Molecular Modeling of the Structure and Dynamics of the Interlayer Species of ZnAlCl Layered Double Hydroxide

Layered double hydroxides for corrosion-related applications—Main developments from 20 years of research at CICECO

This work describes the main advances carried out in the field of corrosion protection using layered double hydroxides (LDH), both as additive/pigment-based systems in organic coatings and as conversion films/pre-treatments. In the context of the research topic “Celebrating 20 years of CICECO”, the main works reported herein are based on SECOP’s group (CICECO) main advances over the years. More specifically, this review describes structure and properties of LDH, delving into the corrosion field with description of pioneering works, use of LDH as additives to organic coatings, conversion layers, application in reinforced concrete and corrosion detection, and environmental impact of these materials. Moreover, the use of computational tools for the design of LDH materials and understanding of ion-exchange reactions is also presented. The review ends with a critical analysis of the field and future perspectives on the use of LDH for corrosion protection. From the work carried out LDH seem very tenable, versatile, and advantageous for corrosion protection applications, although several obstacles will have to be overcome before their use become commonplace.

Effect of Iron Isomorphic Substitution in Mg:Al and Zn:Al-Layered Double-Hydroxide Structures by Means of First Principle Calculations

Layered double hydroxides (LDHs) are important components in terrestrial and extra-terrestrial environments. The presence of iron in these minerals provides them a wide potential application in environmental and materials sciences. In this work, the role of Fe in the crystallographic properties of LDHs M²⁺:M³⁺ 2:1 with Mg:(Fe,Al), Mg:Fe, Zn:(Fe,Al), and Zn:Fe is investigated by means of quantum mechanical calculations based on the density functional theory (DFT). Several relative proportions of Fe are studied. The cation ordering of these LDHs has been explored, finding useful insights for experimental synthetic paths of these minerals. The a and b cell parameters increase with the iron concentration. Some diffraction lines at high angle decrease in angle and increase in intensity with the increasing iron concentration. All of them agree with the experimental results. The iron substitutions tend to aggregate.

Anion exchange behavior of MIIAl layered double hydroxides: a molecular dynamics and DFT study

The ion exchange reaction has been extensively used in the field of synthesis of functionalized supramolecular materials such as layered double hydroxides (LDHs), ion-embedded batteries, sewage disposal and so on. In this work, the factors influencing the anion exchange behavior in the LDH gallery, such as the exchange domain, the exchange order, the driving force, and the diffusion of the anions, are investigated systematically using molecular dynamics (MD) simulations and density functional theory (DFT) methods in view of both thermodynamics and dynamics. 159 models of MIIRAl-A-LDHs (MII = Mg, Ni, Zn; R = 1.4-8, A = OH-, Cl-, Br-, NO3-, HCOO-, C6H5SO3-, CO32-, SO42-, and PO43-, respectively) are calculated. The results reveal that the anion exchange domain (interlayer distance) in LDHs is determined not only by the size and their arrangement modes of the guest anions, but also by the charges the anions carry. The relative binding energies of different anions and the Gibbs free energy changes of the anion exchange reactions in LDHs decrease in the order of PO43- > CO32- > SO42- > OH- > Cl- > Br- > HCOO- > NO3- > C6H5SO3-, which is in accordance with the experimental anion exchange order. The stronger the hydrogen bonding between the anion and the host, the larger the charge transfer, and the smaller the electronegativity of the anion, the more difficult it is for the anion to be exchanged out from LDH interlayer. In addition, for the anions with the same charges, the relative binding energy is linearly well correlated with the interlayer spacing. By analyzing the contribution of each energetic item comprising the total potential energy, it is found that the major driving force of anion exchange is the electrostatic force. The diffusion coefficient (D) along the c direction is nearly equal to zero, suggesting that the diffusion of anions occurs mainly in the ab plane of the LDH cell. It also can be inferred that when the cell parameter c < 24.0 Å, the anion exchange order is mainly determined by the thermodynamic factors, whereas when c > 24.0 Å, both the thermodynamic and the dynamic factors cast the same effect on the anion exchange behavior. This work provides an in-depth understanding of the anion exchange behavior, and is helpful guidance for the design and synthesis of functionalized guest anion intercalated LDHs and related materials using the anion-exchange method.

New insights into the interstratification phenomenon in layered double hydroxides (LDHs): a comparison of experimental and computational results for ZnAl-LDH containing bis-tetrazole

In the present paper, successful preparation of ZnAl layered double hydroxides (LDHs) containing bis-tetrazole anions with both typical and interstratified arrangements is reported. The mechanism of the single-anion interstratified arrangement remains a long-standing and overwhelming challenge in the chemistry of LDHs. To address this issue, the arrangement of layers, the positioning of anions in the interlayer space, and the cationic ratio of layers were studied by the application of a series of laboratory methods including X-ray diffraction (XRD), thermal analyses (TGA, DTG, and DTA), elemental analysis (CHN), and energy dispersive X-ray (EDX) methods, together with computer simulations performed by using Dmol3, Forcite, and Reflex modules. The obtained information demonstrated the dependence of interstratification on the type, size, and charge distribution of the intercalated anions, and the cationic ratio of the LDH layers. At the end, a new comprehensive mechanism is proposed for single-anion interstratification in layered double hydroxides by considering the results of this research study and other related works.

Molecular design confirmation for proposition of improved photophysical properties in a dye-intercalated layered double hydroxides

In the present research, Zn₂Al layered-double hydroxide (LDH) intercalated with Acid Red 27 was prepared by coprecipitation method, while solutions of Zn(ii) and Al(iii) nitrate salts reacted with an alkaline solution of Acid Red 27.

Preparation of cubane-1,4-dicarboxylate–Zn–Al layered double hydroxide nanohybrid: comparison of structural and optical properties between experimental and calculated results

In this work, we report the preparation of cubane-1,4-dicarboxylate–Zn₂Al layered double hydroxide (LDH) nanohybrid and understanding of the structural and electronic properties of nanohybrid by periodic density functional theory.