Novel route to synthesize CaAl- and MgAl-layered double hydroxides with highly regular morphology

A facile, sol-gel method was developed to obtain Al-containing layered double hydroxides (LDHs) with Ca or Mg divalent cations. Ca- and Al-alkoxide were added to aqueous NaNO3 solution, and, after rapid gelation, a solid product, phase-pure, highly crystalline CaAl-LDH was formed with exceptionally regular morphology without impurities for the first time with sol-gel method. The lack of salt in the solution used for the hydrolysis resulted in a non-desirable by-product (katoite). For the sol-gel synthesis of MgAl-LDH, it was found that its formation was less sensitive to the presence of nitrate ions, and pure water or aqueous NaOH worked equally well. The product was also a highly crystalline material with thin, plate-like morphology as revealed by X-ray diffractometry and scanning electron microscopy. IR measurements indicate the lack of organic substance in the interlamellar space for both materials. [GRAPHICS] HighlightsA novel version of sol-gel synthesis was utilized to prepare two types of layered double hydroxides.The platelets have well-defined hexagonal morphology.The products have thin crystals with high aspect ratio.