Abstract
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LaFeO3/SiO2 precursors were prepared by a sol-gel method involving citrate complex.Nano sized and/or amorphous LaFeO3 on SiO2 particles were formed upon calcination.High surface area and porous texture were obtained for the formed nanocomposites.The work links the colloidal and surfaces phenomena to the nanocomposites formation.
A series of 10, 20 and 30% (w/w) La2O3-Fe2O3/silica composites were synthesized by mixing of La-Fe citrate complex gels with spherical silica sols. This was followed by calcination of the formed xerogel at 550°C and 750°C for 3h. The materials were characterized by XRD, simultaneous thermal analyses (TGA-DTA), FTIR, N2 gas adsorption/desorption isotherms at ⿿196°C, and TEM techniques. Results indicated complete decomposition of the precursor complex upon calcination and development of porous composites with high surface area. However, processing of the La-Fe citrate complex gel or the silica precursors without mixing led to formation of LaFeO3 perovskite oxide type and silica with very low surface area amounting to 4 and 11m2/g, respectively. Thus the process led to the formation of nanosized amorphous-like LaFeO3 phase (as a shell) on the surface of the spherical silica particles (core). The enhancement of surface area and porosity of the composites was correlated to the dispersion of La-Fe precursor on the surface of silica sol. The method can be generalized for other mixed oxides.