CaAl-layered Double Hydroxide Research Articles

Immobilisation remediation of arsenic-contaminated soils with promising CaAl-layered double hydroxide and bioavailability, bioaccessibility, and speciation-based health risk assessment

Arsenic (As)-contaminated soil poses great health risk to human mostly through inadvertent oral exposure. We investigated CaAl-layered double hydroxide (CaAl-LDH), a promising immobilising agent, for the remediation of As-contaminated Chinese soils. The effects on specific soil properties and As fractionation were analyzed, and changes in the health risk of soil As were accurately assessed by means of advanced in vivo mice model and in vitro PBET-SHIME model. Results showed that the application of CaAl-LDH significantly increased soil pH and concentration of Fe and Al oxides, and effectively converted active As fractions into the most stable residual fraction, guaranteeing long-term remediation stability. Based on in vivo test, As relative bioavailability was significantly reduced by 37.75%. Based on in vitro test, As bioaccessibility in small intestinal and colon phases was significantly reduced by 25.65% and 28.57%, respectively. Furthermore, As metabolism (reduction and methylation) by the gut microbiota inhabiting colon was clearly observed. After immobilisation with CaAl-LDH, the concentration of bioaccessible As(Ⅴ) in the colon fluid was significantly reduced by 61.91%, and organic As (least toxic MMA(V) and DMA(V)) became the main species, which further reduced the health risk of soil As. In summary, CaAl-LDH proved to be a feasible option for immobilisation remediation of As-contaminated soils, and considerable progress was made in relevant health risk assessment.

A Tablet-Operated Portable Wireless Sensing Platform for Field Simultaneous Rapid Detection of both Cd (II) and Pb (II) Using CaAl-Layered Double Hydroxide Nanocomposite Modified Integrated Screen-Printed Three-Electrode

It’s very essential to exploit a portable wireless integrated sensing platform for field simultaneous, on-site detection of heavy metal ions pollution that has been exhibited to Serious ecological and health risks even under trace levels, including Cd (II) and Pb (II) ions. In this work, we developed a portable sensing platform, consisting of an integrated screen-printed electrode (SPE) with the calcium/aluminum-layered double hydroxide (CaAl-LDH) nanocomposite based on carboxyl functionalized multi-walled carbon nanotubes (MWCNTs-COOH), a hand-held wireless electrochemical potentiostat and a tablet with a specially designed app, for field simultaneous rapid detection of both Cd (II) and Pb (II) in water environmental sample. The CaAl-LDH was produced through a facilely hydrothermal method, and the CaAl-LDH nanocomposite with MWCNTs-COOH was prepared by a one-step ultrasonic route, which demonstrated superior sensing performance for simultaneous determination of both Cd (II) and Pb (II) with a broad detection range (2–250 μg L−1 for Cd (II) and 5–250 μg L−1 Pb (II)) and low limit of detection (LOD) (0.96 μg L−1 Cd (II) and 0.74 μg L−1 for Pb (II)).Furthermore, the proposed tablet-operated portable wireless sensing platform was utilized for detection of both Cd (II) and Pb (II) in farmland irrigation canals with acceptable recoveries.

Enhancement of the flame retardant properties of PPS-based composites via the addition of melamine-coated CaAl-LDH fire-retardant filler

Addressing the global energy crisis and its environmental implications has become a critical challenge, prompting a growing interest in electric vehicles (EVs) as an alternative to fossil fuel-dependent vehicles. Engineering plastics (EPs), with their lightweight and cost-effective properties, are attractive candidates for various applications, including automotive components. However, certain drawbacks, such as poor thermal conductivity and fire resistance, have limited their widespread adoption. In this study, we focus on polyphenylene sulfide (PPS) as a promising super-engineering plastic with high thermal stability and mechanical properties but low thermal conductivity. To enhance its properties, we explore the incorporation of CaAl layered double hydroxide (CaAl-LDH) as a fire-retardant filler, with melamine coating to improve thermal stability. When fabricating composites at high filler ratio (over 30 %), the CaAl-LDH filler thermally decomposes and loses its flame retardant performance. To prevent this, our group attempted to provide thermal stability through melamine coating. The resulting PPS/GF/40 m-CaAl-LDH composites exhibited improved thermal conductivity of 0.37 W/m•K which is almost twice that of the PPS/GF composite, and mechanical properties, along with exceptional flame-retardant behavior, achieving a UL94 V-0 rating and limited oxygen index of 52.74 %. After a fire test, PPS/GF/40 m-CaAl-LDH composites shows improved tensile strength due to the molten m-CaAl-LDH wrapped the entire surfaces protecting from the flames. This research presents a promising strategy for developing high-performance PPS-based materials with applications in diverse industrial fields, including the automotive industry.

Thermoelectric performance of chalcogenide-free CaAl-layered double hydroxide–antimony trioxide nanowire composites with low thermal conductivity

Thermoelectric (TE) materials have attracted considerable interest for their potential and the figure of merit ZT serves as a crucial metric for evaluating TE performance. Chalcogenide materials, such as tellurium (Te) and selenium (Se), have been favored for high-performance TE applications. However, their toxic nature raises concerns, demanding exploration of non-toxic alternatives suitable for human-contacting devices.This study focused on antimony trioxide (Sb2O3) due to its high Seebeck coefficient and explored the potential of layered double hydroxide (LDH) materials as a non-toxic alternative for efficient TE materials. Composites of Sb2O3 nanowires integrated with 2D CaAl-LDH were synthesized to reduce thermal conductivity and improve TE performance. The composites displayed enhanced electrical conductivity, resulting in a significantly improved power factor. The introduction of CaAl-LDH facilitated the charge carrier transport paths, leading to better electrical performance. Furthermore, the composites exhibited reduced thermal conductivity due to phonon scattering at the heterointerfaces between Sb2O3 and CaAl-LDH. As a result, the Sb2O3/CaAl-LDH_70 composite achieved a maximal ZT value of 0.0485 at 473 K, demonstrating promising potential for LDH-based composites as environmentally friendly TE materials. These findings contribute to sustainable energy conversion technologies, ensuring progress towards more efficient and biocompatible TE materials.

Corrosion Protection Mechanism Study of Nitrite-Modified CaAl-LDH in Epoxy Coatings

In this work, nitrite and molybdate-modified CaAl layered double hydroxide(CaAl-LDH) was first synthesized, and the corrosion protection mechanism of CaAl-LDH intercalated with nitrites in epoxy coatings was investigated. Scanning electronic microscopy (SEM) and the energy dispersive spectroscopy (EDS) was used to characterize the morphology and element composition of the synthesized powder. Fourier transform infrared spectroscopy (FTIR) was used to characterize the information of chemical composition, and X-ray diffraction (XRD) was used to analyze the structure. The SEM and XRD results indicated that the LDH structure was destroyed in the molybdate modification process, and CaMoO4 precipitates were formed. Therefore, molybdates cannot be used to be loaded in CaAl-LDH interlayer space for synthesis of an active corrosion inhibition container. The nitrite release curve and the chloride concentration decreasing curve were measured to study the anion-exchange reaction by UV-Vis spectroscopy and a home-made Ag/AgCl probe, respectively. The corrosion protection effect of the CaAl-LDH loaded with nitrites towards the carbon steel was evaluated in 0.02 M NaCl solution by electrochemical impedance spectroscopy (EIS). Then the powder was added in the epoxy coating with 2% addition (weight vs. epoxy resin). The coating morphology and roughness were evaluated by SEM and laser microscopy, and the corrosion protection effect was investigated by EIS in an immersion period of 21 d. The fitted coating resistance of the sample with 2% LDH intercalated with nitrites was one order of magnitude higher than that with 2% LDH, and the latter one was two orders of magnitude higher than the blank sample. Local electrochemical impedance spectra (LEIS) was used to characterize the corrosion development process in micro-corrosion sites. The corrosion product of the scratched area after salt spray exposure was analyzed by EDS and Raman spectroscopy. The corrosion protection mechanism of the CaAl-LDH loaded with nitrites was proposed based on the above experimental results.

Super-stable mineralization of Cu, Cd, Zn and Pb by CaAl-layered double hydroxide: Performance, mechanism, and large-scale application in agriculture soil remediation

The synthesized CaAl-layered double hydroxide (CaAl-LDH) shows excellent performance in potentially toxic metals (PTMs) removal, and the removal capacity of CaAl-LDH toward Cu2+, Zn2+ and Pb2+ in aqueous solution is 502.4, 315.2 and 600.0 mg/g respectively. Cu2+ and Zn2+ are removed through isomorphic substitution of laminate Ca and dissolution-reprecipitation, leading to the formation of CuAl-LDH and ZnAl-LDH mineralization products. Pb2+ is removed by the complexation and precipitation to form Pb3(CO3)2(OH)2. The application of CaAl-LDH in laboratory-scale soil remediation shows that target PTMs are gradually mineralized into relatively stable oxidizable and residual state, and the immobilization efficiency of available Cu, Zn, Cd and Pb reaches 84.62 %, 98.66 %, 96.81 % and 70.27 % respectively. In addition, practical application in farmland results in the significant reduction of available Cu, Zn, Cd and Pb with the immobilization efficiency of 30.15 %, 67.30 % and 57.80 % and 38.71 % respectively. Owing to the super-stable mineralization effect of CaAl-LDH, the content of PTMs in the roots, stems and grains of cultivated buckwheat also decreases obviously, and the growth and yield of buckwheat are not adversely affected but improved. The above prove that the super-stable mineralization based on CaAl-LDH is a promising scheme for the remediation of PTMs contaminated agriculture soil.

Highly efficient removal of aqueous Cu(II) and Cd(II) by hydrothermal synthesized CaAl-layered double hydroxide

Adsorbents with a large adsorption capacity and rapid removal rate are required for wastewater treatment containing heavy metal ions. Thus, CaAl-layered double hydroxide (CaAl-LDH) was successfully fabricated by a simple hydrothermal method as an efficacious sorbent to capture Cu(II) and Cd(II) ions in water. The as-synthesized CaAl-LDH exhibited the representative peaks of an LDH, good crystallinity, and a hexagonal lamellar structure. The entire adsorption process of CaAl-LDH for aqueous Cu(II) and Cd(II) was highly efficient and fast. The theoretical maximum removal capacities of CaAl-LDH for Cd(II) and Cu(II) were 1035.4 and 381.9 mg/g, respectively. Cu(II) and Cd(II) ions were adsorbed quickly in the first 60 min, and the kinetics data were generally consistent with a pseudo-second-order model. CaAl-LDH had a large distribution coefficient for Cd(II) (7.55 ×105 mL/g) and Cu(II) (4.78 ×105 mL/g). The possible mechanisms were precipitation, isomorphic substitution, and surface complexation. The results of this study demonstrate the potential applicability of CaAl-LDH for adsorption of heavy metals from aqueous solution.

Permanganate loaded Ca-Al-LDH coating for active corrosion protection of 2024-T3 alloy

Ca-Al-Layered Double Hydroxide (Ca-Al-LDH) coating was explored on 2024-T3 aluminium alloy by in situ growth methodology following a 1 h treatment at atmospheric pressure. Mn-based species were successfully incorporated into the Ca-Al-LDH structure by a low-temperature post-treatment (Ca-Al-LDH-Mn). Both LDH coatings disclosed a flaky-like morphology and low thickness (~0.6 µm). Ca-Al-LDH-Mn coating showed optimal paint adhesion and the highest long-term corrosion resistance in 3.5 wt% NaCl solution. Evaluation of scribed LDH specimens by SEM/EDS techniques up to 7 days of immersion in 3.5 wt% NaCl solution revealed that the presence of Mn species in the Ca-Al-LDH-Mn provided active corrosion protection.

Synthesis of Calcium/Aluminium-Ciprofloxacin-Layered Double Hydroxide for a New Antibacterial Drug Formulation

An antibacterial drug, ciprofloxacin (Cipro) was successfully encapsulated into Ca/Al-layered double hydroxide (CLDH) with molar ratio Ca/Al = 3:1 (R3) by anion exchange method at optimum concentration of 0.2 M Cipro. The successful intercalation was confirmed by patterns analysis of powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), elemental analysis (CHNS) and accelerated surface area and porosity (ASAP) analysis. Basal spacing of CLDH synthesized in this study is 8.7 Å. Due to the inclusion of Cipro into the layered CLDH, basal spacing expanded to 16.2 Å in Ca/Al-Cipro-LDH (CCLDH) compare to in CLDH. The FTIR spectra of the hybrid nanocomposite show resemblance peaks of the layered double hydroxide (LDH) and Cipro, indicating the inclusion of the drug anion into the LDH interlamellae. The percentage loading of Cipro calculated from the data obtained from CHNS is 75.9% (w/w). This shows that Ca/Al-layered double hydroxide, CLDH has prospective application as the host for ciprofloxacin (1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid), an antibacterial drug for a novel drug delivery formulation.

Oxidation of Cysteinate Anions Immobilized in the Interlamellar Space of CaAl-Layered Double Hydroxide.

L-Cysteinate-intercalated CaAl-layered double hydroxide (LDH) was prepared by the co-precipitation method producing highly crystalline hydrocalumite phase with a well-pillared interlayer gallery. The obtained materials were characterized by X-ray diffractometry, IR as well as Raman spectroscopies. By performing interlamellar oxidation reactions with peracetic acid as oxidant, oxidation of cysteinate to cystinate in aqueous and cysteinate sulfenic acid in acetonic suspensions occurred. The oxidations could be performed under mild conditions, at room temperature, under neutral pH and in air. It has been shown that the transformation pathways are due to the presence of the layered structure, that is, the confined space of the LDH behaved as molecular reactor.

Super-stable mineralization of cadmium by calcium-aluminum layered double hydroxide and its large-scale application in agriculture soil remediation

Cadmium (Cd) contaminated cropland has posed severe risks to human health. While in-situ Cd immobilization by stabilizer has been widely adopted in practice, there is still a huge challenge to develop cost-effective stabilizers with strong and long-term immobilization ability. In this work, we report a CaAl-layered double hydroxide (CaAl-LDH) as an efficient stabilizer for Cd2+in-situ immobilization both in lab scale and practice remediation. This material presents fast sorption rate (ca. 5 min) and high capture capacity (592 mg/g) towards Cd2+ in solution, and high immobilization efficiency (up to 96.9%) in soil remediation. Detailed investigations suggest that Cd2+ induces the reconstructing of CaAl-LDH to CdAl-LDH, with Cd being stabilized in a super stable state. In a large-scale and long-term application (in soil of 10 ha for continuous three years’ test), we observe that the CaAl-LDH enables a low Cd content in wheat grain (0.06 mg/kg) that is below the national standard (0.1 mg/kg). By employing a scaling-up production in 3000 ton per year, we demonstrate the CaAl-LDH would be a promising competitive candidate for facile and cost-efficient remediation of Cd contaminated soil.

Novel fluoride rechargeable dental composites containing MgAl and CaAl layered double hydroxide (LDH)

ObjectiveThis study aims to incorporate 2:1 MgAl and 2:1 CaAl layered double hydroxides (LDHs) in experimental dental-composites to render them fluoride rechargeable. The effect of LDH on fluoride absorption and release, and their physico-mechanical properties are investigated. Methods2:1 CaAl and 2:1 MgAl LDH-composite discs prepared with 0, 10 and 30wt% LDH were charged with fluoride (48h) and transferred to deionized water (DW)/artificial saliva (AS). Fluoride release/re-release was measured every 24h (ion-selective electrodes) with DW/AS replaced daily, and samples re-charged (5min) with fluoride every 2 days. Five absorption-release cycles were conducted over 10 days. CaAl and MgAl LDH rod-shaped specimens (dry and hydrated; 0, 10 and 30wt%) were studied for flexural strength and modulus. CaAl and MgAl LDH-composite discs (0, 10, 30 and 45wt% LDH) were prepared to study water uptake (over 7 weeks), water desorption (3 weeks), diffusion coefficients, solubility and cation release (ICP-OES). ResultsCaAl LDH and MgAl LDH-composites significantly increased the amount of fluoride released in both media (P<0.05). In AS, the mean release after every recharge was greater for MgAl LDH-composites compared to CaAl LDH-composites (P<0.05). After every recharge, the fluoride release was greater than the previous release cycle (P<0.05) for all LDH-composites. Physico-mechanical properties of the LDH-composites demonstrated similar values to those reported in literature. The solubility and cation release showed a linear increase with LDH loading. SignificanceLDH-composites repeatedly absorbed/released fluoride and maintained desired physico-mechanical properties. A sustained low-level fluoride release with LDH-composites could lead to a potential breakthrough in preventing early stage carious-lesions.

The Structure and Release Kinetics of Ca–Al Layered Double Hydroxide by Intercalating with Diclofenac Sodium

Diclofenac sodium (DS) is an aryl acetic acid nonsteroidal anti-inflammatory drug which is widely used in various types of chronic bone and joint pains, but its terminal plasma half life is short, often accompanied with gastrointestinal side effects. We try to find an inexpensive and effective drug carrier to prolong the administration interval, maintain a stable blood concentration and reduce side effects. In our work, DS had been intercalated into a layered inorganic host, Ca–Al layered double hydroxide (LDH) by co-precipitation under a nitrogen atmosphere to control the release. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM) were used to investigate the change of chemical structure and morphological structure when DS was inserted into the interlayer of LDH. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) were employed to characterize the electron binding energy of calcium and aluminum cations both on the surface and in the bulk of the samples. The results of absorption peaks, morphologies and the basal spacing increased from 8.6[Formula: see text]Å to 29.59[Formula: see text]Å gave the evidences for the intercalation of DS into the interlayer of CaAl-LDH. The results of XPS and XANES spectra revealed the complexation of –OH and [Formula: see text] with Ca[Formula: see text] and Al[Formula: see text] were both were affected by the loading of DS with CaAl-LDH, but no new chemical bonds were formed. Inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis showed the dissolving process of Ca and Al ions from CaAl-LDH in the solution. In addition, the results of the drug release profile and release kinetic of intercalated LDHs showed that release behavior of DS from intercalated compounds was well controlled.

β-Isocupreidinate‒CaAl-layered double hydroxide composites—heterogenized catalysts for asymmetric Michael addition

β-isocupreidinate (β-iCu) anions having well-known structure and catalytic activity in various asymmetric reactions, were incorporated into the interlayer gallery of hydrocalumite (CaAl-LDH) by the partial delamination-restacking method. Silylation of the outer surface of the LDH with trimethyl silane was also employed to avoid the adsorption of β-iCu on the outer surface and to block the basic sites there. The obtained materials were characterized by a range of instrumental methods (X-ray diffractometry, scanning electron microscopy, ATR-IR and grazing incidence IR spectroscopies). The catalytic activities of the composites were tested in the asymmetric Michael addition of β-nitrostyrene and ethyl 2-fluoroacetoacetate. The β-iCu-pillared LDHs proved to be active and recyclable catalysts with very good diastereoselectivities and acceptable and in 2-propanol very good enantioselectivities. The silylated composite retained its activity and diastereoselectivity even in the third repeated run, when heptane was the solvent.

Effect of polarization switching on piezoelectric and dielectric performance of electrospun nanofabrics of poly(vinylidene fluoride)/Ca–Al LDH nanocomposite

ABSTRACTAt present, highly flexible, durable, and lightweight piezoelectric nanogenerators with high‐power density and energy conversion efficiency are of great interest. The present study reports a new synthetic route for Ca–Al layered double hydroxide (LDH) nanosheets and incorporation of these two‐dimensional nanosheets as filler material into poly(vinylidene fluoride) (PVDF) to produce composite nanofabrics by electrospinning. The polymorphism, crystallinity, and the interaction between PVDF and LDH were studied by Fourier transform infrared spectroscopy, X‐ray diffraction, and differential scanning calorimetry techniques. The synergetic effect of PVDF–LDH interaction and in situ stretching due to electrospinning facilitates the nucleation of electroactive β phase up to 82.79%, which makes it a suitable material for piezoelectric‐based nanogenerators. The piezoelectric performance of PVDF/Ca–Al LDH composite nanofabrics was demonstrated by hand slapping and frequency‐dependent mechanical vibration mode, which delivered a maximum open circuit output voltage of 4.1 and 5.72 V, respectively. Moreover, the composite nanofabrics exhibited a high dielectric constant and low dielectric loss due to superior interfacial polarization at low‐frequency region with LDH loading, promising its potential applications in electronic devices. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48697.

Congo Red Dye Removal Using Ca-Al Layered Double Hydroxide: Kinetics and Equilibrium

This In this study, the Ca-Al layered double hydroxide was used as a potential adsorbent for the removal of Congo red from aqueous solutions. The effects of Initial concentration and contact time on the adsorption properties of Congo red by Ca-Al LDHs were studied. The removal rate of Conge red reached to 59.416 mg/g under room temperature with 0.2g of adsorbent, initial concentration of 50 ppm, adsorption time of 210 min, shaking speed of 90r/min. The experimental equilibrium data for the removal of Congo red were evaluated by various isotherm models. The pseudo-second-order kinetic models were found to fit the adsorption kinetics, and the equilibrium data were appropriately fitted to Langmuir and Freundlich model adsorption isotherm.

Esterification reactions with acetate- or benzoate-containing CaAl-layered double hydroxide samples

Layered double hydroxides (LDHs) consist of layers with two or three positively charged metal ions surrounded by hydroxide ions, water molecules and partially or fully hydrated exchangeable charge-compensating anions between the layers. These materials have many application possibilities. In this work, CaAl-LDH samples were synthesized and used as catalysts. The esterification reactions of acetate and benzoate ions were studied with benzyl bromide under solvent-free conditions over CaAl-LDH samples. The as-prepared as well as the used LDH samples were characterized with X-ray diffractometry, and the reaction products were identified by ATR-IR spectroscopy.

Co(II)-amino acid–CaAl-layered double hydroxide composites – Construction and characterization

The construction of Co(II)-amino acid complexes (l-histidine, l-cysteine, l-tyrosine) among the layers of CaAl-layered double hydroxide was attempted. The stepwise intercalation (introducing the anionic form of the amino acid first, then constructing the Co(II) complex) proved to be unsuccessful, while the direct ion exchange of the anionic form of the separately prepared complex provided with the Co(II) complex intercalated substances. The success of the intercalation was verified by X-ray diffractometry. The resulting composite materials were structurally characterized by a range of instrumental methods like UV–vis, inductively coupled plasma–optical emission, mid-range as well as far infrared spectroscopies and scanning electron microscopy.

Preparation of Ca/Al-Layered Double Hydroxide and the influence of their structure on early strength of cement

Ca/Al-Layered Double Hydroxide (Ca/Al-LDH), was a kind of important anionic clays with broad applications owing to its properties of exchangeable anion and adjustable particle size. In this study, Ca/Al-LDH had been successfully prepared by co-precipitation method, and it was found that the particle size, crystallinity and morphology of Ca/Al-LDH could be tuned via changing ethanol/water ratio of solution. More interestingly, with the increase of the Ca/Al-LDH’s dosage, the different crystal structure of Ca/Al-LDH had promoting effect on the development of the early strength of the cement slurries, however, the change trend of the strength growth rate of various kinds of cement slurries were quite different. Meanwhile, experimental results disclosed that the crystallinity and particle size of Ca/Al-LDH determined its interaction with cement hydration particles. That was likely to lead to a change in tricalcium silicate (C3S) and tricalcium aluminate (C3A) hydration process of accelerating or retarding under the different Ca/Al-LDH content, thus enabling the early strength development of slurry to exhibit different trends. And this finding could provide further interpretation for the effect of hydrotalcite-like materials on cement hydration process and offer a theoretical exploration for its practical application in the future.

Immobilization of palladium nanoparticles as a recyclable heterogeneous catalyst for the Suzuki–Miyaura coupling reaction

This work describes the synthesis of Pd nanoparticles that are stabilized on CaAl-layered double hydroxide functionalized with Tris (tris(hydroxymethyl)aminomethane). The synthesized catalyst is characterized by several different analyses and has been successfully applied to the Suzuki–Miyaura reaction.