typical coal-based solid waste, coal gasification fine slag (GFS) will have an annual discharge of more than 50 million tons in 2025 in China alone. However, the difficulty of its resource utilization lies in the precise separation of carbon and ash due to their complex distribution pattern. There is an urgent need to develop GFS-based materials for comprehensive utilization of carbon and ash. In this study, a combined process of acid leaching and pyrolysis was designed, in which active metal iron was leached from ash and immobilized on the surface of residual carbon in the form of Fe-N-C. The unique structure of Fe-N doped carbon/ash synergistically improved the efficiency of electrocatalytic degradation of organic wastewater by 72.78 ± 1.37%. The hierarchical porous structure of residual carbon considerably enhanced the accessibility of ash catalytic sites. Abundant ash defects and Fe-N active sites promoted the conversion of free radical precursors to reactive oxygen species (ROS). The removal rate of various organic wastewater within 35 min reached more than 100 ± 1.83% %, with excellent electrocatalytic performance and pH adaptability. Fe-NCPE had a high specific surface area (318.36 m2·g−1), orderly graphite phase (002 crystal surface size 1.3 nm), and abundant catalytic sites. We also proposed the catalytic mechanism by combining molecular simulation with experiments. The high adsorption capacity above 24.07 ± 0.12 mg·g−1 ensured the continuous and rapid supply of pollutants and H2O2 near the catalytic site·H2O2 was converted into ROS mainly composed of hydroxyl groups through the valence state change of aluminum or Fenton-like reaction of nitrogen-linked iron. The ROS then attacked organic molecules to degrade pollutants. The above two processes corresponded to two cyclic catalytic reactions. Therefore, this study provides an innovative and promising approach for comprehensive utilization of carbon and ash in GFS.

Sequential doping of exogenous iron and nitrogen to prepare Fe-N structured biochar to enhance the activity of OTC degradation

In order to prepare high-performance biochar for application in the treatment of antibiotic wastewater by persulfate oxidation, the feasibility of preparing Fe-N biochar from waste chestnut shells by sequential doping of exogenous iron, nitrogen was investigated. Biochar containing Fe-N structure (Fe3N-BC) was successfully prepared by using K2FeO4 as the iron source and urea as the nitrogen source. It can effectively activate PS and remove 98% of oxytetracycline (OTC) within 20 min. The main mechanism of PS activation by Fe3N-BC for OTC degradation is a non-radical pathway dominated by 1O2 generation and direct electron transfer. The formation of Fe-N structure in biochar changed the electron distribution on the catalyst surface and improved the electron transfer efficiency while inhibiting the leaching of iron ions, verifying the unique role of heteroatoms in iron-based catalysts. The study also identified the degradation intermediates of OTC and suggested possible degradation pathways. Showing that demethylation, deamidation and dehydroxylation are the prior steps for degradation. This study provides a new idea for the preparation of Fe-N structured biochar for OTC degradation.

Highly efficient peroxymonosulfate activation on Fe-N-C catalyst via the collaboration of low-coordinated Fe-N structure and Fe nanoparticles for enhanced organic pollutant degradation

Supporting Fe catalysts on N doped carbon (Fe-N-C) renders a promising way towards peroxymonosulfate (PMS) activation for water decontamination, but constructing high-efficiency Fe-N-C remains challenging due to the insufficient understanding of the structure-performance relationship. Herein, the N doped carbon nanotube supported Fe catalysts (Fe-NCNT) were prepared towards PMS activation for organic pollutants removal, in which the Fe-N coordination number and Fe species were tuned through changing the pyrolysis temperature to study their roles in PMS activation. Results showed increasing the pyrolysis temperature converted the Fe-N4 structure in Fe-NCNT to low-coordinated Fe-N3 structure and produced Fe nanoparticles (FeNP, encapsulated in carbon). The Fe-NCNT with Fe-N3 and FeNP exhibited a remarkably high specific activity (0.119 L min−1 m−2), which was 1.8 times higher than that of Fe-NCNT with only Fe-N4 and obviously outperformed those of the state-of-the-art PMS activators. The low-coordinated structure and FeNP promoted the PMS reduction on Fe2+ of Fe-Nx for •OH and SO4•− production, which served as major oxidants for pollutants degradation. The experimental results and theoretical calculation corroborated the low-coordinated structure and FeNP jointly enhanced the PMS adsorption and electron density on Fe center, which accelerated electron transfer from Fe center to PMS for radical production.

Accelerating the oxygen adsorption kinetics to regulate the oxygen reduction catalysis via Fe3C nanoparticles coupled with single Fe-N4 sites

• The single-atom Fe catalyst was synthesized by Fe 3 C|Fe-N 4 coupled sites on 1D and 2D doped-carbon structures. • The formed Fe 3 C|Fe-N 4 sites can positively regulate the electronic structure of the Fe center in the catalyst. • DFT calculations indicate that the adjacent Fe 3 C activated single Fe-N 4 sites accelerate the oxygen adsorption kinetics. • The catalyst assembled ZABs manifested a higher power density and better stability than the Pt/C-based ZABs. Manipulating the electronic structure of Fe-N 4 single-sites to accelerate the oxygen adsorption kinetics is a commendable approach to improve the oxygen reduction reaction (ORR) performance of single-atom Fe catalysts but remains a challenge. Here we propose an endogenous regulation strategy to in situ design the single-atom Fe catalyst (Fe 3 C@NCNTs) derived from 1,8-diaminonaphthalene, iron trichloride, and graphitic carbon nitride via Fe-N 4 single-sites strongly coupled with Fe 3 C nanostructures, in which the combination of 1D and 2D doped-carbon structures and the formation of Fe 3 C|Fe-N 4 coupled sites can endow the catalyst with a considerably enhanced electrocatalytic activity and remarkable cycling stability to the ORR in Zn-air batteries. Theoretical calculations further reveal that endogenous Fe 3 C nanostructures can effectively activate the atomically dispersed Fe-N 4 sites, narrowing the energy barriers of the rate-limiting steps of ORR to promote the ORR catalytic performance. This work provides an effective way to in situ tune the electronic structure of metal atoms to boost the ORR performance of single-atom catalysts for electrochemical energy systems.

Switching the Oxygen Reduction Reaction Pathway via Tailoring the Electronic Structure of FeN4/C Catalysts

FeN4-type carbon-based materials are promising non-precious-metal catalysts for the oxygen reduction reaction (ORR). However, FeN4/C catalysts always exhibit different ORR activities and selectivities, and their structure–performance relationship remains elusive. Herein, we design a covalent triazine framework with abundant N4 units (CTF-N4) to anchor Fe ions to precisely prepare a FeN4-type precursor (CTF-FeN4) that undergoes the 2e– ORR pathway with high selectivity. Interestingly, such a 2e– ORR pathway can be switched to a 4e– route through the modulation of the electronic structure by a controlled-pyrolysis process. Both X-ray photoelectron and synchrotron X-ray absorption spectra verify that all of the samples maintain the atomically dispersed FeN4 type configuration before and after the heat treatment, but the nonplanarity of FeN4/C increases dramatically with the carbonization temperature. Density functional theory calculations reveal that the introduced Fe atoms and the enhanced nonplanarity enhance the binding energy of *OOH on C adjacent to the pyridinic N, which favors the 4e– ORR path. Our study provides a fundamental understanding of the ORR mechanism on FeN4/C with a tunable electronic structure, hence paving the way for the development of cost-effective electrocatalysts for specific applications.

Molecule-confined modification of graphitic C3N4 to design mesopore-dominated Fe-N-C hybrid electrocatalyst for oxygen reduction reaction

To design inexpensive carbon catalysts and enhance their oxygen reduction reaction (ORR) activity is critical for developing efficient energy-conversion systems. In this work, a novel Fe-N-C hybrid electrocatalyst with carbon nanolayers-encapsulated Fe3O4 nanoparticles is synthesized successfully by utilizing the molecular-level confinement of graphitic C3N4 structures via hemin biomaterial. Benefiting from the Fe-N structure prevalent on the carbon nanosheets and large mesopore-dominated specific surface area, the synthesized catalyst under optimized conditions shows excellent electrocatalytic performance for ORR with an EORR at 1.08 V versus reversible hydrogen electrode (RHE) and an E1/2 at 0.87 V vs. RHE, and outstanding long-term stability, which is superior to commercial Pt/C catalysts (EORR at 1.04 V versus RHE and E1/2 at 0.84 V versus RHE). Moreover, the low hydrogen peroxide yield (<11%) and average electron transfer number (~3.8) indicate a four-electron ORR pathway. Besides, the maximum power density of the home-made Zn-air battery using the obtained catalyst is 97.6 mW cm−2. This work provides a practical route for the synthesis of cheap and efficient ORR electrocatalysts in metal-air battery systems.

In situ electrogeneration and activation of H2O2 by atomic Fe catalysts for the efficient removal of chloramphenicol

Heterogeneous electron-Fenton processes have been regarded as promising, environmentally friendly techniques for the removal of refractory organics. A new strategy has been brought forward for an electron-Fenton-like process with in situ H2O2 production, but regarding the catalysts, their geometric stability, H2O2 selectivity, and applicability under high pH values still need to be improved. Herein, bifunctional catalysts were proposed for a heterogeneous Fenton-like reaction by introducing Fe atoms into defect-enriched graphene sheets (Fe/N-DG). The structural and compositional results suggested that the excellent dispersing stability of Fe atoms is mainly attributed to the abundant pyridinic-N sites. Optimized Fe1/N-DG exhibited superior mass activity (5.28 A mgFe−1 at 0.6 V vs. RHE) and H2O2 selectivity (86%) under the synergistic effects of Fe‒N and Fe‒O sites. The Fe/N-DG catalysts maintained superior activities for chloramphenicol removal, even under extreme pH conditions (pH≤4 or pH≥10). Of these catalysts, Fe1/N-DG with a predominant Fe-N structure exhibited the best catalytic performance, achieving the complete removal of chloramphenicol within 180 min under alkaline conditions. The possible mechanism for chloramphenicol removal under alkaline conditions was proposed, along with those for the production and activation of H2O2. This study gives new insights into atomic Fe-based catalysts exhibiting excellent selectivity and stability for antibiotic wastewater treatment.

In-situ self-templated preparation of porous core–shell Fe1−S@N, S co-doped carbon architecture for highly efficient oxygen reduction reaction

Abstract Transition metal compound (TMC)/carbon hybrids, as prospering electrocatalyst, have attracted great attention in the field of oxygen reduction reaction (ORR). Their morphology, structure and composition often play a crucial role in determining the ORR performance. In this work, we for the first time report the successful fabrication of porous core–shell Fe1−xS@N, S co-doped carbon (Fe1−xS@NSC-t, t represents etching time) by a novel in-situ self-template induced strategy using Fe3O4 nanospheres and pyrrole as sacrificial self-template. The post-polymerization of pyrrole can be accomplished by the Fe3+ released through the etching of Fe3O4 by HCl acid. Thus, the etching time has a significant effect on the morphology, structure, composition and ORR performance of Fe1−xS@NSC-t. Based on the characterizations, we find Fe1−xS@NSC-24 can realize effective and balanced combination of Fe1−xS and NSC, possessing porous core–shell architecture, optimized structure defect, specific surface area and doped heteroatoms configurations (especially for pyridinic N, graphitic N and Fe-N structure). These features thus lead to outstanding catalytic activity and cycling stability towards ORR. Our work provides a good guidance on the design of TMC/carbon-based electrodes with unique stable morphology and optimized structure and composition.

Non-Noble Metal Oxygen Reduction Reaction Catalysts Based on Tungsten Carbide Supports and Fe-N Structures: Rrde Studies in Acid and Alkaline Media

Tungsten carbide (WC) has been receiving considerable attention in recent years due to its interesting properties, such as, a Pt-like catalytic behavior, [1] high electrical conductivity, chemical stability in acidic electrolytes, and much lower cost compared to platinum. [2] Non-noble catalysts of the type Fe-N/C (iron atoms coordinated to nitrogen atoms in a graphene packed structure) have also been considerably studied given their high catalytic activity toward the oxygen reduction reaction in both, alkaline and acid electrolytes. In this work, Fe-N structures were incorporated into various tungsten carbide nanostructures and their catalytic activities toward the oxygen reduction reaction are assessed in both, acid and alkaline media. Nanostructured tungsten carbides supported on carbon (WC(20, 30, 40%)/C) were prepared by depositing suitable amounts of WO3 on the Vulcan XC72R carbon black, followed by a thermal treatment at 850 0C for 4 hours in a controlled CH4/H2 atmosphere with a subsequent passivation step in a Ar/O2 (99%/1%) atmosphere for 12 hours at 25 oC. The Fe-N structure precursor was obtained by complexing an iron salt ((NH4)2Fe(SO4)2 x 6 H2O) with a nitrogen ligand (2,4,6-Tris(2-pyridyl)–1,3,5–Triazina), followed by deposition on the various WC/C supports with a subsequent pyrolysis step at 700 0C or 800 0C for 2 hours in a controlled N2 atmosphere. The electrocatalysts were physically characterized by X-ray Diffraction, X-ray Photoelectron Spectroscopy and Energy-dispersive X-ray spectroscopy. XRD spectra revel that the WC(30%)/C presents the highest WC proportion among the different supports, while the deconvoluted XPS spectra (W4f peak) evidence the presence of W+6, W+4 and W+2 at the surface of the material, with a much higher proportion of W+2 compared to insignificant amounts of W+6 and W+4. In contrast, when Fe-N structures are prepared on the WC(30)/C support, a higher proportion of W+6 is observed. The catalytic activity of these composites were assessed through cyclic voltammetry on a thin catalyst layer rotating ring-disk electrode, where the durability of the catalysts were conducted, followed with EDX analyses of the thin layer. Considering the ORR electrocatalytic activity, as a trend, it was seen that the Fe-N/WC/C catalyst presents higher activity compared to the support itself (WC/C) in both acidic and alkaline media with a prevalence of the direct 4e- reaction pathway. Further results for the dissolution of Fe upon accelerate durability test revels loss of metal along the cycling, and this information was important for the understanding of the ORR characteristics in these hybrid nanomaterials. Acknowledgements: Authors acknowledge the São Paulo Research Foundation (FAPESP - Procs. 2013/16930-7, 2016/07848-3), Brazil, for financial supports. The authors also wish to thank Brazilian Nanotechnology National Laboratory (LNNano) for assisting with the XPS measurements.

Application of electrical resistivity imaging (ERI) for the assessment of peat properties: a case study of the Ca\u0142owanie Fen, Central Poland

Complex studies were carried out to recognize the fen structure and peat properties in the Całowanie Fen area, belonging to the Natura 2000 network. The studies were conducted in two study areas that differ significantly in terms of peat thickness. Electrical resistivity imaging (ERI) was used to identify the properties of the peat and its substrate, such as thickness and electrical resistivity. Comparison of the field studies with the laboratory tests has shown that the ash content rises electrical resistivity in peat. In addition, the study has shown that the application of non-invasive geophysical methods in protected areas is justified. The fen, as a medium containing mostly water, was a proper test area for the ERI measurements.

Suppression of superconductivity in superconductor/ferromagnet multilayers

Suppression of the superconducting transition temperature (<TEX>$T_c$</TEX>) of NbN thin films in superconductor/ferromagnet multilayers has been investigated. Both superconducting NbN and ferromagnetic FeN layers were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an <TEX>$Ar-N_2$</TEX> gas mixture. The thickness of FeN films was fixed at 20 nm, while the thickness of NbN films was varied from 3 nm to 90 nm. <TEX>$T_c$</TEX> suppression was clearly observed in NbN layers up to 70 nm thickness when NbN layer was in proximity with FeN layer. For a given thickness of NbN layer, the magnitude of <TEX>$T_c$</TEX> suppression was increased in the order of Si/FeN/NbN, Si/NbN/FeN, and Si/FeN/NbN/FeN structure. This result can be used to design a spin switch whose operation is based on the proximity effect between superconducting and ferromagnetic layers.

Unravelling the structure of electrocatalytically active Fe-N complexes in carbon for the oxygen reduction reaction.

Non-precious Fe/N co-modified carbon electrocatalysts have attracted great attention due to their high activity and stability in oxygen reduction reaction (ORR). Compared to iron-free N-doped carbon electrocatalysts, Fe/N-modified electrocatalysts show four-electron selectivity with better activity in acid electrolytes. This is believed relevant to the unique Fe-N complexes, however, the Fe-N structure remains unknown. We used o,m,p-phenylenediamine as nitrogen precursors to tailor the Fe-N structures in heterogeneous electrocatalysts which contain FeS and Fe3 C phases. The electrocatalysts have been operated for 5000 cycles with a small 39 mV shift in half-wave potential. By combining advanced electron microscopy and Mössbauer spectroscopy, we have identified the electrocatalytically active Fe-N6 complexes (FeN6, [Fe(III)(porphyrin)(pyridine)2]). We expect the understanding of the FeN6 structure will pave the way towards new advanced Fe-N based electrocatalysts.

Strain effect of multilayer FeN structure on GaAs substrate

Overly doped FeN multilayer structure on GaAs substrate was fabricated. After the post-annealing process, FeN martensite in each Fe/FeN layer formed partially chemically ordered Fe16N2, which was observed by X-ray diffraction. To detect the saturation magnetization (Ms) depth profile, polarized neutron reflectivity was conducted. Fe/FeN layer showed a significant improvement of Ms for each layer compared to Ms of Fe. More importantly, different FeN layers showed different Ms according to the physical distance to the substrate GaAs. The most enhanced Ms (exceeding the limit of Fe65Co35 Ms) observed at the bottom part of the film, consistent with previous reports, should be attributed to the lattice strain by GaAs substrate. In order to detect the lattice constant, In-plane X-ray Diffraction was done and a large in-plane lattice constant was determined.

Improvement of Luminance and Luminous Efficiency Using New Electrode Structures in AC Plasma Display

Two new electrode structures, namely, fence electrode (Fen) and combination of coplanar and fence electrodes (CoFen), employing an elevated bus electrode in the conventional surface discharge structure with three electrodes are suggested. In this paper, various comparisons between the conventional and two new structures are made to validate the effectiveness of the proposed structures. The firing and sustain voltages, displacement and discharge currents, cell capacitance, luminance, and luminous efficiency for three electrode structures are measured for various pressure ranges used in the conventional plasma displays. Consequently, the experimental results show that the CoFen structure has lower firing and sustain voltages than the conventional and Fen structures for all pressure ranges from 100 to 700 torr. In addition, the Fen structure realizes over 80% brighter and approximately 18% higher luminous efficiency than the conventional one.

Study of the phases of iron–nitride with a stoichiometry near to FeN

Most of the Fe–nitride phases have been studied in much detail. Nevertheless, there is still some uncertainty regarding the characterisation of the FeNy compounds with y>0.5. On the basis of theoretical calculations, two FeN compounds are predicted with different phases: γ″-FeN and the γ‴-FeN. However, up to now there is no conclusive experimental evidence for the existence of these two phases.In the present work we present strong evidence that FeNy (y>0.5) contains only one pure phase, the γ″-FeN, with some vacancies.We developed two new methods to grow FeNy (y>0.5) phases: by evaporating Fe in the presence of a flow of atomic nitrogen and by post-nitriding under certain condition a thin epitaxial γ′-Fe4N sample.The stoichiometry of the samples was determined from resonant RBS with an accuracy of better than 1%. The samples were investigated by room temperature conversion electron Mössbauer spectroscopy (CEMS). For samples grown at a temperature lower than 300°C CEMS spectra can be fitted by a singlet line corresponding to a phase with 4-fold-symmetry, plus a quadrupole doublet that can be explained by symmetry breaking due to the presence of vacancies. We will show that the number of N vacancies (with respect to the FeN stoichiometry) determined by resonant RBS and the relative fraction of the singlet line in the CEMS-spectra agree well with this interpretation of the spectra, if the γ″-FeN structure is assumed. The interpretation is supported by theoretical band structure calculations that were performed.

GaN [formula omitted] surface doped with Fe atoms

The results of valence band electronic structure study of GaN ( 0 0 0 1 _ ) 1 × 1 (N-side) clean surface covered by Fe atoms and annealed are presented. The very first stage of Fe deposition (below 1 ML) leads to the Fe doping contribution to the GaN valence band electronic structure. With sequential Fe depositions (above 1 ML) the islands of Fe are created and sharp Fermi edge is appearing over the edge of the GaN valence band. Annealing (500 °C) of the sample in ultra high vacuum conditions, leads to the diffusion of Fe atoms to the surface region of GaN. It leads to the decrease of the contribution of Fe islands and increase of Fe 3d electrons contribution to the valence band of Ga 1− x Fe x N. Spectra obtained after annealing possess elements of structure well corresponding to the calculated electronic structure of FeN.

Magnetic and Structural Properties of Iron Nitride thin Films Obtained by Argon-Nitrogen Reactive Radio-Frequency Sputtering

Fe-N thin films have attracted considerable attention because they are potential candidates for magnetic recording with their large saturation magnetization and their good corrosion resistance1. It has even been demonstrated that saturation magnetization can be larger than the bulk iron one for low nitrogen contents2. The origin of the enhanced magnetic moment could occur from the metastable α″ Fe16N2 phase or from an expanded bcc FeN structure which is also called α FeN.

Flag Fen: the vegetation environment

The discovery of the timber platform in fen peat poses a number of questions relating to the local ecology and environment in which the structure was constructed and the character of local land use and economic subsistence. Pollen and plant macro-fossil studies were initiated at the outset of discovery of the Flag Fen structure. Special attention has been paid to the changing fen flora reflecting local hydrological changes as well as evidence for the vegetation and land use on areas of nearby dry land. In addition to the evidence for temporal changes in the environment obtained from ‘long peat cores’, sampling on a grid-square basis is being carried out on sands thought to have been floor covering. It is hoped that these will yield information on the use of the platform. Pollen data are now available from Flag Fen and the nearby Power Station site at Fengate. This short contribution seeks to provide a general summary of the vegetation and environment of the fen and its near terrestrial environs with data coming largely from the analysis of the ‘Mere Section’ (see Introduction, FIGURE 6 for location) although some reference will be made to the Fengate site (see Introduction, FIGURE6 for location). Results ofthe completed study will be presented in a forthcoming monograph.