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Layered double hydroxides (LDHs) constitute a unique group of 2D materials that can deliver exceptional catalytic, optical, and electronic performance. However, they usually suffer from low stability compared to their oxide counterparts. Using density functional calculations, we quantitatively demonstrate the crucial impact of the intercalants (i.e., water, lactate, and carbonate) on the stability of a series of common LDHs based on Mn, Fe, and Co. We found that intercalation with the singly charged lactate results in higher stability in all these LDH compounds, compared to neutral water and doubly charged carbonate. Furthermore, we show that the dispersion effect aids the stability of these LDH compounds. This investigation reveals that certain intercalants enhance LDH stability and alter the bandgap favourably.

Transition‐metal‐based layered double hydroxides (TM‐LDHs) nanosheets are promising electrocatalysts in the renewable electrochemical energy conversion system, which are regarded as alternatives to noble metal‐based materials. In this review, recent advances on effective and facile strategies to rationally design TM‐LDHs nanosheets as electrocatalysts, such as increasing the number of active sties, improving the utilization of active sites (atomic‐scale catalysts), modulating the electron configurations, and controlling the lattice facets, are summarized and compared. Then, the utilization of these fabricated TM‐LDHs nanosheets for oxygen evolution reaction, hydrogen evolution reaction, urea oxidation reaction, nitrogen reduction reaction, small molecule oxidations, and biomass derivatives upgrading is articulated through systematically discussing the corresponding fundamental design principles and reaction mechanism. Finally, the existing challenges in increasing the density of catalytically active sites and future prospects of TM‐LDHs nanosheets‐based electrocatalysts in each application are also commented. Current fabrication strategies to design transition‐metal‐based layered double hydroxides (TM‐LDHs) nanosheets are summarized. The electrocatalytic applications of these as‐fabricated TM‐LDHs nanosheets in oxygen evolution reaction, hydrogen evolution reaction, urea oxidation reaction, nitrogen reduction reaction, small molecule oxidation, and biomass derivatives upgrading are articulated through systematically discussing the corresponding fundamental design principles and reaction mechanism.

Currently, Layered Double Hydroxides (LDH) is a hot area of research on inorganic layered materials. The present book, Applications of Layered Double Hydroxides, edited by Dr. Rjib Lochan Goswamee and Dr. Pinky Saikia, is a collection of articles from various researchers from different parts of the world mainly on structure and property relationships of various types of LDH and their related application prospects. How these application prospects can be related to the most pressing problems of humanity like drug delivery, global warming, green catalysis, electrochemical energy storage and generation etc. are clearly discussed in the articles inside. The book provides a thorough up-to-date review of recent literature on applications of LDH available in the global scientific and technical media. For example, the book lucidly describes the behaviour of LDH nanocarriers in biological fluids, their low cytotoxicity and high levels of cellular internalization, and high drug loading capacity. Similarly, the book examines why hybrid nanocomposites of LDH-MOF are considered promising materials due to their diverse functionality, flexible properties and tailored end-use properties. Likewise, application of LDH in secondary batteries and electro-chemical supercapacitors with a thorough up-to-date review is included in the book. Also, basic research articles on structural properties and measurements of a special class of unique LDH Li-Al-LDHs are included. Editors also have written their own articles on their findings on the prospective application of dispersions of LDH nanocomposites on structured catalysts for green-house gas emission. Overall, the book gives a short glimpse of wonderful opportunities that LDH can provide in solving many global socio-economic problems of today.

Although artificial bone repair scaffolds, such as titanium alloy, bioactive glass, and hydroxyapatite (HAp), have been widely used for treatment of large‐size bone defects or serious bone destruction, they normally exhibit unsatisfied bone repair efficiency because of their weak osteogenic and angiogenesis performance as well as poor cell crawling and adhesion properties. Herein, the surface functionalization of MgAlEu‐layered double hydroxide (MAE‐LDH) nanosheets on porous HAp scaffolds is reported as a simple and effective strategy to prepare HAp/MAE‐LDH scaffolds for enhanced bone regeneration. The surface functionalization of MAE‐LDHs on the porous HAp scaffold can significantly improve its surface roughness, specific surface, and hydrophilicity, thus effectively boosting the cells adhesion and osteogenic differentiation. Importantly, the MAE‐LDHs grown on HAp scaffolds enable the sustained release of Mg2+ and Eu3+ ions for efficient bone repair and vascular regeneration. In vitro experiments suggest that the HAp/MAE‐LDH scaffold presents much enhanced osteogenesis and angiogenesis properties in comparison with the pristine HAp scaffold. In vivo assays further reveal that the new bone mass and mineral density of HAp/MAE‐LDH scaffold increased by 3.18‐ and 2.21‐fold, respectively, than that of pristine HAp scaffold. The transcriptome sequencing analysis reveals that the HAp/MAE‐LDH scaffold can activate the Wnt/β‐catenin signaling pathway to promote the osteogenic and angiogenic abilities. MgAlEu‐LDH nanosheet‐modified hydroxyapatite scaffolds are designed and fabricated for efficient bone repair and vascular regeneration, which exhibit excellent angiogenic and osteogenic performance due to the improved surface roughness, specific surface, and hydrophilicity as well as the sustained release of Mg2+ and Eu3+ ions.

In order to overcome burgeoning energy demands along with the ecological crisis caused by dwindling amounts of fossil fuel and increasing levels of carbonaceous emission, there is an immediate need to develop economical, eco-friendly systems for energy applications. To overcome this issue, use of non-carbon materials has been suggested, but their commercial usage is limited due to intermittency and high operational costs. Currently, layered double hydroxides (LDHs) are prospective contenders for energy applications by virtue of unique physicochemical properties and excellent theoretical specific capacitance. Additionally, LDH–polymer matrix composites (PMCs) have also emerged as nexus materials in energy storage sector since they surpass disadvantages of both LDHs and polymers and broaden the horizons for their practical applications. The current review highlights applications of LDH–PMCs as supercapacitors in terms of maximum specific capacitance, energy density, power density, and rate capability along with insights into mechanism of capacitance, thereby outlining their utility in energy storage. Graphical abstract

Constructing heterojunctions with vacancies has garnered substantial attention in the field of piezo‐photocatalysis. However, the presence of interfacial vacancies can serve as charge‐trapping sites, leading to the localization of electrons and hindering interfacial charge transfer. Herein, dual oxygen vacancies in the NiFe‐layered double hydroxide and Bi2MoO6−x induced interfacial bonds have been designed for the piezo‐photocatalytic N2 oxidation to NO3−. Fortunately, it achieves sensational nitric acid production rates (7.23 mg g−1 h−1) in the absence of cocatalysts and sacrificial agents, which is 6.03 times of pure Bi2MoO6 that under ultrasound and light illumination. Theoretical and experimental results indicate that interfacial bonds act as “charge bridge” and “strain center” to break the carrier local effect and negative effects with piezocatalysis and photocatalysis for promoting exciton dissociation and charge transfer. Moreover, the strong electronic interaction of the interfacial bond induces internal reconstruction under ultrasound for promoting the local polarization and adsorption of N2, which accelerates the fracture of the N≡N bonds and reduces the activation energy of the reaction. The research not only establishes a novel approach for optimizing the combined effects of piezo‐catalysis and photocatalysis, but also achieves equilibrium between the synergistic impacts of vacancies and heterojunctions. NiFe‐layered double hydroxide and Bi2MoO6−x heterojunction with dual oxygen vacancies and interfacial bonds is designed for enhancing piezo‐photocatalytic nitrogen oxidation to nitric acid. The interfacial bonds act as “charge bridge” and “strain center” to promote exciton dissociation and charge transfer as well internal reconstruction for molecular activation.

The development of electrocatalysts with optimized intermediate adsorption and low energy barriers is crucial for the oxygen evolution reaction (OER). In this work, the d‐band center position of high‐entropy layered double hydroxides (HE‐LDHs) is modulated by substituting Mg2⁺ sites with Fe2+, Cu2+, Co2+, and Ni2+. It is demonstrated that the d‐band center position relative to the Fermi level is modified, reaching an optimal energy in (FeCuCoNi)6Al2‐LDH. The nature of the incorporated transition metals significantly influenced OH− adsorption kinetics and reduced the overpotential for OER by 55%, compared to native LDH. The stepwise substitution of Mg2⁺ by Fe2⁺ particularly induces charge carrier transfer, switching into Faradaic processes favorable to the enhancement of OER kinetics. This work provides an effective approach that allows decreasing the OER overpotential through adjusting the position of the d‐band center, and suggests that d‐band tuning via multication insertion can directly shift the material toward an optimal binding strength region, which underlies the observed performance. The d‐band center position of layered double hydroxide is adjusted via multication insertion in the octahedral site. The optimal position of the d‐band, near the Fermi level, enhances OER performance through optimal OH− adsorption kinetics, resulting in a 55% reduction in overpotential compared to the native catalyst.

This work highlights the use of Fe-modified MgAl-layered double hydroxides (LDHs) to replace dye and semiconductor complexes in dye-sensitized solar cells (DSSCs), forming a layered double hydroxide solar cell (LDHSC). For this purpose, a MgAl-LDH and a Fe-modified MgAl LDH were prepared. X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy were used to analyze the structural properties, morphology, and success of the Fe-modification of the synthesized LDHs. Ultraviolet-visible (UV-Vis) absorption spectroscopy was used to analyze the photoactive behavior of these LDHs and compare it to that of TiO2 and dye-sensitized TiO2. Current-voltage (I–V) solar simulation was used to determine the fill factor (FF), open circuit voltage (VOC), short circuit current (ISC), and efficiency of the LDHSCs. It was shown that the MgFeAl-LDH can act as a simultaneous photoabsorber and charge separator, effectively replacing the dye and semiconductor complex in DSSCs and yielding an efficiency of 1.56%.

Charmarite, Mn4Al2(OH)12CO3·3H2O, is a hydrotalcite supergroup member (or layered double hydroxide, LDH) with a previously unknown crystal structure and a Mn2+-analogue of quintinite (commonly erroneously reported as '2:1 hydrotalcite'). The single-crystal X-ray diffraction (XRD) data were obtained from the specimen from Mont Saint-Hilaire, Quebec, Canada and are best processed in the space group P3̄, a=10.9630(4), c=15.0732(5) Å and V=1568.89(12) Å3. The crystal structure has been solved by direct methods and refined to R1=0.0750 for 3801 unique reflections with Fo>2σ(Fo). The charmarite structure has long-range periodicity in the xy plane due to 2√3α'×2√3α' scheme (or 11×11 Å) determined for LDHs for the first time (where α' is a subcell parameter ≈3.2 Å). This periodicity is produced by the combination of two superstructures formed by: (1) Mn2+ and Al3+ ordering in the metal-hydroxide layers [Mn4Al2(OH)12]2+ according to the √3α'×√3α' pattern and (2) the (CO3)2- ordering according to the 2α'×2α' pattern in the [CO3(H2O)3]2- interlayer sheet in order to avoid close contacts between adjacent carbonate groups. The √3α'×√3α' superstructure is an example of the adaptability of the components of the interlayer space to the charge distribution of the metal-hydroxyl layers. The Mn2+ and Al3+ cations have a large difference in size, which apparently leads to the considerable degree of their order as di- and trivalent cations resulting in a higher degree of statistical order of the interlayer components. Both powder and single-crystal XRD data show that the samples studied belong to the hexagonal branch of two-layer polytypes (2T or 2H) with d00n≈7.57 Å The chemical composition of the samples studied is close to the ideal formula. The Raman spectrum of charmarite is reported and the band assignment is provided.