Effect of divalent metal ions on the stability of Cu-containing layered double hydroxides

Abstract

We proposed a periodic interaction model for the CuM2Al-layered double hydroxides (CuM2Al- 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 CuM2Al-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 CuM2Al-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 CuM2Al-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 CuCo2Al-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. © Editorial office of Acta Physico-Chimica Sinica.