NiFe-Layered Double Hydroxide Synchronously Activated by Heterojunctions and Vacancies for the Oxygen Evolution Reaction

The development of earth-abundant transition-metal-based electrocatalysts with bifunctional properties (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is crucial to commercial hydrogen production. In this work, layered double hydroxide (LDH)-zinc oxide (ZnO) heterostructures and oxygen vacancies are constructed synchronously by plasma magnetron sputtering of NiFe-LDH. Using the optimal conditions, ZnO nanoparticles are uniformly distributed on the NiFe-LDH nanoflowers, which are prepared uniformly on the three-dimensional porous Ni foam. In the LDH-ZnO heterostructures and oxygen vacancies, electrons are depleted at the Ni cations on the NiFe-LDH surface and the active sites change from Fe cations to Ni cations during OER. Our theoretical assessment confirms the change of active sites after the deposition of ZnO and reveals the charge-transfer mechanism. Owing to the significant improvement in the OER dynamics, overall water splitting can be achieved at only 1.603 V in 1 M KOH when the Ni/LDH-ZnO and Ni/LDH are used as the anode and cathode, respectively. The work reveals a novel design of self-supported catalytic electrodes for efficient water splitting and also provides insights into the surface modification of catalytic materials.

Zn-Al Layered Double Hydroxide Film Functionalized by a Luminescent Octahedral Molybdenum Cluster: Ultraviolet-Visible Photoconductivity Response

A novel UV-Vis photodetector consisting of an octahedral molybdenum cluster-functionalized Zn₂Al layered double hydroxide (LDH) has been successfully synthesized by co-precipitation and delamination methods under ambient conditions. The electrophoretic deposition process has been used as a low-cost, fast, and effective method to fabricate thin and transparent nanocomposite films containing a dense and regular layered structure. The study provided evidence that the presence of the Mo₆ cluster units between the LDH does not affect the ionic conduction mechanism of the LDH, which linearly depends on the relative humidity and temperature. Moreover, the photocurrent response is remarkably extended to the visible domain. The reproducibility and stabilization of the photocurrent response caused by the Mo₆ cluster-functionalized LDH have been verified upon light excitation at 540 nm. Additionally, it was demonstrated that the films show advantageously strong adherence properties for application requirements.

Preconcentration of digoxin using a synthetic imprinted polymer deposited upon the surface of double-layered hydroxides on porous anodised aluminium wire a triple solid-phase microextraction fibre

INTRODUCTION

A new solid-phase microextraction fibre is fabricated through polymerisation of molecularly imprinted polymer on the surface of a layered double hydroxide framework that has been fabricated via the in situ synthesis on a non-porous anodic aluminium oxide/aluminium wire as both the substrate and the aluminium source.

OBJECTIVE

The synthesized SPME fiber was performed to analyze trace digoxin in real samples.

MATERIAL AND METHOD

A one-at-a-time optimization strategy was applied for optimizing the important extraction parameters such as extraction solvent, extraction time, stirring rate, pH, ionic strength, and desorption time.

RESULT

Aluminum surface before and after anodizing and LDH structure reveal that anodizing and preparation LDH increases the surface area and adsorption capacity of aluminum wire.

CONCLUSION

Under optimum conditions, the repeatability for one fibre (n = 3), expressed as relative standard deviation (RSD %), was 5.2%.

In vitro cytotoxicity studies of smart pH-sensitive lamivudine-loaded CaAl-LDH magnetic nanoparticles against Mel-Rm and A-549 cancer cells

In this study, an effective nano-drug delivery system was prepared by the co-precipitation method via two steps; the preparation of Fe₃O₄ magnetic nanoparticles and its surface modification with layered double hydroxide (LDH) and loading lamivudine on this nanocarrier (Fe₃O₄@CaAl-LDH@Lamivudine). The developed nanoparticles (NPs) were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, Fourier-transformed infrared spectroscopy, vibrating-sample magnetometry, thermogravimetric analysis, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller. The prepared system demonstrated an average size of 130 nm. Also, the drug entrapment efficiency was estimated at ∼70%. In vitro, drug release investigations showed a controlled and pH-dependent lamivudine release over 300 min. The in vitro cytotoxic activity of Fe₃O₄@CaAl-LDH@Lamivudine NPs was explored against Mel-Rm and A-549 cancer cell lines in comparison with lamivudine and nanocarrier using lactate dehydrogenase colorimetric and MTT assay. The results of the MTT assay revealed that the Fe₃O₄@CaAl-LDH@Lamivudine NPs significantly inhibited the proliferation of Mel-Rm and A-549 cells in a dose-dependent manner. The influences of Fe₃O₄@CaAl-LDH@Lamivudine on the cancer cell lines by different therapeutic investigation illustrated the remarkable effect in comparison with free drug. Finally, the achieved consequences confirm the anticancer properties of Fe₃O₄@CaAl-LDH@Lamivudine and indicate that they may be a cost-effective substitute in the treatment of lung and skin cancer.Communicated by Ramaswamy H. Sarma.

Co-Induced Electronic Optimization of Hierarchical NiFe LDH for Oxygen Evolution

Developing efficient and stable non-noble electrocatalysts for the oxygen evolution reaction (OER) remains challenging for practical applications. While nickel-iron layered double hydroxides (NiFe-LDH) are emerging as prominent candidates with promising OER activity, their catalytic performance is still restricted by the limited active sites, poor conductivity and durability. Herein, hierarchical nickel-iron-cobalt LDH nanosheets/carbon fibers (NiFeCo-LDH/CF) are synthesized through solvent-thermal treatment of ZIF-67/CF. Extended X-ray adsorption fine structure analyses reveal that the Co substitution can stabilize the Fe local coordination environment and facilitate the π-symmetry bonding orbital in NiFeCo-LDH/CF, thus modifying the electronic structures. Coupling with the structural advantages, including the largely exposed active surface sites and facilitated charge transfer pathway ensured by CF, the resultant NiFeCo-LDH/CF exhibits excellent OER activity with an overpotential of 249 mV at 10 mA cm^-1 as well as robust stability over 20 h.

Birnessite: A New Oxidant for Green Rust Formation

Iron and manganese are ubiquitous in the natural environment. Fe^II-Fe^III layered double hydroxide, commonly called green rust (GR), and Mn^III-Mn^IV birnessite (Bir) are also well known to be reactive solid compounds. Therefore, studying the chemical interactions between Fe and Mn species could contribute to understanding the interactions between their respective biogeochemical cycles. Moreover, ferromanganese solid compounds are potentially interesting materials for water treatment. Here, a {Fe(OH)₂, Fe^II_aq} mixture was oxidized by Bir in sulphated aqueous media in the presence or absence of dissolved O₂. In oxic conditions for an initial Fe^II/OH^- ratio of 0.6, a single GR phase was obtained in a first step; the oxidation kinetics being faster than without Bir. In a second step, GR was oxidised into various final products, mainly in a spinel structure. A partial substitution of Fe by Mn species was suspected in both GR and the spinel. In anoxic condition, GR was also observed but other by-products were concomitantly formed. All the oxidation products were characterized by XRD, XPS, and Mössbauer spectroscopy. Hence, oxidation of Fe^II species by Bir can be considered as a new chemical pathway for producing ferromanganese spinels. Furthermore, these results suggest that Bir may participate in the formation of GR minerals.

Step-by-Step Assembly of 2D Confined Chiral Space Endowing Achiral Clusters with Asymmetric Catalytic Activity for Epoxidation of Allylic Alcohols

Endowing achiral polyoxometalates (POMs) with asymmetric catalytic properties is always an intriguing but challenging topic because of their high catalytic activities yet highly symmetrical molecular structures. In this work, a novel strategy was proposed to fabricate a series of two-dimensional chiral POM catalysts. Following the steps of exfoliation, covalent modification, and reassembly, the achiral POMs were orderly confined into the chiral interstitial domains of chiral ionic liquid (CIL)-modified layered double hydroxide materials with a decreased molecular symmetry. The chirality of POM molecules was induced by the l- or d-pyrrolidine-type CILs, and their asymmetric catalytic activity was enhanced by the confinement effect. Compared with the reported chiral POM-based catalysts [e.g., 8 turnover frequency (TOF) and 79% enantiomeric excess (ee) for chiral POM-based metal-organic frameworks], the constructed chiral POM catalysts showed a significantly higher TOF and enantioselectivity (up to 240 TOF and 93% ee) for the asymmetric epoxidation of allylic alcohols. The facilitated mass transfer in the IL channels and the increased binding efficiency between the chiral catalytic sites and reactants render this strategy highly promising for constructing efficient chiral catalysts from the catalytically active while achiral building blocks.

Synthesis and Properties of New Multilayer Chitosan@layered Double Hydroxide/Drug Loaded Phospholipid Bilayer Nanocomposite Bio-Hybrids

A novel bio-hybrid drug delivery system was obtained involving a Mg/Al-NO₃ layered double hydroxide (LDH) intercalated either with ibuprofenate anions (IBU) or a phospholipid bilayer (BL) containing a neutral drug, i.e., 17β-estradiol, and then embedded in chitosan beads. The combination of these components in a hierarchical structure led to synergistic effects investigated through characterization of the intermediates and the final bio-composites by XRD, TG, SEM, and TEM. That allowed determining the presence and yield of IBU and of BL in the interlayer space of LDH, and of the encapsulated LDH in the beads, as well as the morphology of the latter. Peculiar attention has been paid to the intercalation process of the BL for which all available data substantiate the hypothesis of a first interaction at the defect of the LDH, as well as on the interaction mode of these components. ¹H, ³¹P and ²⁷Al MAS-NMR studies allowed establishing that the intercalated BL is not homogeneous and likely formed patches. Release kinetics were performed for sodium ibuprofenate as well as for the association of 17β-estradiol within the negatively charged BL, each encapsulated in the LDH/chitosan hybrid materials. Such new bio-hybrids offer an interesting outlook into the pharmaceutical domain with the ability to be used as sustained release systems for a wide variety of anionic and, importantly, neutral drugs.

Integration of Oxygen-Vacancy-Rich NiFe-Layered Double Hydroxide onto Silicon as Photoanode for Enhanced Photoelectrochemical Water Oxidation

Photoelectrochemical (PEC) water splitting has the potential to efficiently convert intermittent solar energy into storable hydrogen fuel. However, poor charge separation and transfer ability as well as sluggish surface oxygen evolution reaction (OER) kinetics of the photoelectrode severely hinder the advance in PEC performance. Herein, a facile electrodeposition method was used to integrate Mo-doped NiFe-layered double hydroxide onto a NiOx /Ni-protected Si photoanode for enhanced PEC water oxidation. Mo doping contributed to an increased amount of oxygen vacancies, whereas a dynamic surface self-reconstruction was induced by Mo leaching under PEC OER conditions. This led to enhanced PEC performance with an onset potential of 0.87 V vs. reversible hydrogen electrode (RHE), a photocurrent density of 39.3 mA cm-2 at 1.23 V vs. RHE, a fill factor of 0.38, and a solar-to-oxygen conversion efficiency of 5.3 %, along with a stability of 130 h continuous PEC reaction. The performance was superior to that of the undoped NiFe-LDH/NiOx /Ni/Si (4.3 %), which was attributed to the elevated interface charge separation, fast charge transfer, and accelerated OER kinetics.

Superhydrophobic ZIF-8-Based Dual-Layer Coating for Enhanced Corrosion Protection of Mg Alloy

Magnesium (Mg) and its alloys are regarded as the most promising engineering materials because of their unique property. However, the Mg alloys were easily corroded in humid environments, which restricted their wider applications. Herein, the superhydrophobic ZIF-8/PVDF/LDH (SZPL) double-layered coating was fabricated on Mg alloys via electrodeposition and dip-coating methods, which consisted of the underlying layered double hydroxide (LDH) transition structure and top superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer. Besides, the LDH transition structure not only worked as a protection shield but also strengthened the binding force between the substrate and the top superhydrophobic ZIF-8 layer. The top superhydrophobic ZIF-8 layer could serve as an armor on the LDH layer to further prevent the corrosive ions from infiltrating the microporous defects. In addition, the as-prepared SZPL double-layered coating showed robust superhydrophobic and self-cleaning properties, which could block the electrolyte invasion. Furthermore, the electrochemical tests demonstrated that the SZPL coating highly enhanced the corrosion protection ability of Mg alloys. Moreover, the superhydrophobic ZIF-8-based coating could still retain excellent anticorrosion property after immersion in 3.5 wt % NaCl solution for 7 days. The enhanced anticorrosion ability was ascribed to the fact that a synergistic effect of the underlying LDH transition layer hindered the transmission of aggressive ions and the top superhydrophobic ZIF-8-based coating decreased the contact area of the substrate with corrosive solution. Therefore, such coatings offer a new strategy for fabricating excellent anticorrosive coatings with robust superhydrophobicity and self-cleaning performance on metal substrates.

Charge Reversion Simultaneously Enhances Tumor Accumulation and Cell Uptake of Layered Double Hydroxide Nanohybrids for Effective Imaging and Therapy

Nanotheranostics have been actively sought in precision nanomedicine in recent years. However, insufficient tumor accumulation and limited cell uptake often impede the nanotheranostic efficacy. Herein, pH-sensitive charge-reversible polymer-coated layered double hydroxide (LDH) nanohybrids are devised to possess long circulation in blood but reserve surface charges in the weakly acidic tumor tissue to re-expose therapeutic LDH nanoparticles for enhanced tumor accumulation and cell uptake. In vitro experimental data demonstrate that charge-reversible nanohybrids mitigate the cell uptake in physiological conditions (pH 7.4), but remarkably facilitate internalization by tumor cells after charge reversion in the weakly acidic environment (pH 6.8). More significantly, about 6.0% of injected charge-reversible nanohybrids accumulate in the tumor tissue at 24 h post injection, far higher than the average accumulation (0.7%) reported elsewhere for nanoparticles. This high tumor accumulation clearly shows the tumor tissues in T₁ -weighted magnetic resonance imaging. As a consequence, >95% inhibition of tumor growth in the B16F0-bearing mouse model is achieved via only one treatment combining RNAi and photothermal therapy under very mild irradiation (808 nm laser, 0.3 W cm^-2 for 180 s). The current research thus demonstrates a new strategy to functionalize nanoparticles and simultaneously enhance their tumor accumulation and cell internalization for effective cancer theranostics.

Comparison of Nanomaterials for Delivery of Double-Stranded RNA in Caenorhabditis elegans

RNA interference is a promising crop protection technology that has seen rapid development in the past several years. Here, we investigated polyamino acid biopolymers, inorganic nanomaterials, and hybrid organic-inorganic nanomaterials for delivery of dsRNA and efficacy of gene knockdown using the model nematode Caenorhabditis elegans. Using an oral route of delivery, we are able to approximate how nanomaterials will be delivered in the environment. Of the materials investigated, only Mg-Al layered double-hydroxide nanoparticles were effective at gene knockdown in C. elegans, reducing marker gene expression to 66.8% of that of the control at the lowest tested concentration. In addition, we identified previously unreported injuries to the mouthparts of C. elegans associated with the use of a common cell-penetrating peptide, poly-l-arginine. Our results will allow the pursuit of further research into promising materials for dsRNA delivery and also allow for the exclusion of those with little efficacy or deleterious effects.

Crepe Cake Structured Layered Double Hydroxide/Sulfur/Graphene as a Positive Electrode Material for Li-S Batteries

Solving the polysulfide shuttle problem is one of the core challenges for the industrialization of lithium-sulfur batteries. In this work, a triphasic composite of LDH/sulfur/rGO (LDH: layered double hydroxide, rGO: reduced graphene oxide) with a crepe cake like structure is designed and fabricated as a positive electrode material for lithium-sulfur batteries. Sulfur nanoparticles are embedded in the interlayer space of the composite and thus are well protected physically via three-dimensional wrapping and chemically via strong interaction of LDH nanoflakes with lithium polysulfides, such as ionic bonds and S···H hydrogen bonds. In addition, the flexible lamellar structure of the composite with soft graphene layers can tolerate the volume expansion of sulfur during lithiation as well as facilitate ionic permeability and electron transport, which is favorable for the redox reactions of polysulfide. The present work sheds light on the future development and industrialization of lithium-sulfur batteries.

LDH-Co-Fe-Acetate: A New Efficient Sorbent for Azoic Dye Removal and Elaboration by Hydrolysis in Polyol, Characterization, Adsorption, and Anionic Exchange of Direct Red 2 as a Model Anionic Dye

A new, double hydroxide based on Co and Fe was elaborated on by forced hydrolysis in a polyol medium. Complementary characterization techniques show that this new phase belongs to the layered double hydroxide family (LDH) with Co2+ and Fe3+ ions located in the octahedral sites of the bucite-like structure. The acetate anions occupy interlayer space with an interlamellar distance of 12.70 Å. This large distance likely facilitates the exchange reaction. Acetates were exchanged by carbonates. The as-obtained compound Co-Fe-Ac/Ex shows an interlamellar distance of 7.67 Å. The adsorption of direct red 2 by Co-Fe-Ac-LDH has been examined in order to measure the capability of this new LDH to eliminate highly toxic azoic anionic dyes from waste water and was compared with that of Co-Fe-Ac/Ex and Co-Fe-CO3/A (synthesized in an aqueous medium). The adsorption capacity was found to depend on contact time, pH, initial dye concentration, and heating temperature. Concerning CoFeAc-LDH, the dye uptake reaches a high level (588 mg/g) due to the occurrence of both adsorption processes: physisorption on the external surface and chemical sorption due to the intercalation of dye by exchange with an acetate anion. The study enables us to quantify the uptake amount of each effect in which the intercalation has the most important amount (418 mg/g).

Layered Double Hydroxide-Modified Organic Electrochemical Transistor for Glucose and Lactate Biosensing

Biosensors based on Organic Electrochemical Transistors (OECTs) are developed for the selective detection of glucose and lactate. The transistor architecture provides signal amplification (gain) with respect to the simple amperometric response. The biosensors are based on a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) channel and the gate electrode is functionalised with glucose oxidase (GOx) or lactate oxidase (LOx) enzymes, which are immobilised within a Ni/Al Layered Double Hydroxide (LDH) through a one-step electrodeposition procedure. The here-designed OECT architecture allows minimising the required amount of enzyme during electrodeposition. The output signal of the biosensor is the drain current (I_d), which decreases as the analyte concentration increases. In the optimised conditions, the biosensor responds to glucose in the range of 0.1–8.0 mM with a limit of detection (LOD) of 0.02 mM. Two regimes of proportionality are observed. For concentrations lower than 1.0 mM, a linear response is obtained with a mean gain of 360, whereas for concentrations higher than 1.0 mM, I_d is proportional to the logarithm of glucose concentration, with a gain of 220. For lactate detection, the biosensor response is linear in the whole concentration range (0.05–8.0 mM). A LOD of 0.04 mM is reached, with a net gain equal to 400.

In vitro spectroscopic investigation of groove binding interaction of Fe3O4@CaAl-LDH@L-Dopa with calf thymus DNA

The principal goal of this study is to evaluate the interaction of Fe₃O₄@CaAl-LDH@L-Dopa and Fe₃O₄@CaAl-LDH nanoparticles with calf thymus DNA. The magnetic nanoparticles were previously prepared by a chemical co-precipitation method, and the surface of the Fe₃O₄ nanoparticles was coated with CaAl layered double hydroxides. The antiparkinsonian drug "L-Dopa" was carried by this core-shell nanostructure to achieve the drug delivery system with suitable properties for biological applications. Also, the interaction of Fe₃O₄@CaAl-LDH@L-Dopa and Fe₃O₄@CaAl-LDH nanoparticles with CT-DNA was studied using, UV-Visible spectroscopy, viscosity, circular dichroism (CD), and fluorescence spectroscopy techniques. The results of investigations demonstrated that Fe₃O₄@CaAl-LDH@L-Dopa and Fe₃O₄@CaAl-LDH nanoparticles have interacted via minor groove binding and intercalated to CT-DNA, respectively.

Use of ZnAl-Layered Double Hydroxide (LDH) to Extend the Service Life of Reinforced Concrete

This work investigated the use of ZnAl-layered double hydroxide (LDH) intercalated with nitrate or nitrite ions for controlling the corrosion of steel in reinforced concrete. The work started by analyzing the stability of the powder in the 1–14 pH range and the capacity for capturing chloride ions in aqueous solutions of different pH. The effect of the ZnAl-LDH on the corrosion of steel was studied in aqueous 0.05 M NaCl solution and in mortars immersed in 3.5% NaCl. It was found that the LDH powders dissolved partially at pH > 12. The LDH was able to capture chloride ions from the external solution, but the process was pH-dependent and stopped at high pH due to the partial dissolution of LDH and the preferential exchange of OH^– ions. These results seemed to imply that ZnAl-LDH would not work in the alkaline environment inside the concrete. Nonetheless, preliminary results with mortars containing ZnAl-LDH showed lower penetration of chloride ions and higher corrosion resistance of the steel rebars.

Wearable Textile-Based Co-Zn Alkaline Microbattery with High Energy Density and Excellent Reliability

Wearable in-plane Zn-based microbatteries are considered as promising micropower sources for wearable electronics due to their high capacity, low cost, high safety, and easy integration. However, their applications are severely impeded by inadequate energy density arising from unsatisfactory capacity of cathode and poor cycling stability caused by degradation of electrode materials and Zn dendrite. Additionally, the short-circuit induced safety issue caused by Zn dendrite is still a roadblock for Zn-based microbatteries. Herein, a textile-based Co-Zn microbattery with ultrahigh energy density and excellent cycling stability is demonstrated. Benefiting from the fast electron transport of three-dimensional (3D) porous Ni-coated textile and synergistic effect from the hierarchical Co(OH)₂ @NiCo layered double hydroxide (LDH) core-shell electrode, the fabricated Co-Zn microbattery with high flexibility delivers superior energy/power densities of 0.17 mWh cm^-2 /14.4 mW cm^-2 , outperforming most reported micro energy storage devices. Besides, the trench-type configuration as well as the 3D porous Zn@carbon clothes can avoid the short-circuit-induced safety issues, resulting in excellent cycling stability (71% after 800 cycles). The unique core-shell structure and novel configuration provide a brand-new design strategy for high-performance wearable in-plane microdevices.

Holey Assembly of Two-Dimensional Iron-Doped Nickel-Cobalt Layered Double Hydroxide Nanosheets for Energy Conversion Application

Layered double hydroxides (LDHs) containing first-row transition metals such as Fe, Co, and Ni have attracted significant interest for electrocatalysis owing to their abundance and excellent performance for the oxygen evolution reaction (OER) in alkaline media. Herein, the assembly of holey iron-doped nickel-cobalt layered double hydroxide (NiCo-LDH) nanosheets ('holey nanosheets') is demonstrated by employing uniform Ni-Co glycerate spheres as self-templates. Iron doping was found to increase the rate of hydrolysis of Ni-Co glycerate spheres and induce the formation of a holey interconnected sheet-like structure with small pores (1-10 nm) and a high specific surface area (279 m²  g^-1 ). The optimum Fe-doped NiCo-LDH OER catalyst showed a low overpotential of 285 mV at a current density of 10 mA cm^-2 and a low Tafel slope of 62 mV dec^-1 . The enhanced OER activity was attributed to (i) the high specific surface area of the holey nanosheets, which increases the number of active sites, and (ii) the improved kinetics and enhanced ion transport arising from the iron doping and synergistic effects.

Incorporation of Lutein on Layered Double Hydroxide for Improving the Environmental Stability

To overcome the poor stability of natural lutein to environmental factors, layered double hydroxide was incorporated by a green mechanical grinding process. The influences of external factors (chemical reagents, heating and light) on the stability of lutein before and after being loaded were evaluated. The results confirmed that lutein was mainly adsorbed on the surface of layered double hydroxide (LDH) via the chemical interaction. Compared with pure lutein, the thermal decomposition of lutein/LDH was improved from 100 °C to 300 °C, and the retention ratio of lutein was increased by about 8.64% and 21.47% after 96 h of light exposure and accelerated degradation, respectively. It is expected that the stable lutein/LDH composites may constitutean additive in animal feed.

Aspect Ratio Control of Layered Double Hydroxide Nanosheets and Their Application for High Oxygen Barrier Coating in Flexible Food Packaging

We report a method to rationally control the aspect ratio of layered double hydroxide for use as a barrier coating for food packaging films. The reconstruction of a Mg₂Al-layered double oxide (LDO) in concentrated aqueous glycine solutions produces dispersions of Mg₂Al-LDH nanosheets. The nanosheet thickness decreases and diameter increases with increasing reconstruction time from 16 to 96 h. We observe a limiting nanosheet aspect ratio of ca. 336 ± 170. These Mg₂Al-LDH nanosheets can be dispersed in PVA to give a water-based dispersion that can be used to coat flexible polymeric films. Oxygen transmission rate (OTR) of a PET film decreases when the thickness of the dried coated layer increases, an OTR of <0.005 mL·m^-2·day^-1 is observed for a coating with thickness of 1175 ± 101 nm.

Engineering Active Fe Sites on Nickel-Iron Layered Double Hydroxide through Component Segregation for Oxygen Evolution Reaction

Nickel-iron layered double hydroxide (NiFe LDH) is a promising oxygen evolution reaction (OER) electrocatalyst under alkaline conditions. Much research has been performed to understand the structure-activity relationship of NiFe LDH under OER conditions. However, the specific role of the Fe species remains unclear and under debate. Herein, based on DFT calculations, it was discovered that the edge Fe sites show higher activity towards OER than either the edge Ni sites or lattice sites. Therefore, a facile acid-etching method was proposed to controllably induce the formation of edge Fe sites in NiFe LDH, and the obtained sample exhibited higher OER activity. X-ray absorption near edge structure and extended X-ray absorption fine structure analyses further revealed that the interaction of the edge Fe species with Ni is believed to contribute to the enhancement of the OER performance. This work provides a new understanding of the structure-activity relationship in NiFe LDH and offers a facile method for the design of efficient electrocatalysts in an alkaline environment.

Layered Double Hydroxide Nanoparticles to Overcome the Hydrophobicity of Ellagic Acid: An Antioxidant Hybrid Material

Ellagic acid (EA), a polyphenolic antioxidant of poor water solubility, was intercalated into biocompatible layered double hydroxide (LDH) nanoparticles by the coprecipitation method. Structural investigation of the composite revealed that the lactone bonds split under the synthetic experimental conditions, and EA was transformed to 4,4',5,5',6,6'-hexahydroxydiphenic acid during intercalation. To improve the surface properties of the EA-LDH composite, the samples were treated with different organic solvents. The antioxidant activity of the LDH hybrids was assessed in test reactions. Most of the obtained hybrids showed antioxidant activity comparable to the one of the free EA indicating that the spontaneous structural transformation upon immobilization did not change the efficiency in radical scavenging. Treatments with organic solvents influenced the activities of the materials remarkably. The main advantage of the immobilization procedure is that the products can be applied in aqueous samples in high concentrations overcoming the problem related to the low solubility of EA in water. The developed composites of high antioxidant content can be applied as efficient reactive oxygen species scavenging materials during biomedical treatments or industrial manufacturing processes.

Multifunctional Bioactive Resin for Dental Restorative Materials

Resin-based composites are widely used as dental restorative materials due to their excellent properties. They must have high modulus, high hardness, and be chemically inert while minimizing moisture uptake. To fulfill these higher standard prerequisites and properties, continuous improvements in each of their components are required. This study develops novel composites with multiple biofunctions. Light-cured Bis-GMA/TEGDMA dental resin (RK)/layered double hydroxide intercalated with fluoride ions (LDH-F)/calcium bentonite (Bt) hybrid composites were prepared. The loading ratio of LDH-F to Bt was varied, ranging from 2.5/2.5 to 10/10 parts per hundred RK and structural, mechanical, and biological properties were studied. The incorporation of even small mass fractions (e.g., 2.5 wt% of LDH-F and 2.5 wt% of Bt) in RK dental resin significantly improved the mechanical properties of the pristine resin. The synthetized materials showed antibacterial and antibiofilm effects against three bacterial strains isolated from healthy volunteers’ saliva (Streptococcus spp., Bacteroides fragilis, and Staphylococcus epidermidis) without affecting its ability to induce dental pulp stem cells differentiation into odontoblast-like cells. The capability to balance between the antibiofilm activity and dental pulp stem cells differentiation in addition with improved mechanical properties make these materials a promising strategy in preventive and restorative dentistry.

Monometallic Cerium Layered Double Hydroxide Supported Pd-Ni Nanoparticles as High Performance Catalysts for Lignin Hydrogenolysis

Monometallic cerium layered double hydroxides (Ce-LDH) supports were successfully synthesized by a homogeneous alkalization route driven by hexamethylenetetramine (HMT). The formation of the Ce-LDH was confirmed and its structural and compositional properties studied by XRD, SEM, XPS, iodometric analyses and TGA. HT-XRD, N2-sorption and XRF analyses revealed that by increasing the calcination temperature from 200 to 800 °C, the Ce-LDH material transforms to ceria (CeO2) in four distinct phases, i.e., the loss of intramolecular water, dehydroxylation, removal of nitrate groups and removal of sulfate groups. When loaded with 2.5 wt% palladium (Pd) and 2.5 wt% nickel (Ni) and calcined at 500 °C, the PdNi-Ce-LDH-derived catalysts strongly outperform the PdNi-CeO2 benchmark catalyst in terms of conversion as well as selectivity for the hydrogenolysis of benzyl phenyl ether (BPE), a model compound for the α-O-4 ether linkage in lignin. The PdNi-Ce-LDH catalysts showed full selectivity towards phenol and toluene while the PdNi-CeO2 catalysts showed additional oxidation of toluene to benzoic acid. The highest BPE conversion was observed with the PdNi-Ce-LDH catalyst calcined at 600 °C, which could be related to an optimum in morphological and compositional characteristics of the support.

LDH-stabilized ultrasmall iron oxide nanoparticles as a platform for hyaluronidase-promoted MR imaging and chemotherapy of tumors

Development of unique theranostic nanoplatforms for tumor imaging and therapy remains an active topic in current nanomedicine. Here, we designed a novel targeted theranostic nanoplatform for enhanced T1 -weighted magnetic resonance (MR) imaging-guided chemotherapy by constructing layered double hydroxide (LDH)-stabilized ultrasmall iron oxide (Fe3O4) nanoparticles with hyaluronic acid (HA) modified as targeting agents, and anticancer drug doxorubicin (DOX) loaded with a high loading efficiency. Methods: The structure and release property of LDH-Fe3O4-HA/DOX nanoplatforms were characterized systematically. B16 melanoma cells with CD44 receptors overexpressed were used as model cells to determine the biocompatibility, targeting capability, and therapeutic efficiency of nanoplatforms. For in vivo experiment, hyaluronidase (HAase) pretreatment was combined with nanoplatform administration to investigate the MR imaging and chemotherapeutic effect. Results: The LDH-Fe3O4-HA nanohybrids possess good colloidal stability and cytocompatibility, display an r1 relaxivity 10-fold higher than the pristine ultrasmall Fe3O4 (4.38 mM-1 s-1vs 0.42 mM-1 s-1), and could release drug in a pH-responsive manner. In vitro experiments demonstrate that LDH-Fe3O4-HA/DOX nanohybrids are able to specifically target B16 cells overexpressing CD44 receptors and effectively release DOX to nucleus. In vivo results show that with the pretreatment of tumor tissue by HAase to degrade the overexpressed HA in extra-cellular matrix, the designed nanoplatforms have a better tumor penetration for significantly enhanced MR imaging of tumors and tumor chemotherapy with low side effects. Conclusion: The designed LDH-Fe3O4-HA/DOX nanohybrids may be developed as a novel targeted theranostic nanoplatform for enhanced T1 -weighted MR imaging-guided chemotherapy of CD44 receptor-overexpressing tumors.

Synthesis of Nanocrystalline Mg-Al Hydrotalcites in the Presence of Starch-the Effect on Structure and Composition

The study describes the synthesis of Mg-Al hydrotalcite (Ht) with the use of starch as a structure controlling biotemplate. Syntheses were carried out at room temperature, by co-precipitation at pH = 10. The investigated synthesis parameters included the nature of the precipitating agent (NaOH/Na₂CO₃ or NH₃aq/(NH₄)₂CO₃), the nature of starch (potato, corn and cassava), the method of starch addition to reagents, the method of drying and the effect of washing. The materials were examined with X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy and infrared spectroscopy. The data show that synthesis of Ht materials in the presence of starch, with use of the ammonia-based precipitant, enabled preparation of nanocrystalline Ht with very fine (<50 nm) particle size. All investigated starches had a similar effect on the crystallinity and the grain size of Ht precipitates. Ht with the smallest nanocrystals was obtained when starch was present in all solutions used for synthesis, and the final product subjected to freeze drying. Washing with water was found to enhance recrystallization and exchange of nitrates for carbonates. Infrared spectra showed that an interaction exists between the biopolymer template and the Ht particles, resulting in a higher degree of order within the Ht-adhering starch component.

Developing a novel packed in-tube solid-phase extraction method for determination ∆ 9-tetrahydrocannabinol in biological samples and cannabis leaves

A novel plate-like nano-sorbent based on copper/cobalt/chromium layered double hydroxide was synthesized by a simple coprecipitation method. The synthesized nanoparticels were introduced into a stainless steel cartridge using a dry packing method. Then, the packed cartridge was introduced as a novel on-line "packed in-tube" configuration and followed by high performance liquid chromatography for the determination of trace amounts of ^∆ 9-tetrahydrocannabinol from biological samples and cannabis leaves. The as-prepared sorbent exhibited long lifetime, good chemical stability, and high anion-exchange capacity. Several important factors affecting the extraction efficiency, such as extraction and desorption times, pH of the sample solution and flow rates of the sample and eluent solutions, were investigated and optimized. Under optimized conditions, this method showed good linearity for ^∆ 9-tetrahydrocannabinol in the ranges of 0.09-500, 0.3-500, and 0.4-500 µg/L with coefficients of determination of 0.9999, 0.9991, and 0.9994 in water, serum and plasma samples, respectively. The inter- and intra-assay precisions (n = 3) were respectively in the ranges of 1.8-4.6% and 1.9-4.0% at three concentration levels of 10, 50, and 100 µg/L. The limits of detection were also in the range of 0.02-0.1 µg/L.

Encapsulation of a Neutral Molecule into a Cationic Clay Material: Structural Insight and Cytotoxicity of Resveratrol/Layered Double Hydroxide/BSA Nanocomposites

Resveratrol (RES) is a stilbenoid polyphenol with interesting antitumor activity compromised by its poor solubility and bioavailability; thus, new approaches are necessary to improve its therapeutic effectiveness. In the present study, bovine serum albumin coated layered double hydroxide (LDH-BSA) was employed to encapsulate RES in order to overcome the above-mentioned usage limits. To evaluate the feasibility of neutral RES complexation with cationic LDH, we carried out molecular dynamics simulation in order to predict its structure and stability. In the supramolecular complex formed with LDH, RES disposes itself in the interlamellar region of LDH where it is stabilized by intermolecular interactions. The physico-chemical characteristics of the resulting nanocomplexes were studied by X-ray powder diffraction, transmission electron microscopy, and attenuated total reflection Fourier transform infrared spectroscopy. The encapsulation efficiency and drug release studies were also performed. The combined experimental and computational approach were highly effective in giving insight into the interaction mode of the neutral RES with the charged LDH. Finally, the nanohybrid's anticancer ability was evaluated in human lung cancer cell line (A549) resulting in higher activity with respect to bare RES. Overall, the results showed that the nanocomposites are suitable for biomedical applications as delivery agents of RES.

Multi-Fold Enhancement in Compressive Properties of Polystyrene Foam Using Pre-delaminated Stearate Functionalized Layer Double Hydroxides

Developing an environmentally benign styrene foam is a critical environmental need. Supercritical CO₂ use in foams has proven to be a valuable path. Adding fillers to increase bubble nucleation has been pursued concurrently. A prominent filler used is high surface area fillers, such as smectic clays. However, all studies to date show a limit of 152% in compressive moduli and 260% in the compressive stress. The values, even with such gains, limit structural application. A seminal work in 1987 by Suh and Cotton proved that carbonyl linkages in calcium carbonates and CO₂ interact and impact nucleation efficiency and performance in supercritical CO₂ foams. In this paper, a high surface area clay (layer double hydroxides) which begins in an exfoliated state, then functionalized with a long chain alkyl carboxylate (stearic acid) is synthesized. The result is a remarkable multi-fold improvement to the compressive properties in comparison to polystyrene (PS); a 268% and 512% increase in compressive modulus and strength, respectively. Using a pre-delaminated approach, the higher surface area was achieved in the clays. The presence of the stearate improved the interactions between the clay galleries and PS through hydrophobic-hydrophobic interactions. The glass transition temperature of the nanocomposites was observed to shift to higher values after foaming. The results point to a new path to increase performance using a pre-delaminated clay with functional groups for environmentally benign foams.

Performance of Halloysite-Mg/Al LDH Materials for Aqueous As(V) and Cr(VI) Removal

This research focused on the investigation of layered double hydroxide (LDH)/halloysite materials’ adsorption efficiency and mechanisms in reactions with aqueous As(V) and Cr(VI) in a broad pH range. The materials consisting of Mg/Al LDH and halloysite were synthesized using both direct precipitation and physical mixing methods. The XRD, FTIR, DTA, SEM and XPS methods were used to evaluate the quality of the obtained materials and get insight into removal mechanisms. The XRD, FTIR and DTA confirmed LDH formation and showed the dominating presence of intercalated carbonates in the LDH structure. The SEM of the materials revealed characteristic agglomerates of layered LDH particles deposited on halloysite tubular forms. The raw LDH phases showed high removal efficiency of both As(V) and Cr (VI) for initial pH in the range of 3–7. In the studied concentration range the materials containing 25 wt % of LDH exhibited a removal efficiency very similar to the raw LDH. In particular, the halloysite presence in the materials’ mass had a positive effect in the reactions with As(V), which was removed by chemisorption. At a low pH the LDH component underwent partial dissolution, which lowered the adsorption efficiency. Apart from the anion exchange mechanism at a low pH the Cr(VI) was removed via formation of MgCrO₄ with Mg (II) being released from the LDH structure. The XPS spectra for As(V) did not show changes in oxidation state in the reactions. In turn, a partial reduction of Cr(VI) to Cr(III) was observed, especially at a high pH. The use of materials composed of two different minerals is promising due to reduction of costs as well as prevention of adsorbent swelling. This opens the possibility of its use in dynamic adsorption flow through systems.

Enhanced Photoelectrochemical Performance of WO3 -Based Composite Photoanode Coupled with Carbon Quantum Dots and NiFe Layered Double Hydroxide

An attractive photoanode material, WO₃ , has suffered from its limited visible-light absorption and sluggish surface reaction kinetics, as well as poor stability in neutral electrolytes. Herein, a NiFe/CQD/WO₃ composite photoanode was designed and fabricated, with loading of carbon quantum dots (CQDs) and electrodeposition of NiFe layered double hydroxide. The NiFe/CQD/WO₃ photoanode obtained a photocurrent density of 1.43 mA cm^-2 at 1.23 V vs. reversible hydrogen electrode, which is approximately three times higher than that of bare WO₃ . During the test period of 3 h, the stability of WO₃ was improved substantially after the loading of cocatalysts. Furthermore, mechanistic insights of the favored band structure and beneficial charge-transfer pathway elucidate the high photoelectrochemical performance of the NiFe/CQD/WO₃ composite photoanode.

Strongly Coupled Interface Structure in CoFe/Co3 O4 Nanohybrids as Efficient Oxygen Evolution Reaction Catalysts

The quest for developing electrochemical energy-storage and -conversion technologies continues to be a great impetus to develop cost-effective, highly active, and electrochemically stable electrocatalysts for overcoming the activation energy barriers of the oxygen evolution reaction (OER). Co₃ O₄ nanocrystals have great potential as OER catalysts, and research efforts on improving the catalytic activity of Co₃ O₄ are currently underway in many laboratories. Herein, CoFe layered double hydroxide (LDH) nanosheets were directly grown on the active Co₃ O₄ substrate to form nanohybrid electrocatalysts for OER. The CoFe LDH/Co₃ O₄ (6:4) nanohybrid exhibited superior catalytic performance with a low overpotential and a small Tafel slope in alkaline solution. The outstanding performance of the CoFe LDH/Co₃ O₄ (6:4) nanohybrid was primarily owing to the synergistic effects induced by the strongly coupled interface between CoFe LDH and Co₃ O₄ ; this feature enhanced the intrinsic OER catalytic activity of the nanohybrid and favored fast charge transfer. Compared with other Co₃ O₄ -based catalysts, the nanohybrid shows advantages and offers a feasible avenue for improving the activity of Co₃ O₄ -based catalysts.

Chemically Bonding NiFe-LDH Nanosheets on rGO for Superior Lithium-Ion Capacitors

Layered double hydroxides (LDHs) have attracted tremendous interest for applications in energy harvest and storage. However, the aggregation of nanosheets compromises the accessible active sites and limits their electrochemical performance, especially at high rates. The present study reports the synthesis of highly dispersed NiFe-LDH nanosheets anchored on reduced graphene oxide (NiFe-LDH/rGO) composites chemically bonded via a facile one-step hydrothermal method. Defect-riched rGO provides abundant active sites for heterogeneous nucleation of NiFe-LDH nanosheets, achieving the much efficient charge transfer between rGO and NiFe-LDH as compared to physically mixed NiFe-LDH + rGO. The crystallite size can effectively reduce to 5.5 nm smaller than 15.1 nm of NiFe-LDH without rGO, beneficial to expose more active surface for fast ion diffusion and redox reactions. NiFe-LDH/rGO as an anode material in lithium-ion batteries shows superior lithium storage capacity with 1202 mAh g^-1 after 100 cycles at 100 mA g^-1 and high-rate performance with 543 mAh g^-1 even at 2000 mA g^-1. The corresponding lithium-ion capacitor with NiFe-LDH/rGO anode and mesoporous carbon microsphere cathode exhibits high energy density and power density simultaneously, with 133 Wh kg^-1 at 25 W kg^-1 and 4016 W kg^-1 at 58 Wh kg^-1, showing the great potential for high-performance hybrid energy storage systems.

Surface Charge Modulation of Perovskite Oxides at the Crystalline Junction with Layered Double Hydroxide for a Durable Rechargeable Zinc-Air Battery

Perovskite oxides have emerged as promising oxygen electrocatalysts for fuel cells and batteries, yet their catalytic activity and long-term stability are under debate because of local surface alterations and instabilities under sustained oxidative potential. Interconnected particles (40 nm) of Ba_0.6Sr_0.4Co_0.79Fe_0.21O_2.67 (BSCF) are decorated by 10-50 wt % Ni_0.6Fe_0.4(OH)_x [NiFe] layered double hydroxide (LDH) sheets via polyethylenimine linkage. This composite renders modulation of surface charges through Coulombic interaction and provides a leeway for electron mobility between the two components, which bestows relief to the BSCF surface from oxidative degradation. NiFe-LDH (25 wt %) bound to BSCF (BSCF/NiFe-25) is found to be the optimized bifunctional composite after considering the total overpotential of oxygen evolution and reduction reactions. With BSCF/NiFe-25 at the air electrode of a prototype-rechargeable Zn-air battery, a low discharge-charge voltage gap (1.16 V at 10 mA cm^-2), unaltered cyclic stability over 100 h, and an energy density of 776.3 mW·h·g_Zn^-1 are achieved. BSCF/NiFe-25 outperforms BSCF and is comparable to 20% Pt/C-RuO₂ cathodes in all the standard figures of merit. Our work presents a general strategy to circumvent the reconstructions of perovskite oxide surface under oxidative potentials, by creating highly active, stable, and inexpensive bifunctional composite electrocatalysts for future electrochemical energy storage and conversion devices.

Functional Layered Double Hydroxide Nanohybrids for Biomedical Imaging

Biomedical investigations using layered double hydroxide (LDH) nanoparticles have attracted tremendous attentions due to their advantages such as biocompatibility, variable-chemical compositions, anion-exchange capacity, host-guest interactions, and crystallization-dissolution characters. Bio-imaging becomes more and more important since it allows theranostics to combine therapy and diagnosis, which is a concept of next-generation medicine. Based on the unique features mentioned above, LDHs create novel opportunities for bio-imaging and simultaneous therapy with LDHs-based nanohybrids. This review aims to explore the recent advances in multifunctional LDH nanohybrids ranging from synthesis to practical applications for various bio-imaging with therapeutic functions. Furthermore, their potential both as diagnostic agents and drug delivery carriers will be discussed with the improvement in noninvasive bio-imaging techniques.

Vitamin C Loaded Poly(urethane-urea)/ZnAl-LDH Aligned Scaffolds Increase Proliferation of Corneal Keratocytes and Up-Regulate Vimentin Secretion

A novel poly(urethane-urea) (PUU) based on poly(glycolide-co-ε-caprolactone) macro-diol with tunable mechanical properties and biodegradation behavior is reported for corneal stromal tissue regeneration. Zn-Al layered double hydroxide (LDH) nanoparticles were synthesized and loaded with vitamin C (VC, VC-LDH) and dispersed in the PUU to control VC release in the cell culturing medium. To mimic the corneal stromal EC, scaffolds of the PUU and its nanocomposites with VC-LDH (PUU-LDH and PUU-VC-LDH) were fabricated via electrospinning. Average diameters of the aligned nanofibers were recorded as 325 ± 168, 343 ± 171, and 414 ± 275 nm for the PUU, PUU-LDH, and PUU-VC-LDH scaffolds, respectively. Results of hydrophilicity and mechanical properties measurements showed increased hydrophobicity and reduced tensile strength and elongation at break upon addition of nanoparticles to the PUU scaffold. VC release studies represented that intercalation of the drug in Zn-Al-LDH controlled the burst release and extended the release period from a few hours to 5 days. Viability and proliferation of stromal keratocyte cells on the scaffolds were investigated via AlamarBlue assay. After 24 h, the cells showed similar viability on the scaffolds and the control. After 1 week, the cells showed some degree of proliferation on the scaffolds, with the highest value recorded for PUU-VC-LDH. SEM images of the scaffolds after 24 h and 1 week confirmed good penetration and attachment of keratocytes on all the scaffolds and the cells oriented with the direction of nanofibers. After 1 week, the PUU-VC-LDH scaffold was fully covered by the cells. Immunocytochemistry assay (ICC) was performed to investigate secretion of vimentin protein, ALDH3A1, and α-SMA by the cells. After 24h and 1 week, remarkably higher levels of vimentin and ALDH3A1 and lower level of α-SMA were secreted by keratocytes on PUU-VC-LDH compared to those on the PUU and PUU-LDH scaffolds and the control. Our results suggest that the aligned PUU-VC-LDH is a promising candidate for corneal stromal tissue engineering due to the presence of zinc and vitamin C.

Flexible Visible-Blind Ultraviolet Photodetectors Based on ZnAl-Layered Double Hydroxide Nanosheet Scroll

Visible-blind ultraviolet (UV) photodetectors have received a great deal of attention for realizing Internet of Things technologies as well as for monitoring the level of UV exposure to humans. Realizing next-generation flexible and visible-blind UV photodetectors requires development of new functional material systems with easy fabrication, selectively strong UV light absorption, environmental friendliness, and high stability regardless of ambient conditions. Herein, flexible visible-blind UV photodetectors are successfully fabricated on the basis of two-dimensional ZnAl-layered double hydroxide (LDH) nanosheets with scroll structures grown on flexible substrates. The ZnAl-LDH nanosheet scrolls exhibit highly resistive semiconducting properties with a band gap of 3.2 eV and work function of 3.64 eV. The photodetector based on the ZnAl-LDH shows photoresponse in the UV spectral range below 420 nm, indicating visible-blind spectral response. In addition, the UV photodetector shows a maximum responsivity of 17 mA/W under illumination with 365 nm light. Moreover, the flexible photodetector shows reproducible photoresponse even after 1000 bending cycles, which indicates the acceptable stability of the ZnAl-LDH nanosheet scrolls.

Fabrication of Highly Dispersed Cu-Based Oxides as Desirable NH3-SCR Catalysts via Employing CNTs To Decorate the CuAl-Layered Double Hydroxides

In this study, three kinds of CuAl-LDO/CNT (LDO, layered double oxide) catalysts were prepared by the assembly of CNTs and CuAl-LDH (LDH, layered double hydroxides) as well as subsequently structural topological transformation. The effects of the assembly method on the surface structure property and the DeNO_x performance of the prepared samples were systematically investigated. It was found that three CuAl-LDO/CNT catalysts showed preferable NH₃-SCR catalytic performance compared with CuAl-LDO where the catalyst CuAl-LDO/CNTs(I) exhibited optimum NO_x conversion (>80%) and N₂ selectivity (>90%) within 180-300 °C. Such fine catalytic performance can be attributed to the proper surface acidity and redox ability of the catalyst, which might be correlated with the high dispersion of Cu-based active centers caused by the induced nucleation and effective separation action of LDH by carbon nanotubes. In addition, the outstanding H₂O and SO₂ resistance of the CuAl-LDO/CNTs(I) catalyst was also obtained because of the synergistic effect between CuAl-LDO and CNTs, which could greatly promote the activation and decomposition of ammonium sulfate at lower temperatures.

Zingiber officinale Extract (ZOE) Incorporated with Layered Double Hydroxide Hybrid through Reconstruction to Preserve Antioxidant Activity of ZOE against Ultrasound and Microwave Irradiation

We prepared Zingiber officinale extract (ZOE) incorporated in a layered double hydroxide (LDH) hybrid through a reconstruction method in order to preserve the antioxidant activity of ZOE from ultrasound and microwave irradiation. X-ray patterns, infrared spectroscopy, and scanning electron microscopy suggested that ZOE moieties were encapsulated in the interparticle space of reconstructed LDH, thus preserving its intact structure. Dynamic light scattering and zeta-potential measurement also supported the hypothesis that ZOE moieties were located in the interparticle pore of LDH rather than at the surface of LDH particles. Thermogravimetry analysis revealed that thermal stability of encapsulated ZOE could be enhanced by LDH encapsulation. Radical scavenging assay showed that antioxidant activity of ZOE-LDH hybrid was increased after ultrasound and microwave irradiation, while ZOE itself dramatically lost its antioxidant activity upon ultrasound and microwave treatment.

Incorporation of Glycine max Merrill Extract into Layered Double Hydroxide through Ion-Exchange and Reconstruction

We incorporated extract of Glycine max Merrill (GM), which is generally known as soybean, into a layered double hydroxide (LDH) nanostructure through two different methods, ion-exchange and reconstruction. Through X-ray diffraction, field-emission scanning electron microscopy, and zeta-potential measurement, GM moiety seemed to be simply attached on the surface of LDH by ion-exchange process, while the extract could be incorporated in the inter-particle pore of LDHs by reconstruction reaction. The quantification exhibited that both incorporation method showed comparable extract loading capacity of 15.6 wt/wt% for GM-LDH hybrid prepared by ion-exchange (GML-I) and 18.6 wt/wt% for GM-LDH hybrid by reconstruction (GML-R). On the other hand, bioactive substance in both GM-LDH hybrids, revealed that GML-R has higher daidzein content (0.0286 wt/wt%) compared with GML-I (0.0108 wt/wt%). According to time-dependent daidzein release, we confirmed that GML-R showed pH dependent daidzein release; a higher amount of daidzein was released in pH 4.5 physiological condition than in pH 7.4, suggesting the drug delivery potential of GML-R. Furthermore, alkaline phosphatase activity and collagen fiber formation on human osteoblast-like MG-63 cells displayed that GML-R had superior possibility of osteoblast differentiation than GML-I. From these results, we concluded that reconstruction method was more effective for extract incorporation than ion-exchange reaction, due to its pH dependent release property and alkaline phosphatase activity.

Layered Double Hydroxide Fluoride Release in Dental Applications: A Systematic Review

This systematic review appraises studies conducted with layered double hydroxides (LDHs) for fluoride release in dentistry. LDH has been used as antacids, water purification in removing excess fluoride in drinking water and drug delivery. It has great potential for controlled fluoride release in dentistry, e.g., varnishes, fissure sealants and muco-adhesive strips, etc. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement was followed with two reviewers performing a literature search using four databases: PubMed, Web of Science, Science Direct and Ovid Medline with no date restrictions. Studies including any LDH for ion/drug release in dentistry were included, while assessing the application of LDH and the value of the methodology, e.g., ion release protocol and the LDH production process. Results: A total of 258 articles were identified and four met the inclusion criteria. Based on two in vitro studies and one clinical study, LDH was previously studied in dental materials, such as dental composites and buccal muco-adhesive strips for fluoride release, with the latter studied in a clinical environment. The fourth study analysed LDH powder alone (without being incorporated into dental materials). It demonstrated fluoride release and the uptake of volatile sulphur compounds (VSC), which may reduce halitosis (malodour). Conclusion: LDHs incorporated in dental materials have been previously evaluated for fluoride release and proven to be clinically safe. LDHs have the potential to sustain a controlled release of fluoride (or other cariostatic ions) in the oral environment to prevent caries. However, further analyses of LDH compositions, and clinical research investigating any other cariostatic effects, are required.

Attuning the Electronic Properties of Two-Dimensional Co-Fe-O for Accelerating Water Electrolysis and Photolysis

Two-dimensional (2D) materials such as layered double hydroxides (LDH) are promising electrocatalysts, especially for water oxidation, owing to their unique physical and electronic properties besides having adequate surface area and availability of unsaturated active metal centers. Herein, we illustrate the high-temperature transformation of bimetallic LDH to semicrystalline 2D metal oxide nanoplates that can maneuver their electronic properties and thereby accelerate the water dissociation reactions. The nanoplates prepared at 300 °C require only 280 ± 13 and 177 ± 7 mV overpotentials for oxygen/hydrogen evolution reactions (OER and HER) to achieve a current density of ±10 mA cm^-2 in 1 M KOH, respectively. In a two-electrode water splitting cell, while this bifunctional catalyst needs 1.69 V to deliver a current density of 10 mA cm^-2, the LDH precursor demands a cell voltage of 1.93 V. However, both the catalysts demonstrate excellent durability for more than 200 h. When the bifunctional metal oxide electrolyzer is connected to perovskite solar cells for unassisted solar-driven water splitting, impressively, such an integrated photovoltaic-electrolyzer can achieve a solar-to-hydrogen (STH) efficiency of 9.3%. The predominantly superior catalytic activity of the nanoplates is due to the abundance of unsaturated oxygen which decreases the free energy of adsorption of the intermediates.

Hierarchical NiCo2S4@Nickel-Cobalt Layered Double Hydroxide Nanotube Arrays on Metallic Cotton Yarns for Flexible Supercapacitors

Constructing high capacitance active materials and three-dimensional (3D) conductive networks inside textile yarn frames is a promising strategy to synthesize yarn supercapacitor electrodes. In this study, growing NiCo₂S₄@Ni-Co layered double hydroxide (LDH) nanotube arrays on Au-metalized cotton yarns yields a novel yarn supercapacitor electrode material. The resulting yarn electrode possesses numerous merits, including high electrical conductivity from NiCo₂S₄ and Au-metalized cotton yarns, high capacitance of Ni-Co LDH nanosheets, and the 3D hierarchical electrode structure. The unique electrode structure leads to excellent electrochemical properties including high capacitance (5680 mF cm^-2), excellent rate performance, and stable cycling performance. A two-ply symmetric yarn supercapacitor assembled from the NiCo₂S₄/Ni-Co LDH/Au/cotton yarn electrode reaches an areal energy density of 3.5 μW h cm^-2.

Synthesis and properties of magnetic nanotheranostics coated with polyethylene glycol/5-fluorouracil/layered double hydroxide

Background

Cancer treatments are being continually developed. Increasingly more effective and better-targeted treatments are available. As treatment has developed, the outcomes have improved.

Purpose

In this work, polyethylene glycol (PEG), layered double hydroxide (LDH) and 5-fluorouracil (5-FU) were used as a stabilizing agent, a carrier and an anticancer active agent, respectively.

Characterization and methods

Magnetite nanoparticles (Fe3O4) coated with polyethylene glycol (PEG) and co-coated with 5-fluorouracil/Mg/Al- or Zn/Al-layered double hydroxide were synthesized by co-precipitation technique. Structural, magnetic properties, particle shape, particle size and drug loading percentage of the magnetic nanoparticles were investigated by XRD, TGA, FTIR, DLS, FESEM, TEM, VSM, UV-vis spectroscopy and HPLC techniques.

Results

XRD, TGA and FTIR studies confirmed the formation of Fe3O4 phase and the presence of iron oxide nanoparticles, polyethylene glycol, LDH and the drug for all the synthesized samples. The size of the nanoparticles co-coated with Mg/Al-LDH is about 27 nm compared to 40 nm when they were co-coated with Zn/Al-LDH, with both showings near uniform spherical shape. The iron oxide nanoparticles retain their superparamagnetic property when they were coated with polyethylene glycol, polyethylene glycol co-coated with Mg/Al-LDH and polyethylene glycol co-coated with Zn/Al-LDH with magnetic saturation value of 56, 40 and 27 emu/g, respectively. The cytotoxicity study reveals that the anticancer nanodelivery system has better anticancer activity than the free drug, 5-FU against liver cancer HepG2 cells and at the same time, it was found to be less toxic to the normal fibroblast 3T3 cells.

Conclusion

These are unique core-shell nanoparticles synthesized with the presence of multiple functionalities are hoped can be used as a multifunctional nanocarrier with the capability of targeted delivery using an external magnetic field and can also be exploited as hypothermia for cancer cells in addition to the chemotherapy property.

Enhancing Electrocatalytic Activity through Liquid-Phase Exfoliation of NiFe Layered Double Hydroxide Intercalated with Metal Phthalocyanines in the Presence of Graphene

Earth-abundant transition-metal-based catalysts are attractive for alkaline water electrolysis. However, their catalytic properties are often limited by their poor electrical conductivity. Here, we present a strategy for enhancing the electrical conductivity of NiFe layered double hydroxide (LDH) in order to further improve its properties as an electrocatalyst for the oxygen evolution reaction (OER) in alkaline media. We show that NiFe LDH containing metal tetrasulfonate phthalocyanine in the interlayers between the NiFe oxide galleries can be coupled with graphene during liquid-phase exfoliation by taking advantage of their π-π stacking capabilities. A substantial enhancement in the electrocatalytic activity of NiFe LDH with respect to the OER was observed. Moreover, the activity and selectivity of the catalyst materials towards the oxygen reduction reaction were investigated, demonstrating that both the metal hydroxide layer and the interlayer species contribute to the electrocatalytic performance of the composite material.

Interface Electronic Coupling in Hierarchical FeLDH(FeCo)/Co(OH)2 Arrays for Efficient Electrocatalytic Oxygen Evolution

The oxygen evolution reaction (OER) with sluggish kinetics is the key half-cell reaction for several sustainable energy systems, such as electrochemical water splitting, fuel cells, and rechargeable metal-air batteries. Two-dimensional transition-metal hydroxides have good prospects for the OER. Herein, 2D hierarchical FeLDH(FeCo)/Co(OH)₂ (LDH=layered double hydroxide) arrays were fabricated by growing 2D-ZIF-67 (ZIF=zeolitic imidazolate framework) on carbon cloth, transformation of 2D-ZIF-67 into Co(OH)₂ , and electrodeposition of FeLDH(FeCo) on Co(OH)₂ at ambient temperature. The optimized hierarchical catalyst exhibits high OER activity that requires a small overpotential of only 242 mV to drive 10 mA cm^-2 (279 mV for 100 mA cm^-2 ) and prolonged durability for 100 h at 20 mA cm^-2 in 1 m KOH. The FeLDH(FeCo)/Co(OH)₂ interfaces are observed to be the electrocatalytically active centers for the OER. The interfaces contribute to accelerating the OER kinetics owing to fast transfer of intermediate oxygen species. Furthermore, the FeCo alloy promotes electron transfer among the newly formed interfaces related to CoOOH in the OER process, which leads to improved durability. This work gives insight into the design and synthesis of hierarchical bimetallic hydroxide arrays with high OER activity and durability, as well as understanding of the origin of the OER promotion by metals and metal hydroxides.

Rosette-like Layered Double Hydroxides: Adsorbent Materials for the Removal of Anionic Pollutants from Water

Rosette-like layered double hydroxide (roseLDH) crystals with interlayer CO₃^2- anions were synthesized by the reaction of Mg(NO₃)₂, Al(NO₃)₃, and hexamethylenetetramine (HMT) at 140 °C over 4 days. Crystals as large as 20 μm were produced when using a specific range of HMT concentrations. The substitution of CO₃^2- interlayer ions with ClO₄^- or Cl^- anions was achieved by the addition of perchloric acid or hydrochloric acid, respectively, to dispersion of material in methanol. The products were denoted as CO₃^2-roseLDH, ClO₄^-roseLDH, and Cl^-roseLDH, respectively. These LDHs were characterized using X-ray diffraction under controlled relative humidity, as well as by Fourier transform infrared spectroscopy and scanning electron microscopy. Adsorption experiment with anions such as phosphate (HPO₄^2-) and nitrate (NO₃^-) was conducted by using ClO₄^-roseLDH and Cl^-roseLDH. The results indicate that both anions were adsorbed through an ion-exchange mechanism. The maximum HPO₄^2- adsorption capacity at equilibrium on ClO₄^-roseLDH was 1.6 mmol g^-1 (49.6 mg P g^-1), which corresponds to approximately 75% of the total positive layer charge. Cl^-roseLDH showed a similar adsorption capability. Commercially available platelike LDH particles were essentially impermeable to water flow due to clogging, while the roseLDH crystals showed excellent permeability, an order of magnitude higher than that exhibited by the platelike LDH synthesized using a homogeneous precipitation method with different growth conditions. Anion adsorption during batch and flow-through test with the ClO₄^-roseLDH (mean particle diameter ∼ 38 μm) in a packed bed showed good uptake of HPO₄^2- and NO₃^- from aqueous solutions. These results demonstrate the potential of roseLDH materials to serve as a column filler adsorbent of the hazardous anions.

Cr-Dopant Induced Breaking of Scaling Relations in CoFe Layered Double Hydroxides for Improvement of Oxygen Evolution Reaction

Monodentate adsorption of oxygen intermediates results in a theoretical overpotential limit of ≈0.35 V for oxygen evolution reaction (OER), which causes the sluggish kinetics of the OER process. In this work, nonprecious chromium dopant is introduced into the self-supported CoFe layered double hydroxides (LDHs) on nickel foam (Cr-CoFe LDHs/NF) via a facile one-step hydrothermal method, which exhibits a preeminent electrocatalytic activity toward the OER with an ultralow overpotential of 238 mV to obtain 10 mA cm^-2 and a high stability after cyclic voltammetry for 5000 cycles in alkaline solution (1 m KOH). Density functional theory (DFT) calculations unveil that Cr dopants as new active sites could improve the electron-donation ability of the resultant Cr-CoFe LDHs due to the smaller electronegativity of Cr in comparison with Fe and Co. Therefore, the scaling relation of adsorption energy among four oxygen intermediates is broken and consequently the OER performance is further promoted. This work provides a strategy to develop efficient metal layered double hydroxide OER catalysts.

Carbon nanotube/layered double hydroxide nanocomposite as a fibre coating for determination the essential oils of Achillea eriophora DC with the headspace solid-phase microextraction

The present study was conducted to synthesise a carbon nanotube/layered double hydroxide nanocomposite by an in situ growth route via electrostatic force. The fabricated carbon nanotube/layered double hydroxide nanocomposite was successful in deposition on a stainless-steel wire for the preparation of the solid-phase microextraction fibre. The produced fibers are enduring with high suitability being chemically and thermally stable capable of coupling to GC and GC/MS. The important extraction parameters including extraction temperature, extraction time, sample mass and added water were simultaneously optimised using an optimisation approach. I comparison to hydrodistillation (HD), headspace single drop micro-extraction) HS-SPME (is advantageous regarding little sample level, time-efficiency, convenience and low cost.