| Spinels are a typical magnetically soft material and play a significant role in the development of numerous aspects of solid-state physics and chemistry. These materials in the form of fine powers are finding applications in dehydrogenation catalysis, sensor, pigment, humidity-sensing and photoelectrical materials.Currently, the main method of synthesis of spinel ferrite is conventional solid-state reaction (further referred to as the nonactivated sample). However, in conventional solid-state reaction, inadequate mixing of the reaction components, low contact surface, and strong diffusion resistance make it difficult to reaction completely. The formations of complex oxides with the spinel structure using the conventional solid-state reaction between simple oxides proceeds especially slowly and requires prolong exposure at considerably elevated temperatures. Directed to this problem, new methods of material synthesis have received increased attention in recent years. Of particular interest are low-temperature technique, such as room-temperature ball-milling, which offer the possibility of forming structures exhibiting new and unusual properties. The mechanochemical route for the preparation of spinel ferrite has been reported starting from MeO and α-Fe2O3 powder in equimolar ratio. But in this method, the reactant is also the nonactivated α-Fe2O3/ MeO mixture, so a single homogeneous spinel is also difficult to achieve.Alternative wet chemical methods have been proposed including coprecipitation from aqueous solution, sol-gel synthesis involving supercritical drying to provide aerogels and use of micellar microemulsions. In these cases, it is difficult to prevent contamination of the product by cations arising from the precipitants or organic residues from the precursor mixtures. In order to avoid compromising the purity and properties of spinel ferrite and related materials, it would be desirable to prepare them from a single solid precursor, which can be prepared in a pure state in which the Me2+ and Fe3+ cations are uniformly distributed on an atomic level. In this Report, we show how synthesis of a Layered Double Hydroxide precursor with the correct stoichiometry allows this objective to be realized.Layered double hydroxide hydrotalcite are a kind of two-dimensional nanometric material, represented typically by the hydrotalcite Mg6Al2(OH)16CO3·4H2O. The structure of it consists of brucite-like, positively charged layers of magnesium and aluminum hydroxide octahedral sharing edges and has interstitial carbonate anions to charge compensate. Water molecules are also between the metal hydroxide layers. Layered double hydroxides (LDHs) can be obtained, when Mg2+, Al3+ and CO32- are substituted by other cations or anions. The LDHs generic formula is [MⅡ1-XMⅢX (OH)2]X+(An-)X/n·mH2O, where MⅡis a divalent cation (Mg2+, Ni2+, Co2+, Zn2+ or Cu2+); MⅢ is a trivalent cation ( Al3+, Cr3+, Fe3+or Sc3+)in the octahedral interstices of the hydroxide layer and An- is the charge-balancing interlayer gallery anion (CO32-, NO3-, Cl-, OH-, SO42- or PO43-).It is well known that spinel can be achieved from LDHs at high temperature (above 750 oC). But in LDHs, the divalent cation is always present in greater amounts than the trivalent cation (the stoichiometric coefficient x above is usually found in the range 0.2 – 0.33, corresponding to MII/MIII ratios of 2 – 4) whereas in a spinel the required ratio is MII/MIII = 0.5. So in the calcined products of LDHs, there are always mixed with the non-magnetism oxide of the divalent metal.Based on this fact, we put forward the substitution by Fe2+ in hydrotalcite layers to synthesize MeFe(Ⅱ)Fe(Ⅲ)-LDHs, which are potential precursors to pure MeFe2O4 spinels since the Fe2+ ions will be oxidized on calcination in air to give additional Fe3+ ions, thus overcoming the deficiency of trivalent ions discussed above. In this report, we have synthesized MgFe(Ⅱ)Fe(Ⅲ)-LDHs, CoFe(Ⅱ)Fe(Ⅲ)-LDHs, NiFe(Ⅱ)Fe(Ⅲ)-LDHs and NiZnFe(Ⅱ)Fe(Ⅲ)-LDHs precursors with the composition req...
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