Mössbauer Spectroscopy

Stievano, Lorenzo; Wagner, F. E.

doi:10.1002/9783527645329.ch10

Cited by 13 publications

(7 citation statements)

References 77 publications

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“…But the two fitted Mössbauer parameters, i.e., the isomer shift (δ) and the quadrupole splitting energy (Δ E QS ) of the ZVI particles (S-N(C)-mZVI bm , N(C)-mZVI bm , and mZVI bm ) were different from each other (Figure S9). Since these two parameters originate from hyperfine interactions between the Fe nucleus and its surrounding electronic environment, they should vary with the iron oxidation state, spin state, and chemical surroundings. − The differences in the δ and Δ E QS parameters of S-N(C)-mZVI bm , N(C)-mZVI bm , and mZVI bm indicate that S and N have influenced the coordination properties of Fe species on S-mZVI bm and S-N(C)-mZVI bm . Since the XANES spectra of S-N(C)-mZVI bm at the S K-edge showed the formation of FeS and Mössbauer spectra of N(C)-mZVI bm proved the presence of Fe-N X (C), it can be inferred that Fe-N X (C) might have been formed on/in S-N(C)-mZVI bm .…”

Section: Resultsmentioning

confidence: 99%

Coincorporation of N and S into Zero-Valent Iron to Enhance TCE Dechlorination: Kinetics, Electron Efficiency, and Dechlorination Capacity

Gong

Qiu

Dong

et al. 2021

Environ. Sci. Technol.

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Sulfidated zero-valent iron (S-ZVI) enhances the degradation of chlorinated hydrocarbon (CHC) in contaminated groundwater. Despite numerous studies of S-ZVI, a versatile strategy to improve its dechlorination kinetics, electron efficiency (ε e ), and dechlorination capacity is still needed. Here, we used heteroatom incorporation of N(C) and S by ball-milling of microscale ZVI with melamine and sulfur via nitridation and sulfidation to synthesize S-N(C)-mZVI bm particles that contain reactive Fe-N X (C) and FeS species. Sulfidation and nitridation synergistically increased the trichloroethene (TCE) dechlorination rate, with reaction constants k SA of 2.98 × 10 −2 L•h −1 •m −2 by S-N(C)-mZVI bm , compared to 1.77 × 10 −3 and 8.15 × 10 −5 L•h −1 •m −2 by S-mZVI bm and N(C)-mZVI bm , respectively. Data show that sulfidation suppressed the reductive dissociation of N(C) from S-N(C)-mZVI bm , which stabilized the reactive Fe-N X (C) and reserved electrons for TCE dechlorination. In addition to lowering H 2 production, S-N(C)-mZVI bm dechlorinated TCE to less reduced products (e.g., acetylene), contributing to the material's higher ε e and dechlorination capacity. This synergistic effect on TCE degradation can be extended to other recalcitrant CHCs (e.g., chloroform) in both deionized and groundwater. This multiheteroatom incorporation approach to optimize ZVI for groundwater remediation provides a basis for further advances in reactive material synthesis.

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Section: Resultsmentioning

confidence: 99%

Coincorporation of N and S into Zero-Valent Iron to Enhance TCE Dechlorination: Kinetics, Electron Efficiency, and Dechlorination Capacity

Gong

Qiu

Dong

et al. 2021

Environ. Sci. Technol.

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“…Namely, for spectra recorded in the absence of a strong external magnetic field, metallic iron and iron carbides result in sextets (except for the paramagnetic γ-Fe structure, leading to a singlet), whereas the fingerprint of FeN x C y moieties is a quadrupole doublet. Its two Mössbauer parameters are the isomer shift (δ) and the quadrupole splitting energy (Δ E QS ). − These two parameters originate from hyperfine interactions between the iron nucleus and the surrounding electronic environment and vary, therefore, with the iron oxidation state, spin state, and its chemical surrounding …”

Section: Introductionmentioning

confidence: 99%

Understanding Active Sites in Pyrolyzed Fe–N–C Catalysts for Fuel Cell Cathodes by Bridging Density Functional Theory Calculations and ⁵⁷Fe Mössbauer Spectroscopy

et al. 2019

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Pyrolyzed Fe-N-C materials are promising platinum-group-metal free catalysts for protonexchange membrane fuel cell cathodes. However, the detailed structure, oxidation and spin states of their active sites is still undetermined. 57 Fe Mössbauer spectroscopy has identified FeN x moieties as the most active sites, with their fingerprint being a doublet in lowtemperature Mössbauer spectra. However, the interpretation of the doublets for such materials has lacked theoretical basis. Here, we applied density functional theory to calculate the quadrupole splitting energy of doublets (E QS) for a range of FeN x structures in different oxidation and spin states. The calculated and experimental values are then compared for a reference Fe-N-C catalyst, while further information on the Fe oxidation and spin states was obtained from electron paramagnetic resonance, superconducting quantum interference device and 57 Fe Mössbauer spectroscopy under external magnetic field. The combined theoretical and experimental results identify the main presence of FeN x moieties in Fe(II) low-spin and Fe(III) high-spin states while a minor fraction of sites could exist in Fe(II) S = 1 state. From the analysis of the 57 Fe Mössbauer spectrum under external magnetic field and the comparison of calculated and measured E QS values, we assign the experimental doublet D1 with mean E QS value around 0.9 mm•s-1 to Fe(III)N 4 C 12 moieties in high spin and the experimental doublet D2 with mean E QS value around 2.3 mm•s-1 to Fe(II)N 4 C 10 moieties in low and medium spin. These conclusions indicate that D1 corresponds to surface-exposed sites while D2 may correspond either to bulk sites that are inaccessible to O 2 or to surface sites that bind O 2 weaker than D1.

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“…3 ) to Fe 2+ located at M1 and M2 sites, respectively, confirming that also in this case, there is no cationic site preference for the iron ions. The third doublet (green line), less intense than the other two, is characteristic of octahedral Fe 2+ in pyroxene [(Mg,Fe)Si 2 O 6 ] [ 29 ]. Such results agree with the composition determined by XRD analysis, which detected the presence of forsterite, enstatite ferroan and clinochlore [ 20 ].…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, the observed formation of Fe 3+ agrees well with the observations of Raman spectroscopy. The sample measured after 150 min of milling is characterized by the four doublets described previously attributed to Fe 2+ in the two sites of olivine, pyroxene site and superparamagnetic Fe 3+ oxides [ 28 , 29 ]. As the relative area of Fe 3+ doublet increases, those of Fe 2+ sites related to pristine olivine decrease, while the relative area of Fe 2+ related to the pyroxene site remains almost unchanged up to 180 min.…”

Section: Resultsmentioning

confidence: 99%

Unveiling redox mechanism at the iron centers in the mechanochemically activated conversion of CO2 in the presence of olivine

et al. 2022

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The transformation of olivine during the conversion of CO2 to light hydrocarbons activated by mechanochemical treatments at different impact frequencies was studied by a combination of several complementary characterization methods including X-ray diffraction, Raman and 57Fe Mössbauer spectroscopy. Several olivine samples were studied as a function of the milling time, indicating the gradual transformation of FeII-containing olivine into new FeIII-containing weathering products including iron oxides, magnesium iron carbonates and silicates. The results presented here complement those of a previous study on the weathering process of olivine promoted by mechanochemical activation, by demonstrating the role of the redox activity of the iron species during the activation process. These additional spectroscopic results allow us to thoroughly understand the complex weathering mechanism and to correlate it with the efficiency of the CO2 conversion and storage properties of mechanochemically activated olivine.

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Mössbauer Spectroscopy

Cited by 13 publications

References 77 publications

Coincorporation of N and S into Zero-Valent Iron to Enhance TCE Dechlorination: Kinetics, Electron Efficiency, and Dechlorination Capacity

Coincorporation of N and S into Zero-Valent Iron to Enhance TCE Dechlorination: Kinetics, Electron Efficiency, and Dechlorination Capacity

Understanding Active Sites in Pyrolyzed Fe–N–C Catalysts for Fuel Cell Cathodes by Bridging Density Functional Theory Calculations and ⁵⁷Fe Mössbauer Spectroscopy

Unveiling redox mechanism at the iron centers in the mechanochemically activated conversion of CO2 in the presence of olivine

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Mössbauer Spectroscopy

Cited by 13 publications

References 77 publications

Coincorporation of N and S into Zero-Valent Iron to Enhance TCE Dechlorination: Kinetics, Electron Efficiency, and Dechlorination Capacity

Coincorporation of N and S into Zero-Valent Iron to Enhance TCE Dechlorination: Kinetics, Electron Efficiency, and Dechlorination Capacity

Understanding Active Sites in Pyrolyzed Fe–N–C Catalysts for Fuel Cell Cathodes by Bridging Density Functional Theory Calculations and 57Fe Mössbauer Spectroscopy

Unveiling redox mechanism at the iron centers in the mechanochemically activated conversion of CO2 in the presence of olivine

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Understanding Active Sites in Pyrolyzed Fe–N–C Catalysts for Fuel Cell Cathodes by Bridging Density Functional Theory Calculations and ⁵⁷Fe Mössbauer Spectroscopy