Magnetic and Mössbauer spectroscopy studies of nanocrystalline iron oxide aerogels

Carpenter, Everett E.; Long, Jeffrey W.; Rolison, Debra R.; Logan, Michael S.; Pettigrew, Katherine A.; Stroud, Rhonda M.; Kuhn, Luise Theil; Hansen, Britt Rosendahl; Mørup, S.

doi:10.1063/1.2176894

Cited by 28 publications

(12 citation statements)

References 10 publications

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“…Thermal treatment in Ar induces signicant changes, particularly in the rst coordination sphere (Fe-O peak centered at $1.5 Å in the Fourier transforms data) of FeO x , resulting in a local structure that is closely related to g-Fe 2 O 3 (maghemite), On the basis of the synchrotron PXRD, EXAFS, and TEM results, we posit that our material consists of domains of nanocrystalline magnetite-like and amorphous, maghemite-like oxide, similar to our previous assessment of FeO x aerogels that showed mixed magnetite/maghemite character. 46 This broad, amorphous PXRD pattern has previously been observed for core-shell maghemite/magnetite FeO x nanoparticles. 47…”

Section: Characterization Of Vfe 2 O X Aerogel Structure and Compositionsupporting

confidence: 66%

Defective by design: vanadium-substituted iron oxide nanoarchitectures as cation-insertion hosts for electrochemical charge storage

Chervin

Miller

et al. 2015

J. Mater. Chem. A

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Vanadium-substituted iron oxide aerogels (2 : 1 Fe : V ratio; VFe 2 O x ) are synthesized using an epoxideinitiated sol-gel method to form high surface-area, mesoporous materials in which the degree of crystallinity and concentration of defects are tuned via thermal treatments under controlled atmospheres. Thermal processing of the X-ray amorphous, as-synthesized VFe 2 O x aerogels at 300 C under O 2 -rich conditions removes residual organic byproducts while maintaining a highly defective g-Fe 2 O 3 -like local structure with minimal long-range order and vanadium in the +5 state. When assynthesized VFe 2 O x aerogels are heated under low partial pressure of O 2 (e.g., flowing argon), a fraction of vanadium sites are reduced to the +4 state, driving crystallization to a Fe 3 O 4 -like cubic phase.Subsequent thermal oxidation of this nanocrystalline VFe 2 O x aerogel re-oxidizes vanadium +4 to +5, creating additional cation vacancies and re-introducing disordered oxide domains. We correlate the electrochemical charge-storage properties of this series of VFe 2 O x aerogels with their degree of order and chemical state, as verified by X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. We find that the disordered O 2 -heated VFe 2 O x aerogel yields the highest Li +and Na + -insertion capacities among this series, approaching 130 mA h g À1 and 70 mA h g À1 , respectively. Direct heat-treatment of the VFe 2 O x aerogel in flowing argon to yield the partially reduced, nanocrystalline form results in significantly lower Li + -insertion capacity (77 mA h g À1 ), which improves to 105 mA h g À1 by thermal oxidation to create additional vacancies and structural disorder.

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Section: Characterization Of Vfe 2 O X Aerogel Structure and Compositionsupporting

confidence: 66%

Defective by design: vanadium-substituted iron oxide nanoarchitectures as cation-insertion hosts for electrochemical charge storage

Chervin

Miller

et al. 2015

J. Mater. Chem. A

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“…Sextets with isomer shifts values of δ oct1 = 0.50 (0.02) mm/s are assigned to Fe 3+ ions in the octahedral B sites. The third sextet with the highest value of isomer shift δ oct2 = 0.70 (0.04) mm/s arises due to the presence of Fe 2+ cations confirming the formation of Fe 3 O 4 phase of magnetic oxide …”

Section: Resultsmentioning

confidence: 73%

One-Pot Synthesis of Highly Monodispersed Ferrite Nanocrystals: Surface Characterization and Magnetic Properties

Verma

Dhanapal

2011

Langmuir

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In the present study, a facile one-pot synthetic route, utilizing a strong polar organic solvent, N-methyl 2-pyrrolidone (NMP), is demonstrated to obtain highly monodispersed ferrite nanocrystals. The equimolar mixture of oleic acid, C(17)H(33)COOH (R-COOH), and oleylamine, C(18)H(35)NH(2) (R'-NH(2)), was used to coat the magnetic nanocrystals. Structural and magnetic properties of the ferrite nanocrystals were studied by a multitechnique approach including X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), and Mössbauer spectroscopy. FTIR spectral analysis indicates oleylamine helps in deprotonation of oleic acid, resulting in the formation of an acid-base complex, R-COO¯:NH(3)(+)-R', which acts as binary capping agent. Structural and coordination differences of iron were studied by XPS and Mössbauer spectral analysis. XPS analysis was carried out to examine the oxidation state of iron ions in iron oxide nanocrystals. The presence of a magnetically dead layer (∼0.38 and ∼0.67 nm) and a nonmagnetic organic coating (∼2.3 and ∼1.7 nm) may substantially reduce the saturation magnetization values for CoFe(2)O(4) and Fe(3)O(4) nanocrystals, respectively. The energy barrier distribution function of magnetic anisotropy was derived from the temperature dependent decay of magnetization. A very narrow energy barrier distribution elucidates that the ferrite nanocrystals obtained in this study are highly monodispersed.

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“…The individual nanoparticles comprising an iron oxide aerogel were shown to be magnetically interactive for phase-pure forms, such as g-Fe 2 O 3 , whereas for mixed-phase Fe 3 O 4 /g-Fe 2 O 3 aerogels, magnetic coupling between the individual nanoparticles is frustrated. 193 The interaction of B6-nm Au with multiple B12-nm TiO 2 particles (Fig. 17(b)) played a specific role in the catalytic activity observed of TiO 2 -Au aerogels for the roomtemperature oxidation of CO. 194 Silica monolithic samples prepared without aging in the mother-liquor sol, supercritically dried, and then densified by heat treatment showed differences in pore structure and substantially different mechanical properties than a standard silica aerogel after thermal densification.…”

Section: Characterization Of Interparticle Interactionsmentioning

confidence: 94%

Multifunctional 3D nanoarchitectures for energy storage and conversion

et al. 2009

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The design and fabrication of three-dimensional multifunctional architectures from the appropriate nanoscale building blocks, including the strategic use of void space and deliberate disorder as design components, permits a re-examination of devices that produce or store energy as discussed in this critical review. The appropriate electronic, ionic, and electrochemical requirements for such devices may now be assembled into nanoarchitectures on the bench-top through the synthesis of low density, ultraporous nanoarchitectures that meld high surface area for heterogeneous reactions with a continuous, porous network for rapid molecular flux. Such nanoarchitectures amplify the nature of electrified interfaces and challenge the standard ways in which electrochemically active materials are both understood and used for energy storage. An architectural viewpoint provides a powerful metaphor to guide chemists and materials scientists in the design of energy-storing nanoarchitectures that depart from the hegemony of periodicity and order with the promise--and demonstration--of even higher performance (265 references).

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Magnetic and Mössbauer spectroscopy studies of nanocrystalline iron oxide aerogels

Cited by 28 publications

References 10 publications

Defective by design: vanadium-substituted iron oxide nanoarchitectures as cation-insertion hosts for electrochemical charge storage

Defective by design: vanadium-substituted iron oxide nanoarchitectures as cation-insertion hosts for electrochemical charge storage

One-Pot Synthesis of Highly Monodispersed Ferrite Nanocrystals: Surface Characterization and Magnetic Properties

Multifunctional 3D nanoarchitectures for energy storage and conversion

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