第5章辅助材料_阴离子型黏土插层复合材料.ppt

文献 2 Stoichiometric Synthesis of Pure MFe2O4 (M: Mg, Co, and Ni) Spinel Ferrites from Tailored Layered DoubleHydroxide (Hydrotalcite-Like) Precursors From Chemistry of Materials In this paper a novel synthetic route of pure MFe2O4 (M : Mg, Co, and Ni) spinel ferrites is reported. The key feature of this method is using a single molecular precursor. The pure spinel ferrites can be obtained by calcination of tailored hydrotalcite-like layered double hydroxides (LDHs) of the type [M1-X-YFe2+YFe3+X(OH)2]X+(SO42-)X/2amH2O (M: Mg, Co, and Ni) precursors at 900 °C for 2 h, in which the molar ratio of M2+/(Fe2+ + Fe3+) is adjusted to the same value as that in single spinel ferrite itself. The structural characteristics of the as-synthesized LDHs and their resulting calcined products are obtained by powder X-ray diffraction (XRD), chemical analysis, Fourier transform infrared spectroscopy (FT-IR), simultaneous thermogravimetric and differential thermal analysis (TG-DTA), and Mo¨ssbauer spectroscopy. The saturation magnetizations of the materials produced by calcinations of LDHs are higher than those of the spinel ferrites produced by the conventional ceramic and wet chemical routes, although the compositions of the materials are similar. The major advantage of the new method is that it affords uniform distribution of all metal cations on an atomic level in the LDH precursors; hence, the formation of spinel ferrites starting from the LDHs requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring. Experimental Section Synthesis of M-Fe2+-Fe3+-LDH sulfates (M: Mg, Co, and Ni). A mixture of Fe2(SO4)3, FeSO4, and M(NO3)2 (M : Mg, Co, and Ni) was dissolved in N2-saturated deionized water ([M2+ + Fe2+ + Fe3+] ) 0.8 mol/L). A base solution ([NaOH] 1.5 M) in N2-saturated deionized water was added dropwise to the stirred mixture at 25 °C until the pH reached 11.0 for the reaction solution containing Mg2+ cations and 7.0 fo