Cu–Al Layered Double Hydroxides as Precursors to Operando-Formed Dendritic Cu for Electrochemical CO 2 Reduction

The role of dispersion of LDH in fire retardancy: The effect of different divalent metals in benzoic acid modified LDH on dispersion and fire retardant properties of polystyrene– and poly(methyl-methacrylate)–LDH–B nanocomposites

Synthesis of layered double hydroxide nanosheets in an aqueous solvent and their Ni2+ uptake characteristics

New treatment method for boron in aqueous solutions using Mg–Al layered double hydroxide: Kinetics and equilibrium studies

Recyclable Mg–Al layered double hydroxides for fluoride removal: Kinetic and equilibrium studies

Iron-modified hydrotalcite-like materials as highly efficient phosphate sorbents

Sonication-assisteddelamination of layered double hydroxides (LDHs) resulted in smaller-sizedLDH nanoparticles (∼50–200 nm). Such delaminated Co–AlLDH, Zn–Al LDH, and Co–Zn–Al LDH solutions wereused for the preparation of highly dispersed isotactic polypropylene(iPP) nanocomposites. Transmission electron microscopy and wide-angleX-ray diffraction results revealed that the LDH nanoparticles werewell dispersed within the iPP matrix. The intention of this studyis to understand the influence of the intralayer metal compositionof LDH on the various properties of iPP/LDH nanocomposites. The sonicatedLDH nanoparticles showed a significant increase in the crystallizationrate of iPP; however, not much difference in the crystallization rateof iPP was observed in the presence of different types of LDH. Thedynamic mechanical analysis results indicated that the storage modulusof iPP was increased significantly with the addition of LDH. The incorporationof different types of LDH showed no influence on the storage modulusof iPP. But considerable differences were observed in the flame retardancyand thermal stability of iPP with the type of LDH used for the preparationof nanocomposites. The thermal stability (50% weight loss temperature(T0.5)) of the iPP nanocomposite containingthree-metal LDH (Co–Zn–Al LDH) is superior to that ofthe nanocomposites made of two-metal LDH (Co–Al LDH and Zn–AlLDH). Preliminary studies on the flame-retardant properties of iPP/LDHnanocomposites using microscale combustion calorimetry showed thatthe peak heat release rate was reduced by 39% in the iPP/Co–Zn–AlLDH nanocomposite containing 6 wt % LDH, which is higher than thatof the two-metal LDH containing nanocomposites, iPP/Co–Al LDH(24%) and iPP/Zn–Al LDH (31%). These results demonstrated thatthe nanocomposites prepared using three-metal LDH showed better thermaland flame-retardant properties compared to the nanocomposites preparedusing two-metal LDH. This difference might be due to the better charformation capability of three-metal LDH compared to that of two-metalLDH.

Co/Ni/Mg/Al Layered Double Hydroxides as Precursors of Catalysts for the Hydrogenation of Nitriles: Hydrogenation of Acetonitrile

Heavy metal pollution threatens aquatic systems worldwide, and mining activities are an important pollution source. Currently, the treatment of polluted water using a cost-effective technology that can purify multiple pollutants and is sustainable, environmentally friendly, and simple is a major challenge. The in situ preparation of Mg–Al layered double hydroxides (LDHs) and the concurrent treatment of Zn, Cd, and Pb from mining wastewater are important for preventing multiple steps and increasing adsorption sites. This study focused on mining wastewater containing high concentrations of Mg2+ and Al3+, with anion chemistry controlled by SO42−, which facilitates the formation of LDHs. The required amounts of Mg2+ and Al3+ ions were added to the wastewater, and the conditions for the creation of Mg–Al LDHs were controlled. The heavy metals in the experimental wastewater were effectively removed after the treatment via Mg–Al LDH formation. The X-ray diffraction of the post-treatment products suggested the formation of Mg–Al LDHs. The Mg/Al molar ratio (2.3:1) in the product approached the initial ratio (2:1), which meets the general limits of Mg–Al LDH formation. Scanning electron microscopy revealed that the products had a sheetlike stacked morphology, providing evidence for the formation of Mg–Al LDHs. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that SO42− might be the intercalated anion in the Mg–Al LDH layers. Consequently, SO42− was removed from the mining wastewater, as it was captured between the LDH layers during the formation reaction of Mg–Al LDHs.

LDH conversion films for active protection of AZ31 Mg alloy

In order to comprehensively improve the strength, toughness, flame retardancy, smoke suppression, and thermal stability of polypropylene (PP), layered double hydroxide (LDH) Ni0.2Mg2.8Al–LDH was synthesized by a coprecipitation method coupled with the microwave-hydrothermal treatment. The X-ray diffraction (XRD), morphology, mechanical, thermal, and fire properties for PP composites containing 1 wt %–20 wt % Ni0.2Mg2.8Al–LDH were investigated. The cone calorimeter tests confirm that the peak heat release rate (pk–HRR) of PP–20%LDH was decreased to 500 kW/m2 from the 1057 kW/m2 of PP. The pk–HRR, average mass loss rate (AMLR) and effective heat of combustion (EHC) analysis indicates that the condensed phase fire retardant mechanism of Ni0.2Mg2.8Al–LDH in the composites. The production rate and mean release yield of CO for composites gradually decrease as Ni0.2Mg2.8Al–LDH increases in the PP matrix. Thermal analysis indicates that the decomposition temperature for PP–5%LDH and PP–10%LDH is 34 °C higher than that of the pure PP. The mechanical tests reveal that the tensile strength of PP–1%LDH is 7.9 MPa higher than that of the pure PP. Furthermore, the elongation at break of PP–10%LDH is 361% higher than PP. In this work, the synthetic LDH Ni0.2Mg2.8Al–LDH can be used as a flame retardant, smoke suppressant, thermal stabilizer, reinforcing, and toughening agent of PP products.

Porous materials of hydrotalcite-like layered double hydroxides (LDHs) have been used for removal of anionic contaminants from solution. However, local coordination structures of anions adsorbed on LDHs are not fully understood because of the lack of spectroscopic studies. In this study, we utilized X-ray absorption fine structure spectroscopy to clarify the coordination structure of Re in Mg–Al LDH as a surrogate of Tc. Adsorption experiments of ReO4− on calcined and uncalcined Mg–Al LDHs were conducted in aqueous solutions with different concentrations of NaCl, NaNO3, and Na2SO4. The tested calcined and uncalcined Mg–Al LDHs were characterized by chemical composition analysis, scanning electron microscopy (SEM), and BET surface area. Calcined Mg–Al LDH showed much higher adsorption than uncalcined one. The adsorption of ReO4− was reversible, and decreased with increasing concentration of competing anions like Cl−, NO3−, or SO42−. Rhenium LIII-edge X-ray absorption near edge structure suggested that neither redox reaction nor change of coordination structure occurred during intercalation of Re into Mg–Al LDH. Analysis of Re LIII-edge extended X-ray absorption fine structure indicated that ReO4− was adsorbed as an outer-sphere complex on Mg–Al LDH. The observed Re adsorption–desorption behavior, which was sensitive to the presence of competing anions, was consistent with the formation of outer sphere-complex.

The Mg–Al layered double hydroxide (LDH) conversion coatings were first synthesized in situ to modify the AZ91D alloy through urea hydrolysis to adjust the pH values (9.4, 10.4, 11.2 and 11.4). The pH 11.2 Mg–Al LDH possessed the best compactness and good crystallinity compared to other in situ LDH coatings and obtained the lowest corrosion current density ( i corr ) of (2.884 × 10 −6 ± 0.345 × 10 −6 ) A·cm −2 , which was attributed to the anion‐exchange reaction of LDH and the physical barrier against corrosion owing to the twisted penetration pathway of the interlaced LDH sheets. Core–shell structured Zn–Al LDH@ZIF‐8 powder modified with stearic acid (SA) was further wrapped with polyvinylidene fluoride (PVDF) to prepare a hydrophobic double‐layered coating on the underlying pH 11.2 Mg–Al LDH (SLLZ). The water contact angle (CA) of the SLLZ coating reached 105.6°, and its i corr decreased to (3.524 × 10 −7 ± 0.214 × 10 −7 ) A·cm −2 compared with a single pH 11.2 film. The SLLZ coating exhibited high durability and corrosion protection, even after 15 days of immersion in NaCl solution. The PVDF, SA and ZIF‐8 nano‐shells contributed to good hydrophobicity, effectively forming a physical barrier. The Zn–Al LDH core and underlying in situ Mg–Al LDH were beneficial for synergistically promoting anion‐exchange reaction between the intercalated anions of LDH and chlorides in corrosive media. This work provides a promising approach that combines core–shell LDH@ZIF‐8 with LDH film on a Mg alloy surface to construct a hydrophobic film with excellent long‐term anti‐corrosion performance.

Synthesis and Thermal Decomposition of Mn–Al Layered Double Hydroxides

Layered double hydroxides (LDHs) of various compositions, i.e. Mg–Al, Mg–Mn–Al, are applied as the precursors of metal oxides for the preparation of N-doped carbon materials via chemical vapour deposition (CVD) with acetonitrile (as carbon and nitrogen source) at 600 and 700 °C. The use of Mn-containing LDHs for the preparation of the carbon materials is a novelty. The impact of transition metal species, i.e. MnxOy, in a blend of metal oxides derived from LDHs on the amount of carbon deposit and its composition, morphology, textural and capacitive properties is investigated. Mn-containing species occurring in a mixture of metal oxides enhance the quantity of carbonaceous product compared to those derived from Mg–Al LDHs. Thermally heated Mg–Mn–Al LDHs contain structural defects due to manganese oxides, which promote the formation of carbon deposit, especially higher production of amorphous carbons. The addition of Mn into Mg–Al LDHs matrix leads to carbon particles with increased N-doping and enhanced volume of mesopores. Furthermore, graphitic domains occurring in the carbon materials obtained with Mg–Mn–Al LDHs are thicker than those in the corresponding samples obtained with Mg–Al LDHs as Mn-containing species influence the concentration and location of N-containing groups in graphitic array. The specific capacitance of the carbon materials produced by CVD with the compounds derived from Mg–Al LDHs or Mg–Mn–Al LDHs is comparable (20–25 μF cm−2). The formation of electrical double layer at electrode/electrolyte interface is easier for the carbon materials prepared at 700 °C than for the carbon materials prepared at 600 °C. The maximum charge is stored either in the shallow parts of carbon particles for the former, as they contain bottleneck mesopores, or in the deep parts of carbon particles for the latter, as they contain slit-shaped mesopores.Graphical abstract

Treatment of gaseous hydrogen chloride using Mg−Al layered double hydroxide intercalated with carbonate ion