Preparation Of Layered Double Hydroxides Research Articles

Alkali treatment modulated borate anions in layered double hydroxides as precursors of highly efficient Au-based catalysts for water-gas shift reaction

Layered double hydroxides (LDHs) as an adjustable layered materials were considered as good candidates for the supports of water-gas Shift (WGS) catalysts. However, there is rare report about the exfoliation preparation and WGS application of LDHs containing BO33− as intercalated anions. Herein, we reported a mild alkali treatment modulation of the intercalated borate anions in LDHs for improving the WGS catalytic performance of Au-based catalysts. Compared with inactive Au supported LDHs without alkali treatment, the moderate alkali treatment consumes intercalated BO33− anions in LDHs, arousing the WGS activities of Au-based catalysts. Among the different alkali treatment concentration, Au-LDHs-1M treated with 1 M NaOH present the highest WGS activity and excellent stability with a reduction of only 10 % for 60 h. The moderate alkali treatment promotes the exfoliation of LDHs into nanosheets covered Co3O4 small nanoparticles, which facilitated the high dispersion of Au species and also easily converted into active Fe3O4 and metallic Co phases. While Au-LDHs-5M presents such large Au particles that it exhibits low activity, and Au-LDHs-0M is inactive due to the formation of B2O and Fe23B6 poison phases for the WGS reaction.

Advances of Layered Double Hydroxide-Based Materials for Tumor Imaging and Therapy.

Layered double hydroxides (LDH) are a class of functional anionic clays that typically consist of orthorhombic arrays of metal hydroxides with anions sandwiched between the layers. Due to their unique properties, including high chemical stability, good biocompatibility, controlled drug loading, and enhanced drug bioavailability, LDHs have many potential applications in the medical field. Especially in the fields of bioimaging and tumor therapy. This paper reviews the research progress of LDHs and their nanocomposites in the field of tumor imaging and therapy. First, the structure and advantages of LDH are discussed. Then, several commonly used methods for the preparation of LDH are presented, including co-precipitation, hydrothermal and ion exchange methods. Subsequently, recent advances in layered hydroxides and their nanocomposites for cancer imaging and therapy are highlighted. Finally, based on current research, we summaries the prospects and challenges of layered hydroxides and nanocomposites for cancer diagnosis and therapy.

Hybridization of layered double hydroxides with functional particles.

Layered double hydroxides (LDHs) are a class of materials with useful properties associated with their anion exchange abilities as well as redox and adsorptive properties for a wide range of applications including adsorbents, catalysts and their supports, electrodes, pigments, ceramic precursors, and drug carriers. In order to satisfy the requirements for each application as well as to find alternative applications, the preparation of LDHs with the desired composition and particle morphology and post-synthetic modification by the host-guest interactions have been examined. In addition, the hybridization of LDHs with various functional particles has been reported to design materials of modified, improved, and multiple functions. In the present article, the preparation, the heterostructure and the application of hybrids containing LDHs as the main component are overviewed.

Rapid preparation of Ni/Fe-LDH@ stainless steel mesh with interfacial emulsion breaking effect for efficient oil-in-water emulsion separation

Oil-water separation materials are particularly important for today's polluted water, especially the easy preparation of separation materials and the efficient separation of emulsions. The excellent properties of layered double hydroxide (LDH) have led to its successful application in the field of oil-water separation, but most of the existing studies have used high-temperature and long-time hydrothermal methods for the growth of LDH. Here, we present a stainless-steel mesh material for the preparation of LDH by electrochemical methods, which can be prepared in a few minutes, greatly improving the production efficiency. Adjusting the electrodeposition time of LDH can well regulate the aperture of the stainless-steel mesh to realize the sieving of emulsion droplets, in addition, the positive charge of LDH is helpful to promote the rupture of emulsion droplets and improve the emulsion separation efficiency. The separation efficiency of this rapidly prepared separation material for oil-in-water emulsions was stabilized at more than 99.3%. In addition, the preparation with low energy consumption is more in line with the concept of green development and more conducive to practical applications.

Highly atom-economic synthesis and scale-up production of zinc-aluminum layered double hydroxides

ZnAl layered double hydroxides (LDHs) has been widely applied as functional additives in polymers. The common coprecipitation method used to synthesize ZnAl LDHs has an atomic utilization of only 44.35 %, and is accompanied with the formation of sodium salt by-product, ZnO impurities and lots of waste water. In this work, we proposed a green and cost-effective synthesis route with 100 % atom economy to prepare ZnAl LDHs from mixed metal oxides and hydroxides. Pure ZnAl LDHs was synthesized at 120 °C. A dissolution-nucleation-diffusion reaction mechanism was proposed through structural and morphological studies and reaction kinetics calculations. The prepared ZnAl LDHs exhibited excellent smoke suppression properties, with a reduction in the smoke density of PVC from 705 to 340. This proposed method was successfully scaled-up and applied on a 1000 t/a industrial production line, providing a valuable opportunity for the reaction design and large-scale preparation of LDHs and other inorganic compounds.

Ternary MnFeZn layered double hydroxides as an efficient material for the electrochemical sensing of flutamide

Layered double hydroxides (LDHs) have been gaining interest in electrochemical sensors due to their ease of making and significant performances. In this work, we have developed a simple and low-cost method for the preparation of ternary LDH. The MnFeZn-LDH was prepared and initially characterized to explore its formation. Further, the glassy carbon electrode (GCE) modified with MnFeZn-LDH was employed for the electrochemical analysis of flutamide (FLA). Thus, the prepared ternary MnFeZn-LDH was prominent with better sensitivity of about 5.04 μAμM−1 cm−2 and selective over several interferants injected over the MnFeZn-LDH fabricated electrode. The limit of detection was appreciable with a linear range of 0.019–2735.79 µM about 12.9 nM. Also, other technical analyses showed good electrochemical performances as a higher rate of repeatability and reproducibility. The stability of the electrode was retained for 50 cycles and the real sample detection in river water showed significant potentiality. Thus, the as-described work evolves the better enhancement with MnFeZn-LDH towards FLA detection. The better electrocatalytic properties of the prepared LDH paves the way for its exploration in various application.

Design of Self-Supported Flexible Nanostars MFe-LDH@ Carbon Xerogel-Modified Electrode for Methanol Oxidation.

Layered double hydroxides (LDHs) have emerged as promising electrodes materials for the methanol oxidation reaction. Here, we report on the preparation of different LDHs with the hydrothermal process. The effect of the divalent cation (i.e., Ni, Co, and Zn) on the electrochemical performance of methanol oxidation was investigated. Moreover, nanocomposites of LDHs and carbon xerogels (CX) supported on nickel foam (NF) substrate were prepared to investigate the role of carbon xerogel. The results show that NiFe-LDH/CX/NF is an efficient electrocatalyst for methanol oxidation with a current density that reaches 400 mA·m−2 compared to 250 and 90 mA·cm−2 for NiFe-LDH/NF and NF, respectively. In addition, all LDH/CX/NF nanocomposites show excellent stability for methanol oxidation. A clear relationship is observed between the electrodes crystallite size and their activity to methanol oxidation. The smaller the crystallite size, the higher the current density delivered. Additionally, the presence of carbon xerogel in the nanocomposites offer 3D interconnected micro/mesopores, which facilitate both mass and electron transport.

A simple, environmentally friendly synthesis of recyclable magnetic γ-Fe2O3/Cd2+-Ni2+-Fe3+-CO32− layered double hydroxides for the removal of fluoride and cadmium ions. Adsorption capacity and the underlying mechanisms

The homogeneous precipitation assisted by fluoride ions as a complexing agent was successfully applied for the synthesis of novel, raster-shaped γ-Fe2O3/Cd2+-Ni2+-Fe3+- layered double hydroxides (LDHs) starting from NiCl2·6H2O, FeCl3·6H2O, and wastewater enriched with F− and Cd2+ ions. The material comprises large, platelet-shaped particles with uniformly dispersed γ-Fe2O3 on the LDHs surface that induce strong magnetic properties and allow easy separation during the recycling process. Moreover, large specific surface area (156 m2/g) and small band gap (2.40 eV) of γ-Fe2O3/Cd2+-Ni2+-Fe3+-CO32−LDHs indicate great potential applicability as adsorbents and photocatalysts. Based on the experimental data, the formation mechanism of γ-Fe2O3/Cd2+-Ni2+-Fe3+-CO32−LDHs was proposed. Fluoride ions form [FeF6]3− complexes with a portion of iron in the solution and reduce the amount of iron(III)-hydroxide, which increases the pH range for Fe3+ deposition. This promotes co-precipitation of Ni2+ and Cd2+ and the formation of Cd2+-Ni2+-Fe3+-CO32−LDHs at higher pH values. The presence of Cd2+ in the solution induces the transformation of Fe(OH)3 into γ-Fe2O3 particles located at the surface of the Cd2+-Ni2+-Fe3+-CO32−LDHs platelet. The main mechanism for Cd2+ removal from the aqueous solution was coprecipitation via the formation of Cd2+-Ni2+-Fe3+-CO32− LDHs. Owing to the small ionic radius of F− and the high adsorption capacity of LDHs, the fluoride ions were adsorbed between the layers of LDHs, and their concentration was effectively reduced at the desired level. This novel method for the preparation of magnetic LDHs simultaneously removes harmful ions from wastewater and improves the magnetic properties of recyclable materials, which provides a new pathway for the material preparation and application.

Investigation of Structural and Luminescent Properties of Sol-Gel-Derived Cr‑Substituted Mg3Al1-xCrx Layered Double Hydroxides.

In the present work, Cr-substituted Mg3Al1−xCrx layered double hydroxides (LDHs) were synthesised through the phase conversion of sol-gel-derived mixed-metal oxides in an aqueous medium. The chromium substitution level in the range of 1 to 25 mol% was investigated. It was demonstrated that all synthesised specimens were single-phase LDHs. The results of elemental analysis confirmed that the suggested synthetic sol-gel chemistry approach is suitable for the preparation of LDHs with a highly controllable chemical composition. The surface microstructure of sol-gel-derived Mg3Al1−xCrx LDHs does not depend on the chromium substitution level. The formation of plate-like agglomerated particles, which consist of hexagonally shaped nanocrystallites varying in size from approximately 200 to 300 nm, was observed. Optical properties of the synthesised Mg3Al1−xCrx LDHs were investigated by means of photoluminescence. All Cr-containing powders exhibited characteristic emission in the red region of the visible spectrum. The strongest emission was observed for the sample doped with 5 mol% Cr3+ ions. However, the emission intensity of samples doped with 1–10 mol% Cr3+ ions was relatively similar. A further increase in the Cr3+ ion concentration to 25 mol% resulted in severe concentration quenching.

Development of sodium alginate@ZnFe-LDHs functionalized beads: Adsorption properties and mechanistic behaviour of phosphate and nitrate ions from the aqueous environment

Phosphate and nitrate are the vital micro-nutrients and a substantial contributor to the growth of biomass, energy storage, and agricultural activities. However, in their increased concentrations, they also cause potential health problems to human and all other living beings. Layered double hydroxides (LDHs) are highly selective and efficient material for the remediation of the ions of phosphate and nitrate from water, but agglomerate easily due to their high surface properties and are difficult to recover from aqueous solutions. The preparation of LDHs functionalized beads of the biopolymeric background is an alternative to overcome these difficulties. Herein, the present work examined the adsorptive removal of the above-mentioned toxic ions from water using ZnFe-LDHs assembled alginate (ZnFe-LDHs@Alg) beads. The removal efficiency and percentage were examined along with various influencing factors like sorbent dosage, solution pH, contact time, and co-ions also carried out. ZnFe-LDHs@Alg beads revealed an extreme removal efficiency of 94.64 and 74.12 mg/g for the ions of phosphate and nitrate, respectively. The phosphate and nitrate removal by ZnFe-LDHs@Alg beads showed reliability with the Freundlich isotherms. The above findings suggested that ZnFe-LDHs@Alg beads can be used as an efficient and selective sorbent for the remediation of toxic ions from water/ wastewater. • A Facile ZnFe-LDHs@Alg beads were fabricated and used for the removal of phosphate and nitrate ions • Electrostatic interaction, ion exchange and complexation are main mechanisms. • ZnFe-LDHs@Alg beads obeyed for pseudo-second-order kinetic and Freundlich isotherm model. • Field studies were opted to analyze the performance of the ZnFe-LDHs@Alg beads

Confined Growth of NiAl-Layered Double Hydroxide Nanoparticles Within Alginate Gel: Influence on Electrochemical Properties.

NiAl Layered Double Hydroxide (LDH) alginate bionanocomposites were synthesized by confined coprecipitation within alginate beads. The NiAl based bionanocomposites were prepared either by impregnation by divalent and trivalent metal cations of pre-formed calcium cross-linked alginate beads or by using the metal cations (Ni2+, Al3+) as crosslinking cationic agents for the biopolymer network. The impregnation step was systematically followed by a soaking in NaOH solution to induce the LDH coprecipitation. Powder x-ray diffraction (PXRD), infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), thermogravimetry analysis (TGA), electron microscopies (SEM and TEM) confirmed the biotemplated coprecipitation of LDH nanoparticles ranging from 75 to 150 nm for both strategies. The drying of the LDH@alginate beads by supercritical CO2 drying process led to porous bionanocomposite aerogels when Ca2+ cross-linked alginate beads were used. Such confined preparation of NiAl LDH was extended to bionanocomposite films leading to similar results. The permeability and the electrochemical behavior of these NiAl@alginate bionanocomposites, as thin films coated on indium tin oxide (ITO) electrodes, were investigated by cyclic voltammetry, demonstrating an efficient diffusion of the K4Fe(CN)6 redox probe through the LDH@alginate based films and the improvement of the electrochemical accessibility of the Ni sites.

Granular Mg-Fe layered double hydroxide prepared using dual polymers: Insights into synergistic removal of As(III) and As(V)

Controlling the particle size and aggregation of nanosheet layers in layered double hydroxides (LDHs) is critical for their application. Herein, we report the preparation of Mg-Fe LDH through a co-precipitation method. The LDH was embedded using polyacrylamide (PAM) and polyvinyl alcohol (PVA; the LDH was designated as PAM/PVA-LDH) for As(III) and As(V) removal. We found that doping with 0.3 mL PVA (2 g L-1) and 0.4 mL (20 g L-1) PAM solution delaminated the nanosheet layers of 1 g of the LDH (PAM40/PVA30-LDH) and restructured the crystal phase from monoclinic to orthorhombic. This increased the surface area and pore volume. Furthermore, PAM40/PVA30-LDH exhibited higher affinity for As(III) and As(V) removal with maximum adsorption capacities of 14.1 and 22.8 mg g−1, respectively, compared to LDH alone with adsorption capacities of 7.1 and 7.9 mg g−1, respectively. It was found that the highest adsorption capacities of As(III) and As(V) using PAM40/PVA30-LDH occurred at pH ∼7 and pH 2.5, respectively. X-ray photoelectron spectroscopy analysis revealed that the removal of As(III) and As(V) on PAM40/PVA30-LDH was mainly attributable to ion exchange with intercalated SO42-, hydrogen bonding, and complexation mechanisms. These findings illustrate that PAM40/PVA30-LDH would be an excellent adsorbent for the remediation of arsenic-polluted wastewater.

Functionalized layered double hydroxide applied to heavy metal ions absorption: A review

Abstract The use of functional material can help mitigate the pollution by heavy metals, which presents an array of risks to human production and life. This work provides a comprehensive review of the current knowledge on functionalized layered double hydroxide (LDH) as a heavy metal absorption material, by synthesizing the information from a total of 141 relevant publications published since 2005. LDH provides a potentially highly efficient method to adsorb heavy metal ions, which is simple to prepare and of low cost. The lack of functional groups and structural components of pristine LDH, however, limits the absorption capacity and widespread applications of LDH. Through intercalation, surface modification, or loading on substrates, functional groups or structural components are introduced into the pristine LDH to prepare functionalized LDH. In this process, the hydroxyl group and the valence state of [Mg(OH)6] octahedrons play a crucial role. Functionalized LDH can be endowed with selective absorption capacity and enhanced stability and recyclability. After adsorbing heavy metal ions, functionalized LDH can be readily separated from the liquid phase. These aspects are discussed, along with the structure and composition, shape and size, and synthesis methods and research tools of LDH. This work concludes with the discussion of preparation and utilization and a look to the future in terms of identified research needs regarding the preparation, use, and recycling (or upcycling) of economical and environmental-friendly LDH.

Hydrothermal carbonization of sewage sludge and in-situ preparation of hydrochar/MgAl-layered double hydroxides composites for adsorption of Pb(II)

Hydrothermal carbonization is a novel technology for dewatering of sewage sludge. Layered double hydroxides (LDHs) are a widely used functional material, which can be prepared by hydrothermal method. In this study, we proposed a new process combining hydrothermal carbonization of sludge and in-situ preparation of LDHs. The addition of Mg and Al salts (as LDHs precursor) to the slurry before hydrothermal treatment can act as a sludge conditioner to effectively accelerate the sludge sedimentation. The obtained products hydrochar/LDHs (HL) composites with various mass ratios were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that the well-crystallized LDHs slice is thinner after combining with hydrochar. The HL products can be used as a highly effective adsorbent for removal of Pb2+ from water. The adsorption experiment results showed that the adsorption behavior of Pb2+ onto HL composites can be well expressed by a pseudo-second-order kinetic model and Langmuir isotherm with the maximum adsorption capacity of 62.441 mg/g. Ionic strength had no significant effect on the adsorption capacity. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectra indicated that the adsorption mechanisms of Pb2+ by HL composites mainly included electrostatic interaction and surface coprecipitation. Therefore, this is a cost-effective method to obtain a high efficiency adsorbent.

On Demand One-Pot Mild Preparation of Layered Double Hydroxides and Their Hybrid Forms: Advances through the Epoxide Route.

Epoxide ring opening driven alkalinization process was explored with the aim of preparing layered double hydroxide (LDH) phases on demand, at room temperature. Employing iodide as nucleophilic agent, the precipitation reaction can be driven under much lower halide concentrations. This scenario favors the selective intercalation of concomitant bulky oxo anions as nitrate or perchlorate in the LDH products, allowing for the one-pot synthesis of an LDH able to delaminate in formamide. Even large dicarboxylic acids, - O2 C-(CH2 )n -CO2 - , with n up to 8, can be quantitively intercalated within the growing LDH phase, providing a versatile one-pot route for hybrid LDHs as well. Under the mild conditions employed, governed by a continuous pH rise from a starting acid condition, a MII to M*III ratio of 2 prevails, independently from the overall cationic composition. However, after moderate hydrothermal aging LDH phases bearing a cationic ratio higher than 2 could result. The solubility of a given chloride-containing MII 2 M*III LDH can be approximated as a linear combination of the solubility of the pure hydroxylated phases of the constitutive cations, M(OH)2 and M* (OH)3 .

Preparation of Layered Double Hydroxides toward Precisely Designed Hierarchical Organization

Layered double hydroxides (LDHs) are a class of materials with useful properties associated with their anion exchange abilities for a wide range of materials’ applications including adsorbent, catalyst and its support, ceramic precursor, and drug carrier. In order to satisfy the requirements for the detailed characterization and the practical application, the preparation of LDHs with varied composition and particle morphology has been examined extensively. The versatility of the preparation methods led LDHs with varied composition and micro/macroscopic morphology, which makes the application of LDHs more realistic. In the present review article, synthetic methods of LDHs are overviewed in order to highlight the present status of the LDHs for practical application.

Synthesis, characterization and sinterability of pure and Ni-doped nano layered double hydroxides from aluminum dross

Abstract Synthesis of pure and Ni-doped nano Mg-Al layered double hydroxides (LDHs) using aluminum dross is the main goal of the present study. Moreover, the sintering of prepared LDHs to produce sintered spinel at relatively low temperature was also performed. Extraction of nano Al(OH)3 from aluminum dross was firstly conducted and the extracted hydroxide was utilized in preparation of LDHs in the presence of Mg(NO3)2.6H2O and Ni(NO3)2.6H2O. LDHs were synthesized by co-precipitation method followed by hydrothermal treatment up to 180 °C. The synthesized powders and/or suspensions were investigated by different tools such as XRD, FTIR, SEM, TEM, particle size distribution and zeta potential. The prepared LDHs were uni-axially pressed and sintered at 1500 °C.The physical properties and microstructures of sintered bodies were also investigated. The results revealed that Al(OH)3 synthesized using NaOH had lower particle size than that prepared using NaOH and HCl. The optimum hydrothermal temperature at which LDHs completely formed was 180 °C. Both Al(OH)3 and LDH were successfully prepared in the nano range. The sintering of nano LDHs led to production of sintered spinel with improved properties at relatively lower temperature (1500 °C). The developed microstructure was composed of nano grains agglomerated together forming micro-sized grains.

Preparation of Layered Double Hydroxides with Different Divalent Metals for the Adsorption of Methyl Orange Dye from Aqueous Solutions

Preparation of Layered Double Hydroxides with Different Divalent Metals for the Adsorption of Methyl Orange Dye from Aqueous Solutions

Evaluation of ultraviolet aging resistance of bitumen containing different organic layered double hydroxides

Layered double hydroxides (LDHs) have been alternatively employed to improve the ultraviolet (UV) aging resistance of bitumen due to their high UV reflectance, but LDHs particles cannot be dispersed into bitumen uniformly and stably since their poor compatibility with bitumen. Therefore, the problem of poor compatibility must be solved before its application. Generally, organic modification can change the surface characteristics of inorganic particle and then improve the compatibility. The objectives of this work are to evaluate the effect of prepared various organic LDHs on the anti-UV aging property of bitumen and then determine an optimal organic LDHs for bitumen modification. For these purposes, three organic anions, sodium dodecyl benzenesulfonate (SDBS), sodium dodecyl sulfate (SDS) and sodium dodecyl sulfonate (SDSO), were used as organic modifiers to prepare organic LDHs (OCLDHs), then the storage stability and anti-UV aging of OCLDHs modified bitumen were investigated. Experimental results show the organic modification can suppress the separation phenomenon of OCLDHs modified bitumen during the high temperature storage, indicating the compatibility and stability of the mixture is ameliorated. Compared with LDHs modified bitumen, OCLDHs modified bitumens show lower aging degree during UV exposure, which indicates that OCLDHs exhibit better effect in enhancing the anti-UV aging performance of bitumen. FTIR analysis indicates that OCLDHs effectively retard the formations of oxygen-containing functional groups and aromatic structure of bitumen. Furthermore, SDBS is a preferable modifier for the preparation of organic LDHs due to the most effective improvement in compatibility with bitumen and UV aging resistance of bitumen as compared with SDS and SDSO.

Anticorrosion Performance of LDH Coating Prepared by CO2 Pressurization Method

Many surface treatment methods are used to improve the corrosion resistance of magnesium alloys. LDH (layered double hydroxides) conversion coatings are currently found in the most environmentally friendly and pollution-free coatings of magnesium alloy. In this study, the CO2 pressurization method was applied to the preparation of LDH coating on magnesium alloy for the first time. The effect of CO2 pressurization on the formation and corrosion resistance of LDH coating on AZ91D alloy was investigated. The hardness and adhesion were significantly higher on LDH coating in the case of CO2 pressurization than it is in atmospheric pressure. The surface and cross-sectional morphologies show that LDH coating is more compact in the case of CO2 pressurization than with atmospheric pressure. The results of the polarization curve, hydrogen evolution, and immersion tests indicate that the corrosion resistance of the LDH coating prepared by the CO2 pressurization method was significantly improved.