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Here, in-house Co N C and Fe N C have been prepared by, first, chelating the metals (Co or Fe) with ethylene diamine tetra acetic acid, known as EDTA (nitrogen precursor). UV–Visible (UV–Vis) spectrometry has been used to ensure the chelated metal formation. In the next step, the chelated metals have been deposited on a high surface area oxidized carbon support to increase the electrical conductivity. The latter composite material has been thermally treated at 800 °C (CoNC8 and FeNC8) or 1000 °C (CoNC10 and FeNC10) in nitrogen atmosphere in order to create the catalytic sites that will be able to perform the oxygen reduction reaction (ORR) in the acid medium. Electrochemical tests have been carried out to investigate the activity and durability of the electro-catalysts for the ORR. Methanol tolerance properties have been also evaluated for a possible application in direct methanol fuel cells. It appears that FeNC8 is the most active electrocatalyst in the presence of methanol in the base electrolyte, thus showing promising characteristics for direct methanol fuel cells. Instead, stability tests of these metal nitrogen catalysts indicate the best resistance to corrosion for the catalysts treated at 1000 °C. [ABSTRACT FROM AUTHOR]

The biological slow filtration reactor (BSFR) process has been found to be moderately effective for the removal of refractory dissolved organic matter (DOM) in the treatment of reused water. In this study, bench scale experiments were conducted using a mixture of landscape water and concentrated landfill leachate as feed water, to compare a novel iron oxide (Fe x O)/FeNC modified activated carbon (Fe x O@AC) packed BSFR, with a conventional activated carbon packed BSFR (AC-BSFR), operated in parallel. The results showed that the Fe x O@AC packed BSFR had a refractory DOM removal rate of 90%, operated at a hydraulic retention time (HRT) of 10 h at room temperature for 30 weeks, while under the same conditions the removal by the AC-BSFR was only 70%. As a consequence, the treatment by the Fe x O@AC packed BSFR substantially reduced the formation potential of trihalomethanes, and to a less extent, haloacetic acids. The modification of Fe x O/FeNC media raised the conductivity and the oxygen reduction reaction (ORR) efficiency of the AC media to accelerate the anaerobic digestion by consuming the electrons that are generated by anaerobic digestion itself, which lead to the marked improvement in refractory DOM removal. [Display omitted] • Fe x O@AC-BSFR removed 90% DOM by HRT of 10 h for 30 weeks to AC packed BSFR (70%). • Fe x O@AC-BSFR can effectively reduce the formation potential of trihalomethanes (THMs). • Fe x O/FeNC raised ORR efficiency and accelerate the anaerobic digestion for DOM removal. [ABSTRACT FROM AUTHOR]

The objective of this study was to understand the role of iron and the heat treatment steps involved in nitrogen-coordinated iron-carbon (FeNC) catalyst synthesis. We have studied the oxygen reduction reaction (ORR) performance of these catalysts as they evolve from their most crude and inactive form to their most active form. Electrochemical half-cell and fuel cell tests suggest that the presence of Fe was crucial in these samples. The high-temperature heat treatment (once in argon and then in ammonia) at temperatures ≥950 °C were also critical in imparting these catalysts with their highest activity; however, significant loss of activity was observed with cycling and potential hold at 0.5 V for 100 h. In addition, acid-washing after the first or the second pyrolysis steps produced a marked decrease in ORR activity relative to their unwashed counterparts. We also report findings from our efforts towards benchmarking FeNC catalysts for oxygen reduction reaction electrocatalysis. Specifically, we focus on correlating the specific kinetic current (i) at 0.75 V to electrochemically accessible surface area (EASA) and roughness factor (RF) determined from electrochemical double layer capacitance measurements. Fe Mössbauer spectroscopy was employed to shed light into the nature of active sites in FeNC catalysts and provide insights into their deactivation behavior caused by acid-washing. The results suggest planar FeN doublet (Fe, low spin) as an active site in these materials, which may be leached away in acid, explaining their decreased activity after acid washing. Results for characterization experiments using X-ray photoelectron spectroscopy, temperature programmed oxidation and X-ray absorption spectroscopy, superconducting quantum interference device magnetometry are also presented. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Mechanically ground magnetically FeNC/Fe 3 O 4 demonstrated excellent desulfurization efficiency of dibenzothiophene (DBT), easy separation process, and good regeneration performance with an external field, which was certified by theoretical calculation and thermodynamics analysis. [Display omitted] • The FeNC displays a sheet like porous structure which enables efficient adsorption of aromatic sulfur derivatives. Thermodynamics investigation demonstrates a negative value of ΔG, ΔH, ΔS, suggesting that the adsorption is exothermic reaction with spontaneous process. • The FeNC was mechanically ground with Fe 3 O 4 to construct FeNC-700/Fe 3 O 4 adsorbent for DBT adsorption which can be recycled for five successive runs with magnet in a quite easy, economical and eco-friendly manner. Herein, a series of 3D nitrogen doped porous carbon nanomaterials (FeNC) at different pyrolysis temperature were prepared, followed by a mechanical grinding method to construct magnetically nanocomposite (FeNC/Fe 3 O 4) which was demonstrated for the desulfurization of dibenzothiophene (DBT) in model oils. The FeNC derived from the pyrolysis of iron salt and nitrogen-doped carbon precursors possess abundant porous structure, which is highly active in the physical adsorption of aromatic sulfur derivatives. Impressively, the as-prepared FeNC-700 are evidenced to yield an excellent desulfurization efficiency (95.1% for 200 ppmw), a remarkable estimated adsorption capacity (25.08 mg S/g for 200 ppmw), and a high selectivity for DBT. Theoretical calculation revealed that the adsorption behaviors towards DBT followed the pseudo-second-order kinetic model, displays a better fitting coefficient based on Langmuir isotherm equation. The thermodynamics results indicate that adsorption process over FeNC-700 was spontaneous and exothermic reaction since ΔG, ΔH, ΔS, all shows negative signs. Subsequently, the FeNC-700 was mechanically mixed with 20 nm Fe 3 O 4 to produce magnetically nanocomposite (FeNC-700/Fe 3 O 4) for the adsorption of DBT in a simple separation process by external field and can be regenerated five runs without significant weight loss. Therefore, this strategy greatly simplifies the experimental procedure and favors the regeneration of the adsorbents. [ABSTRACT FROM AUTHOR]

In this study, a green Fe and FeN co-doped carbon nanocomposite catalyst (FeNC) was synthesized by a simple and economical method and applied to activate peroxodisulfate (PDS) for the efficient oxidation of chloramphenicol (CAP). Characterization analysis found that the surface of Fe and FeN nanoparticles supported on nitrogen-doped carbon was wrapped by nitrogen-doped carbon nanosheets, forming a "core-shell" structure. The FeNC@PDS system has good catalytic activity, and the CAP degradation efficiency reaches 91.2% within 60 min. FeNC@PDS system exhibits excellent catalytic degradation performance under a wide pH range (2.4–8.3) and shows good reusability. The calculated % reaction stoichiometric efficiency (RSE) reached values up to 18.86%, which exceeds than those of various reported heterogeneous Fenton-like systems. Quenching experiments and electron paramagnetic resonance characterization confirmed that both free-radicals and non-radicals were involved in the activation of PDS by FeNC. In addition, the possible mechanism of the PDS activation by FeNC was proposed. Finally, the degradation pathway of CAP was determined based on the intermediates. This work provided a novel reference for the design of efficient heterogeneous catalysts to remove organic pollutants efficiently. [Display omitted] • A nanocomposite catalyst (FeNC) was prepared via a facile and economical process. • FeNC exhibited excellent catalytic activity for PDS oxidation of CAP. • Both radical and non-radical pathways were involved in the degradation of CAP. • The reaction stoichiometric efficiency of the FeNC@PDS system reached 18.86%. [ABSTRACT FROM AUTHOR]

This paper provides an overview of the studies that were conducted in our laboratories in the last decade on hetero-atom doped carbon structures as potential oxygen reduction reaction (ORR) catalysts for PEM fuel cells. These studies include evaluating the potential of nitrogen doped carbon nanostructures as cathode catalysts for proton exchange membrane and direct methanol fuel cells and examining the nature of the transition metal used as growth catalysts in synthesis of these materials, through activity and in situ and ex situ characterization experiments. These studies also shed some light on the ongoing debate about the differences and similarities between two classes of materials used for ORR, namely FeNC and CN catalysts, through activity and stability tests, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, temperature-programmed techniques and selective poisoning experiments designed to probe the active sites. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In light of the debate about the role of the transition metal in non-precious metal catalysts (NPMCs), two different NPMCs, CNx and FeNC, were compared for activity toward oxygen reduction in acidic media and characterized using various techniques, including X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), superconducting quantum interference device (SQUID) magnetometry, inductive-couple plasma optical emission spectrometry (ICP-OES), and temperature-programmed oxidation (TPO). The effect of acid-washing as well as long-term exposure to fuel cell and half-cell environment on both catalysts was also studied. Although FeNC exhibited a much higher initial activity than CNx, it was seen to degrade rapidly in both half-cell and fuel cell environments, while CNx retained much of its initial activity. The results discussed are sought to clarify some of the ambiguity in the role of the transition metal in these two catalysts and help establish that they are indeed two different materials with different active sites that catalyze ORR. [ABSTRACT FROM AUTHOR]

Iron-nitrogen-carbon (FeNC) catalysts derived from zeolitic-imidazolate frameworks (ZIFs) are worldwide accepted to be the most promising candidates for the oxygen reduction reaction (ORR), but the insufficient stability, the low FeN x exposure and poor density restrict their ORR activity. Here, we demonstrate a strategy to synthesize FeN x sites embedded in a micro/mesoporous N, S co-doped graphitic carbon (FeNC/MUS) by tuning the ligand linkers via the addition of 2-undecylimidazole as a co-ligand in ZIF precursors, and optimizing the electronic structure of Fe center by an in-situ addition of thiourea molecules as sulfur (S) source. 2-undecylimidazole offered an open porous structure to incorporate more FeN x , while the S-doping increased the density of FeN x . Besides, 2-undeclyimidazole cooperatively with S-doping caused favorable changes into the catalyst structure, particularly improved the exposure and density of FeN x sites and doubled the Brunauer-Emmetter-Teller surface area to 1132 m 2 g -1 contrasted to the pristine FeNC/M (544 m 2 g -1 ). FeNC/MUS displayed an accelerated ORR activity with a higher half-wave potential of 0.86 V (vs. reversible hydrogen electrode (RHE)) than that of Pt/C (0.84 V) in addition of a longer durability with a 11 % of activity decay after 30000 s in alkaline media. This work offers a new insight to design optimal ZIFs precursor and a facile electron withdrawing S-doping strategy for efficient electrocatalysis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Abstract: We report an ab initio calculation, at the MR-SDCI+Q+ E rel/[Roos ANO (Fe), aug-cc-pVQZ (C, N)] level of theory, of the potential energy surface for 6Δ i FeNC. From the ab initio results, we have computed values for the standard spectroscopic parameters of FeN12C and FeN13C. Analytical representations of the potential energy surfaces have been fitted through the ab initio points, and the resulting functions have been used for directly solving the rotation–vibration Schrödinger equation by means of the MORBID program and by means of an adiabatic-separation method. For 6Δ i FeNC, our ab initio calculations show that the equilibrium structure is linear with r e (Fe–N)=1.9354Å and r e (N–C)=1.1823Å. We find that the bending potential is very shallow, and the MORBID calculations show that the zero-point averaged structure is bent with the expectation values 〈r (Fe–N)〉=1.9672Å, 〈r(N–C)〉=1.1866Å, and . The experimentally derived bond length r 0 (N–C)=1.03(8)Å reported for 6Δ i FeNC by Lie and Dagdigian [J. Chem. Phys. 114 (2001) 2137–2143] is much shorter than the corresponding ab initio r e-value and the averaged value from MORBID. Our calculations suggest that this discrepancy is caused by the inadequate treatment of the large-amplitude bending motion of 6Δ i FeNC. It would appear that for floppy triatomic molecules such as FeNC, r 0-values have little physical meaning, at least when they are determined with the effects of the large-amplitude bending motion being ignored, i.e., under the assumption that the r 0 structure is linear. [Copyright &y& Elsevier]

Nitrogen-doped porous carbons containing atomically dispersed iron are prime candidates for substituting platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. These carbon catalysts are classically synthesizedviacomplicated routes involving multiple heat-treatment steps to form the desired Fe-N x sites. We herein developed a highly active FeNC catalyst comprising of exclusive Fe-N x sites by a simplified solid-state synthesis protocol involving only a single heat-treatment. Imidazole is pyrolyzed in the presence of an inorganic salt-melt resulting in highly porous carbon sheets decorated with abundant Fe-N x centers, which yielded a high density of electrochemically accessible active sites (1.36 × 10 19 sites g -1 ) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E 1/2 ) of 0.905 V RHE in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E 1/2 of 0.760 V RHE is achieved at a low loading level (0.29 mg cm -2 ). In PEMFC tests, a current density of 2.3 mA cm -2 is achieved at 0.90 V iR-free under H 2 -O 2 conditions, reflecting high kinetic activity of the optimized catalyst., Competing Interests: Declaration of Competing Interest There are no conflicts to declare., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Pyrolyzing precursors containing iron, nitrogen and carbon elements is a commonly used process for synthesizing FeNC catalysts for oxygen reduction reaction (ORR). Generally, aggregation of iron-based species is prone to occur because of a lack of chemical bonds between iron-based species and carbon matrix and synthesizing highly porous FeNC catalysts is difficult because carbon skeleton is prone to collapse during pyrolysis. Herein, highly porous FeNC catalysts with fine iron-based species are synthesized by selecting glucose as carbon source, FeCl 3 as iron source, and urea-derived g-C 3 N 4 as nitrogen source, iron anchoring and stabilizing species, and pore-forming template. The multi-role g-C 3 N 4 -derived catalyst synthesized at 1100 °C (FeNC1100) has fine iron-based species, large specific surface area (737 m 2 g -1 ), and extremely high pore volume (2.66 cm 3 g -1 ). Accordingly, FeNC1100 shows a larger half-wave potential (E 1/2  = 0.894 V), a higher stability (ΔE 1/2  = 6 mV) after 10,000 potential cycles in alkaline media, and a higher peak power density (P = 152 mW cm -2 ) when employed as ORR catalyst of zinc-air battery, which are all superior to those of the commercial Pt/C catalyst (E 1/2  = 0.864 V, ΔE 1/2  = 30 mV, P = 134 mW cm -2 ). The present work brings a new method for synthesizing highly porous FeNC catalysts decorated with fine active sites for ORR., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)