Banca de DEFESA: INDIRA ARITANA FERNANDES DE MEDEIROS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : INDIRA ARITANA FERNANDES DE MEDEIROS
DATA : 04/07/2018
HORA: 09:00
LOCAL: Auditório do CCET
TÍTULO:

"Nanostructuring of Cobalt Ferrites (Co_xFe_3-xO₄): effect on the catalysis and on the gas detection."

PALAVRAS-CHAVES:

Cobalt Ferrite, nanocube, nanooctahedrons, catalysis, gas detection.

PÁGINAS: 130
GRANDE ÁREA: Engenharias
ÁREA: Engenharia Química
SUBÁREA: Processos Industriais de Engenharia Química
ESPECIALIDADE: Processos Inorgânicos
RESUMO:

The present thesis aims to study the cobalt ferrite (Co_xFe_3-xO₄) nanocrystallites morphology and composition effects on their catalytic and detection properties. Different synthesis methods such as hydrothermal, solvothermal and thermal decomposition were used to control nanoparticles shape and composition. Moreover, the effect of synthesis parameters variations, such as addition of different surfactants, different solvents, surfactant concentration, temperature and time of synthesis were also investigated. The powders were characterized by X-ray Diffraction and Transmission Electron Microscopy and analyzed by Dispersive Energy Spectroscopy. The catalytic and detection properties were evaluated in CO atmosphere in the range of 100 to 300°C and in NO₂ atmosphere at 150 and 200°C. CoFe₂O₄ nanooctahedra with 15-20 nm were produced by hydrothermal synthesis using different surfactants (CTAB, SDS and PVP). Co_xFe_3-xO₄ with x = 1.5 and x = 1.8 were also synthesized by hydrothermal method. However, the TEM analysis showed that the amount of Co present in Co_xFe_3-xO₄ is limited at x = 1.5. When ethylene glycol was used as solvent, Co_1,8Fe_1,2O₄ of 4 nm with irregular shape and homogeneous composition was obtained. A mixture of nanocubes (18 nm) and nanospheres (10 nm) of CoFe₂O₄ were produced by solvothermal synthesis using oleylamine as surfactant. In the thermal decomposition, nanospherical CoFe₂O₄ were produced in benzyl alcohol, while nanooctahedra of Co_0.5Fe_2.5O₄ were produced in dibenzyl ether. The nanooctahedra with composition x = 1.5 and the mixture of nanocubes and nanospheres were tested in the CO catalysis. The nanocubes and nanospheres mixtures were also tested in the detection of NO₂. The results were compared with those obtained for the nanooctahedra with x=1 existent in the literature.  The applications results showed that the shape and composition have an effect on the nanoparticles catalytic activity. The powder of Co_xFe_3-xO₄ with x = 1.5 has higher activity and lower temperature needed for the maximum CO conversion. For the detection test, the mixture of cubes and spheres presented lower sensitivity than the nanooctahedra for all temperatures analyzed. The maximum sensor response obtained was 49.9% when the sensor was subjected to 50 ppm of NO₂ at 200 ° C.

 

 

 

MEMBROS DA BANCA:
Interno - 2929066 - ANDRE LUIS LOPES MORIYAMA
Presidente - 349801 - CARLSON PEREIRA DE SOUZA
Externo ao Programa - 000.000.000-00 - CHRISTINE LEROUX - UTV
Externo à Instituição - MADJID ARAD - USTV
Externo à Instituição - MIGUEL ALEXANDRE NOVAK - UFRJ
Externo ao Programa - 000.000.000-00 - VÉRONIQUE MADIGOU - USTV