Interlaminar Anionic Transport in Layered Double Hydroxides: Estimation of Diffusion Coefficients

Abstract

Layered double hydroxides (LDHs) are materials with capacity of conducting anions. To get insight into the mechanisms controlling LDH intrinsic anionic transport properties, it is investigated the effect of composition on the anion diffusion coefficients in LDHs containing Mg or Zn as divalent cation, Al or Ga as trivalent cation, and OH − or Cl − as interlaminar anion. Diffusion coefficients are estimated simulating diffusion with a kinetic Monte Carlo algorithm on a potential energy surface (PES) associated with the dry interlayer anion. The PES is calculated using density functional theory. We find that at room temperature, diffusion coefficients increase as the difference in electronegativity between metal atoms composing the layers grows. However, at higher temperatures, systems with narrower PES basins become the ones with larger diffusion coefficients, owing to shorter residence times prior to hopping to a neighbor basin. We also find that Cl − has smaller diffusion coefficient than OH − owing to the less capacity of the former to form hydrogen bonds than the latter. These results illustrate the connection between the LDH atomic composition and its properties, knowledge that is desirable for rationally design LDHs with improved properties.

Mechanism of LDH Direct Growth on Aluminum Alloy Surface: A Kinetic and Morphological Approach

“…At this point, the growth is not influenced anymore by the nucleation rate but it is controlled by the diffusion of the reactants, over the concentration gradient in the solution, to the crystallization sites. 70,71,75,76 In addition to the above kinetic calculations, the evolution of the LDH flake size "L" was determined using the Scherrer equation (eq 3). 72,77,78…”

“…After the nucleation step, the growth continues following a diffusion-controlled reaction. At this point, the growth is not influenced anymore by the nucleation rate but it is controlled by the diffusion of the reactants, over the concentration gradient in the solution, to the crystallization sites. ,,, …”

Theoretical Study of the Catalytic Performance of Activated Layered Double Hydroxides in the Cyanoethylation of Alcohols

“…All electronic structure calculations are performed using DFT in the Kohn–Sham formulation with periodic boundary conditions. The Perdew–Burke–Enzerhof (PBE) approximation to the exchange–correlation functional is used, as it has been shown by several groups to adequately describe the structure and dynamical properties of LDH materials. − Moreover, PBE is used in this work to be able to compare with the previous results obtained by some of us and reported elsewhere on the anion–layer interactions in bulk MgAl-OH. , The projector-augmented wave , method is used together with a plane-wave basis set, as implemented in the VASP code version 5.4.1. − Calculations are performed with a plane-wave cutoff energy of 650 eV as well as 4 × 4 × 4 and 4 × 4 × 1 Monkhorst–Pack k -point meshes for sampling the bulk and surface Brillouin zones, respectively. Isolated water and methanol molecules are calculated with the methodology described above but using an orthorhombic supercell with a large vacuum region in the three lattice directions to avoid interaction between periodic images.…”

Unraveling the Hydroxide Ion Transportation Mechanism along the Surface of Two-Dimensional Layered Double Hydroxide Nanosheets

“…8 It shows superior thermal and chemical stability as well as rare intrinsic hydroxide ion conductivity, although the ionic conductivities are typically lower than 10 −3 S/cm. 9,10 Most of the previous studies focused on incorporating LDH nanoparticles into an anion-conductive matrix to enhance the stability and barrier property. 11−13 Being a layered compound, LDH can be exfoliated into twodimensional (2D) nanosheets.…”

“…Layered double hydroxide (LDH) is a class of clay-like compounds consisting of alternatively stacked positively charged metal hydroxide layers and hydrated interlayer charge-compensating anions . It shows superior thermal and chemical stability as well as rare intrinsic hydroxide ion conductivity, although the ionic conductivities are typically lower than 10 –3 S/cm. , Most of the previous studies focused on incorporating LDH nanoparticles into an anion-conductive matrix to enhance the stability and barrier property. − Being a layered compound, LDH can be exfoliated into two-dimensional (2D) nanosheets. The physical and chemical properties of these 2D nanosheets can be dramatically different from their bulk counterparts and may provide new choices for the design of ionic sieving membranes. , …”