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.