Rietveld Refinement, μ‑Raman, X‑ray
Photoelectron, and Mössbauer Studies of Metal Oxide-Nanoparticles
Growth on Multiwall Carbon Nanotubes and Graphene Oxide
posted on 2021-03-08, 17:38authored byJuan A. Ramos-Guivar, J. C. Gonzalez-Gonzalez, F. Jochen Litterst, Edson C. Passamani
Applying
a modified coprecipitation method, maghemite and anatase
nanoparticles embedded in graphene oxide and multiwall carbon nanotube
frameworks were prepared, and a detailed structural characterization
is presented. Transmission electron images have revealed that the
multiwall carbon nanotubes and graphene oxide act as substrates to
reduce the nanoparticle agglomeration with narrow sizes of ca. 9–20
nm, in agreement with the results of the Rietveld refinement, which
have also indicated their crystallite apparent size and shapes using
the spherical harmonics approach. In structural studies of maghemite
nanoparticles by Raman spectroscopy, it was found that the effect
of optical density and laser power intensity plays a significant role.
When no optical filter was located between the powder sample and the
laser source, a transformation from the γ-Fe2O3 to the α-Fe2O3 phase was observed,
as demonstrated by the disappearance of the characteristic broad Raman
peak (A1g) of the γ-Fe2O3 phase
when increasing the laser power. X-ray photoelectron spectroscopy
has also brought insights into the functionalization mechanism, suggesting
that the one-pot reduction of the graphene oxide is favored by the
alkaline γ-Fe2O3 nanoparticle growth.
The temperature dependence of the 57Fe Mössbauer
spectra has indicated that the effective anisotropy constant of Fe
oxide-based nanoparticles is similar to that of bulk maghemite, and
magnetic relaxation of Fe3+ spins depends on particle sizes.