doctoralThesis
Síntese de nanocompósitos a base de Fe2SiO4-Fe7Co3 dispersos na SBA-15: aplicação como adsorvente e fotocatalisador magneticamente separável
Fecha
2020-07-22Registro en:
SILVA, Monickarla Teixeira Pegado da. Síntese de nanocompósitos a base de Fe2SiO4-Fe7Co3 dispersos na SBA-15: aplicação como adsorvente e fotocatalisador magneticamente separável. 2020. 107f. Tese (Doutorado em Química) - Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Natal, 2020.
Autor
Silva, Monickarla Teixeira Pegado da
Resumen
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 Ar adsorption 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.