| Mg-Al hydrotalcite is a kind of inorganic material with layered structure structure and anion exchange capacity. It is widely used in the fields of catalysis, adsorption, separateion, and medicine, et al. Many experimental works have been performed in the preparation and application of hydrotalcite during the past decades. It has been found that the slab of Mg-Al hydrotalcite possesses a regular shape such as hexagon, rhombus, and so on.It is reported that the structure, properties, preparation and application of hydrotalcite in this paper. Reseatches on the structure of hydrotalcite by quantum chemistry was few. In this paper, based on a single-layer hydrotalcite model, various computations with DFT theory were carried out for the purpose of investigating the relationship between the Al/Mg ratio and the stable properties of single -layer hydrotalcite. With the increase of the Al/Mg ratio, both Al-O and Mg-O distances will gradually become large and get maximums at the data of 7:12. But once the Al-O-Al triple is formed by continually increasing the ratio, these cases are different dramatically and the hydrotalcite structure phase would be dissolved. In consideration of the bond energy difference between Al-O and Mg-O, the structures formed at Al/Mg ratio of 6:13 and 7:12 are much more stable among all of the constructed ones. In fact, if these results are extended to single layer hydrotalcite, high symmetry structures with the ratio of 1:2 and 1:3 will be obtained easily in experiment. Therefore, in the case of avoidance of Al-O-Al triple formed, the best synthesizing scheme may be heightening the ratio of Al/Mg.
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