Theoretical studies of the interaction of terephthalate anion in MgAl-layered double hydroxides
Theoretical studies of the interaction of terephthalate anion in MgAl-layered double hydroxides
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DOI：
10.1016/j.clay.2015.01.014
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发表时间：
2015-04
影响因子：
5.6
通讯作者：
Inna M. Nangoi;Viviane S. Vaiss;Wladmir F. Souza;S. Chiaro;A. A. Leitão-A.
中科院分区：
文献类型：
--
作者：
Inna M. Nangoi;Viviane S. Vaiss;Wladmir F. Souza;S. Chiaro;A. A. Leitão-A.
采用基于密度泛函理论的第一性原理计算方法，研究了Mg-Al-TA（TA =对苯二甲酸根阴离子）层状双氢氧化物的结构和电子性质，其中x =NAl/（NAl+NMg）= 1/4，1/3和1/2.由于所谓的阳离子回避规则，x = 1/2的值在文献中是不寻常的;尽管如此，一些实验结果已经证明，使用TA作为反离子是可能获得的。计算的几何参数与实验数据吻合良好。应用含规范投影缀加波方法计算了对苯二甲酸酯碳原子在x = 1/3结构下的固体核磁共振化学位移。TA旋转角的最小能量与化学位移之间有很好的相关性。根据电子密度差和Bader电荷分析讨论了层间相互作用。计算结果表明，当摩尔比增大时，层间区的电子密度变化不大。这一结果与Bader的分析一致。计算结果表明，当摩尔比增大时，水分子与层之间的电荷密度差比阴离子与层之间的电荷密度差有较大的变化。这一结果证明了水分子在具有较高层电荷的LDHs的稳定中的重要性。此外，几何因素有助于形成x = 1/2的结构。也就是说，层中每个正电荷所占据的面积需要足够大，以使TA阴离子沿着沿着结构矢量位于层间空间中。
We used first principles calculations based on Density-Functional Theory to investigate the structural and electronic properties of Mg–Al-TA (TA = terephthalate anion) layered double hydroxides for the relationsx=NAl/(NAl+NMg) equal to 1/4, 1/3 and 1/2. Value ofx= 1/2 is unusual in the literature due to the so-called cation avoidance rule; notwithstanding, some experimental results have demonstrated that it is possible to be obtained using TA as counterion. The calculated geometric parameters are in good agreement with available experimental data. The gauge-including projector augmented wave method was applied to compute solid state nuclear magnetic resonance chemical shifts of terephthalate's carbons for structure withx= 1/3. A good correlation between the minimum energy for TA rotating angle and the chemical shifts was obtained. The interlayer interactions were discussed on the basis of electronic density differences and Bader charge analysis. Our calculations show that the electron density in the interlayer region does not change significantly while the molar ratioxincreases. This result is in line with the Bader analysis. The calculations show that there is a major change in the difference of charge density between water molecules and layer than anion and layer when the molar ratioxincreases. This result demonstrates the importance of water molecules in the stabilization of LDHs with higher layer charge. Also, a geometric factor helps in the formation of structures withx= 1/2. That is, the area occupied by each positive charge in the layers needs to be large enough to have the TA anions in the interlayer space along thecstructural vector.