Mg-Al LDHs Research Articles

Humidity Effects on Sub-Ambient Direct Air Capture of CO2 with Amine Functionalized Mg-Al LDHs and MMOs

Humidity Effects on Sub-Ambient Direct Air Capture of CO₂ with Amine Functionalized Mg-Al LDHs and MMOs

Step-by-step in-situ preparation of magnesium-aluminum layered double hydroxide film to improve the corrosion resistance of AZ31 magnesium alloy

In this study, a hydrothermal method was employed to cultivate Mg(OH)2 precursor layers on the surface of AZ31 magnesium alloy samples. Subsequently, Mg-Al LDHs films were successfully synthesized through an in-situ growth approach. The phase composition of the films were analyzed using X-ray diffraction and infrared spectroscopy. The growth process and surface morphology of the films at the microstructure level were examined and interpreted using scanning electron microscopy and EDS. The corrosion resistance of the films was assessed through potentiodynamic polarization curves, electrochemical impedance spectroscopy, and hydrogen evolution tests. The findings indicate that the Mg(OH)2 precursor effectively mitigates defects in the Mg-Al LDHs films and improves the LDHs microstructure. Moreover, the precursor synthesized at a pH range of 10–12 better enhances the corrosion resistance of the Mg-Al LDHs film.

Effects of hydrotalcites with different laminate element composition on the properties of sulfoaluminate cement-based materials

Sulfoaluminate cement-based materials (SCBMs) are widely used for grout reinforcement. It is common to use a large water-to-binder ratio in the construction of sulfoaluminate cement-based materials (SAGMs) to obtain good workability and permeability, which results in poor early strength. Nanotechnology has been increasingly employed to enhance the mechanical properties of cementitious materials. Nano Zn-Mg-Al hydrotalcite-like (LDHs) and nano Mg-Al LDHs increased the early compressive strength, while nano Zn-Al LDHs had the opposite effect. However, the reason for this observation remains unclear. In this study, the influence of LDHs structures with different laminar element compositions on the hydration and hardening processes of SCBMs was analysed. The results showed that nano-ZnAl-LDHs, ZnAl-LDHs, and MgAl-LDHs could provide nucleation sites for ettringites. The three hydrotalcite-like materials slowly released different concentrations of zinc and/or magnesium ions and carbonate ions in the cement paste. Zinc ions entered the hydration product of ettringite and aluminum gel and promoted the transformation of amorphous aluminum gel to bayerite, which inhibited the hydration reaction of SCBMs. Magnesium ions could also enter the ettringite, and carbonate ions promoted the formation of calcium carbonate, which facilitated the hydration reaction of SCBMs. The nucleation effect and the release of zinc and/or magnesium ions and carbonate ions acted synergically to influence the hydration rate, pore size distribution, and compressive strength of SCBMs.

Adsorption and Visible Photocatalytic Synergistic Removal of a Cationic Dye with the Composite Material BiVO4/MgAl–LDHs

Adsorption and photocatalysis are effective in removing organic pollutants from wastewater. This study is based on the memory effects of MgAl–layered double hydroxides (MgAl–LDHs) after high-temperature calcination. By introducing bismuth vanadate (BiVO4) during the reformation of the layered structure via contact with water, a composite material BiVO4/MgAl–LDHs with enhanced adsorption and visible light catalytic performance was synthesized. The effects of the calcination temperature, ratio, initial methylene blue (MB) concentration, and catalyst dosage on the adsorption and photocatalytic performance were investigated. The BiVO4/MgAl–LDHs showed better photocatalytic performance than the pure BiVO4 and MgAl–LDHs. Under the optimal conditions, the proportion of MB adsorbed in 20 min was 66.1%, and the percentage of MB degraded during 100 min of photolysis was 92.4%. The composite photocatalyst showed good chemical stability and cyclability, and the adsorption-degradation rate was 86% after four cycles. Analyses of the adsorption and photocatalytic mechanisms for the composite material showed that synergistic adsorption and visible light photocatalysis contributed to the excellent catalytic performance of the BiVO4/MgAl–LDHs. A highly adsorbent photocatalytic composite material exhibiting outstanding performance was prepared via a simple, cost-effective, and environmentally friendly method, providing reference information for the removal of organic pollutants from liquids.

Unraveling the aging dynamics in the simultaneous immobilization of soil metal(loid)s using oxides

Immobilization represents the most extensively utilized technique for the remediation of soils contaminated by heavy metals and metalloids. However, it is crucial to acknowledge that contaminants are not removed during this process, thereby leaving room for potential mobilization over time. Currently, our comprehension of the temporal variations in immobilization efficacy, specifically in relation to amendments suitable for industrial sites, remains very limited. To address this knowledge gap, our research delved into the aging characteristics of diverse oxides, hydroxides, and hydroxy-oxides (collectively referred to as oxides) for the simultaneous immobilization of arsenic (As), cadmium (Cd), and antimony (Sb) in soils procured from 16 contaminated industrial sites. Our findings unveiled that Ca-oxides initially showed excellent immobilization performance for As and Sb within 7 days but experienced substantial mobilization by up to 71 and 13 times within 1 year, respectively. In contrast, the efficacy of Cd immobilization by Ca-oxides was enhanced with the passage of time. Fe- and Mg-oxides, which primarily operate through encapsulation or surface complexation, exhibited steady immobilization performances over time. This reliable and commendable immobilization effect was observed across distinct soils characterized by varying physicochemical properties, including pH, texture, CEC, TOC, and EC, underscoring the suitability of such amendments for immobilizing metal(loid)s in diverse soil types. MgO, in particular, displayed even superior immobilization performance over time, owing primarily to gradual hydration and physical entrapment effects. Remarkably, Mg-Al LDHs emerged as the most effective candidate for the simultaneous immobilization of As, Cd, and Sb. The results obtained from this study furnish valuable data for future investigations on the immobilization of metals and metalloids in industrial soils. They enable the projection of immobilization performance and offer practical guidance in selecting suitable amendments for the immobilization of metal(loid)s.

Preparation of Mg-Al Layered Double Hydroxides Ultrathin Nanosheets and Its Application in Adsorption of Methyl Orange

In this paper, well-defined Mg-Al LDHs nanosheets with high yield are prepared by the following sequential procedures: hydrothermal preparation of Mg-Al-CO[Formula: see text] LDHs, followed by expanding interlayer spacing by NH4NO3 treatment. The results show that the concentration of the layer expansion agent (NH4NO[Formula: see text] and the exfoliation solvent play a key role in the exfoliation result. The basal spacing changed from 0.758[Formula: see text]nm to the range of 0.758–0.895[Formula: see text]nm when the concentration of NH4NO3 was increased up to 5 M, which infers that the increase of layer space is caused by the synergy of NH[Formula: see text] and NO[Formula: see text]. Among the three exfoliation solvents (formamide, N-methyl pyrrolidone and isopropyl alcohol), formamide showed the highest exfoliation effect. From the characteristic XRD patterns, the as-obtained colloidal aggregates of the exfoliated nanosheets do not show the characteristic diffractions of LDHs, while the typical peaks at 10.562[Formula: see text], 20.032[Formula: see text] and 21.185[Formula: see text] assigned to LDHs are observed after drying of the colloidal aggregates. Moreover, a transparent LDH film is also successfully prepared by coating colloidal aggregates of nanosheets on a glass substrate without using any adhesive. The stable film exhibits the strong adsorption ability of Methyl Orange.

Polypropylene (PP) nanocomposites with transition metal (MgCoAl, MgNiAl, MgCuAl, MgZnAl) layered double hydroxides (t-LDHs): Flammability, thermal and mechanical analysis

Over the last few years, transition metal based LDHs are drawing more and more attention. This is especially true for tri-metal LDHs due to their wide range of applications. This research work highlights four types of tri-metal layered double hydroxide (t-LDH) that were synthesized and used in polypropylene (PP) nanocomposites. The effect and interaction of cobalt (Co), nickel (Ni), copper (Cu) and zinc (Zn) containing MgAl LDHs in PP nanocomposite were prepared and tested. These t-LDHs (MgCoAl, MgNiAl, MgCuAl, MgZnAl) were synthesized using the urea hydrolysis method. The t-LDH/PP nanocomposites were prepared using melt mixing in a small-scale compounder. Structural and morphological analysis of t-LDH and their PP nanocomposites were done using XRD spectroscopy and SEM. The thermal behaviour of the nanocomposites was studied using DSC and TGA. Rheological analysis was done using a rheometer, flammability was analysed using limiting oxygen index (LOI) and UL94 testing. Mechanical properties were compared by a UTM and Charpy impact test. The thermal stability, flame retardancy and mechanical strength are increased with the addition of these t-LDHs. MgCuAl/PP nanocomposites showed superior thermal and mechanical properties as compared to MgAl/PP, MgCoAl/PP, MgNiAl/PP, MgZnAl/PP nanocomposites. In comparison to pure PP with the addition of only 5 wt.% of MgCuAl-LDH the degradation temperature was 43 °C higher.

Enhanced Bactericidal Effect of Calcinated Mg-Fe Layered Double Hydroxide Films Driven by the Fenton Reaction.

Osteogenic and antibacterial abilities are the permanent pursuit of titanium (Ti)-based orthopedic implants. However, it is difficult to strike the right balance between these two properties. It has been proved that an appropriate alkaline microenvironment formed by Ti modified by magnesium-aluminum layered double hydroxides (Mg-Al LDHs) could achieve the selective killing of bacteria and promote osteogenesis. However, the existence of Al induces biosafety concerns. In this study, iron (Fe), an essential trace element in the human body, was used to substitute Al, and a calcinated Mg-Fe LDH film was constructed on Ti. The results showed that a proper local alkaline environment created by the constructed film could enhance the antibacterial and osteogenic properties of the material. In addition, the introduction of Fe promoted the Fenton reaction and could produce reactive oxygen species in the infection environment, which might further strengthen the in vivo bactericidal effect.

Use of Photocatalytically Active Supramolecular Organic–Inorganic Magnetic Composites as Efficient Route to Remove β-Lactam Antibiotics from Water

Considerable efforts have been made in recent years to identify an optimal treatment method for the removal of antibiotics from wastewaters. A series of supramolecular organic-inorganic magnetic composites containing Zn-modified MgAl LDHs and Cu-phthalocyanine as photosensitizers were prepared with the aim of removing β-lactam antibiotics from aqueous solutions. The characterization of these materials confirmed the anchorage of Cu-phthalocyanine onto the edges of the LDH lamellae, with a negligible part inserted in the interlayer space. The removal of the β-lactam antibiotics occurred via concerted adsorption and photocatalytic degradation. The efficiency of the composites depended on (i) the LDH: magnetic nanoparticle (MP) ratio, which was strongly correlated with the textural properties of the catalysts, and (ii) the phthalocyanine loading in the final composite. The maximum efficiency was achieved with a removal of ~93% of the antibiotics after 2 h of reaction.

Enhancing the phosphorus content of layered double hydroxide fertilizers by intercalating polymeric phosphate instead of orthophosphate: A feasibility study

HypothesisLayered double hydroxide (LDH) loaded with orthophosphate (PO4) are suggested as slow-release P fertilizers. However, PO4-LDHs have a low maximal P content, related to high charge HPO42−/PO43− anions occupying the anion exchange capacity (AEC) of LDHs. We postulate that the P content of LDHs can be enhanced by exchanging them with polymeric-P (i.e. trimetaphosphate, P3O9), which has a lower molar charge/P ratio than its monomer. ExperimentsAdsorption capacities were compared between PO4 and P3O9 for as-synthesized and calcined MgAl LDHs with Mg/Al ratio of 2, 3, or 4; the P-LDHs were characterized (XRD, FTIR). Dialysis and soil incubation experiments were performed with PO4−LDHs, P3O9−LDHs, and corresponding soluble fertilizers to compare their P release and P solubility (CaCl2 extract). FindingsThe P adsorption capacities were 1.25–1.60 fold larger for P3O9 compared to PO4, yet the high theoretical P contents with P3O9 were not achieved (incomplete loading, P3O9 depolymerization). P3O9-Mg3Al released polymeric-P whereas P3O9-Mg2Al released depolymerized PO4, and P release from P3O9-LDHs was slower than that of PO4-LDHs. With soil incubation, soluble P from P3O9-LDH was initially lower but later converged to that of PO4-LDH as result of continued hydrolysis, yet did not exceed that of the soluble P3O9 and PO4 fertilizers.

Ultrasonic-assisted preparation of ultrafine Pd nanocatalysts loaded on Cl−-intercalated MgAl layered double hydroxides for the catalytic dehydrogenation of dodecahydro-N-ethylcarbazole

N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NEC/H12-NEC) is a promising LOHC, and the development of a catalyst with high activity and stability is the key to realizing its reversible hydrogen storage process. In this paper, ultrafine Pd nanocrystalline catalysts (Pd/LDHs-us) supported on Cl--intercalated MgAl LDHs were prepared by a simple ultrasonic-assisted reduction method and applied in the dehydrogenation of 12H-NEC. In the process of ultrasonic-assisted reduction, the instantaneous high temperature generated by cavitation decomposed part of the CO32– in LDHs interlayer, and promoted PdCl42- to enter the interlayer and become new intercalated ions. At the same time, hydroxyl groups on the surface of LDHs were excited to generate hydrogen radicals (•H) with strong reducibility, which reduced PdCl42- to Pd nanoparticles (PdNPs) in situ. The remaining Cl- ions continued to exist in the interlayer as intercalated ions. The agglomeration of PdNPs was effectively inhibited, and the average particle size was 1.8 nm, which was uniformly dispersed on LDHs, which improved the catalytic activity of Pd/LDHs-us. The coordination between PdNPs and oxygen in the hydroxyl groups on the surface of LDHs improved its catalytic stability. Using Pd/LDHs-us catalyst, the conversion rate of H12-NEC was 100.0 %, and the dehydrogenation efficiency was 99.3 % at 180℃. When the reaction temperature drops to 170℃, the dehydrogenation efficiency can still reach 94.6 %, showing excellent catalytic performance. The study of dehydrogenation kinetics shows that the apparent activation energy of Pd/LDHs-us catalyst is only 90.97 kJ/mol. This provides a new method and idea for the preparation of efficient dehydrogenation catalysts in the future.

Insights into the Design and Electrocatalytic Activity of Magnesium Aluminum Layered Double Hydroxides: Application to Nonenzymatic Catechol Sensor.

The design of an efficient electrocatalyst for effective trace level determinations of noxious synthetic and or biological compounds is the unceasingly noteworthy conceptual approach for rapid technology. In this work, we designed a magnesium-aluminum layered double hydroxides (Mg-Al LDHs) nanocatalyst and applied it to the electrocatalytic determination of an extremely carcinogenic catechol sensor. A coprecipitation method was employed for synthesizing the nanocatalyst, and the structure, porous nature, and morphology were confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption-desorption isotherm, field emission-scanning electron microscopy, and transmission electron microscopy. The elemental composition was observed by energy dispersive X-ray analysis. The electrochemical studies were investigated with the help of cyclic voltammetry and differential pulse voltammetry techniques. The Mg-Al LDHs-based electrocatalyst was used to detect catechol by electrochemical measurements with different parameters. The proposed catechol sensor shows a wide dynamic range (0.007-200 μM) with a lower level of detection (2.3 nm) and sensitivity (3.57 μA μM-1 cm-2). The excellent sensor performance is attributed to the high surface area, fast electron transfer, more active sites, and excellent flexibility. This study depicts the proposed sensor as probable to practical in a scientific investigation. In addition, the modified electrode showed greater selectivity and was used in the detection of fatal contaminants in instant treatment strategies. Moreover, the Mg-Al LDHs confirmed auspicious real sample scrutiny with noteworthy retrieval outcomes in lake water samples which exposed improved consequences.

Enrichment of scandium and aluminum from limonitic laterite during the nitric acid pressure leaching process

The presence of 50–100 (g/t) scandium in limonitic laterite makes it an important source for the extraction of Sc together with nickel and cobalt. This study aims to separate and enrich Sc and Al from limonitic laterite during the nitric acid pressure leaching (NAPL) process for treating limonitic laterite without interfering with the main nickel‑cobalt production circuit. Extractions of 86.2% Sc and 71.0% Al were obtained under the most suitable conditions for leaching limonitic laterite. The Sc and Al were selectively, homogeneously precipitated with MgCO3 suspension after adjusting the pH to 4.5 at 60 °C. The precipitate contains about 27% Al and 0.037% Sc. Moreover, 0.68% of Ni and 3.62% of Mg were also found in the Sc-containing Al precipitate and their precipitation behaviour and mechanism were examined. Specifically, a small amount of Mg and Al co-precipitate to produce the layered double hydroxides (MgAl LDHs). The Sc-containing Al precipitate was leached by NaOH with initial concentration of 20% and liquid-to-solid ratio of 3.5 mL/g at 80 °C for 1 h allowing 94.6% of Al to be dissolved. The resultant sodium aluminate solution contains 65.4 g/L of Al, which could be directly applied to the recovery of Al. Scandium enrichment in the leach residue achieved a content of 0.245%. The proposed method demonstrates the potential to enhance the economic value of limonitic laterite through the recovery of Sc and Al.

Nickel (II) coordination on cross-linked poly triazine-urea-sulfonamide grafted onto Mg-Al LDHs: As a green catalytic system for the synthesis of tetrazolo[1,5-a] pyrimidines

In this study, the surface of Mg-Al LDHs was functionalized with cross-linked poly triazine-urea-sulfonamide (Poly TUSA) to synthesize a novel heterogeneous support (LDH@TUSA). Afterwards, nickel(II) chloride was added on the prepared support and, we used LDH@TUSA@Ni in order to construct tetrazolo[1,5-a] pyrimidines from the reaction of aldehydes, 2-aminotetrazole, and substituted acetophenones. The prepared green heterogeneous catalyst can be recycled and recovered six times without significant loss in the catalytic activity.

Hierarchical zeolite-LTA@Mg-Al layered double hydroxide core@shell structure with enhanced corrosion protection of steel in saturated Ca(OH)2 solution

In this article, a novel type of core@shell Linde type A zeolite@Mg-Al layered double hydroxides (zeolite-LTA@ Mg-Al LDHs) was fabricated via in situ co-deposition method for efficient corrosion protection of carbon steel. The corrosion inhibition effect of fabricated zeolite-LTA@ Mg-Al LDH on steel was decided by a comparative experiment in saturated Ca(OH)2 solution. The batch experiment on the equilibrium isotherms of chloride binding in the solution clearly demonstrated that compared to pure Mg-Al LDHs, the zeolite-LTA@Mg-Al LDHs exhibited an higher chloride binding capacity due to the highly dispersed LDHs with large surface area on the zeolite-LTA support. In addition, a better corrosion inhibition capacity of zeolite-LTA@Mg-Al LDHs was proved by the measurements of open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PP) and optical microscopy (OM). Some nitrate ions on the steel surface detected by X-ray photoelectron spectroscopy (XPS) confirmed the dual effects of aggressive chloride removal and simultaneously released NO3−, which were responsible for the ultimate inhibition effect of zeolite-LTA@Mg-Al LDHs.

Efficient Exfoliation of Layered Double Hydroxides; Effect of Cationic Ratio, Hydration State, Anions and Their Orientations.

The exfoliation ability of nitrate based Mg1−xAlx(OH)2(NO3)x·mH2O layered double hydroxides (Mg-Al LDH) in formamide into single or multilayer nanosheets depends strongly on nitrate anion orientation and layer charge. Our systematic studies used materials that were likely to disclose differences with respect to anion type and their concentrations in the interlayer gallery. We assured to avoid any carbonate incorporation into the galleries for nitrate, chloride, iodide, and sulfate based Mg-Al LDHs. Furthermore, the comparative exfoliation experiments were conducted for fully hydrated samples with as similar particle morphology as possible. The exfoliation of nitrate Mg-Al LDH is far superior to similar clays with carbonate, sulfate, chloride, or iodide as charge balancing anions. Quantitative analysis of exfoliation yield for pre-treated, fully hydrated samples, shows an optimum composition for exfoliation into single nanosheets of around x ≈ 0.25, while double or triple layered sheets are encountered for other x-values. We observe a clear correlation between the expansion of the interlayer gallery due to progressing tilts of nitrate anions and water molecules out of the horizontal interlayer plane, suspension turbidity, and degree of exfoliation. The established correlations extends to nitrate Ni-Al LDH materials. We finally claim that morphology is a dominating parameter, with house-of-card morphology particles exfoliation far less than platelet-like particles. Hence, hydrothermal treatment may be favorable to enhance exfoliation yields.

Synthesis ratios of Mg-Al and Zn-Al layered double hydroxides efficiency and selectivity in nitrate removal from solution

Four diverse chlorides layered double hydroxides with diverse ratios, i.e. Mg-Al (3:1), Mg-Al (4:1), Zn-Al (4:1), and Zn-Al (3:1) LDHs, were prepared to evaluate their efficiency and selectivity towards nitrate removal from aquatic solutions. A batch experiment was done at the initial nitrate concentration of 5-1000 mg/L, pH 5 to 12, and contact time of 5-180 min. Isotherms of nitrate adsorption on LDHs, soil and soil-LDH mixtures were studied. Kinetics of adsorption, temperature effect, nitrate adsorption in nitrate adsorption, simulated soil solution and desorption on Mg-Al-LDH (4:1) were measured. At an optimum speed of 250 rpm, pH value of 7 and adsorbent dosage of 2 g/L, the amounts of nitrate adsorption on Mg-Al- LDH (3:1) and Mg-Zn-LDH (3:1) and also on Mg-Al- LDH (4:1) and Mg-Zn-LDH (4:1) were obtained after 30 and 60 min, respectively. Isotherm studies indicated that nitrate adsorption on soil, soil-LDH mixture, and LDH fitted Langmuir linear isotherm. The highest nitrate adsorption on Mg-Al-LDH (4:1) and a mixture of soil-Mg-Al-LDH (4:1) were 188.67 and 107.52 mg/g, respectively. Among the studied kinetic equations for nitrate adsorption on Mg-Al-LDH (4:1), the pseudo-second-order with R2=0.998 had the best fitness. Negative values of ∆H in different nitrate concentrations indicated the exothermic process of nitrate adsorption on Mg-Al-LDH (4:1). In the presence of other anions, Mg-Al-LDH (4:1) removed nitrate preferentially. Moreover, Mg-Al-LDH (4:1) could exchange nitrate 20 times in different concentrations with no reduction in its adsorption capacity.

Synthesis of Fe3O4-decorated Mg-Al layered double hydroxides magnetic nanosheets to improve anti-ultraviolet aging and microwave absorption properties used in asphalt materials

Previous studies showed that Mg-Al layered double hydroxides (Mg-Al LDHs) had well anti-ultraviolet (anti-UV) aging properties when used in the asphalt materials, but it cannot contribute to improve the self-healing properties to repair cracks caused by UV aging under the microwave radiation. Fe3O4 has well microwave absorption and based on the layered structure and large surface area of Mg-Al LDHs, the primary objective of this work was to synthesize Fe3O4-decorated Mg-Al layered double hydroxides magnetic nanosheets, to envisage that the added bitumen modifier has both enhanced anti-UV aging properties and microwave absorption properties. Three modifiers were obtained by the adhesion of Fe3O4 magnetic particles on the surface of Mg-Al LDHs nanosheets, and named as L1F1 (the mass ratio of LDHs: Fe3O4 = 1:1), L2F1 (the mass ratio of LDHs: Fe3O4 = 2:1) and L1F2 (the mass ratio of LDHs: Fe3O4 = 1:2). Morphology, phase composition, chemical structure, anti-UV aging properties, static magnetic properties and microwave absorption properties of them were detected by different analytical methods. Results demonstrate that all magnetic nanosheets present the ferromagnetic behavior, L2F1 shows the lowest MS value among three types of magnetic nanosheets, and the value increases from 28.67 emu·g−1 to 56.78 emu·g−1 with augmented Fe3O4-LDHs ratio. Additions of Fe3O4 significantly enhance the anti-UV aging properties and microwave absorption properties of Mg-Al LDHs. The maximum RL value of L1F2 is recorded as more than two times of that of LDHs, and L1F2 shows the best anti-UV aging properties and microwave absorption properties among all magnetic nanosheets.

Arginine and lysine-functionalized layered double hydroxides as efficient sorbents for radioactive Co2+ removal by chelate-facilitated immobilization

An increase in heavy metal contamination in aquatic environments require an efficient sorbent for the removal and reuse of toxic elements. We attempted to synthesize arginine/lysine-functionalized MgAl LDHs in one-pot without using any hazardous alkaline reagents. The LDHs produced at lower temperatures showed larger numbers of amino acids on their surfaces, while these are exchanged with CO32− at higher temperatures. The arginine/lysine present on the surface of LDH enhanced the adsorption of Co2+ and showed the highest adsorption capacity of 1.159 and 1.170 mmol/g for the LDHs functionalized with lysine and arginine, respectively. Kinetics studies indicated that the adsorption of Co2+ occurred by multiple mechanisms. The Co2+ adsorption on these amino acid functionalized LDHs occurs by the formation chelation complex with amino acid, which provide better vicinity of Co2+ to basic LDH that facilitating the enhanced immobilization. The sorption of other divalent metal ions on these arginine/lysine functionalized LDHs followed the order of Co2+ > Ni2+ > Mn2+ > Fe3+. The Co2+ forms diamine-like coordination that is stable on the surface of LDH and causes higher sorption densities, while other metals form partial glycine-like coordination that detaches the amino acid from the surface of LDH, thereby leading to lesser sorption capacity. The conversion of anionic LDH in to a cationic sorbent was successfully fabricated by these arginine/lysine-assisted methods and explored for the remediation of Co2+ from aqueous solution.

Fabrication and characterization of an actively protective Mg-Al LDHs/Al2O3 composite coating on magnesium alloy AZ31

A magnesium-aluminum layered-double-hydroxides (MgAl LDHs) coating was fabricated on the surface of Mg alloy AZ31, followed by electrophoretic deposition of an Al2O3 nanoparticles layer. The morphology, structure and composition of the composite coatings were investigated by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). Ball on disc tests were carried out for measurements of the friction coefficient, wear loss and morphology of worn surfaces. Corrosion behavior of the coatings was investigated using potentiodynamic polarization curves and electrochemical impedance spectroscopy. Results indicate that the LDHs/Al2O3 composite coatings fabricated with 2.5 g/L Al2O3 nanoparticles solution exhibited best wear resistance, while best corrosion resistance was associated with the composite coating fabricated with 0.5 g/L Al2O3 nanoparticle solution. A sound mechanism for improving wear-resistance of the resulting coatings was proposed.