Banca de DEFESA: MONICKARLA TEIXEIRA PEGADO DA SILVA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : MONICKARLA TEIXEIRA PEGADO DA SILVA
DATE: 22/07/2020
TIME: 08:30
LOCAL: Remotamente pelo google meet
TITLE:

Synthesis of nanocomposites based on Fe₂SiO₄-Fe₇Co₃ dispersed in SBA-15: Application as adsorbent and magnetically separable photocatalyst  

KEY WORDS:

 magnetic nanocomposite, Fe₇Co₃ alloy, Fe₂SiO₄ oxide, adsorption, photocatalysis, dyes, SBA-15.

PAGES: 84
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SPECIALTY: Cinética Química e Catálise
SUMMARY:

The present study describes the synthesis of a new type of Fe₂SiO₄-Fe₇Co₃ based nanocomposite dispersed in the mesoporous material SBA-15 in order to apply in the dyes adsorption, in the photocatalytic degradation of methylene blue (MB) and consequent magnetic separation. The parameters studied were: the reduction temperature and amount of hydrogen used in the synthesis and how these affect the physicochemical properties of the oxide-alloy mixture with iron and cobalt, as well as the adsorption capacity and photodegradation of methylene blue. The prepared materials were characterized by X-ray diffraction (XRD), Mössbauer spectroscopy (MS), X-ray photoelectron spectroscopy (XPS), vibratory sample magnetometry (VSM), temperature programmed reduction (H₂-TPR), N₂ or Aradsorption and desorption isotherms , Scanning electron microscopy (SEM-FEG) and Transmission electron microscopy (TEM). The XRD results together with the TPR profiles confirmed the formation of Fe₂SiO₄-Fe₇Co₃-based nanocomposites at temperatures between 690 and 720 °C and amount of H₂ between 0.5 and 2%. The increase of the reduction temperature and the increase of H₂ content in the reduction mixture led to the formation of a higher amount of alloy compared to oxide according to the data obtained by the Rietveld refinement. Low-angle XRD, N₂ isotherms, and TEM images show the formation of the SBA-15-based mesoporous support with a high specific area of 640 m/g². However, the surface area and mesoporous structure of the silica was slightly altered (to 420 m/g²) after Fe and Co insertion due to partial pore filling by the composite. For samples containing the metals dispersed on SBA-15, there may be an interconnection between mesopores according to scanning hysteresis loop from N₂ and Ar isotherms accompanied by mathematical models. Adsorption tests confirmed that the material reduced at 700 °C using 2% of H₂ had the highest adsorption capacity for methylene blue (MB) dye. The nanocomposites obtained have good adsorption capacity for MB dye and can be easily separated from the final dispersion by applying an external magnetic field after adsorption. The photocatalysis results confirmed that the silica support is essential to optimize the photocatalytic activity of the Fe and Co species in the dye degradation, favoring the accessibility of active sites.  The attraction of the dye by the nanocomposite occurs mainly by π-π interactions and the mixing of Fe₂SiO₄ and Fe₇Co₃ phases leads to a synergistic effect which favor the methylene blue adsorption and the photocatalytic activity process compared to the same isolated phases. The degradation of the MB occur through a sequence of reactions both on the solid surface and on the solution.

BANKING MEMBERS:
Externo à Instituição - JOSÉ MARCOS SASAKI - UFC
Interna - 1805556 - LUCIENE DA SILVA SANTOS
Interna - 1308577 - SIBELE BERENICE CASTELLA PERGHER
Presidente - 2087667 - TIAGO PINHEIRO BRAGA
Externo à Instituição - VINÍCIUS PATRÍCIO DA SILVA CALDEIRA - UERN