First-Principles Study on Interlayer Spacing and Structure Stability of NiAl-Layered Double Hydroxides

Interlayer spacing and structure stability of layered double hydroxides (LDHs) on their application performance in adsorption, ion exchange, catalysis, carrier, and energy storage is important. The effect of different interlayer anions on the interlayer spacing and structure stability of LDHs has been less studied, but it is of great significance. Therefore, based on density functional theory (DFT), the computational model with 10 kinds of anions intercalated Ni3Al-A-LDHs (A = Cl-, Br-, I-, OH-, NO3-, CO32-, SO42-, HCOO-, C6H5SO3 -, C12H25SO3-) and four NiRAl-Cl-LDH models with different Ni2+/Al3+ ratios (R = 2, 3, 5, 8) were constructed to calculate and analyze interlayer spacing, structural stability, and their influence factors. It was found that the interlayer spacing order of Ni3Al-A-LDHs intercalated with different anions is OH- < CO32- < Cl- < Br- < I-< HCOO- < SO42- < NO3- < C6H5SO3- < C12H25SO3-. The hydrogen bond network between the base layer and the interlayer anions affects the arrangement structure of the interlayer anions, which affects the interlayer spacing. For interlayer monatomic anions Cl-, Br-, and I- and the anion of comparable size in each direction SO42-, the interlayer spacing is positively correlated with the interlayer anion diameter. The larger difference between the long-axis and short-axis dimensions of the polyatomic anions results in the long axis of the anion being perpendicular to the basal layer, increasing interlayer spacing. The long-chain anion C12H25SO3- intercalation system exhibits the largest layer spacing of 24.262 A. As R value increases from 2 to 8, the interlayer spacing of NiRAl-Cl-LDHs gradually increases from 7.964 to 8.124 A. The binding energy order between the interlayer anion and basal layer is CO32- > SO42- > OH- > Cl- > Br- > I-> HCOO- > NO3 - > C12H25SO3- > C6H5SO3-. The smaller the interlayer spacing, the higher the binding energy and the stronger the structural stability of LDHs. The factors affecting structural stability mainly include the bond length and bond angle of the hydrogen bond and the charge interaction between the basal layer and interlayer anion. In the CO32- intercalated system, the hydrogen bond length exhibits the shortest of 1.95 A and the largest bond angle of 163.68 degrees. The density of states and energy band analysis show that the higher the number of charges carried by the anion, the stronger its ability to provide electrons to the basal layer.