Layered Double Hydroxide Compounds Research Articles

Construction of CuNiAl-LDHs electrocatalyst with rich-Cu+ and —OH for highly selective reduction of CO2 to methanol

In this work, a high-performance CuNiAl-LDHs catalyst was innovatively synthesized for electrochemical carbon dioxide reduction (CO2RR) of methanol (CH3OH) through the modulated synthesis of Cu-based layered double hydroxide (LDHs). It was found that the optimal CuNiAl-LDHs has superior CH3OH selectivity compared to CuAl-LDHs and CuMgAl-LDHs, with the Faraday efficiency (FE) of 76.4% for CH3OH generation at −1.2 V. And their FE and current density (4.8 mA·cm−2) remained stable during up to 24 h of electrolysis. Meanwhile, this study confirms the significant performance advantages of CuNiAl-LDHs over their derived composite oxides. Series characterization further proves that the excellent catalytic performance of CuNiAl-LDHs is importantly associated with their richness in Cu+ and hydroxyl group (—OH). The research expands the application fields of LDHs compounds. Meanwhile, the series of discoveries provide a new insight for the preparation of CH3OH by constructing CO2RR.

Computational atomic‐scale design and experimental verification for layered double hydroxide as an efficient alkaline oxygen evolution reaction catalyst

Electrochemical water splitting is one of the most efficient techniques to produce hydrogen in an environmentally friendly way. However, a sluggish anodic reaction, namely oxygen evolution reaction (OER), requires the use of an efficient electrocatalyst for achieving economic hydrogen production. Transition-metal-based layered double hydroxides (LDHs) are promising electrocatalysts for reducing the overpotential of OER in alkaline electrolyte, which is essential for efficient water electrolysis. Nickel-iron-based LDHs (Ni-Fe LDH) have been regarded as the best OER electrocatalysts under alkaline conditions. Hence, a number of research studies have been conducted on further improving the electrocatalytic performance of Ni-Fe LDH. Although the chemical blending of other transition metals with Ni-Fe-LDH is a simple and reliable strategy to enhance the OER activity of Ni-Fe-LDH, a systematic investigation on designing Ni-Fe-LDH with different additional elements is still lacking. In addition, the design of multi-metallic LDH compound via only experimental method is very costly and time-consuming process. In this study, atomic-scale computational and experimental studies are performed to design OER electrocatalysts including unary, binary, and ternary LDH compounds consisting of Ni, Fe, Al, and Co. Density functional theory calculations predict that Ni-Fe-Co ternary LDH can lead to the lowest overpotential for alkaline OER among various computationally modeled LDH systems. Further, experimental verifications successfully demonstrate the computational prediction wherein Ni-Fe-Co-LDH exhibits superior catalytic performance compared with Ni-Fe-LDH and benchmark IrO2 catalysts.

Stability Trends in Mono-Metallic 3d Layered Double Hydroxides.

Layered double hydroxides (LDHs) constitute a unique group of 2D materials that can deliver exceptional catalytic, optical, and electronic performance. However, they usually suffer from low stability compared to their oxide counterparts. Using density functional calculations, we quantitatively demonstrate the crucial impact of the intercalants (i.e., water, lactate, and carbonate) on the stability of a series of common LDHs based on Mn, Fe, and Co. We found that intercalation with the singly charged lactate results in higher stability in all these LDH compounds, compared to neutral water and doubly charged carbonate. Furthermore, we show that the dispersion effect aids the stability of these LDH compounds. This investigation reveals that certain intercalants enhance LDH stability and alter the bandgap favourably.

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.

Retention of Iodide and Chloride by Formation of a Green Rust Solid Solution GR-Cl1-xIx: A Multiscale Approach.

The uptake of iodide and chloride during the synthesis of green rust (GR), the Fe endmember of the layered double hydroxide (LDH) group, was investigated. GR compounds were prepared by aerial oxidation of Fe(OH)2 in suspension, considering various I/Cl ratios at constant ionic strength. Only GR compounds formed in all experiments, and the associated I/Cl ratio increased with that of the starting suspension. No preferential uptake of any halide could be detected, and all compounds had comparable morphology. Furthermore, the height of the interlayer gallery increased with the I/Cl ratio from ∼7.7 Å for the chloride endmember to ∼8.3 Å for the iodide endmember, and the observed linear increase was attributed to increasing interlayer iodide content. In all compounds, Fe K-edge X-ray absorption spectroscopy evidenced the presence of sixfold coordinated iron with a Fe2+/Fe3+ ratio of 3, homogeneously distributed within flattened octahedral sites, with six Fe as next-nearest neighbors. The Fe short-range environment was not affected by the interlayer composition, and no halide from the interlayer could be detected. Furthermore, iodide and chloride anions are located in a water-like environment, being loosely bound by weak electrostatic interactions to the octahedral sheet likely above ferric iron. Results consistently hint at the formation of a solid solution between chloride and iodide GR endmembers, certainly facilitated by the crystallization of both compounds in the same space group. This study provides further insights into the ability of LDH to simultaneously accommodate several anionic species of various sizes. The formation of such LDH compounds in a deep geological repository for nuclear waste thus represents a possible retention barrier to the migration to the far field of anionic species like 36Cl- and 129I- mobilized from the waste matrix. The extent of retention in disposal sites will depend, among others, on the availability of GR and on the concentration of competing anions.

A sustainable approach to fabricate new 1D and 2D nanomaterials from natural abundant palygorskite clay for antibacterial and adsorption

It is always highly desirable to synthesize functional nanomaterials using cheap, naturally abundant clay deposits as starting materials, but the major challenge is lack of new way to utilize all of components in clay deposits and minimize the generation of waste. In order to resolve the problem, we proposed a “split” and “reconstruct” strategy to tailor palygorskite (Pal) clay deposits, and used each component to synthesizing three new nanomaterials with different morphologies and functions: copper silicate nanotube (CuSiO3), silica nanotube@Cu nanoparticles (SiO2-NT@Cu), and Mg-Al-Fe layered double hydroxide (LDH). The Pal clay deposits were first subjected to an acid bleaching process to obtain silica nanorods and solution rich in Mg(II), Al(II), Fe(III) ions. The silica as a Si source may react with Cu(II) to form CuSiO3 nanotube, which was allowed to be in-situ reduced in vapor or liquid phase to produce coral-like SiO2-NT@Cu nanocomposite with well-distributed Cu nanoparticles (CuNPs). The solution rich in Mg(II), Al(II), Fe(III) was used to synthesize Mg-Al-Fe LDH nanosheets by a simple co-precipitation process. It was confirmed that the tubular SiO2-NT@Cu nanocomposite can inhibit effectively the growth of E. coli and S. aureus, with the minimal inhibitory concentration (MIC) of 2.0 mg/mL and 0.6 mg/mL, respectively. The 2D nanolayered LDH compounds can capture efficiently and selectively anionic dye Congo Red (CR) with a maximum adsorption capacity of 254.14 ± 7.72 mg/g, due to an ion exchange and electrostatic attraction mechanism. This work provides a universal, cost-efficient and sustainable way to utilize all of components in low-grade natural clay deposits to synthesize useful nanomaterials with special functions, and also opens a new avenue for high-value utilization of abundant clay deposits.

Removal of Cl-from WFGD Wastewater by Electrocoagulation using Layered Double Hydroxide Compounds as Granule Electrodes

Removal of Cl-from WFGD Wastewater by Electrocoagulation using Layered Double Hydroxide Compounds as Granule Electrodes

Titanium Dioxide-Layered Double Hydroxide Composite Material for Adsorption-Photocatalysis of Water Pollutants.

Although adsorption has gained favor among numerous water treatment technologies as an effective pollutant removal method, its application is often hindered by challenges with its resource- and energy-intensive regeneration procedure once the available adsorption sites are exhausted. Herein, we present adsorption-photocatalysis composite materials combining layered double hydroxides (LDHs) and titanium dioxide (TiO2) for water treatment. Incorporation of the photocatalyst into the material opens opportunities to harness light from the sun or lamps for oxidative degradation of the adsorbed contaminants on the material surface, to free adsorption sites for material reuse. In addition to allowing photocatalytic regeneration, the addition of TiO2 to colloidal suspensions of delaminated LDH enabled the formation of TiO2-LDH composites with far superior adsorptive performances compared to their parent LDH compounds. During the material synthesis, positively charged LDH layers and negatively charged TiO2 particles combine through electrostatic attraction to yield composites with dramatically enhanced adsorption capacities toward model contaminants, methyl orange and 2,4-dichlorophenoxyacetic acid, by 16.0 and 76.7 times, respectively. Combining delaminated LDH with TiO2 allowed us to maximize the exposure of positively charged surfaces to the contaminants, in a form that can be used as a solid adsorbent. After regeneration, the material regained up to 92% of its adsorption efficiency toward model contaminants. In light of our findings showing significantly different kinetics of adsorption and photocatalytic regeneration, we propose a new scheme to utilize adsorption-photocatalysis systems, in which the two processes are separated to better utilize their unique strengths.

A Composite Corrosion Inhibitor of MgAl Layered Double Hydroxides Co-Intercalated with Hydroxide and Organic Anions for Carbon Steel in Simulated Carbonated Concrete Pore Solutions

Corrosion of steel in concrete has resulted in shorter service life of concrete constructions and it may also cause serious safety accident. Chloride attack and carbonation of the concrete are two of the most crucial trigger factors for the initiation of corrosion. In order to protect the reinforced steel in concrete from corrosion, in this work, a composite inhibitor of layered double hydroxides (LDHs) intercalated with organic phthalates (PTL) and hydroxide ions (MgAl-LDHs-OH-PTL) were synthesized by calcination-reconstruction methods in ambient atmosphere. The structure, composition and morphology of the prepared MgAl-LDHs-OH-PTL were obtained by X-ray diffraction, Fourier transform infrared spectroscopy and Scanning Electron Microscopy, respectively. The electrochemical measurements indicated that the inhibition efficiency of MgAl-LDHs-OH-PTL for carbon steel in the simulated carbonated concrete pore (SCCP) solutions reached more than 90% when its concentration was 20 g/L. It was found that the MgAl-LDHs-OH-PTL possessed multifunctional protection roles for the carbon steel in concrete, which mainly included decrease of aggressive Cl− ions, increase of the pH of SCCP solutions and release of PTL anions to the solution gradually. The work indicated the promising potential of LDHs compounds as effective multifunctional inhibitors in the field of corrosion protection of reinforced concrete.

Layered double hydroxide and microwave assisted functionalized carbon based nanocomposites as controlled release vehicle for antibiotics

In this work, the preparation of new composite from layered double hydroxide (LDH) and surface modified carbon (AC) was elaborated. The basic carbon was obtained by carbonizing Ipomoea carnea stems at 500 °C. The LDH compound was furthermore intercalated with antibiotic molecule norfloxacin (NOR). The chemically activated functionalized carbon particles had surface negative charge which helped in intense interaction with LDH basal positive charges. The prepared nanocomposites were characterized by powder XRD, FT−IR, FE−SEM with EDS, TGA, Zeta potential and BET surface specific area. Powder XRD and SEM studies proved that LDH was deposited over the AC surface homogeneously. The increase of the basal spacing from 0.78 nm to 1.33 nm indicated that not all LDH sheets were intercalated by NOR. Additionally, the water dispersional stability test has shown remarkable advantage compared to simple LDH. The thermal analysis results further showed a good improvement of NOR stability after intercalation into AC−LDH nanocomposite. The release behavior of NOR from the nanocomposite and its antibacterial activity were also investigated. The gradual release of NOR from AC−LDH−NOR nanocomposite suggests its prospective application as an effective delivery system for prolonged drug release.

Impact of temperature dependent octahedra distortions on magnetic properties of Co-containing double layered hydroxides

Abstract Distortions of hydroxide octahedral complexes in the CoIInAlIII layered double hydroxides (LDHs) (n = CoII/AlIII = 2 and 3) were studied as a function of the ratio of divalent-to-trivalent cations and temperature. A method for calculation the magnetic susceptibility of polycrystalline samples taking into account the statistical distribution of divalent and trivalent cations, and their effect on the distortions of the original structure is proposed. It is shown that the presence of a local maximum on the magnetic susceptibility curve of ConAl LDHs compounds near T ∼ 160 K is due to freezing of the lattice parameters and, as a consequence, freezing of the tilting fluctuations of the O–H bonds.

Analysis of the Secondary Phases Formed by Corrosion of U₃Si₂-Al Research Reactor Fuel Elements in the Presence of Chloride Rich Brines.

Corrosion experiments with non-irradiated U3Si2-Al research reactor fuel samples were carried out in synthetic MgCl2-rich brine to identify and quantify the secondary phases because depending on their composition and on their amount, such compounds can act as a sink for the radionuclide release in final repositories. Within the experimental period of 100 days at 90 °C and anoxic conditions the U3Si2-Al fuel sample was completely disintegrated. The obtained solids were subdivided into different grain size fractions and non-ambient X-ray diffraction (XRD) was applied for their qualitative and quantitative phase analysis. The secondary phases consist of lesukite (aluminum chloro hydrate) and layered double hydroxides (LDH) with varying chemical compositions. Furthermore, iron, residues of non-corroded nuclear fuel (U3Si2), iron oxy hydroxides and chlorides were also observed. In addition to high amorphous contents (>45 wt %) hosting the uranium, the quantitative phase analysis showed, that LDH compounds and lesukite were the major crystalline phases. Scanning electron microscopy (SEM) and energy dispersive -Xray spectroscopy (EDS) confirmed the results of the XRD analysis. Elemental analysis revealed that U and Al were concentrated in the solids. However, most of the iron, added as Fe(II) aqueous species, remained in solution.

Controlled Release of Nitrate and Molybdate Intercalated in Zn-Al-Layered Double Hydroxide Nanocontainers towards Marine Anticorrosion Applications

Zn-Al layered double hydroxides (LDHs) intercalating with molybdate anions was developed to inhibit the corrosion of mild steel in neutral chloride conditions. The LDH compounds were prepared by a method involving co-precipitation and anion-exchange and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The anticorrosion capabilities of the LDHs hybrids were analyzed by using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve. A significant reduction of the corrosion rate is observed in the presence of a 2 g/L concentration of the LDHs hybrids in the corrosive media. The mechanism is that the intercalated molybdate anion can slowly diffuse out of the inner structure of LDHs in a controllable way and result in a relatively long-term effect of corrosion inhibition. The result presented here underlines the great potential of the controlled release mechanism for marine anticorrosion applications.

Magnetic phenomena in Co-containing layered double hydroxides

Magnetic behavior of CoII(n)AlIII layered double hydroxides (LDHs) (n = Co/Al = 2 and 3) intercalated with nitrate was studied as a function of temperature. Both LDH compounds are paramagnetic above about 8 K. A rapid increase of their magnetic moments occurs below this temperature until the moments reach the maximum values at Tmax of 4.0 K and 3.2 K for Co(2)Al–NO3 and Co(3)Al–NO3, respectively. Below Tmax, the zero-field-cooled and the field-cooled static magnetization curves are strongly different. Along with this low-temperature phenomena, Co(2)Al–NO3 and Co(3)Al–NO3 demonstrate anomalous behavior of their temperature dependence magnetic susceptibility in a higher-temperature range: between 75 and 175 K, both the paramagnetic Curie temperature and the effective magnetic moment change in a non-monotonous way. Possible structural reasons of the observed magnetic behavior of the CoII(n)AlIII LDHs are discussed.

Strategic phosphate removal/recovery by a re-usable Mg–Fe–Cl layered double hydroxide

Abstract Excess phosphorus (P) in freshwater bodies is one of the major causes of eutrophication. The regulations for removing phosphate from wastewater treatment plant (WWTP) are becoming more stringent and thus the alternative technologies are sought to enhance the P removal efficiency. In this study, Mg–Fe–Cl based layered double hydroxide (LDH) compounds were synthesized and used for phosphate removal. Implementing LDH as a tertiary treatment process for the removal and recovery of phosphate is proposed. Results show that LDH dosage of 2 g/l can reduce phosphate concentration down to 0.1 mg/l from an initial value of 10 mg/l at an equilibrium contact time of 2 and 3 h, respectively. The adsorption kinetics of phosphate onto Mg–Fe–Cl LDH is well governed by the pseudo-second-order kinetic model, and adsorption data fit well to the Langmuir and Freundlich isotherms. The study on pH effect of adsorbate solution suggested that pH range between 3–7.5 is suitable for unaffected phosphate removal. The repeated use of this LDH by both batch and fixed bed column experiment showed that total phosphate reduction was about 95% and desorption percentage was about 91% through six cycles of adsorption–desorption processes. It is likely that this LDH compounds can be applied to remove and recover phosphate from secondary effluent of domestic wastewater treatment plant and thereby, to meet future stringent discharge regulations.

OXIDATION OF CYCLOHEXANOL ON PHOSPHOTUNGSTIC ACID ANION INTERCALATED LAYERED DOUBLE HYDROXIDES WITH AQUEOUS H2O2 AS OXIDANT

The layered double hydroxides (LDH) of Mg2AlNi and Mg3Al pillared by Keggin-type phosphotungstic acid anion (POM), i.e. Mg2AlNi-POM LDH and Mg3Al-POM LDH were synthesized by an ion-exchange method. The synthesized POM intercalated LDH compounds were characterized using various techniques such as FTIR, XRD, TGA and BET. The observed results show that the obtained catalysts retain the layer structure of LDH. Compared with the binary Mg3Al-POM LDH, the ternary Mg2AlNi-POM LDH catalyst indicated a higher thermal and chemical stability. The catalytic activity of the resulting LDH-POM was also assessed in the green oxidation of cyclohexanol with aqueous H2O2 as an oxidant. The Mg2AlNi-POM LDH showed a much higher conversion and selectivity for cyclohexanone than the corresponding Mg3Al-POM LDH catalyst.

Flame Retardant Efficiency of Melamine Pyrophosphate with Added Mg-Al-Layered Double Hydroxide in Medium Density Fiberboards

The main objective of this study was to investigate the flame retardant (FR) efficiency of melamine pyrophosphate (MP) with added layered double hydroxide (LDH) in medium density fiberboards (MDFs) to be used as building decorative materials. The thermal degradation, FR efficiency, and combustion properties of MDF were analyzed by Fourier transform infrared spectra (FTIR), thermogravimetric analysis (TGA), limiting oxygen index (LOI) test, and cone calorimetric test. The TGA results showed that the combination of MP and LDH led to a lower decomposition temperature than the pure MP and pure LDH. The LOI results showed that the LOI values increased with the addition of the FRs. The cone calorimetric results showed that the addition of four proportions (1:1, 2:1, 1:2, and 1:3) of the compounds into MDF can clearly decrease the peak heat release rate (PHRR) and mean heat release rate (MHRR). The results indicated that the MP and LDH compounds have a synergistic effect to improve the flame retardancy and smoke suppression in the MDFs. The combination of MP and LDH in a 1:1 ratio under 10 wt% FR addition has the best flame retardant efficiency in the MDFs.

Highly biocompatible behaviour and slow degradation of a LDH (layered double hydroxide)-coating on implants in the middle ear of rabbits.

Chronic inflammation can irreversibly damage components of the ossicular chain which may lead to sound conduction deafness. The replacement of impaired ossicles with prostheses does not reduce the risk of bacterial infections which may lead to loss of function of the implant and consequently to additional damage of the connected structures such as inner ear, meninges and brain. Therefore, implants that could do both, reconstruct the sound conduction and in addition provide antibacterial protection are of high interest for ear surgery. Layered double hydroxides (LDHs) are promising novel biomaterials that have previously been used as an antibiotic-releasing implant coating to curb bacterial infections in the middle ear. However, animal studies of LDHs are scarce and there exist only few additional data on the biocompatibility and hardly any on the biodegradation of these compounds. In this study, middle ear prostheses were coated with an LDH compound, using suspensions of nanoparticles of an LDH containing Mg and Al as well as carbonate ions. These coatings were characterized and implanted into the middle ear of healthy rabbits for 10 days. Analysis of the explanted prostheses showed only little signs of degradation. A stable health constitution was observed throughout the whole experiment in every animal. The results show that LDH-based implant coatings are biocompatible and dissolve only slowly in the middle ear. They, therefore, appear as promising materials for the construction of controlled drug delivery vehicles.

Synthesis of Ca-based Layered Double Hydroxide from Blast Furnace Slag and Its Catalytic Applications

A Ca-based layered double hydroxide (LDH) was synthesized from blast furnace slag (BFS) via a facile and low-cost manufacture process. The synthesis was performed through a two-step method including (i) an acid-dissolution and (ii) an alkali-precipitation process using BFS as a sole metal source. The formation of Ca–Al LDH crystals occurred above pH 9, and under the optimal synthetic conditions (at 373 K and pH 11.5) a well-crystallized stoichiometric hydrocalumite (Ca:Al:Cl=2:1:1) incorporating the slag-derived metallic elements in its structure was obtained with a metal recovery rate of 85%. The impacts of synthesis pH and temperature on the material structures were investigated in detail. The catalytic properties of the thus synthesized LDH material was demonstrated on industrially important several chemical reactions including (1) oxidation of alkyl aromatics with O2, (2) CO2 fixation reaction and (3) biodiesel synthesis from vegetable oil. These results open up a new route to fabricate a low-cost LDH compound and its potential availability as an alternative solid base catalyst.

Study on the sorption–desorption–regeneration performance of Ca-, Mg- and CaMg-based layered double hydroxides for removing phosphate from water

• Ca-LDHs can remove higher P than Mg-LDHs for the same dose and pHs 3.5–10.5. • Ca-LDHs cannot be reused due to the loss of the layered structure after the first run. • Mg-LDHs have stable structure and are reusable for P removal at higher doses. • Ca–Mg mixed LDHs, Ca 1.5 Mg 0.5 –Fe(Cl)(NO 3 )-450, has higher P removal (95%). • Ca–Mg mixed LDHs are reusable with 64% P removed at the 4th cycle. Various layered double hydroxides (LDHs) were prepared by the co-precipitation method using the most common divalent and trivalent metal precursors. The resulting LDHs were studied for their performance in removing phosphate from aqueous test solution. The results have clearly demonstrated the influence of Ca and Mg as pre-cursor metals in synthesizing LDH compounds for removing phosphate. For the same LDH’s dose, more phosphorus was removed by Ca-based LDHs than Mg-based LDHs. Real effluent from a wastewater treatment plant with high phosphate concentration (3.4–10.4 mg-P/L) can also be treated with >90% removal by both Ca- and Mg-based LDHs depending on the selection of suitable dose. For Ca-based LDHs, the main removal process was observed to be as calcium-phosphate precipitation. Due to the loss of layered structure after first sorption/precipitation operation, Ca–(Fe or Al)-LDHs cannot be regenerated for reuse. However, Mg-based LDHs showed potentially applicable for the regeneration and reuse due to their stable nature in aqueous phase than Ca-based LDHs. On the other hand, when choosing CaMg-based LDHs for the phosphorus removal, the nature of Ca dissolution from such LDHs needs to be taken into account although they were demonstrated to be reusable with the efficiency of phosphate removal up to 64% at the fourth cycle.