The effect of the preparation method on the physicochemical and magnetic properties of Fe/MCM-41

M. I. OLIVA; V. R. ELÍAS; G. A. EIMER; S. P. SILVETTI; S. E. URRETA

Rio de Janeiro – Brasil

Congreso; Nano 2008. 9th International Conference on nanostructured Materials; 2008

Mesoporous silicates named MCM-41 exhibit a particular structure with one-dimensional parallel pores (like nanotubes) of about 1-10 nm in diameter. They have a high surface area and become especially attractive to encapsulate different compounds inside these pores, leading to nanophase systems with technological applications in areas such as electronics, optics, magnetism, drugs storage, energy storage and catalysis [1-3]. In this work, MCM-41 materials were synthetized and further modified with Fe using two methods: wet and wetness impregnation. In both methods, an aqueous solution of Fe(NO3)3.9H2O with different concentration of Fe+3 was used, depending of the desired iron loading (5 y 10%p/p). In the first case, the silica was flooded with a large volumen of an aqueous iron solution with the requiered concentration for the desired loading. In the second method, the silica was filled with a volume of iron nitrate aqueous solution equal to the pore volume. The materials were then located in an evaporator flask and were rotated to eliminate the solvent. All the solids were calcined in air at 823K. Then, two reduction treatments were applied: in the first one, the solid was heated at a rate of 4K/min up to 873K under H2 flow and then this temperature was mantained for 2 hour. For the second treatment, a heating rate of 2K/min was used reaching a temperature of 698K which was mantained for 24 hours. The materials were characterized by XRD, reflectance UVvis, superficial area (BET) and by magnetical measurements - hysteresis loops- at room temperature. XRD patterns showed that all the matrices had MCM-41 structure, which is consistent with their high surface areas (1000m2/g). Such structures and their areas were largely affected by the impregnation method; the UVvis analysis also showed that depending on the reduction treatment, different iron species appear which are responsible for the magnetic behavior observed. [1] M. Chao, H. Lin, C. Mou, B. Cheng, C. Cheng, Cat. Tod. 97, 81 (2004). [2] K. Napolsky, A. Eliseev, A. Knotko, A. Lukahsin, A. Vertegel, Y. Tretyakov, Mat. Sci. Eng. C 23, 151 (2003) [3] G. Rodríguez, G. González, J. Lujano, P. Silva, Cat. Tod. 107-108, 885 (2005).