Effect of anion addition on the syntheses of Ca–Al layered double hydroxide via a two-step mechanochemical process

• A katoite phase was easily obtained by milling Ca and Al hydroxides.
• A third phase was required to form Ca–Al LDH phase.
• A solvent-free mechanochemical route allowed the synthesis of Ca–Al–X (X = CO32– or Cl−) LDHs.

A pure phase of Ca–Al–X (X = CO32 − or Cl−) layered double hydroxide (LDH) was synthesized via a two-step solvent-free mechanochemical process. Milling Ca and Al hydroxides only gave katoite as the main phase in the product. Further addition of carbonate or chloride during milling operation allowed easy formation of Ca–Al–X LDH. The as-prepared samples were characterized by X-ray diffractometry (XRD),Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The characterization results confirmed the formation of highly crystalline Ca–Al LDH phase. The idea to add a third phase to help stabilize desired compound as LDH in this work may be of help for the synthesis of other substance in general.