Layered Double Hydroxides Layers Research Articles

Boosting the anticancer activity of doxorubicin with a layered double hydroxide nanocarrier

A cationic anticancer drug, doxorubicin (DOX), was intercalated into layered double hydroxide (LDH) with an anionic polymer (polyacrylic acid (PAA)) to introduce the advantages of LDH as a drug carrier to DOX. Through X-ray diffraction patterns, Fourier-transform-infrared spectra, zeta-potential and X-ray photoelectron spectra showed that, PAA and DOX were intercalated in LDH interlayers through electrostatic stabilization between the carboxylate of PAA and LDH layer and between the carboxylate PAA backbone and DOX. Scanning electron microscopic images and dynamic light scattering results revealed that the DOX-PAA-LDH hybrid showed a favorable size for cellular uptake and enhanced permeability and retention, with a ~ 300 nm hydrodynamic radius and ~ 160 nm primary particle size. According to the bio-transmission electron microscopic images and confocal microscopic images, the DOX-PAA-LDH hybrid continuously provides drugs to endosomal cells during endocytosis and exocytosis. In accordance with these results, DOX-PAA-LDH showed improved anticancer activity against human osteosarcoma cells (MG-63) and human lung adenocarcinoma epithelial cells (A549) due to the advantages of LDH as a drug carrier.

Research progress of LDHs as Fenton reaction catalysts

<p indent=0mm>Fenton reaction utilizes the catalytic reaction of H₂O₂ and Fe²⁺ to generate highly active hydroxyl radicals (·OH) quickly to degrade organic compounds without the secondary pollution of by-products, which is widely used in the fields of environmental protection and sewage treatment. However, the difficulty of the regeneration of low-valence metals in the ordinary homogeneous Fenton reaction limits the efficiency of the overall reaction. In addition, the acidic requirements of the reaction system and the introduction of iron ions are not ideal from an environmental perspective. In recent years, layered double hydroxides (LDHs), as a unique layered material, have shown excellent catalytic performance in Fenton reaction and have attracted widespread attention. The active sites of LDHs are usually the metal ions fixed on the solid surface, which can avoid the leaching of metal ions and reduce the pH requirements of the reaction system. Besides, by adjusting the structure of the LDHs layers, a redox cycle of multiple metals can be formed, which promotes the regeneration of the low-valence metals effectively and thus improves the efficiency of the Fenton reaction. This review mainly summarizes the recent progress of LDHs materials as Fenton reaction catalysts. The challenge and prospective trends of LDHs materials as Fenton reaction catalysts are also discussed.

Zn-Al layered double hydroxide as an inhibitive conversion coating developed on AA2024-T3 by one-step hydrothermal crystallization: Crystal structure evolution and corrosion protection performance

In the present work, a ZnAl layered double hydroxide (LDH) conversion coating was synthesized on 2024-T3 aluminum alloy by a one-step hydrothermal method. For this purpose, the effect of synthesis parameters, including the amount of Zn2+ cations and hexamethylenetetramine molecules, on the structural changes were evaluated by using the scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) analysis and X-ray diffraction (XRD) spectroscopy. Also, benzimidazole (BI), as corrosion inhibitor of the AA2024-T3, was intercalated into the LDH film structure by an anion-exchange process. The intercalation of BI molecules into the LHD structure was studied using the SEM-EDS and XRD analysis. Furthermore, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PD), and electrochemical current noise measurements were employed in 3.5 wt% NaCl solution to assess the protection performance of the LDH coating. The PD test results showed that the LDH conversion coating's polarization resistance increases from 24.05 to 131.1 kΩ/cm2 after the intercalation of the BI molecules into the structure of the ZnAl LDH layer. The induction of active protection performance for the LDH film modified with BI molecules was demonstrated through the EIS test results.

Intelligent anti-corrosion and corrosion detection coatings based on layered supramolecules intercalated by fluorescent off-on probes

The metallic engineering structures were commonly covered and protected by the anti-corrosion coatings. The early corrosion under the coatings and at the defects was concealed. Once the corrosion was visible to the naked eye, it indicated that the corrosion has developed seriously. Therefore, it was practical significant to detect the early corrosion of the metal under the coatings and at the defects. The formation of iron ions and anodic acidification were the characteristics of local corrosion process. Based on this fact, iron ions and protons responsive fluorescent on-off probes Rhodamine B Acylhydrazone (RBA) were prepared for the detection of corrosion. In the prepared supramolecules of RBA/LDHs, RBA intercalated and was loaded between layered double hydroxide (LDHs) to protect RBA from premature exposure to corrosive environment and fluorescence quenching. When corrosive Cl− was presented, the RBA loaded by LDHs exchanged with Cl− in corrosive environment, and RBA was released, and Cl− intercalated and was loaded between layers of LDHs. Therefore, the response to corrosion factors and release of RBA were realized, and was accompanied by the capture of Cl− and treatment of corrosion region. In the epoxy coatings, RBA/LDHs indicated the occurrence of corrosion and accurately locate the corrosion site and coating defects in form of fluorescence. Simultaneously, the sheet morphology and dispersion distribution of RBA/LDHs enhanced the shielding performance of the coatings.

Layered double hydroxides as advanced tracks to promote ionic conductivity in metal borohydride

Advanced solid-state electrolytes (SSEs) based on layered double hydroxide (LDH)/metal-borohydrides (M-BH4 with M = Li, Na, Mg) are proposed. The (2D) host layers of LDH serving as an advanced track enable largely improved mobility of free metal ion.

Polymer/Iron-Based Layered Double Hydroxides as Multifunctional Wound Dressings.

This work presents the development of multifunctional therapeutic membranes based on a high-performance block copolymer scaffold formed by polyether (PE) and polyamide (PA) units (known as PEBA) and layered double hydroxide (LDH) biomaterials, with the aim to study their uses as wound dressings. Two LDH layer compositions were employed containing Mg2+ or Zn2+, Fe3+ and Al3+ cations, intercalated with chloride anions, abbreviated as Mg-Cl or Zn-Cl, or intercalated with naproxenate (NAP) anions, abbreviated as Mg-NAP or Zn-NAP. Membranes were structurally and physically characterized, and the in vitro drug release kinetics and cytotoxicity assessed. PEBA-loading NaNAP salt particles were also prepared for comparison. Intercalated NAP anions improved LDH–polymer interaction, resulting in membranes with greater mechanical performance compared to the polymer only or to the membranes containing the Cl-LDHs. Drug release (in saline solution) was sustained for at least 8 h for all samples and release kinetics could be modulated: a slower, an intermediate and a faster NAP release were observed from membranes containing Zn-NAP, NaNAP and Mg-NAP particles, respectively. In general, cell viability was higher in the presence of Mg-LDH and the membranes presented improved performance in comparison with the powdered samples. PEBA containing Mg-NAP sample stood out among all membranes in all the evaluated aspects, thus being considered a great candidate for application as multifunctional therapeutic dressings.

Nanocomposites of polyimide with Various Modified LDHs: Synthesis, characterisation and towards improvement of, morphology, thermal stabilities, mechanical properties, gas permeation and gas selectivity

ABSTRACT Novel polyimide (PI) nanocomposite films were synthesised from diamine monomer (diamine 1B) and Pyromellitic dianhydride (PMDA) with various modified layered double hydroxides (LDHs) particles via solution intercalation polymerisation to poly(amic acid)s, followed by thermal imidization. Modified LDHs particles, including LDH-amino benzoate (M-LDHs) were prepared with the coprecipitation method. The intercalation of PI chains among the LDHs particles was examined using wide-angle X-ray diffraction (XRD) and electron microscopy (TEM) techniques. TEM photographs showed that most LDH layers were dispersed homogeneously into the matrix polymer on the nanoscale, although some particles of LDHs were agglomerated. Moreover, the addition of only a small amount of LDHs particles was enough to improve the thermal stabilities and mechanical properties of PI hybrid films. The thermo-optical properties were measured by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and ultraviolet-visible (UV–vis) spectrometry. As anticipated, though the gas permeability of pure gases, viz., He, N2, CH4 and CO2 exhibited decrease, it was not monotonous. A marked decrease in permeability of gases like CO2 and CH4, in comparison to relatively lower decrease in permeability of He was observed, especially at higher LDH loading. An increase in selectivity: α(He/CO2) and α(He/CH4), especially at higher LDH loading indicated the capability of nanocomposites to tune the selectivity favourably.

Preparation of Cu-doped ZnO nanoparticles via layered double hydroxide and application for dye-sensitized solar cells

It has been reported that doping ZnO with metal ions can alter the band gap and immensely enhance electron transport. In this regard, to increase the efficiency of cost-effective dye-sensitized solar cells (DSSCs), we synthesized Cu-doped ZnO nanocomposites from layered double hydroxide (LDH) precursors via a facile method. LDH layers were homogeneously doped with Cu ions, and mixed metal oxides (MMOs) were obtained after annealing. The morphology and optical and electrochemical properties of the as-synthesized Cu-doped ZnO nanocomposites were systematically studied. The introduction of Cu ions increases the specific surface area of ZnO and increases light absorption in the visible region. The Cu-doped ZnO MMOs were used as the photoanode of DSSCs, and the effect of the amount of the Cu dopant on the performance of the solar cells was studied. At the optimal doping weight percentage of Cu (0.25 wt%), the solar cell based on Cu-doped ZnO MMO and D149 dye achieved the highest short-circuit current of 7.12 mA cm−2 and the highest power conversion efficiency of 1.50%.

Systematic utilization of layered double hydroxide nanosheets for effective removal of methyl orange from an aqueous system by π-π stacking-induced nanoconfinement

Systematic utilization of carbonated Mg–Al layered double hydroxide (LDH) nanosheets for methyl orange removal was investigated with respect to particle dimensions. LDHs with the smallest dimensions were carefully synthesized to have a small lateral size as well as high dispersibility. The other particles, with medium and large sizes, were prepared by hydrothermal treatment and urea hydrolysis to have larger sizes and higher crystallinity. According to kinetics and isotherm analyses, the smallest LDH showed efficient adsorption of methyl orange (1250 mg/g-LDH), which was remarkably higher than the adsorption by the other LDHs with larger lateral sizes. Unlike the larger lateral-sized LDHs, the small ones were shown to utilize all accessible adsorption sites on the nanosheets, generating nanoconfinement of methyl orange molecules. Transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD) patterns indicated that the LDHs with lateral dimensions of ~40 nm fully utilized interlayer nanospace. Monte Carlo simulation suggested that the intercalated methyl orange was stabilized not only through electrostatic interactions with the LDH layer but also by π-π stacking between the methyl orange molecules, which is thought to be the driving force for replacement of carbonate anions.

Synthesis of glutamate intercalated Mg-Al layered double hydroxides: influence of stirring and aging time

An Mg-Al layered double hydroxides (LDHs) intercalated by glutamate ions (Glu/LDH) was obtained using co-precipitation processing. The influence of stirring and aging time on LDH morphology was investigated. The morphology of LDH was characterized by means of XRD, FT-IR, FE-SEM and XPS. The thermal stability, pore volume and specific surface area were probed through thermal gravimetric (TG) analysis and automatic specific surface area analyzer, respectively. The results showed that the stirring and aging time had an insignificant influence on the interlayer distance of Glu/LDH; while it had a critical impact on the crystallinity degree of the Glu/LDH structure. TG analysis designated that the thermal stability of glutamate ion intercalated in LDH layers was higher than that of glutamate ion before intercalation. Glu/LDH exhibited the best adsorption performance at a stirring and aging time of 12 h. A schematic molecular structure model of Glu/LDH was proposed.

Formulation of a Bio-Packaging Based on Pure Cellulose Coupled with Cellulose Acetate Treated with Active Coating: Evaluation of Shelf Life of Pasta Ready to Eat.

An active packaging based on pure cellulose coupled with cellulose acetate coated with layered double hydroxide (LDH), hosting 4-hydroxybenzoate (listed in EC-Directive 10/2011) as an antimicrobial agent, was formulated and realized. The release of 4-hydroxybenzoate ionically bonded to the LDH layers was much slower than the molecule freely dispersed into the coating. The capability of the active packaging to inhibit Pseudomonas, Escherichia coli, Salmonella and Lactic Bacteria was evaluated, as well as the global migration with three different food simulant (i.e., acetic acid at 3% (v/v), ethanol at 50% (v/v) and vegetable oil) that demonstrated, in compliance with the migration limits of the EU regulation, the suitability of the prepared packaging to be employed as food contact material. Ready to east cooked tomato pasta was packaged into the active trays and in uncoated, as control, up to 30 days at 4 °C. Organoleptic characteristics, mold evolution, total mesophilic aerobic counts (TBC), Enterobacteriaceae, Lactic Bacteria and Pseudomonas, and in colony forming unit per gram (CFU/g), showed a significant activity of 4-hydroxybenzoate in increasing the shelf life of the pasta ready to eat.

Layered Double Hydroxides Applications in the High-Performance Magnetic Nanomaterials

Layered double hydroxides (LDHs), which is related to magnetic nanomaterials’ have promising applications due to their unique structural and chemical properties. The easy tunability of cationic metals without changing the LDH structure as well as anion exchange features of LDH interlayer make them potential applications in supercapacitors, batteries, catalysis, water splitting, etc. Moreover, due to the high dispersion of active compounds in the matrix of LDH layers, LDHs have been used to construct various nanostructures such as nanoparticles, 2D monolayer nanosheets and 3D hierarchical’ which are valued in wide nanotechnological applications. Magnetic nanomaterials are an important research area because they have been applied to a wide range of disciplines such as biotechnology, data storage, magnetic fluids, magnetic resonance imaging, environmental remediation and catalysis. LDHs as starting materials including Ni, Fe or/and Co, can be used as magnetic nanomaterials. The combination between LDHs and magnetic nanostructures has improved the magnetic properties of those materials, hence can be used in more applications.

Structured NiFe catalysts derived from in-situ grown layered double hydroxides on ceramic monolith for CO2 methanation

Monolithic catalysts for CO2 methanation have become an active research area for the industrial development of Power-to-Gas technology. In this study, we developed a facile and reproducible synthesis strategy for the preparation of structured NiFe catalysts on washcoated cordierite monoliths for CO2 methanation. The NiFe catalysts were derived from in-situ grown layered double hydroxides (LDHs) via urea hydrolysis. The influence of different washcoat materials, i.e., alumina and silica colloidal suspensions on the formation of LDHs layer was investigated, together with the impact of total metal concentration. NiFe LDHs were precipitated on the exterior surface of cordierite washcoated with alumina, while it was found to deposit further inside the channel wall of monolith washcoated with silica due to different intrinsic properties of the colloidal solutions. On the other hand, the thickness of in-situ grown LDHs layers and the catalyst loading could be increased by high metal concentration. The best monolithic catalyst (COR-AluCC-0.5M) was robust, having a thin and well-adhered catalytic layer on the cordierite substrate. As a result, high methane yield was obtained from CO2 methanation at high flow rate on this structured NiFe catalysts. The monolithic catalysts appeared as promising structured catalysts for the development of industrial methanation reactor.

MgAl Layered Double Hydroxides Intercalated with EDTA: Cu(II) Recovery and Mechanism

AbstractIn water treatment, it is a valid way to remove Cu(II) efficiently via layered double hydroxides (LDHs) intercalated with chelate, but the desorption and its mechanism remain an unsolved difficult problem. To solve this problem, MgAl LDHs intercalated with EDTA (MgAl‐EDTA‐LDHs) was synthesized by one‐step co‐precipitation method, and applied to recover Cu2+. The characterizations of SEM, XRD, XPS, EA and AAS were employed, and the results showed that MgAl‐EDTA‐LDHs exhibited a typical lamellar structure, the adsorption capacity of MgAl‐EDTA‐LDHs on Cu2+ could reach 79.69 mg/g, which was attributed to the chelation of EDTA and chemical bonding of hydroxyl (−OH) on the surface of LDHs layers. In addition, the adsorption capacity could achieve 45.75 mg/g after eluting by Na2CO3 solution, which was relevant to the ion exchange by CO32−. Herein, the adsorption and desorption mechanism of MgAl‐EDTA‐LDHs on Cu2+ was expounded, which may pave a new way to recover the heavy metal and provide a theoretical guidance for future research.

Enhanced removal of Cr(VI) from wastewater by nanoscale zero valent iron supported on layered double hydroxides

The application of nanoscale zero-valent iron (NZVI) in a promising remediation strategy was challenged by easy aggregation and surface passivation. To enhance their performance of Cr(VI) removal, layered double hydroxides (LDHs) supported NZVI (NZVI@LDH) with different loading amount via an in-situ way was successfully synthesized. The structural characterization and morphology revealed LDHs could stabilize and uniformly disperse NZVI on the surface of LDHs layer, however, superabundant NZVI still leaded to a visibly aggregation. Cr(VI) removal by NZVI@LDH was higher than that of the sum of NZVI and LDHs, revealing a synergistic effect within this system. The results of Cr(VI) removal displayed with the growth of iron loading amount, the removal efficiencies were raised firstly but declined afterwards. Kinetics studies for all samples showed Cr(VI) removal well fitted pseudo-second-order model and isotherm data was well described by Langmuir model. The effects of initial concentration and pH on Cr(VI) removal were also examined. Cr(VI) in the wastewater was reduced by NZVI to Cr(III), NZVI was oxidized into Fe(II) and Fe(III). The excellent removal performance suggested a promising strategy in sewage water remediation.

Multifunctional laminated membranes with adjustable infrared radiation for personal thermal management applications

The laminated membranes that combine adjustable infrared emissivity, sunscreen, antibacterial and breathability are of great significance and challenge for personal comfort thermal management applications in civil, medical and military fields. Herein, the laminated membranes composed of zinc–aluminum layered double hydroxides (LDH)/cotton fiber (CF@Zn–Al LDHs) and zinc oxide nanorods/CF (CF@ZNR) were successfully fabricated by orderly assembly using a vacuum filter pump. The personal thermal management properties, including infrared insulation and heat dissipation, can be controlled via controlling the infrared emissivity of CF@Zn–Al LDHs layer. The antibacterial and ultraviolet resistance properties can be achieved by in-situ growth of ZnO nanorods on CF surface. For the inner layer, the aluminum nano-coating onto the CF (CF@ANC), as the aluminum source for LDH, shows low infrared emissivity (30.2%), which can reduce human body heat radiation to achieve infrared insulation. The Zn–Al LDHs with gradients in morphologies were obtained by in-situ growth on the CF, which exhibit the enhanced infrared emissivity (maximum emissivity of 0.98) to achieve infrared dissipation. For the outer layer, ZnO nanorods arranged vertically on CF (CF@ZNR), which possess high infrared transmittance of about 83.0%, may promote the loss of the human body heat. In addition, the laminated membranes also possess the desired flexibility and breathability. Therefore, the versatility and clever design strategies of laminated membranes have potential application value in the field of personal comfort thermal management.

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.

Preparation of Zn–Al layered double hydroxide intercalated with carboxymethyl-β-cyclodextrin by anion exchange method and its Ni2+ adsorption property

ABSTRACT Recently, layered double hydroxides (LDHs) have been extensively researched for their anion exchange capabilities and exhibit a layered structure with a host layer of octahedrally coordinated metal cations and a guest layer (interlayer) of anions. In this study, we synthesized a CM-β-CD•Zn–Al LDH by anion exchange method to study the anionization of cyclodextrin (CD) to promote its incorporation into the LDH interlayers and its stability therein. Ni2+ adsorption by the CMCD•Zn–Al LDH by the anion exchange method was compared with the results co-precipitation method. The X-ray diffraction spectra of NO3•Zn–Al LDH and CM-β-CD•Zn–Al LDH synthesized by the anion exchange method exhibit that the product peaks were attributable to and possessed an LDH structure. Furthermore, all CM-β-CD•Zn–Al LDHs exhibited the presence of some CM-β-CD. The CM-β-CD•Zn–Al LDH was hypothesized to be composed of two types of layers: a CM-β-CD layer in which two molecules of CM-β-CD7 -, with cavity axes perpendicular to the LDH host layer, are vertically overlaid, and a NO3-type Zn–Al LDH layer used as a precursor. CM-β-CD•Zn–Al LDH adsorbed Ni2+ in an aqueous solution. To determine whether Ni2+ adsorption by the CM-β-CD•Zn–Al LDH is driven chemically or physically, we fitted the data to the Freundlich and Langmuir adsorption models; the results showed that Ni2+ adsorption by the CM-β-CD•Zn–Al LDH is consistent with the Langmuir equation and could be considered a chemical adsorption.

Fabrication of Mg-Al Layered Double Hydroxide Thin Membrane for All-Solid-State Alkaline Fuel Cell Using Glass Paper as a Support

Layered double hydroxides (LDHs) are promising solid electrolytes for all solid-state alkaline fuel cells (AFCs) because of inorganic clay-like materials. However, LDHs were usually obtained as powder, and the formation of thin membranes as a separator of a fuel cell is rather difficult. In this study, a glass paper, non-woven fabric of fine glass fibers with more than 90% porosity, was used as a support for Mg-Al LDH powder, and self-standing, thin membranes for all solid-state AFCs were fabricated. Crystals of Mg-Al LDH were deposited in the inside of the glass paper by repeated immersion in Mg-Al LDH-dispersed solution and drying. Thickness of the obtained Mg-Al LDH thin membrane was about 150 µm, and LDH layer showed c-axis orientation because of the plate-like structure. The H2-O2 fuel cell using the Mg-Al LDH thin membrane as an electrolyte showed open circuit voltage of more than 0.9 V, indicating that the Mg-Al LDH thin membrane is dense and has high gas barrier property. The H2-O2 fuel cell using the Mg-Al LDH thin membrane showed higher power density compared with that using pelletized Mg-Al LDH powder as the electrolyte. The glass paper is proved to be very effective support for making thin Mg-Al LDH electrolyte membrane.

Enantioselectivity Enhanced on LDH Layers in Ruthenium Catalyzed Asymmetric Hydrogenation of Acetophenone

AbstractA novel heterogeneous catalyst has been developed by immobilizing Ru complexes on layered double hydroxide (LDH) via an electrostatic adsorption method. The prepared hybrid was characterized by a series of physical and chemical techniques, and the results confirmed the successful immobilization of the Ru complexes on the LDH support. The prepared heterogeneous Ru catalyst was found to be more enantioselective than the corresponding homogeneous analogue in the asymmetric hydrogenation of acetophenone and its ee value was 10% higher than that of the homogeneous analogue. Furthermore, the prepared heterogeneous catalyst could be recovered easily and reused at least six times without a significant loss in catalytic activity and selectivity. Density functional theory (DFT) computations revealed the influence of LDH layer on Ru complexes and the enantioselectivity of the immobilized Ru complexes in asymmetric hydrogenation of acetophenone.