Maghemite nanoparticles embedded in SBA-15 pores

A. E. BIANCHI; I. O. PÉREZ DE BERTI; J. F. BENGOA; S. G. MARCHETTI; R. C. MERCADER; G. PUNTE

Santa Marta

Congreso; SARX2012; 2012

Universidad Industrial de Santander

Ordered mesoporous silicates have attracted much interest since the discovery of the M41S family of materials in 1992 because of their use in catalysis, separations, sensors, drug delivery, and optical devices.Zhao et al. [2] extended the family of highly ordered mesoporous silicates by synthesizing Santa Barbara Amorphous (SBA-15) type materials. They have pore size raging between 20 and 300Å, which allow extending the applications in different areas. In this study we investigate by Small Angle X-ray Dispersion (SAXS) the structural characteristics of a SBA-15, modified to obtain larger pore size without altering the typical hexagonal mesoporous structure, supporting pre-synthesized maghemite (γ-Fe2O3) nanoparticles (NP) with 2.5 ± 0.6 nm diameters, as determined by transmission electron microscopy and dynamic light scattering. SAXS data for the pure SBA-15 matrix and from a loaded one were obtained at room temperature at the D11A- SAXS1 line workstation of the Brazilian Synchrotron Light Source, Campinas, Brazil, using a wavelength of  0.1488 nm. The range of q detected was 0.3 £ q £ 1.95 nm-1. Pure SBA-15 SAXS results allowed identifying four diffraction lines that could be indexed as (100), (110), (200), and (210) reflections with a cell parameter a =12.65(5) nm. This result indicates that the sample has a well-ordered two-dimensional (2D) mesostructure (p6mm). The loaded SBA-15 SAXS curve shows a larger slope and a smoother background that might be related to a decrease in the surface roughness. Analysis of Bragg lines allows to index reflections (100), (110) and (200) with a cell parameter a = 12.84(5) nm. These results point to the conservation of the SBA-15 mesoporous structure after the γ-Fe2O3 NPs loading. This finding is consistent with Mossbauer results, which showed that signals coming from the γ-Fe2O3 NPs and those ones coming from loaded SBA-15 exhibited parameters belonging only to Fe3+ ions. In both samples at low temperatures, the spectra were fitted with magnetic relaxing signals that proved to originate in theγ-Fe2O3 and the Fe3+ ions coordinated to the oleic acid that coated the γ-Fe2O3 NPs. [1] J.S. Beck et al.  Nature 359 (1992) 710 and J. Am. Chem. Soc. 114 (1992) 10834.[2] D. Zhao al. Science 279 (1998) 548: J. Am. Chem. Soc. 120 (1998) 6024.