Preparation and formation process of Ni2+-Fe3+ CO32- LDHs materials with high crystallinity and well-defined hexagonal shapes

A new complexing agent assisted homogeneous precipitation technology was successfully developed to synthesize Ni2+-Fe3+ CO32- LDHs materials with crystallinity and well-defined hexagonal shape [1]. By using urea as hydrolysis agent and trisodium citrate as complexing agent, Ni2+-Fe3+ CO32- LDHs with different ratios of Ni2+/Fe3+ were prepared under optimized reaction conditions, and their formation process was discussed on the basis of the experimental results. Ni2+-Fe3+ CO32- LDHs thin hexagonal nanoplates with high crystallinity were obtained for from the ratios of Ni2+/Fe3+ = 3 and 4, while Ni2+-Fe3+ CO32- LDHs material from Ni2+/Fe3+ = 2 could not be obtained due to the formation of impurity beta-Ni(OH)(2). The as-prepared Ni2+-Fe3+ CO32- LDHs materials were completely converted to Cl- LDHs materials by treating with a NaCl-HCl mixed solution, showing a good anion exchange property. Sodium fluoride, tartarate and trisodium citrate with different molecular structures were chosen as a complexing agent to investigate their effect on the crystalline and shape of the as-prepared materials. Not only had the molecular structure of the complexing agents but also the amount had an obvious effect in the formation of the as-prepared materials. Trisodium citrate played a key role for the formation of Ni2+-Fe3+ CO32- LDHs materials with high crystalline and well-defined hexagonal shapes, which made the pH deposition range of Fe(OH)3 increase due to the formation of metal ligand [Fe(C6H4O7)(2)](5-) when the pH of the reaction system was above 8. The formed metal ligand [Fe(C6H4O7)(2)](5-) changed the translation process of Fe(OH)(3) with Ni2+ ions, which reacted with free Ni2+ ions and formed Ni2+-Fe3+ CO32- LDHs materials with high crystallinity and well-defined hexagonal shapes. (C) 2009 Elsevier Masson SAS. All rights reserved.