Atomistic Insight into the Hydration States of Layered Double Hydroxides

Abstract

Effective protective coatings are an essential component of lightweight engineering materials in a large variety of applications as they ensure structural integrity of the base material throughout its whole service life. Layered double hydroxides (LDHs) loaded with corrosion inhibitors depict a promising approach to realize an active corrosion protection for aluminum and magnesium. In this work, we employed a combination of density functional theory and molecular dynamics simulations to gain a deeper understanding of the influence of intercalated water content on the structure, the stability, and the anion-exchange capacity of four different LDH systems containing either nitrate, carbonate, or oxalate as potential corrosion inhibiting agents or chloride as a corrosion initiator. To quantify the structural change, we studied the atom density distribution, radial distribution function, and orientation of the intercalated anions. Additionally, we determined the stability of the LDH systems by calculating their respective hydration energies, hydrogen-bonded network connected to the intercalated water molecules, as well as the self-diffusion coefficients of the intercalated anions to provide an estimate for the probability of their release after intercalation. The obtained computational results suggest that the hydration state of LDHs has a significant effect on their key properties like interlayer spacing and self-diffusion coefficients of the intercalated anions. Furthermore, we conclude from our simulation results that a high self-diffusion coefficient which is linked to the mobility of the intercalated anions is vital for its release via an anion-exchange mechanism and to subsequently mitigate corrosion reactions. Furthermore, the presented theoretical study provides a robust force field for the computer-assisted design of further LDH-based active anticorrosion coatings.

Theoretical Study on the Swelling Mechanism and Structural Stability of Ni3Al-LDH Based on Molecular Dynamics

“…Interlayer water molecules have an important influence on the structure and swelling properties of LDHs, and so, hydration energy is used to analyze the effect of introducing water molecules on the structure and properties of LDHs. The hydration energy is defined , as follows normalΔ U normalH = U ( N w ) − U ( 0 ) n where n is the total number of water molecules, U ( N w ) is the total potential energy of the system, and U (0) is the total potential energy of the system when there are no water molecules. This equation can easily and effectively calculate the hydration energy of interlayer water.…”

“…Interlayer water molecules have an important influence on the structure and swelling properties of LDHs, and so, hydration energy is used to analyze the effect of introducing water molecules on the structure and properties of LDHs. The hydration energy is defined 32,51 as follows…”

“…Moreover, Ni 3 Al-LDH, with excellent performance in energy storage, conversion, and catalysis, has not been reported in studies on swelling. Therefore, this paper developed the molecular dynamics 32 (MD) model of the Ni 3 Al-LDH structure containing interlayer water molecules and ionic column support structure. In this paper, the role of water molecules inserted into the layers is further studied, and the specific distribution state of water molecules between layers and the interaction between water molecules and anions and layers can be more intuitively displayed according to the calculation results of molecular dynamics.…”

Critical role of water structure around interlayer ions for ion storage in layered double hydroxides

“…First, we prepared two model LDH structures with highly charged [Mg 0.66 Al 0.33 (OH) 2 ] layers and weakly charged [Mg 0.833 Al 0.166 (OH) 2 ] layers to analyse the above-described experimental results. Second, the interlayer binding energies, the hydrogen-bonding structure associated with the orientation of interlayer anions and water molecules, and the interlayer distance 38 for both LDHs with various interlayer anion compositions ( x B ) were calculated as a function of the interlayer water content ( m ). The structure with x B = 0.125 in highly charged LDHs and the structure with x B = 0.25 in weakly charged LDHs were employed to investigate the intermediate interlayer structures during the nitrate ion storage.…”

Multiscale Computational Approaches toward the Understanding of Materials

“…[173,174] All the necessary parameters and inputs to carry out the MD simulations are available online. [175] This MD procedure has already been employed by other researchers to understand the structure and processes involving LDHs for different applications, [136,[176][177][178] and was employed in our research group, together with in-house tools, [179] to unveil the acid-base equilibrium, conformation and degree of solvation inside the interlayer galleries of an LDH material intercalating a well-known corrosion inhibitor, 2-mercaptobenzothiazole (MBT). [180] LDH-MBT is a nanostructured coating additive [181] and it was demonstrated that MD simulations can provide insights into the structural characterization performed by powder X-ray diffraction and the processes behind the weight loss indicated by thermogravimetric analysis.…”