Chemical Design of Magnetic Nanocomposites Based on Layered Double Hydroxides

Chemical modification of anion-substituted layered double hydroxides (LDHs) was used for the preparation of anisotropic magnetic nanocomposites. The method combines the simplicity of chemical methods and the possibility to prepare two-, one-, or zero-dimensional nanoparticles in oxide/hydroxide matrices. An LDH structure consists of positively charged hydroxide layers bonded with negatively charged anions, which occupy the interlayer space. During chemical reactions of anions in the interlayer space, reaction zone is spatially constrained by the hydroxide layers, giving rise to the conditions similar to those in two-dimensional nanoreactors, such as Langmuir–Blodgett films and self-assembling monolayers. Here we used LDH precursors for the preparation of the Fe- and Ni-based nanocomposites. The precursors were obtained by intercalation of ethylenediaminetetraacetate (edta) complexes of Fe(III) or Ni(II) into the Mg–Al LDH. Substituted LDHs were reduced by H₂ to give metal nanoparticles entrapped into the inert Mg–Al oxide matrix. Reduction of anion-substituted LDHs with different content of anionic complexes (and ratio Mg/Al in matrix) occurs at a relatively low temperature (～600°C) and results in the formation of metal nanoparticles with different morphology and sizes. The formation of anisotropic metal nanoparticles in the former case is believed to be due to the spatial constraints of the reaction zone and their formation occurs simultaneously with buckling of hydroxide layers.