Zn2Al-layered Double Hydroxide Research Articles

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

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

Pseudomonas Cepacia Lipase Immobilized on Zn2al Layered Double Hydroxides: Evaluation of Different Methods of Immobilization for the Kinetic Resolution of (Rs)-1-Phenylethanol

Pseudomonas Cepacia Lipase Immobilized on Zn2al Layered Double Hydroxides: Evaluation of Different Methods of Immobilization for the Kinetic Resolution of (Rs)-1-Phenylethanol

Layered Double Hydroxides as Slow-Release Fertilizer Compounds for the Micronutrient Molybdenum.

Molybdenum (Mo) is an essential plant micronutrient. Despite low plant Mo requirements, deficiencies are not uncommon and soluble Mo fertilizers are often applied. However, soluble Mo may result in poor Mo use efficiency due to strong sorption (acid weathered soils) or leaching (lighter-textured soils). Here, ZnAl layered double hydroxides (LDHs), loaded with molybdate (MoO4), were examined for their potential as slow-release Mo compounds. Chloride-exchanged LDHs with varying Zn/Al ratios (2, 3, and 4) were exchanged with MoO4. Zn2Al LDH indicated MoO4 intercalation, whereas Zn3Al and Zn4Al LDHs bound MoO4 merely on edge sites. Short-term Mo-LDH incubation identified sulfate, carbonate, and phosphate as the most competitive anions for MoO4 exchange. Long-term Mo-LDH incubation in simulated pH-neutral soil solutions demonstrated slow Mo release from Zn2Al LDH (half-life of 35 h), with a total Mo desorption of up to 85%. For Zn3Al and Zn4Al LDHs, Mo desorption was limited to <20%. Finally, several macronutrient fertilizers were tested as possible carriers for Mo-LDH fertilizer compounds.

Use of central composite design and surface modeling for cadmium (ii) ions removal from aqueous environment using novel modified layer double hydroxide

In this work, Zn2Al-layered double hydroxide (LDH) that modified with Ponceau 4R (E 124) as food coloring, (Zn2Al-LDH/Ponceau) was synthesized and characterized using different techniques including, X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray (EDX) spectroscopy. Zn2Al-LDH/Ponceau was then applied for Cd2+ removal from aqueous solution. The response surface methodology (RSM) approach using central composite design (CCD) was applied to develop a mathematical model and optimize process parameters for Cd2+ removal from aqueous solution using a chemically modified Zn2Al-LDH/Ponceau. The optimal conditions to remove Cd2+ from aqueous solution were found to be initial Cd2+ concentration of 76 mg.L-1, pH value of 4.22, adsorbed amount of 0.04 g, temperature of 30.3 °C, and the contact time of 46 min. The isotherm and kinetics and thermodynamics of the adsorption were investigated in detail. The obtained results suggested the adsorption of Cd2+ onto Zn2Al-LDH/Ponceau follow Langmuir isotherm and the kinetic data are in good agreement with the Elovich kinetic model. In addition, the results of thermodynamic parameters indicated that the adsorption process was instantaneous nature and exothermic.

Adsorption of Orange II Onto Zn2Al–Layered Double Hydroxide Prepared From Zinc Ash

The dye industry is one of the largest water consuming industries, and at the same time generates large quantities of wastewaters. The resulting wastewaters require proper treatment before discharge, because the dye contents have a negative effect on the water body and organisms present in it. The most efficient treatment method for water containing dyes is represented by adsorption processes. The challenge with these adsorption processes is to develop new, efficient, viable, and economic adsorbent materials. Therefore, in the present paper, the performance of Zn2Al-layered double hydroxide, prepared from an industrial waste (zinc ash) as a zinc source, was investigated in the Orange II dye adsorption process. The Zn2Al-layered double hydroxide prepared from secondary sources presents similar morphological and structural characteristics as those prepared from analytical grade reagents. The influence of initial dye concentration, adsorption time, solid:liquid ratio, pH, and temperature was evaluated in order to confirm the benefit of this waste valorization. A comparison with the reference Zn2Al-layered double hydroxide prepared from analytical grade reagents was performed and the results show that due to the small presence of impurities, the material prepared from zinc ash shows better adsorption capacities (qmax,exp = 42.5 mg/g at 293 K) than the material prepared from reagents (qmax,exp = 36.9 mg/g at 293 K), justifying the utilization of secondary sources for layered double hydroxides preparation. The proposed treatment process presents advantages from both economic and environmental protection point of view.

Response Surface Methodology (RSM) for Statistical Optimization of Cd2+ Removal Using Modified Zn2Al-layer Double Hydroxide by Quinoline Yellow

Modified Zn2Al-layered double hydroxide (LDH) intercalated with Quinoline Yellow (Q) (Zn2Al-LDH/Q) was prepared by a facile and simple method and then used to remove of Cd2+ ions from water. The chemical composition and morphology of Zn2Al-LDH/Q was investigated by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Field emission Scanning electron microscopy (FE-SEM) and Energy-dispersive X-ray spectroscopy. Response surface methodology was employed to optimize the adsorption parameters of Cd2+ Such optimization was undertaken to ensure a high efficiency over the experimental ranges employed and to evaluate the interactive effects of the initial concentration of Cd2+, pH, adsorbent dosage, temperature and contact time in order to improve the conditions employed in the batch process. The analysis of variance (ANOVA) indicated that a second-order polynomial regression equation was the most appropriate polynomial for fitting the experimental data. The experimental confirmation tests showed a correlation between the predicted and experimental responses (R2). The optimum adsorption parameters were predicted as an initial Cd2+ concentration of 35 mg l-1, a pH value of 4.17, the adsorbent dosage of 0.03 g/L, a temperature of 32.5 °C and contact time of 51 min. Under optimum conditions, the highest adsorption efficiency and maximum adsorption capacity were 45% and 12.18 mg/g, respectively.

Zn2Al Layered Double Hydroxides Intercalated with Nitrate and p-Aminobenzoate as Ultraviolet Protective Agents in Low-Density Polyethylene Nanocomposites and Natural Insulating Oils

Zn2Al-Cl and Zn2Al-NO3 layered double hydroxides (LDHs) were synthesized through the fixed pH co-precipitation method and used as precursor materials for the intercalation of p-aminobenzoate through anion exchange reactions. Since chloride in Zn2Al-Cl was only partially exchanged with p-aminobenzoate, the phases Zn2Al-NO3 and Zn2Al-N -AB (nitrate exchanged with p-aminobenzoate) were used in different percentages as functional fillers to produce nanocomposites of low-density polyethylene doped with maleic anhydride (LDPE). Analysis of thermal properties showed that the melting and recrystallization temperatures were slightly increased in the nanocomposite containing 5 wt.% Zn2Al-N-AB. Weathering tests performed with neat LDPE and the nanocomposite films showed that the addition of the LDHs improved ultraviolet (UV) absorption and reduced the LDPE degradation by 25 and 76% when using Zn2Al-NO3 and Zn2Al-N-AB, respectively, as fillers, showing a promising UV-shielding effect. Preliminary results also showed a potential application of Zn2Al-N-AB as antioxidant in natural insulating oils (natural ester FR3 and castor oil), opening new opportunity of applications.

A molecular dynamics framework to explore the structure and dynamics of layered double hydroxides

Abstract It is presented a straightforward procedure based on the CLAYFF force field to perform molecular dynamics (MD) computer simulations with the GROMACS open source package of layered double hydroxide (LDH) materials with different intercalated anions. This procedure enables running very long simulations of systems where all atomic positions are allowed to move freely, while maintaining the integrity of the LDH structure intact. Therefore, it has the potential to model different important applications of LDH involving ion-exchange and interlayer equilibrium processes in diverse areas as drug delivery, water purification, and corrosion protection. The magnesium-aluminium based LDH with a metallic ratio 2:1 (Mg2Al) was chosen to validate our computer simulation framework, because of the comprehensive experimental and computational studies reported in the literature devoted to the understanding of the structure of Mg2Al LDH. Potential parameters from the literature were used to model the Mg2Al LDH with different intercalated anions using a new set of atomic point charges calculated with the DDEC6 formalism. Once the model was validated through careful comparisons of the simulated and experimental structures, the procedure was adapted to the Zn2Al LDH materials. Lennard-Jones parameters had to be developed for zinc (II) cations and calibrated using the experimental structural data found in the literature for Zn2Al LDH and the height of the galleries determined experimentally in this work for Zn2Al with intercalated nitrate anions. The consistency of the model is proved by carrying out MD simulations to reproduce in the computer the typical experimental conditions in which the Zn2Al LDH is immersed in a sodium chloride water solution to act as a nanotrap for aggressive anions in corrosion protection applications. The LDH structure is maintained in the MD simulation in which the LDH is free to move alongside the solution and allowing a natural anion exchange between the LDH and the solution as well as dehydration/hydration of the basal space.

DFT study of the intercalation of layered double hydroxides and layered hydroxide salts with dodecylsulfate and dodecylbenzene sulfonate: Exfoliation and hydration properties

DFT calculations were performed for the simulation of the intercalations of Zn2Al-layered double hydroxide and Zn-layered hydroxide salts with dodecylsulfate and dodecylbenzene sulfonate. A structural and energetic analyses of the exfoliation processes were computed and compared with Perdew-Burke-Ernzerhof exchange-correlation (PBE) and Van der Waals-aware density (vdW-DF) functionals and with the semi-empirical approach DFT-D2. It could be concluded that the layers cell parameters were not affected by the applied approach. On the other hand, the basal spacing and the exfoliation energies presented variations with respect to the simulation. The influence of water molecules hydrating the polar heads of the anions intercalated in the interlayer region was also investigated. Furthermore, the interactions between the anions and the positive layers and the influence of hydration waters could be resolved by means of charge density difference plots and Bader charges. Projected density of states (PDOS) showed the possible acid and basic sites of these compounds for both dehydrated and hydrated structures.

Growth of Hierarchical Hexagonal Layered Double Hydroxide Crystals to Large Elongated Spindle Shaped Particles

Large spindle/rod shaped Zn2Al-layered double hydroxide crystals with specific crystallographic orientation of active (101) and (104) facets have been prepared by rapid aqueous co-precipitation followed by hydrothermal treatment. The rods have an average aspect ratio around 12 (length of the major axis to width ratio) and we observed that the aggregation tendency of the particles is significantly low. The evolution of the rod like morphology after the hydrothermal treatment was explained using dissolution and recrystallization mechanism.

Harnessing self-supported Au nanoparticles on layered double hydroxides comprising Zn and Al for enhanced phenol decomposition under solar light

Gold nanoparticles (AuNPs) self-coupled on semiconductors have attracted extensive attentions in the field of catalysis, however, the progress in understanding and optimizing their photocatalytic performance in response to solar light irradiation is limited. In this paper, a series of AuNPs with Zn2Al-layered double hydroxide (LDH) as support was fabricated via self-assembly routes at room temperature and the tuned oxidation state of AuNPs (as Au0, Au3+ as well as mixed Au0/Au3+) was revealed to have a crucial effect on establishing their photocatalytic efficiency for the degradation of phenol from aqueous solution under solar irradiation. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses permitted to characterize the specific interactions of Zn2Al-LDH with AuNPs and to verify that the state of Au0/Au3+NPs appears due to the electron transfer from Zn2Al-LDH to AuNPs when Zn2Al-LDH reconstruction in the aqueous solution of Au(O2CCH3)3 was achieved under solar irradiation. On the basis of these AuNPs–Zn2Al-LDH systems, the possible roles of Au0, Au3+ or Au0/Au3+ in establishing synergetic effects with Zn2Al-LDHs supports for enhancing the photocatalytic response induced by the irradiation with solar light, for manipulating the mechanism, and the catalyst stability in phenol degradation process, are critically discussed.

A controlled release strategy of antifouling agent in coating based on intercalated layered double hydroxides

A controlled release method of antifouling agent was demonstrated via the model coating which was fabricated by sodium paeonolsilate (PAS) intercalated into Zn2Al Layered Double hydroxides (LDH) and then dispersed in the mixture of acrylic resin and colophony with weight ratio of 2:1. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) confirm the intercalation of PAS into the galleries of Zn2Al-LDH. Some larger particles of Zn2Al-PAS-LDH composite in the coating were observed owing to its aggregation, which was revealed by Laser scanning confocal microscope (LSCM). The release tests of the Zn2Al-PAS-LDH coating in 3.5% NaCl solution showed that no burst release phenomenon occurred at the beginning stage and a slower release rate of PAS (0.54ppm/d) was obtained compared with the pristine PAS coating (1.06ppm/d), exhibiting its preferable controlled release behavior. The adhesion experiment using Ulva zoospores indicated that Zn2Al-PAS-LDH composite obviously increases the utilization rate of PAS owing to its controlling release property. Therefore, the present work provided a useful strategy to decrease the waste of antifouling agent and prolong the lifetime of antifouling coatings.

Molecular design confirmation for proposition of improved photophysical properties in a dye-intercalated layered double hydroxides

In the present research, Zn2Al layered-double hydroxide (LDH) intercalated with Acid Red 27 was prepared by coprecipitation method, while solutions of Zn(ii) and Al(iii) nitrate salts reacted with an alkaline solution of Acid Red 27.

An Inexpensive Co-Intercalated Layered Double Hydroxide Composite with Electron Donor-Acceptor Character for Photoelectrochemical Water Splitting.

In this paper, the inexpensive 4,4-diaminostilbene-2,2-disulfonate (DAS) and 4,4-dinitro-stilbene-2,2- disulfonate (DNS) anions with arbitrary molar ratios were successfully co-intercalated into Zn2Al-layered double hydroxides (LDHs). The DAS(50%)-DNS/LDHs composite exhibited the broad UV-visible light absorption and fluorescence quenching, which was a direct indication of photo-induced electron transfer (PET) process between the intercalated DAS (donor) and DNS (acceptor) anions. This was confirmed by the matched HOMO/LUMO energy levels alignment of the intercalated DAS and DNS anions, which was also compatible for water splitting. The DAS(50%)-DNS/LDHs composite was fabricated as the photoanode and Pt as the cathode. Under the UV-visible light illumination, the enhanced photo-generated current (4.67 mA/cm2 at 0.8 V vs. SCE) was generated in the external circuit, and the photoelectrochemical water split was realized. Furthermore, this photoelectrochemical water splitting performance had excellent crystalline, electrochemical and optical stability. Therefore, this novel inorganic/organic hybrid photoanode exhibited potential application prospect in photoelectrochemical water splitting.

Structural characterization and electrocatalytic application of hemoglobin immobilized in layered double hydroxides modified with hydroxyl functionalized ionic liquid

Hemoglobin (Hb) was immobilized in Zn2Al-Layered Double Hydroxides (LDH) modified with Hydroxyl Functionalized Ionic Liquid (HFIL) through adsorption and coprecipitation method, respectively. Adsorption experiments showed that the presence of HFIL could enhance the maximum protein loading. However, the Hb loading through coprecipitation technique was far higher than that for adsorption. The role of HFIL on the interaction between Hb and LDH was investigated by XRD, FTIR, UV–vis and fluorescence spectroscopies. Although the quaternary structure of Hb entrapped in HFIL–LDH through coprecipitation technique (denoted as HFIL–LDH–Hbcop) might be altered slightly more than that in LDH (LDH–Hbcop), its secondary structure and redox-active heme groups kept intact. Morphologies of LDH–Hbcop and HFIL–LDH–Hbcop biohybrids were analyzed through SEM and TEM images. The direct electrochemistry of the immobilized Hb indicated that the coprecipitation bioelectrode performed better than that of the corresponding adsorption one. Regardless of adsorption and coprecipitation, the introduction of HFIL could distinctly promote the electron transport. Among all bioelectrodes, HFIL–LDH–Hbcop/GCE displayed the best electrocatalytic activity for H2O2 determination with a larger electroactive Hb percentage (6.76%), higher sensitivity (40.63A/Mcm2) and lower detection limit (0.0054μmol/L). So HFIL–LDH could effectively immobilize enzymes via coprecipitation technique, which had potential applications in the fabrication of electrochemical biosensors.

Fabrication of (Calcein–ZnS)n Ordered Ultrathin Films on the Basis of Layered Double Hydroxide and Its Ethanol Sensing Behavior

(Calcein–ZnS)n ultrathin films (UTFs) were fabricated through a two-step procedure including the layer-by-layer (LBL) assembly of calcein and exfoliated Zn2Al layered double hydroxide (LDH) nanosheets, followed by an in situ gas/solid reaction with H2S. The assembly process of calcein and exfoliated LDH was monitored by UV–vis absorption measurements to get a stepwise and regular growth of the (calcein–LDH)n UTFs upon increasing the deposited cycles. By an in situ gas–solid reaction with H2S, the resulting sulfurization derivatives denoted as (calcein–ZnS)n UTFs were obtained. The resulting (calcein–ZnS)30 UTF possesses high ethanol sensing performance (response value is 8.9–100 ppm ethanol) at relatively low working temperature (90 °C). The LBL assembly process and chemical conversion technique based on Zn2Al–LDH combine the functional organic molecules and inorganic semiconductor, which enables us to develop innovative composite materials with adjustable compositions for a broad range of applications.

Improved thermal and photostability of an anthraquinone dye by intercalation in a zinc–aluminum layered double hydroxides host

Intercalation of the dianion of the anthraquinone dye Acid Green 28 (1,4-bis[(4-butylbenzene-2-sulphonate)amino]-5,8-dihydroxyanthraquinone) (AG28 2−) into a Zn 2Al–layered double hydroxides (LDH) has been carried out by an anion-exchange method in an effort to improve its thermostability and photostability. The interlayer distance of the LDH was 1.918 nm after reaction with AG28 2− anions, confirming their intercalation into the interlayer galleries of the LDH host. Infrared spectroscopy and thermogravimetric analysis revealed the presence of host–guest interactions between LDH layers and AG28 2− anions. The thermostability of AG28 as its sodium salt and Zn 2Al–AG28–LDH were compared by thermogravimetric–differential thermal analysis and UV–visible spectroscopy. It was found that the thermostability of AG28 was markedly improved by intercalation into the Zn 2Al–LDH host, whilst the photostability was enhanced slightly. In their composites with polyethylene, it was also found Zn 2Al–AG28–LDH possessed better thermostability and photostability than AG28 as its sodium salt.

Tunable Photoluminescence Properties of Fluorescein in a Layered Double Hydroxide Matrix by Changing the Interlayer Microenvironment

This paper reports a novel method to tune the fluorescence properties of fluorescein (FLU) in a 2D matrix of layered double hydroxide (LDH) by changing the interlayer microenvironment. FLU and surfactants with different alkyl chain lengths were cointercalated in the galleries of a Zn2Al LDH by the anion exchange method. Thin films of FLU-CnH2n+1SO3/LDH (n = 5, 6, 7, 10, and 12, respectively; n stands for the number of carbon in the alkyl chain), which possess a well c-orientation revealed by XRD and SEM, were obtained by the solvent evaporation method on Si substrates. It was found that the orientation of FLU and its anisotropy, fluorescence wavelength, fluorescence quantum yield, and lifetime correlate with the microenvironment of the LDH gallery, which can be tuned by simply changing the alkyl chain length of the surfactant. The optimal fluorescence quantum yield, anisotropy, the longest fluorescence lifetime and the strongest photostability of the FLU-CnH2n+1SO3/LDH film can be obtained with n = 7, due...

PVA nanocomposites reinforced with Zn2Al LDHs, intercalated with orange dyes

Zn2Al-layered double hydroxides (LDH) were intercalated with anions of the dyes Orange G, Orange II, and Methyl Orange by alkaline co-precipitation of aqueous solutions of zinc chloride and aluminum nitrate simultaneously in the presence of dye sodium salts. Transparent, homogeneous, and colored nanocomposite films were obtained by casting after dispersing the dye-intercalated LDHs (pigments) into commercial poly(vinyl alcohol) (PVA). The films were characterized by X-ray diffraction, ultraviolet–visible spectroscopy, thermal analysis (thermogravimetric analysis (TGA)) and differential thermal analysis (DTA)), and mechanical testing. Mechanical reinforcement of the PVA compounded with the dye-intercalated LDHs was achieved, and reasonable increases in Young’s modulus and ultimate tensile strength were observed with as little as 0.5% added filler, while larger amounts tended to decrease the reinforcement effect. These results demonstrate the onset of a new range of potential applications for layered double hydroxide intercalated with dyes in the preparation of polymer composite multifunctional materials.

Studies on the Orientation and Polarized Photoluminescence of α-Naphthalene Acetate in the Layered Double Hydroxide Matrix

This paper reports a novel method to tune the fluorescence properties of α-naphthalene acetate (α-NAA) in a two-dimensional matrix of layered double hydroxide (LDH) by changing the orientation of the chromophore. The α-NAA and 1-heptanesulfonic acid sodium (HES) with different molar ratios were co-intercalated in the galleries of Zn2Al LDH by the anion exchange method. Thin films of α-NAA−HES/LDH (x%, x stands for the molar percentage of α-NAA), which have a well c-orientation confirmed by the X-ray diffraction (XRD) and scanning electron microscopy (SEM), were obtained by the solvent evaporation method on Si substrates. On the basis of the results from XRD and fluorescence polarization, the orientation (Ψ angle) of the α-NAA molecule in the LDH matrix was calculated to be 59° (x = 12.1%), 61° (x = 15.1%), 64° (x = 20.0%), 65° (x = 23.3%), 68° (x = 30.0%), and 71° (x = 34.4%) with respect to the normal to the thin film, respectively. Furthermore, the fluorescence wavelength, emission intensity, and lifeti...