Mg-Al类水滑石层板结构中Al/Mg比与稳定性的关系

Relationship between Al/Mg Ratio and the Stability of Single-layer Hydrotalcite

通过改变Mg和Al的数量构建不同Al/Mg比的类水滑石层板模型,采用量子化学密度泛函理论(DFT),优化并计算各种Al/Mg比的水滑石结构,通过对键长、电荷、能量等分析,得出Al/Mg比对水滑石稳定性的影响规律.在实际的水滑石层板结构中,当Al/Mg比为1∶2和1∶3时,最适宜形成稳定水滑石相,且1∶3比1∶2更具优势.

On the basis of a single-layer hydrotalcite model, various computations with density functional theory （DFT） were carded out for the purpose of investigating the relationship between the Al/Mg molar ratio and the stability of single-layer hydrotalcite. With the increase in the Al/Mg molar ratio, both Al-O and Mg-O distances gradually became large and reached maximum at the ratio of 7：12. But once Al-O-Al triple was formed by continuously increasing the ratio, the case was dramatically different and the hydrotalcite structure phase dissolved. In consideration of the difference of the bond energy between Al-O and Mg-O, the structures formed at Al/Mg molar ratios of 6：13 and 7：12 were much more stable among all the constructed ones. In fact, if these results are extended to single layer hydrotalcite, high symmetry structures with the ratios of 1：2 and 1：3 will be easily obtained in experiment. Therefore, in the case, where the formation of Al-O-Al triple is avoided, the best synthesizing scheme may be heightening the ratio of Al/Mg.