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Compact Ag@Fe3O4 core-shell nanoparticles by means of single-step thermal decomposition reaction.

Brollo ME, López-Ruiz R, Muraca D, Figueroa SJ, Pirota KR, Knobel M - Sci Rep (2014)

Bottom Line: Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape.The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature.The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Física Gleb Wataghin - Universidade Estadual de Campinas (UNICAMP) 13083-970 Campinas (SP) Brasil.

ABSTRACT
A temperature pause introduced in a simple single-step thermal decomposition of iron, with the presence of silver seeds formed in the same reaction mixture, gives rise to novel compact heterostructures: brick-like Ag@Fe3O4 core-shell nanoparticles. This novel method is relatively easy to implement, and could contribute to overcome the challenge of obtaining a multifunctional heteroparticle in which a noble metal is surrounded by magnetite. Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape. The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature. The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.

No MeSH data available.


(a) XANES and (b) EXAFS of BLN (red) and P (black) NPs.Also standard bulk FeO (pink), Fe2O3 (blue) and Fe3O4 (green) are shown. All spectra were obtained at room temperature.
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f3: (a) XANES and (b) EXAFS of BLN (red) and P (black) NPs.Also standard bulk FeO (pink), Fe2O3 (blue) and Fe3O4 (green) are shown. All spectra were obtained at room temperature.

Mentions: The oxidation state was studied through X-ray absorption near edge spectra (XANES) and extended X-ray absorption fine structure (EXAFS). A sample of plain Fe3O4 NPs (hereafter named as P) with well-defined cubic geometry (edges of 27(4) nm) was chosen for comparison because of its closer magnetic properties, as will be shown later (see Figure S2 for images). The Fe K-edge XANES spectra of the BLNs and iron oxide references are shown in Figure 3. XANES features at the Fe K-edge mainly resemble those corresponding to magnetite Fe3O4. The pre-edge energy position is compatible with a Fe(III)-Fe(II) mixture35. The main component of the pre-edge peaks of Fe3O4 arises from tetrahedral Fe3+ as it is observed in the first peak for both samples. The shoulder corresponds to octahedral Fe(III)–Fe(II) ions. At lower energies, the characteristic low intensity peak corresponds to hexa-coordinated Fe(II). In BLN sample, the shoulder is shifted to high energies, higher than 1.1 eV. This limb is expected in nanometric samples that contain a maghemite fraction3536. The average iron oxidation state was 2.62(1) for P sample and 2.73(2) for BLN sample. The value expected for the Fe3O4 magnetite phase is 2.67, which reveals that most of the iron oxide phase in BLN is indeed magnetite. A small amount of maghemite phase was also observed, as expected considering the presence of a small fraction of plain nanometric magnetite (which is absent in the P sample), where the surface oxidation becomes more relevant. The peak position, which is sensitive to oxidation state, is slightly shifted to higher energies for the BLN as expected for more oxidized species (see Figure S4). The decrease in the pre-edge peak intensity reveals that the iron environment for BLN is more centrosymmetric than in P.


Compact Ag@Fe3O4 core-shell nanoparticles by means of single-step thermal decomposition reaction.

Brollo ME, López-Ruiz R, Muraca D, Figueroa SJ, Pirota KR, Knobel M - Sci Rep (2014)

(a) XANES and (b) EXAFS of BLN (red) and P (black) NPs.Also standard bulk FeO (pink), Fe2O3 (blue) and Fe3O4 (green) are shown. All spectra were obtained at room temperature.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4213770&req=5

f3: (a) XANES and (b) EXAFS of BLN (red) and P (black) NPs.Also standard bulk FeO (pink), Fe2O3 (blue) and Fe3O4 (green) are shown. All spectra were obtained at room temperature.
Mentions: The oxidation state was studied through X-ray absorption near edge spectra (XANES) and extended X-ray absorption fine structure (EXAFS). A sample of plain Fe3O4 NPs (hereafter named as P) with well-defined cubic geometry (edges of 27(4) nm) was chosen for comparison because of its closer magnetic properties, as will be shown later (see Figure S2 for images). The Fe K-edge XANES spectra of the BLNs and iron oxide references are shown in Figure 3. XANES features at the Fe K-edge mainly resemble those corresponding to magnetite Fe3O4. The pre-edge energy position is compatible with a Fe(III)-Fe(II) mixture35. The main component of the pre-edge peaks of Fe3O4 arises from tetrahedral Fe3+ as it is observed in the first peak for both samples. The shoulder corresponds to octahedral Fe(III)–Fe(II) ions. At lower energies, the characteristic low intensity peak corresponds to hexa-coordinated Fe(II). In BLN sample, the shoulder is shifted to high energies, higher than 1.1 eV. This limb is expected in nanometric samples that contain a maghemite fraction3536. The average iron oxidation state was 2.62(1) for P sample and 2.73(2) for BLN sample. The value expected for the Fe3O4 magnetite phase is 2.67, which reveals that most of the iron oxide phase in BLN is indeed magnetite. A small amount of maghemite phase was also observed, as expected considering the presence of a small fraction of plain nanometric magnetite (which is absent in the P sample), where the surface oxidation becomes more relevant. The peak position, which is sensitive to oxidation state, is slightly shifted to higher energies for the BLN as expected for more oxidized species (see Figure S4). The decrease in the pre-edge peak intensity reveals that the iron environment for BLN is more centrosymmetric than in P.

Bottom Line: Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape.The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature.The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Física Gleb Wataghin - Universidade Estadual de Campinas (UNICAMP) 13083-970 Campinas (SP) Brasil.

ABSTRACT
A temperature pause introduced in a simple single-step thermal decomposition of iron, with the presence of silver seeds formed in the same reaction mixture, gives rise to novel compact heterostructures: brick-like Ag@Fe3O4 core-shell nanoparticles. This novel method is relatively easy to implement, and could contribute to overcome the challenge of obtaining a multifunctional heteroparticle in which a noble metal is surrounded by magnetite. Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape. The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature. The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.

No MeSH data available.