二价金属离子对含铜水滑石结构稳定性的影响

Effect of Divalent Metal Ions on the Stability of Cu-Containing Layered Double Hydroxides

通过构建不同的二价金属离子(M2+=Mg2+,Ca2+,Zn2+,Cd2+,Ni2+,Co2+)部分取代铜离子形成CuM2Al水滑石(CuM2Al-LDHs)的周期性模型,基于密度泛函理论(DFT),用CASTEP程序模块对周期性模型进行几何全优化和性质计算,通过分析各体系的结构参数、电子排布、Mulliken电荷布居、氢键、结合能,总结出含铜水滑石体系结构的稳定性规律.计算结果表明:在CuM2Al-LDHs体系中,主客体间作用力对层板厚度的影响占主要因素;M离子对中心三价铝离子的影响较小,对二价铜离子的影响较大,其中价电子均匀排布的M离子对铜的畸变影响小于价电子不均匀排布的M离子.另外在价电子均匀排布的CuM2Al-LDHs体系中,主客体间的静电作用力和氢键强度逐渐增强.总体上,随着M离子周期数的增加,体系的畸变角增大,结合能绝对值逐渐减小,体系的稳定性下降.价电子不均匀排布的CuCo2Al-LDHs体系的稳定性最差.这有助于从理论上更好地认识含铜水滑石的合成规律.

We proposed a periodic interaction model for the CuM2Al-layered double hydroxides （CuM2AI- LDHs）, where M represents the different divalent metal ions （Mg^（2＋）, Ca^（2＋）, Zn^（2＋）, Cd^（2＋）, Ni^（2＋）, Co^（2＋）） that might partially replace the copper ion. Based on density functional theory, the geometry of CuM2AI-LDHs was optimized using the CASTEP program. The stabilities of Cu-containing LDHs were investigated by analyzing the geometric parameters, electronic distribution, charge populations, hydrogen-bonding, and binding energies. The results showed that the electrostatic interactions between the host layer and the guest played a major role in the laminate thickness of the CuM2AI-LDHs. M ions had only a minor effect on the central Al^（3＋）, whereas they had a major effect on the Cu^（2＋） Furthermore, M ions with a uniform distribution of valence electrons had only a negligible impact. In addition, in the CuM2AI-LDHs, where the valance electrons of the M ion were uniform, both the electrostatic interactions between the host layer and the guest and the level of hydrogen-bonding increased. In general, as the period number of the M ion increased, the distortion angle of the system also increased, and the absolute value of the binding energy and the chemical stability of the system decreased. The stability of the CuCo2AI-LDHs was the lowest of all of those tested because of the nonuniform distribution of the Co^（2＋） valence electrons. These results provide a comprehensive understanding of the rules required for the synthesis of Cu-containing LDHs.