Atomistic Insight into the Hydration States of Layered Double Hydroxides

Different Scenarios for the Origin and the Subsequent Succession of a Hypothetical Microbial Community in the Cloud Layer of Venus

The possible existence of a microbial community in the venusian clouds is one of the most intriguing hypotheses in modern astrobiology. Such a community must be characterized by a high survivability potential under severe environmental conditions, the most extreme of which are very low pH levels and water activity. Considering different scenarios for the origin of life and geological history of our planet, a few of these scenarios are discussed in the context of the origin of hypothetical microbial life within the venusian cloud layer. The existence of liquid water on the surface of ancient Venus is one of the key outstanding questions influencing this possibility. We link the inherent attributes of microbial life as we know it that favor the persistence of life in such an environment and review the possible scenarios of life's origin and its evolution under a strong greenhouse effect and loss of water on Venus. We also propose a roadmap and describe a novel methodological approach for astrobiological research in the framework of future missions to Venus with the intent to reveal whether life exists today on the planet.

Visible light photoreforming of greenhouse gases by nano Cu-Al LDH intercalated with urea-derived anions

The accumulation of anthropogenic greenhouse gases (GHGs) in the atmosphere causes global warming. Global efforts are carried out to prevent temperature overshooting and limit the increase in the Earth's surface temperature to 1.5 °C. Carbon dioxide and methane are the largest contributors to global warming. We have synthesized copper-aluminium layered double hydroxide (Cu-Al LDH) catalysts by urea hydrolysis under microwave (MW) irradiation. The effect of MW power, urea concentration, and MII/MIII ratios was studied. The physicochemical properties of the prepared LDH catalysts were characterized by several analysis techniques. The results confirmed the formation of the layered structure with the intercalation of urea-derived anions. The urea-derived anions enhanced the optical and photocatalytic properties of the nano Cu-Al LDH in the visible-light region. The photocatalytic activity of the prepared Cu-Al LDH catalysts was tested for greenhouse gas conversion (CH4, CO2, and H2O) under visible light. The dynamic gas mixture flow can pass through the reactor at room temperature under atmospheric pressure. The results show a high conversion percentage for both CO2 and CH4. The highest converted amounts were 7.48 and 1.02 mmol mL-1 g-1 for CH4 and CO2, respectively, under the reaction conditions. The main product was formaldehyde with high selectivity (>99%). The results also show the stability of the catalysts over several cycles. The current work represents a green chemistry approach for efficient photocatalyst synthesis, visible light utilization, and GHGs' conversion into a valuable product.

Corrosion Inhibitors Intercalated into Layered Double Hydroxides Prepared In Situ on AZ91 Magnesium Alloys: Structure and Protection Ability

This work first describes the intercalation of corrosion inhibitors into layered double hydroxides LDH-OH/CO₃ nanocontainers (parental LDH) obtained in situ on the surface of magnesium alloy AZ91 in the presence of a chelating agent. Vanadate, as a typical broad inhibitor for active metals, and oxalate, as an inhibitor suitable for magnesium, were selected as a first approach. The optimization of exchange conditions was performed, and the optimal parameters (ambient pressure and 95 °C) were selected. The corrosion protective properties of obtained LDH-based layers were studied using immersion and salt spray tests in NaCl solution, supported by electrochemical impedance spectroscopy and atomic emission spectroelectrochemistry. It is demonstrated that vanadate intercalated into LDH is more effective for the active protection of AZ91 in comparison to the performance of oxalate. A possible mechanism of corrosion inhibition based on the application of LDH nanocontainers is suggested and discussed.

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

layered double hydroxide (LDH) as a kind of 2D layer material has a swelling phenomenon. Because swelling significantly affects the adsorption, catalysis, energy storage, and other application properties of LDHs, it is essential to study the interlayer spacing, structural stability, and ion diffusion after swelling. In this paper, a periodic computational model of Ni₃Al-LDH is constructed, and the supramolecular structure, swelling law, stability, and anion diffusion properties of Ni₃Al-LDH are investigated by molecular dynamics theory calculations. The results show that the interlayer water molecules of Ni₃Al-LDH present a regular layered arrangement, combining with the interlayer anions by hydrogen bonds. As the number of water molecules increases, the hydrogen bond between the anion and the basal layer gradually weakens and disappears when the number of water molecules exceeds 32. The hydrogen bond between the anion and the water molecule gradually increases, reaching an extreme value when the number of water molecules is 16. The interlayer spacing of Ni₃Al-LDH is not linear with the number of water molecules. The interlayer spacing increases slowly when the number of water molecules is more than 24. The maximum layer spacing is stable at around 19 Å. The interlayer spacing, binding energy, and hydration energy show an upper limit for swelling: the number of water molecules is 32. When the number of interlayer water molecules is 16, the water molecules' layer structure and LDH interlayer spacing are suitable for anions to obtain the maximum diffusion rate, 10.97 × 10^-8 cm²·s^-1.

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.

Molecular Dynamics Model to Explore the Initial Stages of Anion Exchange involving Layered Double Hydroxide Particles

A classical molecular dynamics (MD) model of fully unconstrained layered double hydroxide (LDH) particles in aqueous NaCl solution was developed to explore the initial stages of the anion exchange process, a key feature of LDHs for their application in different fields. In particular, this study focuses on the active corrosion protection mechanism, where LDHs are able to entrap aggressive species from the solution while releasing fewer corrosive species or even corrosion inhibitors. With this purpose in mind, it was explored the release kinetics of the delivery of nitrate and 2-mercaptobenzothiazole (MBT, a typical corrosion inhibitor) from layered double hydroxide particles triggered by the presence of aggressive chloride anions in solution. It was shown that the delamination of the cationic layers occurs during the anion exchange process, which is especially evident in the case of MBT^-.

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

Water-containing layered materials have found various applications such as water purification and energy storage. The highly structured water molecules around ions under the confinement between the layers determine the ion storage ability. Yet, the relationship between the configuration of interlayer ions and water structure in high ion storage layered materials is elusive. Herein, using layered double hydroxides, we demonstrate that the water structure is sensitive to the filling density of ions in the interlayer space and governs the ion storage. For ion storage of dilute nitrate ions, a 24% decrease in the filling density increases the nitrate storage capacity by 300%. Quartz crystal microbalance with dissipation monitoring studies, combined with multimodal ex situ experiments and theoretical calculations, reveal that the decreasing filling density effectively facilitates the 2D hydrogen-bond networking structure in water around interlayer nitrate ions along with minimal change in the layered structure, leading to the high storage capacity.