The Influence on Synthetising Mg-Al Hydrotalcite by Using Different Mg and Al Sources as the Precursors

In this paper, Mg-Al hydrotalcite crystals were synthesized using the different Mg sources and Al sources as the precursor via hydrothermal method. The effects of different Mg and Al sources on the microstructure and the growth of LDHs were investigated by the X-ray diffraction (XRD), scanning election microscopy (SEM) and energy dispersive spectrometer (EDS), simultaneity. Besides, according to the ligand theory, its growth mechanism was discussed. The research indicated that the better LDHs crystal could been prepared under the condition of pH=12, hydrothermal temperature of 120°C and time of 12 h. The different Mg and Al sources combination had certain influence on the phase, dispersion, regularity, ratio of thickness, purity, size and microstructure of LDHs products. When the Mg sources was fixed for MgCl2, choosing Al2O3, Al(NO3)3 and AlCl3 as Al sources respectively, the obtained LDHs with poor purity, regularity dispersion and crystallinity were synthesized when Al2O3 was used as Al sources; but the LDHs had better regularity, dispersion, crystalline and purity when Al(NO3)3 and AlCl3 were chosed as Al sources. The reason could be that the different solubility and polarity of anion caused the slight variation of products microstructure. Compared to MgCl2 with high dissolvability, when the Mg sources was fixed for Mg(NO3)2, choosing Al(NO3)3 and AlCl3 as Al sources respectively, it is more advantageous to getting LDHs with better crystalline, regularity, and smaller in size. When both Mg sources and Al sources had higher solubility, the synthesized LDHs were with higher crystalline and regularity. The EDS analysis results showed that the purity of LDHs synthesized with Al2O3 had poor solubility. In addition, LDHs prepared by Mg sources and Al sources with higher solubility do not contain any other anionic impurities, and the average ratio of Mg/Al is about 3, which is very close to the theoretical value.