Microwave-assisted reconstruction of Ni,Al hydrotalcite-like compounds

The microwave-assisted reconstruction of Ni,Al hydrotalcite-like compounds (HTlcs) with Ni/Al molar ratios 2/1 and 3/1 has been studied. Mixed oxides obtained after calcination of the HTlcs are immersed in three different solutions containing carbonate, distilled water and an aqueous NH3 solution, and then heated at different temperatures for increasing periods of time under microwave radiation. The evolution of the structure during the treatment is followed by powder X-ray diffraction, FT-IR and vis–UV spectroscopies and SEM and TEM microscopies. Full recovery of the original layered structure is achieved in short periods of time for the 2/1 samples when the calcined HTlcs are rehydrated in the Na2CO3 solution, but more drastic conditions are necessary for the 3/1 samples and the reconstruction seems not to be complete. Finally, only a partial reconstruction is observed in distilled water or NH3 aqueous solution.