Please use this identifier to cite or link to this item: http://www.repositorio.ufc.br/handle/riufc/9792
Title in Portuguese: Propriedades estruturais e vibracionais de nanotubos e nanofitas de titanato
Author: Viana Neto, Bartolomeu Cruz
Advisor(s): Mendes Filho, Josué
Co-advisor(s): Ferreira, Odair Pastor
Keywords: Espectroscopia de Raman
Nanotecnologia
Nanociência
Issue Date: 2009
Citation: VIANA NETO, B. C. Propriedades estruturais e vibracionais de nanotubos e nanofitas de titanato. 2009. 67 f. Tese (Doutorado em Física) - Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2009.
Abstract in Portuguese: Este trabalho relata o estudo das propriedades estruturais, morfológicas e vibracionais dos nanotubos e das nanofitas de titanato obtidos a partir do tratamento hidrotérmico de TiO2 em solução aquosa de NaOH. As propriedades físicas destas nanoestruturas, como preparadas e tratadas termicamente, são discutidas e comparadas com seus similares sólidos estendidos (Na2Ti3O7 e Na2Ti6O13). Os resultados obtidos por microscopia eletrônica de transmissão, microscopia eletrônica de varredura, espectroscopia de emissão atômica, espectroscopia de energia dispersiva de raios-X, difração de raios-X, espectroscopia de absorção no infravermelho com transformada de Fourier e espectroscopia Raman permitem concluir que as camadas (paredes ou lamelas) de nanotubos e nanofitas de titanato, como preparados, são isoestrutural ao composto lamelar Na2Ti3O7. Nos nanotubos de titanato as ligações químicas são deformadas por causa da curvatura das paredes, enquanto nas nanofitas de titanato as camadas apresentam apenas a desordem estrutural causada pelo efeito do tamanho. O comportamento térmico das nanofitas de titanato é similar ao relatado na literatura para os nanotubos de titanatos, onde mudanças estruturais e morfológicas, com o aumento da temperatura, são observadas e indicam que as nanofitas quando submetidas a altas temperaturas mudam sua morfologia para grandes bastões (sólido estendido) com uma mistura das fases Na2Ti3O7 e Na2Ti6O13. Este resultado é similar ao comportamento do Na2Ti3O7, sólido estendido, quando tratado termicamente. Concluímos que os nanotubos e as nanofitas de titanato têm a mesma composição química Na{2-x}HxTi3O7.nH2O(0·x·2).
Abstract: This work reports a study on the structural, morphological and vibrational properties of titanate nanotubes and nanoribbons obtained from hydrothermal treatment of TiO$_2$ in aqueous NaOH solutions. The physical properties of these as-synthesized and heat-treated nanostructures are discussed in comparison with their bulk (Na$_2$Ti$_3$O$_7$ and Na$_2$Ti$_6$O$_{13}$) counterparts. The results obtained from transmission electron microscopy, scanning electron microscopy, atomic emission spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, infrared and Raman spectroscopies allowed us to conclude that the layers of both as-synthesized titanates nanotubes and nanoribbons are isostructural to the Na$_2$Ti$_3$O$_7$ lamellar compound. In the titanate nanotubes the chemical bonds are deformed because of the curvature of walls while in the titanates nanoribbons the layers present structural disorder by size effects. The thermal behavior of titanate nanoribbons is similar to those reported in literature for titanate nanotubes, where structural and morphological changes with increases of temperature are observed and indicated that the nanoribbons, at high temperatures, change to bulk with a phase mixing of Na$_2$Ti$_3$O$_7$ and Na$_2$Ti$_6$O$_{13}$. This is similar to what happens with the bulk Na$_2$Ti$_3$O$_7$ when thermally treated. Thus, we conclude that the chemical composition of both the titanate nanotubes and the titanate nanoribbons is the same, Na$_{2-x}$H$_x$Ti$_3$O$_7$.nH$_2$O (0$leq$x$leq$2). Also, we suggest that Raman spectroscopy can be used for an easy and quick identification of both morphology and structure changes of the nanosized titanates. Furthermore, in this work we report the synthesis, characterization and application of Ce ion-exchanged titanate nanotubes. The physicochemical properties of these nanotubes are discussed in comparison with their pure titanate nanotube counterparts. The transmission electron microscope images showed that the Ce ion-exchanged titanate nanotubes have the same morphology of the pristine nanotubes and their external walls are decorated with cerium oxide nanoparticles. The mechanism of nanoparticle formation is based on the precipitation of Ce ion at the nanotube surface. We observed a shift of the absorption band edge towards the visible region that is attributed to the effects of Ce$^{4+}$ addition (intercalation) and/or the presence of CeO$_2$ nanoparticles decorating the nanotubes surfaces. A red shift of vibrational modes associated with metal ion - oxygen interaction was observed and identified as being due to the effect of Ce addition to the lattice as well as the anchoring of CeO$_2$ nanoparticles to the nanotube wall. We show that this hybrid system is promising for applications in photocatalysis using the blue region of the electromagnetic spectrum and this was demonstrated for photodegradation of reactive blue 19 textile dye using visible light ilumination.
URI: http://www.repositorio.ufc.br/handle/riufc/9792
metadata.dc.type: Tese
Appears in Collections:DFI - Teses defendidas na UFC

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