Nanotech 2010

Study of the surface chemistry and morphology of single walled carbon nanotube (SWCNT)-magnetite composites

F. Marquez-Linaresa, O. Uwakwehb, N. Lopezc, E. Chavezd, R. Polancoa, C. Morantee, J. M. Sanz e, E. Elizaldee, C. Neira a, S. Nietoa, R. Roque-Malherbea
University of Turabo, School of Science, US

Keywords: composite nanomaterials, supported catalyst, Lewis acid and basic sites

Abstract:

With the help of XRD and Raman spectroscopy were carefully characterized the phase composition and the bulk structure of the studied capped magnetites, SWCNTs and SWCNT-magnetite composites. It was then shown that we are working with pure phases of the corresponding materials. The SEM and FESEM study allowed the measurement of the particle size and the specific surface area of the magnetite. The specific surface area, pore volume and pore size of the studied SWCNT was calculated with the help of the nitrogen adsorption measurements. These measurements show that the magnetite cores are materials with a large specific surface area and therefore highly dispersed. Likewise, is possible to conclude from the adsorption data, that the synthesized SWCNTs have high specific surface area, high micropore volume and a homogeneous pore size, that is these SWCNTs are good supports for catalytically active phases. The TGA study established the detachment of the organic surfactant from the capped magnetite and the linker and the surfactant from the SWCNT-magnetite-1 composite (Fig. 1). Subsequently, with the heat treatment, produced during the TGA study, were produced highly dispersed non-capped magnetite nanoparticles linked to the outer surface of SWCNT with high specific surface area, pore volume and controlled pore size. The DRIFTS data confirmed the existence of magnetite nanoparticles linked to the SWCNT, whose surface did not show any trace of OH groups. These obtained results imply that we have obtained magnetite nanoparticles, showing very high dispersion, which are well supported. The Mössbauer research revealed the occurrence of superparamagnetic doublets in the spectra of the magnetite cores and the magnetite included in the composites (Fig. 2). These peaks are related to coordinatively unsaturated cationic (cus) iron placed in the surface of the magnetite core nanoparticles. These iron sites are electron accepting Lewis sites. As well, since at this surface, are placed oxygen anions which act as electron donating Lewis base sites. Consequently, these whole set of data established that with the heat treatment at 900 0C we have produced highly dispersed magnetite firmly supported on a very appropriate support, because of: its dispersion, developed pore volume and chemical and thermal stability. Additionally, the supported magnetite expose in the surface as cus, more than 50 % of the iron included in this phase. Then we have produced a material which have a surface covered with active Lewis acid and basic sites.
 
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