Ultrasonically-enhanced mechanochemical synthesis of CaAl-layered double hydroxides intercalated by a variety of inorganic anions

• Synthesis of CaAl-LDH by ultrasonically-enhanced milling.
• Identifying the optimum synthesis parameters.
• Efficient introduction of halogenide ions, hard to intercalate with other methods.
• Improvement in the quality of LDHs due to ultrasonic treatment.

CaAl-layered double hydroxides (CaAl-LDHs) were synthesised with various interlayer anions (CO32−, F−, Cl−, Br− and I−) by mechanochemical pre-treatment followed by ultrasonic irradiation in aqueous media. The parameters of the syntheses (duration of pre-milling and sonication, quality of the aqueous media, temperature) were altered in order to optimise the procedure and to understand the formation of LDH and other secondary products. The products were characterised by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The optimisation resulted in close-to-phase-pure CaAl-LDHs, not only with carbonate and chloride interlayer anions, but the hard-to-intercalate bromide and iodide as well.