Banca de DEFESA: YESSICA ACOSTA URIAN

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : YESSICA ACOSTA URIAN
DATE: 01/06/2023
TIME: 10:00
LOCAL: Auditório do IF
TITLE:

Study of the surface properties and particle-particle interactions in oleic acid and oleic acid/essential oilcoated Fe3O4 nanoparticles

KEY WORDS:

Thermal decomposition method; oleic acid-coated Fe3O4 nanoparticles; oleic acid/essential oil-coated Fe3O4 nanoparticles; core/shell structure; magnetic anisotropy; particle-particle interactions.

PAGES: 127
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Magnetite (Fe3O4) nanoparticles coated with organic material are of considerable importance in various areas of engineering, as well as in biomedicine. Several papers show drastic changes in the magnetic properties related to the surface effects and the particle-particle interactions strength. However, there is no consensus about the origin or mechanisms that produce these changes, which could be different depending on the particle size and shape, coating efficiency and particle-particle interaction strength. Aiming to shed light on these issues, oleic acid (OA) coated Fe3O4 nanoparticles with sizes 4, 6 and 9 nm were synthesized by a thermal decomposition method using phenyl ether, benzyl ether and octadecene as organic solvents. These samples were additionally coated with essential oil ((Fe3O4@AO/OE). Structural and microscopic Fe3O4@AO nanoparticles results revealed Fe3O4 nanoparticles with good crystallinity and almostspherical or polyhedral shapes depending on the solvent used for the synthesis. Infrared (FTIR) spectroscopy indicated OA molecules attached to the surface of Fe3O4 NPs via bidentate (chelating and/or bridging) bonds. Thermogravimetric analysis (TGA) confirmed the presence of weakly and strongly bound AO molecules in the Fe3O4@AO samples, suggesting a successful coating of the Fe3O NPs. Magnetization (M) vs. magnetic field (H) curves are consistent with a core/shell structure formed by magnetite/maghemite phases, in consistency with FTIR spectroscopy. Lower than expected saturation magnetization values were determined for bulk magnetite, which was attributed to the probable presence of a fraction of low-spin (LS) iron ions in the maghemite layer on the surface of the particles. In that regard, the analysis by Mössbauer spectroscopy confirmed these results, as well as the better crystalline quality in the samples synthesized with benzyl ether used as the synthesis solvent. The magnetic results show that depending on the amount of AO coating, it is possible to adjust the particleparticle separation distance, avoiding nanoparticle agglomeration and particle-particle interactions. Dependence of magnetization on temperature reveals the presence of interacting and non-interacting NPs. AC magnetic susceptibility measurements are consistent with these results and confirm a superparamagnetic behavior (SPM), attributed to non-interacting NPs, and interacting SPM, attributed to interacting NPs and whose interaction strength is not sufficient to lead to behavior similar to that of spin glass. On the other hand, the FTIR results of the Fe3O4@AO/EO samples indicate the presence of EO without direct connection with the AO or with the metal ions on the surface of the Fe3O4 NPs. These results are consistent with those obtained from the analysis of thermogravimetric curves, where the intermediate-sized sample showed a higher amount of EO. Also, the EO coating had changes in the magnetic response. A reduction in the saturation magnetization and variation in the ZFC and FC curves was observed with lower blocking temperatures and lower activation energies in relation to Fe3O4@AO samples. These results were confirmed by measurements of AC susceptibility as a function of temperature. This suggests a lower degree of particle agglomeration and the weakening of particle-particle interactions as a function of the amount of EO in the Fe3O4@AO/EO samples.

BANKING MEMBERS:
Presidente - 1547480 - JOSE ANTONIO HUAMANI COAQUIRA
Interno - 1764408 - PAULO EDUARDO NARCIZO DE SOUZA
Externo ao Programa - 1652361 - MARCELO HENRIQUE SOUSA
Externo à Instituição - ANTÔNIO OLIVEIRA DE SOUZA - UFOB
Externo à Instituição - ANSELMO FORTUNATO RUIZ RODRIGUEZ - UFAC