Structure Of Layered Double Hydroxides Research Articles

Construction of 3D Ni2+-Al3+-LDH/γ-Fe2O3-Cd2+-Ni2+-Fe3+-LDH structures and multistage recycling treatment of dye and fluoride-containing wastewater

The construction of three-dimensional (3D) Ni2+-Al3+-LDH/γ-Fe2O3-Cd2+-Ni2+-Fe3+-layered double hydroxide (LDH) structures (S1–S6) with magnetic properties and different (γ-Fe2O3-Cd2+-Ni2+-Fe3+-LDH)/(Ni2+-Al3+-LDH) ratios were successfully prepared. The effects of these ratios in these 3D LDH constructions on physicochemical properties were investigated using XRD, SEM, VSM, UV–vis, and BET analyses. The specific surface area and band gap of these materials decreased with increased ratio, while the saturation magnetization increased. The synergistic combination of saturation magnetization, adsorption characteristics, and band gap of six sample types were evaluated. S3 samples were used in a multistage recycling treatment study of dye wastewater and fluoride ion (F−)-containing wastewater, effectively degrading methyl orange (MO) due to its high photocatalytic activity. After this, the memory effect of the calcined product (S3, 300 °C) significantly enhanced the migration and diffusion of F−, resulting in a F− adsorption capacity of 49.25 mg/g. The recycling properties of this composite material for photocatalytic degradation and adsorption capabilities for F− removal were evaluated, showing a reduction in efficiency of only 1 % and 8.6 % for degradation of MO and F− removal respectively, with no significant loss of efficiency after 10 cycles. Adsorption experiments and subsequent sample characterization showed that the F− adsorption mechanism of S3 involved ion exchange mechanism and sorption sites (interlayer, basal, edges and junction sites). The existence of oxygen vacancies and formation of S-scheme heterojunction between γ-Fe2O3-Cd2+-Ni2+-Fe3+-LDH and Ni2+-Al3+-LDH, resulted in the improvement of the photocatalytic activity. The results obtained in this study demonstrated that Ni2+-Al3+-LDH/γ-Fe2O3-Cd2+-Ni2+-Fe3+-LDH composites were a promising adsorbent for degradation of MO and F− removal in practical multilevel utilization due to its simple synthesis, low-cost, recyclability, and high removal capability.

Vital Role of Synthesis Temperature in Co–Cu Layered Hydroxides and Their Fenton-like Activity for RhB Degradation

Cu and Co have shown superior catalytic performance to other transitional elements, and layered double hydroxides (LDHs) have presented advantages over other heterogeneous Fenton catalysts. However, there have been few studies about Co–Cu LDHs as catalysts for organic degradation via the Fenton reaction. Here, we prepared a series of Co–Cu LDH catalysts by a co-precipitation method under different synthesis temperatures and set Rhodamine B (RhB) as the target compound. The structure-performance relationship and the influence of reaction parameters were explored. A study of the Fenton-like reaction was conducted over Co–Cu layered hydroxide catalysts, and the variation of synthesis temperature greatly influenced their Fenton-like catalytic performance. The Co–Cut=65°C catalyst with the strongest LDH structure showed the highest RhB removal efficiency (99.3% within 30 min). The change of synthesis temperature induced bulk-phase transformation, structural distortion, and metal–oxygen (M–O) modification. An appropriate temperature improved LDH formation with defect sites and lengthened M–O bonds. Co–Cu LDH catalysts with a higher concentration of defect sites promoted surface hydroxide formation for H2O2 adsorption. These oxygen vacancies (Ovs) promoted electron transfer and H2O2 dissociation. Thus, the Co–Cu LDH catalyst is an attractive alternative organic pollutants treatment.

Corrosion-Engineered Morphology and Crystal Structure Regulation toward Fe-Based Efficient Oxygen Evolution Electrodes.

The rational regulation of catalysts with a well-controlled morphology and crystal structure has been demonstrated effective for optimizing the electrochemical performance. Herein, corrosion engineering was employed for the straightforward preparation of FeAl layered double hydroxide (LDH) nanosheets and Fe3O4 nanooctahedrons via the feasible modification of dealloying conditions. The FeAl-LDH nanosheets display an excellent catalytic performance for oxygen evolution reactions in 1 M KOH solution, such as low overpotentials (333 mV on glass carbon electrode and 284 mV on Ni foam at 10 mA cm−2), a small Tafel slope (36 mV dec−1), and excellent durability (24 h endurance without deactivation). The distinguished catalytic features of the FeAl-LDH nanosheets comes from the Al and Fe synergies, oxygen vacancies, and well-defined two-dimensional (2D) layered LDH structure.

Enhanced ethylene glycol (EG)-blocking property of cation exchange membrane by layered double hydroxides modification for electrodialysis-based reclamation of EG waste fluid

Recycling toxic ethylene glycol (EG) solutions, which act as an inhibitor in the process of deep water gas fields exploitation activities, is an indispensable procedure for saving economic costs and avoid potential environmental hazards. In the recovery process, electrodialysis (ED) is an alternative technology for removing salts from high-saline EG wastewater caused by seawater infiltration. To further reduce the leakage transport of EG during ED desalination, a cation exchange membrane (CEM) layer facing the dilute cell was fabricated by electrodepositing layered double hydroxides (LDHs). Introduction of a LDH-modified layer enabled CEMs to have better EG-blocking properties without affecting cation transport, which was due to dense and hydrophilic transport channels formed by the two-dimensional (2D) lamellar structure of LDHs. This further led to differences in migration rates between hydrated cations and EG molecules. The results of ED desalination tests showed that these modified CEMs reduced the EG leakage content by 81 and 46%, compared with commercial CEMs in high-saline EG solution, with EG content of 20 and 60 wt%, respectively. Therefore, this study provided new insight for the application of CEMs based on LDHs surface modification in the special ED field of EG solution desalination.

Experimental and Theoretical Studies on the Intercalation of Naproxen into the Mg2Al and Zn2Al Layered Double Hydroxides by Ion Exchange Reaction

In this work, Layered Double Hydroxide (LDH) materials carrying the worldwide administered non-steroidal anti-inflammatory drug naproxen (NAP), and the sodium naproxenate salt (NaNAP) for comparison, were studied by computational approaches aiming to model the structure of hybrid LDH-drug and shed light on NAP intercalation process. Atomic modeling calculations were performed at the quantum mechanical level based on Density Functional Theory and classical force fields based on empirical interatomic potentials. LDHNAP materials were prepared by ion exchange reaction from Mg2Al(OH)6Cl and Zn2Al(OH)6Cl pristine phases. The characterization of the materials confirmed NAP intercalation and also the permanence of the pristine phases in the isolated materials after ion exchange. Crystallographic lattice parameters, elemental analysis, and TGA experimental results were then employed in the calculations, which revealed that NAP anions can completely neutralize the positive charge of the LDH layers: both Mg2Al and Zn2Al LDH structures could be optimized with all Cl− anions substituted by NAP. The drug assumed different dispositions in the NaNAP crystal or when intercalated into LDH. Additionally, infrared wavenumbers calculations agreed with the experimental results and showed useful to support LDHNAP bands assignment. The employed theoretical models to represent the structure of LDHNAP systems are expected to assist the interpretation of future experimental results and to be used as auxiliary tools to tune properties of LDH-drug pharmaceutical formulations.

Comprehension of the Route for the Synthesis of Co/Fe LDHs via the Method of Coprecipitation with Varying pH.

Co/Fe-based layered double hydroxides (LDHs) are among the most promising materials for electrochemical applications, particularly in the development of energy storage devices, such as electrochemical capacitors. They have also been demonstrated to function as energy conversion catalysts in photoelectrochemical applications for CO2 conversion into valuable chemicals. Understanding the formation mechanisms of such compounds is therefore of prime interest for further controlling the chemical composition, structure, morphology, and/or reactivity of synthesized materials. In this study, a combination of X-ray diffraction, vibrational and absorption spectroscopies, as well as physical and chemical analyses were used to provide deep insight into the coprecipitation formation mechanisms of Co/Fe-based LDHs under high supersaturation conditions. This procedure consists of adding an alkaline aqueous solution (2.80 M NaOH and 0.78 M Na2CO3) into a cationic solution (0.15 M CoII and 0.05 M FeIII) and varying the pH until the desired pH value is reached. Beginning at pH 2, pH increases induce precipitation of FeIII as ferrihydrite, which is the pristine reactional intermediate. From pH > 2, CoII sorption on ferrihydrite promotes a redox reaction between FeIII of ferrihydrite and the sorbed CoII. The crystallinity of the poorly crystalized ferrihydrite progressively decreases with increasing pH. The combination of such a phenomenon with the hydrolysis of both the sorbed CoIII and free CoII generates pristine hydroxylated FeII/CoIII LDHs at pH 7. Above pH 7, free CoII hydrolysis proceeds, which is responsible for the local dissolution of pristine LDHs and their reprecipitation and then 3D organization into CoII4FeII2CoIII2 LDHs. The progressive incorporation of CoII into the LDH structure is accountable for two phenomena: decreased coulombic attraction between the positive surface-charge sites and the interlayer anions and, concomitantly, the relative redox potential evolution of the redox species, such as when FeII is re-oxidized to FeIII, while CoIII is re-reduced to CoII, returning to a CoII6FeIII2 LDH. The nature of the interlamellar species (OH−, HCO3−, CO32− and NO3−) depends on their mobility and the speciation of anions in response to changing pH.

Hydroxyapatite film prepared by hydrothermal method on layered double hydroxides coated Mg Alloy and its corrosion resistance

Hydroxyapatite (HA) bioactive film is a standard surface modification method for biodegradable Mg alloys. However, the corrosion resistance of HA film prepared before was mediocre, and the preparation process was complicated. In this study, hydroxyapatite film was prepared for the first time on layered double hydroxides (LDHs) coated Mg alloy by hydrothermal method. The structure and composition of LDHs and HA films were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The corrosion resistance and immersion behavior of the films in simulated body fluid (SBF) were investigated by using potentiodynamic polarization curve, electrochemical impedance spectroscopy (EIS) techniques. The effects of different pH and calcium to phosphorus molar ratios (Ca/P ratios) of HA hydrothermal solution were investigated. The experimental results show that HA films appear in petal-like, filamentous and flower-like. The corrosion resistance of the film first increases and then decreases with the pH from weak acid to alkaline. With the increase of the Ca/P ratio, the film is gradually denser, and the protective effect is enhanced. The immersion test results show that after 7 days of immersion, the impedance modulus of the composite film is about 5 × 103 Ω·cm2, which is ten times higher than the single LDHs film. The effects of the pH and Ca/P ratio of the HA hydrothermal solution on the preparation of HA film are simply explained by thermodynamic theory. The Mg-LDHs-HA composite film provide a corrosion protection barrier for Mg substrate and HA film is biologically active. The barrier effect and the mineralization behavior provide a better corrosion protection for Mg substrate.

Cold sintering yields first layered double hydroxides (LDH) monolithic materials

Layered double hydroxides (LDHs) are key inorganic compounds relevant to a wealth of applicative purposes, by exploiting their layered structure allowing for ion/molecular sequestration or release. However, a technological barrier exists in the fabrication of cohesive LDH monoliths in link with their metastability. In this work, a series of cohesive monoliths of different LDH ionic compositions and structures (namely hydrotalcite, pyroaurite and hydrocalumite) were successfully obtained for the first time, using cold sintering via spark plasma sintering (SPS) at 130 °C. Thanks to the low temperature involved in this non-conventional consolidation approach, the structure and chemical stability of the LDHs are preserved and allow preparing densified LDH scaffolds with internal cohesion, as evidenced by densification rates often above 80 %, SEM microstructural observations and mechanical testing assessments, mainly due to a better alignment of adjacent layered particles. By way of water vapor sorption measurements, we demonstrate that the interfacial/interlayer spaces of the LDH structure remain accessible after cold sintering. Also, the porous network of the monoliths and related access to interfacial surface are shown to be tunable by adding a leachable pore-forming agent such as SiO2 beads. Possible sintering mechanisms are discussed by complementary experiments-simulations coupling, unveiling the role of LDH composition as in the case of Cl-bearing LDH. By overcoming the challenge of monolith fabrication out of LDH compounds, applications are expected to benefit from these findings, as in electronics, energy storage, catalysis, biomaterials and depollution.

Layered Double Hydroxides Containing Rare Earth Cations: Synthesis and Applications

In this mini-review, we describe the currently available literature concerning synthesis and applications of layered double hydroxides (LDHs) containing rare earth cations (RE-LDHs), focusing on the catalytic activity of those compounds. The lack of studies of some rare earth elements (REE) and the insufficient knowledge of their catalytic activity in the structure of LDHs indicate the need for further research.

Simultaneous removal of cesium and iodate using prussian blue functionalized CoCr layered double hydroxide (PB-LDH)

Radioactive cesium and iodine have become an emerging issue because these radionuclides have high radiotoxicity and solubility, and they can easily transport to the surrounding environment. Prussian blue, known as metal hexacyanoferrate compound, has a cubic face-centered structure and similar ionic size to Cs+, known to be used for Cs+ removal. In addition, layered double hydroxides (LDHs) have anion exchange properties and become the promising sorbents of iodine. In this study, based on the advantages of both Prussian blue (PB) and layered double hydroxide (LDH), Prussian blue functionalized layered double hydroxide (PB-LDH) was synthesized to concurrently remove both Cs+ and IO3− from radioactive solutions. During the synthesis of PB-LDH, Fe(CN)64− does not intercalate into the LDH structure, but aggregates on the LDH surface according to electrostatic force and ion-specific effects and forms the PB on the surface of LDH. The synthesized PB-LDH simultaneously removed 32 mg/g of Cs+ and 91 mg/g of IO3− from the mixed waste solutions. The main removal mechanism of Cs+ was redox coupled alkali metal ion transport to form Cs4Co4FeⅡ3(CN)18 species at the surface of PB-LDH. However, IO3− was mainly removed by ion exchange with intercalated Cl− in addition to the redox effect of Co ions.

Bimetallic NiFe hydroxide coated onto commercial graphite foil as efficient supercapacitor electrode

Attaining high specific energy meanwhile detaining the specific power achieved, is a significant challenge faced in modern era supercapacitors. Coupling two highly electroactive metal ions together in an array, holds sanguinity to attain high energy and power proficiencies. Ni(OH)2 being an economical battery-grade electrode material, has respectable charge-storage competence, but suffers from sluggish ion mobility. Benefitting from the lamellar structure and easy tunability of layered double hydroxide (LDH), swifter ion/electron mobility and improved conductivity is achievable. Herein this work, conductive iron (Fe) species incorporated with nickel hydroxide matrix to form LDH structure through facile coprecipitation strategy is proposed. The upshot of varying nickel iron ratio on the structural, functional, morphology and electrochemical characteristics is inspected. The best composition had an admirable specific capacity of 381 C g−1 (1368 F g−1) at 1 A g−1 with an ability to retain 87.5% of the initial capacity even after 5000 successive charge-discharge cycles. The symmetric supercapacitor developed using the optimal NiFe LDH over commercial graphite foil, furnishes a specific energy of 66.13 W h kg−1 at specific power 1483 W kg−1. Moreover, the corrosion and radiation inertness of commercial graphite foil, widens the scope of utilization of the fabricated supercapacitor.

Reconstruction and intercalating anion exchange of ZnAl-layered double hydroxide

Layered double hydroxides (LDHs) have recently attracted considerable attention as a promising multi-functional material due to their controllable properties depending on the type and composition ratio of metal cations and interlayer anions. Despite active research on controlling the composition to improve the properties of LDHs, anion intercalation techniques capable of obtaining the desired morphologies of LDHs have rarely been investigated. Herein, we report the anion exchange of ZnAl-LDHs grown on a silicon substrate using a post-treatment-based reconstruction process. Structural and chemical investigations verified that the calcined ZnAl-LDH was reconstructed by a NaCl solution during the anion exchange process. The anion exchange rate and the reconstructed fraction of the ZnAl-LDH increased as the NaCl concentration increased from 0.15 M to 0.60 M, though they decreased when the NaCl concentration exceeded 0.90 M. Therefore, the anion composition and morphology of the ZnAl-LDHs could be modulated by controlling the NaCl concentration during the reconstruction process. These results provide important information about the probability of controlling the structure and composition of LDHs intercalated with desired anions for a wide variety of device applications, such as memory, sensor, and energy storage.

Aqueous solubility of Zn incorporated into Mg-Al-layered double hydroxides

Hydrotalcite minerals are layered double hydroxides (LDH) which play an important role in immobilizing hazardous compounds to decontaminate industrial wastewaters. The stability of an LDH is mostly evaluated in terms of its low solubility in water. However, the solubility of divalent trace metals immobilized by Mg-Al-type LDHs is not well known. Hydrotalcites containing Zn in solid solution, (Mg+Zn)3-Al-LDH, were synthesized by alkaline co-precipitation. A series of eleven LDH phases with Zn mole fractions XZn = Zn/(Mg+Zn) of 0–1 were characterized by powder X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry (TGA), scanning and transmission electron microscopy (SEM/TEM), Brunauer-Emmett-Teller (BET) surface area analysis, and inductively coupled plasma mass (ICP-MS) spectrometry. The XRD analysis provided sharp characteristic spacings for d003 and d006 which occurred for all samples, confirming a layered LDH structure. Cell parameters (a, c) obeyed Vegard’s law and confirmed the formation of a regular solid-solution series without a mixing gap. An aqueous equilibrium time was determined by kinetic dissolution experiments. Steady-state solubility occurred after 120 days, but the experiments continued up to 240 days. The XRD and SEM/TEM analyses indicated no phase changes during the long-term dissolution experiments; neither were phase impurities detected after 240 days. The solubility products of the Mg- and Zn-bearing endmember compositions were calculated from experimentally determined total cation and anion concentrations using the Visual Minteq code for considering element speciation and ion pairing. The solubility product decreased as the Zn mole fraction increased, suggesting that the Zn-bearing LDH phases were more stable than the pure Mg3-Al-LDHs. Solid-solution aqueous-solution thermodynamic equilibrium modeling using the Lippmann “total solubility product” approach and applying Lippmann diagrams with logarithmic x-axes revealed a log-linear decrease in aqueous Zn solubility. The results are promising for remediation of metal-bearing liquid wastes because the metals that co-precipitated with the LDH were more strongly retained and, therefore, less soluble than the hydroxides or carbonates of the trace metal.

NiO and Co1.29Ni1.71O4 derived from NiCo LDH form S-scheme heterojunction for efficient photocatalytic hydrogen evolution

NiO and Co1.29Ni1.71O4 were generated in situ by oxidizing and calcining NiCo LDH (Layered Double Hydroxide) to erect an S-scheme heterojunction heterogeneous catalyst. After calcination, the lamellar structure of NiCo LDH becomes thinner and part of the lamellar porous, which can provide more active sites for hydrogen precipitation reaction. The amount of hydrogen released by the composite catalyst is 3 times that of NiCo LDH This in-situ generation method will allow NiO and Co1.29Ni1.71O4 to establish a close relationship, form a built-in electric field, and build an S-scheme heterojunction. NiO and Co1.29Ni1.71O4 have good band structure and band gap position matching. S-scheme heterojunction composite catalyst has the best light absorption intensity and photocurrent response, the smallest electronic impedance, and good electron and hole separation efficiency, thereby improving the performance of photocatalytic hydrogen evolution. It was confirmed by a large number of characterization studies.

New insights into interface charge-transfer mechanism of copper-iron layered double hydroxide cathodic electrocatalyst in alkaline electrolysis

Transition metal layered hydroxides are potential catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction in alkaline electrolysis (AE). Recent researches focused on NiFe layered double hydroxide (LDH) as efficient, cost-effective electrocatalyst due to the proton and hydroxide adsorption kinetics by Ni and Fe. However, Cu has been known to exhibit higher adsorption of the proton, thus by replacing Ni with Cu in NiFe LDH shows potential for enhancing the chemical kinetics of HER due to filled d-orbitals and electron transfer. Here, we first demonstrate a strategy of modulating the electronic structure of CuFe LDH, by manipulating Cu/Fe ratio and nanostructure, to improve the HER catalysis of single layer and cost-effective transition metal LDHs in AE. The atomic allocations of Cu and Fe based on the proposed method in the synthesis of LDH allows for optimizing the proton and hydroxide adsorption during electrocatalysis, where the CuFe LDH generate a current density of − 10 mA cm-2 at the overpotential of − 110 mV and a highly enhanced electrolysis stability at − 100 mA cm-2. Meanwhile, a low overpotential of 257 mV (10 mA cm-2) is achieved. Advanced spectroscopic characterizations, including X-ray photoelectron spectroscopy, confirms the electronic structure modulation with adjustment of Cu/Fe ratio; and the synchrotron sourced X-ray absorption spectroscopy unambiguously confirm the higher electron density of Cu and the unique M-O(H)-M’ structure that enhances water splitting by facilitating ion adsorption and electron transfer. The cathodic activation energy of 14.34 kJ mol-1 is achieved by higher electronic density due to electronic modulation of the catalyst structure. This work demonstrates the insights of electronic structure modulation for the rational design of efficient catalysts without noble or rare-earth metals for HER.

Construction of nitrogen-doped graphene quantum dot embedded NiGa layered double hydroxide for high-performance asymmetric supercapacitors

Layered double hydroxides (LDHs) are a promising positive electrode material for super-capacitors (SCs) due to multiple oxidation reduction states. However, the structure of LDH is prone to collapse during the redox reaction and has low conductivity, which further hinders the improvement of capacity performance. Here in, nitrogen-doped graphene quantum dot (N-GQD) is assembled on nickel gallium layered double hydroxide (NiGa-LDH) derived from two-dimension nickel metal organic frameworks (Ni-MOF) on nickel foam (NF) to prepare stable interlaced nano-sheets hybrid structures. As a result of the above synergies, the NiGa-LDH/N-GQD/NF electrode has a high specific capacitance of 2160 F g−1 at 1 A g−1 and good cycling stability with a capacity retention rate of 87.5% in 5000 cycles. In addition, we also make ASC device using NiGa-LDH/N-GQD/NF and Carbon NSs as positive/negative electrodes. The energy density of the assembled ASC device is 78.8 Wh kg−1 at power density of 1432.7 W kg−1, while the capacitance retention after 8000 cycles reaches 81.2%. Meanwhile, individually assembled ASC device can power multiple LEDs in parallel. This work provides an effective way to construct new electrode materials with high energy storage density, good cycling performance and power density by assembling quantum dots into LDH nano-sheets derived from MOF through reasonable design.

Reconstruction of the ZnAl Mixed Oxides Into the Layered Double Hydroxide Catalysts Active in the Aldol Condensation of Furfural: The Role of ZnO Particles.

A memory effect is the ability to restore the original, lamellar layered double hydroxide structure. Herein, we have described 1) the changes in the structural and basic properties of ZnAl mixed oxides during their transformation into ZnAl-reconstructed LDHs (RE-LDHs); 2) the extraordinary properties of ZnAl RE-LDHs compared to the original ZnAl LDHs; and 3) the changes of basic properties during the interaction of ZnAl RE-LDHs with atmospheric CO2. Aldol condensation was selected as probe reaction to prove the catalytic potential of ZnAl RE-LDHs. We have described a target method for preparing ZnAl RE-LDHs with a large number of basic sites. ZnAl RE-LDHs possess significantly higher furfural conversion in the aldol condensation of furfural than MOs. The structural, textural, and basic properties of the studied materials were described by temperature-programmed analysis, X-ray diffraction, N2 adsorption, temperature-programmed desorption of CO2, and in-situ diffuse reflectance spectroscopy.

Synthesis and characterisation of layered double hydroxides with varying divalent metal cations: Mg2+, Zn2+, Ca2+

This study aims to investigate the physicochemical properties of layered double hydroxides (LDH) with different divalent metal (M2+) cations. A series of nitrate-based LDH materials was synthesised by using aluminium (Al3+) as a trivalent cation (M3+) with varying M2+ cations such as magnesium (Mg2+), zinc (Zn2+), and calcium (Ca2+) ions to prepare magnesium–aluminium-layered double hydroxide (MgAl-LDH), zinc–aluminium-layered double hydroxide (ZnAl-LDH), and calcium–aluminium-layered double hydroxide (CaAl-LDH), respectively. MgAl-LDH and ZnAl-LDH were synthesised by the co-precipitation method, whereas CaAl-LDH was prepared by the hydrothermal method. The samples were characterised by powder X-ray diffraction (PXRD), Fourier transform infrared spectra (FTIR), thermogravimetric and differential thermogravimetric analysis (TGA/DTG), field emission scanning electron microscope (FESEM), and accelerated surface area and porosity (ASAP) analysis. The PXRD patterns show that MgAl-LDH (9.8 Å) had the greatest interlayer spacing, followed by ZnAl-LDH (8.9 Å), and CaAl-LDH (8.7 Å). The FTIR spectra clearly confirms the presence of nitrate ions in the LDH structure. Two-step degradation behaviour of the samples was observed in the TGA curve. The LDHs exhibit Type IV isotherms and hexagonal structures were observed on the FESEM images.

Creation of Highly Reducible CuO Species by High-Temperature Calcination of a Cu-Al Layered Double Hydroxide: Selective Hydrogenation of Furfural into Furfuryl Alcohol with Formic Acid

Abstract Highly reducible CuO species were created by the calcination of a Cu-Al layered double hydroxide (CuAl LDH) at 1073 K under air. After this heat treatment, the original layered double hydroxide structure was completely transformed into CuO and CuAl2O4 phases. The synthesized calcined CuAl LDH (calc-CuAl LDH) promoted the catalytic hydrogenation of furfural (FALD) into furfuryl alcohol (FOL) with formic acid (FA) as a hydrogen donor. In the initial stage of the above catalytic reaction, the CuO species in the calc-CuAl LDH matrix transformed into active Cu0 species via the formation of a Cu(HCOO)2-1,4-dioxane complex in the liquid phase. The spent catalyst was also reusable without loss of its high catalytic performance.

Preparation and Flame Retardant Properties of Calcium-Aluminium Hydrotalcite with Root Cutting Silicate Layers as Bamboo Flame Retardants.

Bamboo has been widely used in architecture, decoration and other fields because of its advantages of short growth period, high strength and degradability. However, bamboo, as a combustible material like wood, are easy to burn and cause building fires. However, the existing bamboo water-based flame retardants have some shortcomings, such as strong hygroscopicity and easy loss, which limits the application of bamboo products. In order to improve the flame retardant performance of bamboo, CaAl-SiO2 layered double hydroxide (LDH) as bamboo flame retardant was synthesised by coprecipitation method. The influence of preparation technology on CaAl–SiO3–LDH structures and properties as well as the flame retardant and smoke suppression characteristics of flame retardant-treated bamboo was discussed. The results revealed that the crystallisation temperature, crystallisation time and crystallisation concentration of CaAl–SiO3–LDHs considerably affected its structure and properties. The optimum technological parameters for preparing CaAl–SiO3–LDHs by using the coprecipitation method are as follows: crystallisation temperature of 100 °C, crystallisation time of 9 h and Ca2+ solution molar concentration of 0.33 mol/L. Compared with nonflame-retardant wood, CaAl–SiO3–LDH flame retardant treatment delayed the peak time of the heat release rate by 20 s and the ignition time by 77.78% and increased the carbon residue rate by 9.54%. This study can provide reference for the research of new flame retardant for bamboo products.