Layered Double Hydroxides Sheets Research Articles

Superior tribological and anti-corrosion performance of corrosion inhibitors intercalated LDH-MAO coating on AZ31 Mg alloys

Sodium dodecyl sulfate (SDS) and 8-Hydroxyquinoline (8-HQ) intercalated layered double hydroxides (LDH) sheets were in-situ formed in MAO layer to prepare a composite coating (CI@LDH-MAO) on AZ31 magnesium alloy. This composite coating demonstrates commendable anti-corrosion performance, primarily attributed to the formation of LDH sheets and insoluble Mg(HQ)2 compounds. The electrochemical impedance modulus of the composite coating surpasses that of the MAO coating by three orders of magnitude after immersion of 360 h. Concurrently, the CI@LDH-MAO composite coating exhibits exemplary tribological properties, characterized by a friction coefficient of approximately 0.19 and a wear rate of (11.5 ± 1.5)× 10−6 mm3/(N·m). This outstanding tribological performance can be ascribed to enhanced interaction of lubricants with the friction interface by 8-HQ and SDS anions.

Fluorination of (Mg,Cu,Al,Fe)-based LDHs template for conversion materials usable in all-solid state lithium metal batteries

Iron and copper fluorides are of interest as conversion cathode materials in lithium batteries but they suffer from high hysteresis and low cyclability, respectively. To overcome these limitations and take advantage of the electrochemical properties of each of the fluorides, fluoride mixtures that combine the two redox centers Fe3+ and Cu2+ are synthesized using Layered Double Hydroxides (LDH) as a 2D multi-metallic template. Hydrotalcite-type phases substituted with Cu2+ and Fe3+ ions are prepared by coprecipitation then fluorinated with fluorine gas in static mode at temperatures chosen according to their thermal evolution monitored by mass spectrometry. After each fluorination treatment, the materials are characterized by X-ray diffraction and most LDH materials are found stable up to 200 °C, treatment above leads to the formation of fluorides of each of the cations. The initial dispersion of the cations in the LDH sheets nevertheless allows, after fluorination, a composite of fluorides making them totally accessible to the phenomenon of electrochemical conversion shown here in a metallic lithium battery assembly with a Solid Polymer Electrolyte (SPE). In such All-Solid-State Battery (ASSB) configuration often limiting in terms of columbic efficiency, 76% the first discharge capacity is recovered in charge for an optimized composition (up to 560 mAh.g−1). This good reversibility positions these LDH templates very well for future investigations in the field of electrochemical storage.

A facile strategy for constructing lightweight, fire safety and compression resistance poly(vinylalcohol) aerogels with highly-efficient expansible graphene oxide/layered double hydroxides hybrid synergistic flame retardant

Poly(vinyl alcohol) (PVA) aerogels with excellent environmentally friendly properties have been considered to replace undegradable polymer foams. However, due to highly flammable, hydrophilic, and worse compression resistance performance, PVA aerogels have always been excluded from practical. Herein, a fire safety and compression resistance PVA/expansible graphene oxide (EGO)/Layered double hydroxides (LDHs) (PGL) aerogel was prepared via the freeze-drying method and electrostatic adsorption of flame retardant. The ice crystals from aerogels were sublimated and left a mass of tree-like pore tunnel structures. Meantime, the compound of EGO and LDHs rendered PGL aerogels high compressive strength of 6.0917 MPa (at 80% of strains), a high specific modulus of 19.16 m2/s2, and an ultra-low density of 0.059 g/cm3. Especially, the as-prepared PGL aerogels showed heat release reduced by 55.4%, smoke release reduced by 54.3%, and the limiting oxygen index reaching up to 31%. Moreover, LDHs also enhanced the interface with PVA/EGO resulting in hydrophobic performance improvement. The proposed enhancements mechanism suggested that (i) chemical reactions between EGO and PVA matrix; (ii) a mass of negative potential sites from the interface of PVA/EGO composites made LDHs sheets easily adsorbing; (iii) oxygen-containing groups from EGO and LDHs absorbed mass of heat during combustion; (iv) the compact char residues on the surface of aerogels acting as barriers suppressed smoke and prevented PVA matrix from further combustion. Therefore, electrostatic adsorption as a facile production process was paved for meeting the compression resistance, flame-retardant, heat-insulating, and smoke-suppressed requirements of PVA aerogels in this work.

Enhanced Pseudo-Capacitance Process in Nanoarchitectural Layered Double Hydroxide Nanoarrays Hollow Nanocages for Improved Capacitive Deionization Performance

Layered double hydroxides (LDHs) are perceived as a hopeful capacitive deionization (CDI) faradic electrode for Cl- insertion due to its tunable composition, excellent anion exchange capacity, and fast redox activity. Nevertheless, the self-stacking and inferior electrical conductivity of the two-dimensional structure of LDH lead to unsatisfactory CDI performance. Herein, the three-dimensional (3D) hollow nanocage structure of CoNi-layered double hydroxide/carbon composites is well designed as a CDI anode by cation etching of the pre-carbonized ZIF-67 template. C/CoNi-LDH has a unique 3D hollow nanocage structure and abundant pore features, which can effectively suppress the self-stacking of LDH sheets and facilitate the transport of ions. Moreover, the introduced amorphous carbon layer can act as a conductive network. When employed as the CDI anode, C/CoNi-LDH exhibited a high Cl- removal capacity of 60.88 mg g-1 and a fast Cl- removal rate of 18.09 mg g-1 min-1 at 1.4 V in 1000 mg L-1 NaCl solution. The mechanism of the Cl- intercalation pseudo-capacitance reaction of C/CoNi-LDH is revealed by electrochemical kinetic analysis and ex situ characterization. This study provides vital guidance for the design of high-performance electrodes for CDI.

Biosurfactant assisted in situ green and clean preparation route for layered double hydroxides and their green metrics-based sustainability assessment

Hybrid advanced multifunctional materials based on layered double hydroxides (LDH) and intercalated guest biomolecule(s) are of high industrial and academic importance and have found promising applications in diverse fields such as biomedical, energy, environment, agriculture, etc. This report strategically develops a new innovative green sonochemical route to incorporate rhamnolipid (RL) and surfactin (SR) into 3D hierarchical flower-like Mg-Al-LDH micro-nano-structures. When compared to traditional mechanochemical co-precipitation and ion-exchange methods, the designed one-pot and scalable method was sustainable and green chemistry compliant, with improved time, energy, and solvent efficiency. RL/SR anions act as an interlayer anion and a template for the fabrication of LDH sheets leads to the increase in the basal spacing and impair LDH sheet interaction. Consequently the vesicle-type phase can be fabricated using biosurfactant in aqueous media under the influence of metal cations induced the curved growth of RL/SR-intercalated LDH nuclei and the flower-like assemblage of LDH particles. The structure, morphology, surface properties, and thermal stability were evaluated. The release profile and kinetics of RL/SR of the intercalated LDHs was studied. Slow and controlled release of SR from the Mg/Al-LDH micro-nano-structures was observed for a prolonged time up to 10 h and followed zeroth-order kinetics, whereas RL release was well described in Higuchi model, indicating the release of the biomolecule via a diffusion mechanism. Cytotoxicity (in L929 and 3T3 fibroblast cells) and haemolytic tests suggested that cytotoxic effect in the range of 25–400 mg/ml and the haemolytic ratio was <4 % at 25–600 mg/ml, showing good biocompatibility of the biosurfactant-intercalated LDHs. Taken together, these micro-nano-structures can be used as potential sustained- or extended-release candidate for agricultural, biomedical or water treatment applications.

Influence of Structural Disorders on the Tribological Behavior of Phosphate-Intercalated Layered Double Hydroxide Additives in Polyalphaolefin.

In this work, several phosphate-intercalated Mg-Al layered double hydroxides (LDHs) were synthesized and evaluated as solid lubricant additives in polyalphaolefin (PAO-4) by means of tribotesting on coupled GCr15/cast iron contacts. The effects of test parameters such as normal loads, additive concentrations, and substrate surface roughness were investigated, while the LDH crystal structure received considerable attention. Several types of structural disorder after anion exchange were identified based on X-ray diffraction (XRD) analysis. The unstable structures promote feasible shearing during sliding to improve friction and wear. In addition, antiwear properties correlate well with the anion charge number or the quantity of anion in the interlayer region. Overall, the tribological performance increased in the order HPO42--LDH < PO43--LDH < P2O74--LDH < (PO3)66--LDH. (PO3)66--LDH demonstrated the best antiwear performance with a reduction of 69% of the ball volume loss compared to PAO-4 oil due to the synergy of the disordered stacking LDH sheets and flexible ring structure of the (PO3)66- anion. Furthermore, on polished surfaces, the coefficient of friction (COF) of the (PO3)66--LDH sample dropped significantly by 26%, while the wear loss reduction of more than 80% was also substantial compared to the base oil sample. A performance comparison between the best-performing LDH additive was also conducted against popular nanomaterials, such as hexagonal boron nitride (BN), graphene nanoplatelets (GNPs), and titanium oxide (TiO2). The performance of (PO3)66--LDH was close to that of GNPs.

CeO2/Ni-Al layered double hydroxide composite electrode for the enhancement of specific capacitance and capacitance retention performance

Layered double hydroxides(LDH) possessed excellent capacitive properties but with poor cycling performance and low specific capacitance at high current density. CeO2/Ni-Al LDH (NAHCe) composite was synthesized by a one-step hydrothermal method to improve the electrochemical performance Ni-Al LDH. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results proved the well distribution of cerium on the surface of the Ni-Al LDH laminate structure. The specific capacitance and capacitance retention after 1000 cycles of the optimal composite NAHCe-2.5 reached 879.63 F·g−1 at 1 A g−1 and 90.36% at 2 A g−1, which was higher than that of NAH (541.82 F·g−1 at 1 A·g−1, 62.9% at 2 A·g−1 after 1000 cycles) under the same conditions. The CeO2 particles loaded on Ni-Al LDH sheets effectively reduce the internal electrochemical resistance of the composite electrode which contributed to the improvement of the specific capacitance and capacitance retention performance of the electrode. The idea of CeO2/LDH composite for the enhancement of electrochemical performance could be of help for the synthesis of other new-type supercapacitors.

A self-healing corrosion protection coating with graphene oxide carrying 8-hydroxyquinoline doped in layered double hydroxide on a micro-arc oxidation coating

The fabrication of remarkable self-healing coatings is the key to achieving excellent anti-corrosion of magnesium (Mg) alloys. In this research, 8-hydroxyquinoline@graphene oxide (8-HQ@GO) composite was successfully synthesized through ring-opening reaction and a micro-arc oxidation (MAO) coating was grown on AZ31 beforehand. Afterwards, the 8-HQ@GO composite was doped into the layered double hydroxides (LDHs) sheet by hydrothermal chemical transformation based on the MAO coating without introducing any kind of salts. The incorporation of 8-HQ@GO composite and Mg-Al LDHs sheets can distinctly boost the corrosion resistance of AZ31 alloy. The self-healing performance and the anti-corrosion mechanism of MAO-LDHs/HG coating are discussed.

Increased efficiency and stability of Dye-Sensitized Solar Cells (DSSC) photoanode by intercalation of Eosin Y into Zn/Al layered double hydroxide

Layered Double Hydroxides (LDH) are versatile materials that can be applied to different fields. Recently their employment in Dye-Sensitized Solar Cells (DSSCs) technology has been reported. The heart of this technology is the photoanode, a semiconductor layer sensitized with dye molecules able to absorb the sunlight. However, the traditional dye molecules are quite expensive and sensitive to thermal degradation and the sensitization process requires time and costs. The possibility to directly intercalate the dye in the LDH interlayer makes these materials very promising as innovative photoanodes. This aspect in fact would help to reduce both the time and the costs, overcome charge-transfer and recombination phenomena issues and finally increase the Photo-Conversion Efficiency (PCE) and stability. In this work, an Eosin Y-intercalated ZnAl LDH was prepared by coprecipitation and applied as photoanode material. For this purpose, a screen-printing ink was formulated and then applied onto a conductive transparent substrate. Then, complete DSSC prototypes were assembled and tested. A comparison with an analogous LDH intercalated with terephthalate and sensitized with Eosin Y showed a beneficial effect due to the presence of the dye intercalated in the structure rather than adsorbed on the surface, increasing the stability (tested for 1500 h) and efficiency of the related DSSCs. A 0.11 mA cm−2 of JSC, 568 mV of VOC and a PCE of 0.019% were obtained for the Eosin Y intercalated LDH based photoanode. Moreover, the interaction between the intercalated dye and the LDH sheets allowed to reduce charge recombination phenomena and thus to increase VOC and PCE values.

Growth Dynamics of Vertical and Lateral Layered Double Hydroxide Nanosheets during Electrodeposition.

Layered double hydroxides (LDHs) are a class of lamellar materials with a wide range of potential catalytic applications. LDHs form from positively charged 2D atomic layers separated by charge-balancing anions and solvent molecules. Typically, nanoscale LDH sheets can grow vertical or parallel to a substrate, exposing their different active facets. These two growth modes of LDH nanosheets have a significant impact on their electrocatalytic properties, yet the details of their growth remain unknown, hindering our ability to design and synthesize high-performance LDH-based electrocatalysts. Here, we investigate the growth pathways of LDH nanosheets using in situ electrochemical liquid-phase transmission electron microscopy (TEM) and show that the growth modes of LDH nanosheets can be controlled by tuning the precursor concentrations. Moreover, our observations reveal that LDH nanosheets grow via two pathways: (1) monomer addition, where the adatoms are heterogeneously deposited onto the LDH nanosheets, and (2) coalescence, where adjacent nanosheets merge together.

Removal and Release of the 2,4,5-Trichlorophenoxyacetic Acid Herbicide from Wastewater by Layered Double Hydroxides

The Zn2–Al layered double hydroxides (LDHs) have been used to remove the 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) herbicide, which is used as a model for pesticides from the carboxylate family. The adsorption isotherms are governed by Langmuir model (L type). The characterization by various techniques (XRD, FTIR, SEM) indicates that the 2,4,5-T retention is governed by adsorption on the sites of the LDH surface when the molar ratio 2,4,5-T/Cl ≤ 0.1. For greater ratio values, the herbicide undergoes, in addition, intercalation in the LDH interlayer domain leading to an increase of the interlayer distance from 0.778 to 1.855 nm. The retention capacity reaches 718 mg/g with a removal rate of 96% for an optimal 2,4,5-T/Cl molar ratio of 0.5. This capacity is influenced by the solution pH, the charge density of the LDH sheets, the adsorbent/adsorbate molar ratio and the nature of the interlayer anion of the LDH precursor. The partial or total release of the herbicide was observed to depend on the composition of the desorbing solution. This suggests the possibility of LDH recycling and confirms thus its effectiveness in eliminating this type of pollutant from water. In addition, a well-structured [Zn2–Al-2,4,5-T] hybrid material was obtained after herbicide retention and its characterization by chemical analyses and SEM as well as a proposed structural model are presented.

A class of novel luminescent layered double hydroxide nanotubes.

Herein, we report a class of novel lanthanide-doped self-supported layered double hydroxide (LDH) nanotubes featuring a combination of micro- and mesoporosity. The synthesis of the nanotubes has been achieved by a soft-templating strategy. Incorporation of La3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+ or Tb3+ in the LDHs assisted the self-assembly of the double hydroxide layers onto the surface of Pluronic P-123 worm-like micelles, enabling the formation of the nanotubes. Removal of the micellar template provides accessibility to the mesopores, yielding a network of hollow cylindrical nanotubes with internal diameter of about 10 nm. An antenna molecule (benzene-1,3,5-tricarboxylate, BTC) is hosted in their 1-nanometre-wide micropores. Upon UV excitation, the nanotubes emit light in a set of wavelengths ranging from the ultraviolet to the infrared.

Mesostructuring layered materials: self-supported mesoporous layered double hydroxide nanotubes.

Synthesis of layered materials exhibiting hierarchical porosity remains challenging, but nevertheless worthwhile because it turns such solids into functional materials with high specific surface area. Using a soft-templating strategy in combination with the incorporation of 8-fold coordinated Eu3+, self-assembly of self-supported layered double hydroxide (LDH) nanotubes has been achieved. Heteromorphic equimolar substitution of Al3+ by Eu3+ in Zn2+/Al3+ LDH solids intercalated with 1,3,5-benzenetricarboxylate anions (BTC) assists precipitation of the double hydroxide layers onto the convex surface of Pluronic® P-123 worm-like micelles, yielding multilayer cylinders of BTC-intercalated LDHs. Removal of the micellar template is easily achieved by liquid extraction with methanol, yielding a network of interconnected, well-defined, self-supported, multi-walled, hollow cylindrical nanotubes. Removal of Eu3+ from the synthesis disables formation of the nanotubular morphology, but still yields LDHs containing a network of embedded mesopores, resulting in a specific surface area that is 5-fold higher as compared to standard LDHs.

Degradation of Rhodamine B Under Visible-Light by Cu-Doped ZnAl Layered Double Hydroxide.

The Cu-doped ZnAl layered double hydroxides (LDH) were papered by coprecipitation. The prepared samples were characterized by mutiple techniques including X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse-reflectance spectroscopy (UV-vis DRS). The doping of Cu2+ into the LDH sheets results in formation of the distorted CuO6 octahedrons which contribute for the excitation of electrons under visible light. The doped Cu2+ also serves as photo-generated charges separator and improves the visible-light-driven photocatalytic activity of ZnAl LDH. A degradation mechanism based on the hydroxyl radical as the active species was proposed.

Mg-Al-La LDH-MnFe2O4 hybrid material for facile removal of anionic dyes from aqueous solutions

The urea hydrolysis method was applied to prepare Mg-Al-La layered double hydroxides (LDH) and its hybrids with different amounts of magnetic MnFe2O4 nanoparticles. The new hybrid materials were characterized by X-ray powder diffraction, FTIR and Raman spectroscopy, AFM, SEM, TEM/EDX microscopic methods, BET specific surface area determination and inductively coupled plasma (ICP). The AFM and TEM/EDX analyses clearly showed MnFe2O4 nanoparticles to be predominantly localized on the surface of LDH sheets. Almost two-fold increase of the specific surface area was observed for the Mg-Al-La LDH-MnFe2O4 hybrids compared to the pristine LDH. All synthesized hybrids were studied for their adsorption capacities of Acid orange 7 dye. The adsorption studies were measured at pH 4.0, 7.0 and 10.0. The resulting data were fitted by Langmuir and Langmuir-Freundlich models. The Langmuir isotherm model exhibited a maximum adsorption capacity of Acid orange 7 dye (687.9 mg/g) for Mg-Al-La LDH-MnFe2O4 hybrid material. The lower pH positively affected higher adsorption capacity of Acid orange 7 dye. The prepared Mg-Al-La LDH-MnFe2O4 hybrid materials thus showed to be new promising adsorbents of anionic dyes.

Enhanced Visible-Light-Driven Photocatalytic Activity of ZnAl Layered Double Hydroxide by Incorporation of Co2+

Co-doped ZnAl layered double hydroxides (LDH) were papered by coprecipitation. The prepared samples were characterized by multiple techniques including X-ray Diffraction (XRD), Brunauer−Emmett−Teller (BET) surface area, Scanning Electronic Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS) and UV−Vis Diffuse-Reflectance Spectroscopy (UV−Vis DRS). The incorporation of Co2+ into the ZnAl LDH sheets as CrO6 octahedron forms a new energy level which contributes for the excitation of electrons under visible light. The doped Co2+ at a reasonable content also serves as photo-generated charges separator and improves the visible light photocatalytic activity of ZnAl LDH. A degradation mechanism based on the hydroxyl radical as the active species was proposed.

Quaternized polysulfone‐based nanocomposite membranes and improved properties by intercalated layered double hydroxide

Two anions (dodecylbenzenesulfonate anion and stearate anion) are employed to synthesize intercalated layered double hydroxides (LDH) by co‐precipitation method. Then the intercalated LDHs are incorporated in the casting solutions of chloromethylated polysulfone (CMPSF) for fabricating quaternized polysulfone/LDH nanocomposite membranes. Fourier transform infrared, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and mastersizer laser particle size analysis are used to characterize the structure and morphology of LDHs and membranes. The properties of the composite membranes including water uptake, mechanical property, thermal stability, and ionic conductivity are investigated. Compared with other anion exchange membranes, both nanocomposite membranes containing 5% LDH sheets displayed better balanced performance. They exhibit the ionic conductivity of 3.58 × 10−2 S cm−1 and 3.86 × 10−2 S cm−1 at 60°C, respectively. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Anion-exchange membranes derived from quaternized polysulfone and exfoliated layered double hydroxide for fuel cells

Layered double hydroxides (LDH) are prepared by controlling urea assisted homogeneous precipitation conditions. Morphology and crystallinity of LDHs are confirmed by X-ray diffraction and scanning electron microscope. After LDHs are incorporated into quaternized polysulfone membranes, transmission electron microscope is used to observe the exfoliated morphology of LDH sheets in the membranes. The properties of the nanocomposite membranes, including water uptake, swelling ratio, mechanical property and ionic conductivity are investigated. The nanocomposite membrane containing 5% LDH sheets shows more balanced performances, exhibiting an ionic conductivity of 2.36×10−2Scm−1 at 60°C.

Controlled supramolecular structure of guanosine monophosphate in the interlayer space of layered double hydroxide.

Guanosine monophosphates (GMPs) were intercalated into the interlayer space of layered double hydroxides (LDHs) and the molecular arrangement of GMP was controlled in LDHs. The intercalation conditions such as GMP/LDH molar ratio and reaction temperature were systematically adjusted. When the GMP/LDH molar ratio was 1:2, which corresponds to the charge balance between positive LDH sheets and GMP anions, GMP molecules were well-intercalated to LDH. At high temperature (100 and 80 °C), a single GMP molecule existed separately in the LDH interlayer. On the other hand, at lower temperature (20, 40 and 60 °C), GMPs tended to form ribbon-type supramolecular assemblies. Differential scanning calorimetry showed that the ribbon-type GMP assembly had an intermolecular interaction energy of ≈101 kJ/mol, which corresponds to a double hydrogen bond between guanosine molecules. Once stabilized, the interlayer GMP orientations, single molecular and ribbon phase, were successfully converted to the other phase by adjusting the external environment by stoichiometry or temperature control.

Antibacterial carboxymethyl cellulose/Ag nanocomposite hydrogels cross-linked with layered double hydroxides

This paper deals with the preparation of antibacterial nanocomposite hydrogels through the combination of carboxy methyl cellulose (CMC), layered double hydroxides (LDH), and silver nanoparticles (AgNPs). CMC-LDH hydrogels were prepared by intercalating CMC into different LDHs. Then, Ag/CMC-LDH nanocomposite hydrogels were prepared through in situ formation of AgNPs within the CMC-LDHs. XRD analysis confirmed the intercalating CMC into the LDH sheets and formation of intercalated structures, as well as formation of AgNPs within the CMC-LDHs. SEM and TEM micrographs indicated well distribution of AgNPs within the Ag/CMC-LDHs. The prepared hydrogels showed a pH sensitive swelling behavior. The Ag/CMC-LDH nanocomposite hydrogels have rather higher swelling in different aqueous solutions in comparison with CMC-LDHs. The antibacterial activity of CMC-LDHs increased considerably after formation of AgNPs and was stable for more than one month.