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Investigation about iron(III) incorporation into layered double hydroxides: Compositional and structural properties of Mg2FeyAl(1−y)(OH)6-Cl and Zn2FeyAl(1−y)(OH)6-Cl
Abstract
Layered Double Hydroxides (LDH) and related nanocomposites have attracted much attention for biomedical applications and the development of LDH drug carriers composed by endogenous metals, such as iron, is of obvious interest. However, most of the studies reported so far on iron-containing LDH, mainly focusing on the applications, suffer from insufficient data about the synthesis and the characterization of these materials. In this study, it is addressed compositional and structural properties of two series of LDH materials, Mg2FeyAl(1-y)-Cl and Zn2FeyAl(1-y)-Cl with a M²⁺/M³⁺ molar ratio equal to 2 and 0 ≤ y ≤ 1. By combining crystal-chemical reasoning, Rietveld refinements and pair distribution function analysis (PDF), it was possible to differentiate between contributions from crystalline and amorphous components. Concerning Mg-series, for y > 0.5, the compositions were found to slightly deviate from those expected with an increase in the value of R tending to 3. For Zn-series, more heterogeneous samples were obtained with the presence of amorphous 2-line ferrihydrite clearly demonstrated by PDF analysis. As well as providing a reliable approach to the characterization of Fe-LDH, this study gives useful elements for better understanding and interpreting the results reported in the literature regarding these phases.
... 12−14 In all cases, it was found that M 3+ cations avoid close contact. 13,15 Rozov et al. 16 found crystallographic changes with the presence and content of Fe in MgFe-LDH without considering the Fe distribution along the crystal lattice, which has been subsequently demonstrated by Figueiredo et al. 17 The Fe 3+ cation distribution in the octahedral sheet of minerals can affect some properties, such as the nuclear magnetic resonance (NMR) and infrared spectroscopy properties in clay minerals. 18−20 Taking into account the importance of Fe-bearing LDHs and cation ordering in LDHs, one of the aims of this work is to understand, at an atomic scale, the Fe cation distribution in LDHs and the variation of crystallographic properties of Mg:AlFe and Zn:AlFe LDHs with different relative proportions of Fe by means of first principle calculations. ...
... However, after several trials, no convergence was obtained. Therefore, the best approach for calculating the LDH with Fe 3+ is to use Hubbard correction with the optimized spin state (SP+U) and with the minimal net spin state equal to zero (SP0+U), whose optimized cell parameters are in good agreement with the previously reported experimental results 17 (Table 1). The SP+U method yields the closest cell parameters to the experimental values. ...
... This behavior of the LDH structures has also been observed in Mg-and Zn-LDH crystals synthesized experimentally in the laboratory. 16,17 By comparing both theoretical and experimental results ( Figure 5), we find that the computational method used here not only provides crystal structures with cell parameters in good agreement with those previously reported but also reproduces a slight change in the a/b cell axes measured in synthesis experiments with different iron contents. This behavior was also observed experimentally Figure 6). ...
Layered double hydroxides (LDHs) are important components in terrestrial and extra-terrestrial environments. The presence of iron in these minerals provides them a wide potential application in environmental and materials sciences. In this work, the role of Fe in the crystallographic properties of LDHs M2+:M3+ 2:1 with Mg:(Fe,Al), Mg:Fe, Zn:(Fe,Al), and Zn:Fe is investigated by means of quantum mechanical calculations based on the density functional theory (DFT). Several relative proportions of Fe are studied. The cation ordering of these LDHs has been explored, finding useful insights for experimental synthetic paths of these minerals. The a and b cell parameters increase with the iron concentration. Some diffraction lines at high angle decrease in angle and increase in intensity with the increasing iron concentration. All of them agree with the experimental results. The iron substitutions tend to aggregate.
... For instance, Kruissink et al. (1981) and Vucelic et al. (1997) reported a random cation distribution in LDH structures, whereas Sideris et al. (2008) found by Nuclear Magnetic Resonance (NMR) studies that in LDH cations are not randomly distributed. However, Vucelic et al. (1997) and Sideris et al. (2008) reported experimentally a common result, M 3+ cations avoid close contacts, indicating that LDH could have local order, even if no longrange cation order is identified as other authors (Cadars et al., 2011;Figueiredo et al., 2021). In addition, Richardson and Braterman (2007) reported that LDH can be synthesized without cation ordering, although, due to an aging process, these structures can end up having cation ordering. ...
... Once determined the best theoretical approach to study the LDH structures, both Mg-LDH and Zn-LDH structures with an equal distribution and maximum dispersion of Al 3+ cations on the 3 hydroxide layers, i.e. 2 Al 3+ per layer, were optimized by relaxing atomic positions and crystal lattice (Fig. 3, Table 2). In both optimized LDH structures, i. e. Mg and Zn, the cell parameters agree with those reported for experimental LDH with the same M 2+ :Al 3+ ratio (Ennadi et al., 2000;Lombardo et al., 2008;Mahjoubi et al., 2017;Figueiredo et al., 2021), with previous theoretical calculations of LDH (Andre et al., 2015), and with previous calculations using CASTEP on a monolayer brucite model (Liu et al., 2020). Comparing the results using both theoretical approximations, CASTEP and QE, both can be considered similar. ...
... After the optimization using both CASTEP and Quantum Espresso calculations (Fig. 4), c is higher in the hydrated phases (Table 3), while all other parameters remain close to the values of the anhydrous structure. These results are in good agreement with the experimental results previously reported (Miyata, 1983;Boclair et al., 1999;Ennadi et al., 2000;Lombardo et al., 2008;Mahjoubi et al., 2017;Figueiredo et al., 2021). However, there are still some differences in the c parameters between the theoretical and experimental structures, which are influenced by the total number of water molecules in the interlayers Pisson et al., 2008). ...
Layered double hydroxides (LDH) are interesting materials due to their high absorption and catalytic properties. Their applications in environment, agriculture and pharmaceutical fields are becoming widely important. The interlayer and intralayer cation ordering on layered double hydroxides of Mg:Al 2:1 and Zn:Al 2:1 are studied by means of different ordering models at Density Functional Theory level. The cation ordering in LDH is interesting for monitoring the synthesis of these solids and for the applications of LDH, however it is difficult to determine experimentally. We have explored several ordering arrangements of the cation distribution in Mg:Al 2:1 and Zn:Al 2:1 LDH and the effect of these cation arrangements on some crystallographic and spectroscopic properties.
... [21] The incorporation of Fe III into LDH structure has proven to be a challenging task, conducting to impurities and/or amorphous side phases for increasing amounts of iron, as systematically evaluated in a previous work, in which chloride was the intercalated ion. [22] In vivo experiments performed with tablets of M 2 Fe 0.5 Al 0.5 -Cl (M = Mg or Zn) LDH samples by intramuscular implantation in rats attested their biocompatibility with promotion of angiogenesis, tissue remodelling, and collagen formation. [23] These interesting results motivated further studies about iron-based LDH intercalated with species of biological interest. ...
... Both coprecipitation and ion exchange processes were explored in this work. Samples previously reported, M 2 Fe y Al (1-y) -Cl (M II = Mg or Zn), [22] were here used as precursor phases for NAP intercalation by ion exchange reaction ( Figure 1C). Furthermore, Mg 2 Fe-NAP synthesis by coprecipitation method was tested and compared to Mg 2 Al-NAP LDH composition. ...
... The basal peaks related to the pristine Mg 2 AlÀ Cl phase are clearly visualized and are indicated as (003) Cl and (006) Cl . The visualization of the (113) peak at the similar positions compared to the pristine phase, [22] dependent of the c cell parameter and expected to be displaced toward low angle region with the intercalation of the bulkier anion, is another indication of the presence of the residual LDHÀ Cl phase. Table S1. ...
In this work, Al cation was gradually replaced by FeIII in the composition of Layered Double Hydroxides (LDH) and systematically investigated for LDH application as drug carriers, ultimate aiming to improve their biointegration. The incorporation of FeIII into LDH layers, as well the intercalation of organic anions in the iron‐based materials, is challenging. Several studies approach the intercalation of non‐steroidal anti‐inflammatory drugs such as anionic naproxen (NAP) into Al‐LDH. Thus, NAP was applied here as a model drug for the study of compositional and structural aspects of novel FeIII‐LDH carriers envisaging to shed light on the intercalation of other carboxylate drugs into these materials. LDH of general [M2FeyAl(1‐y)(OH)6]Aⁿ⁻ compositions (MII=Mg or Zn; Aⁿ⁻=anion of charge n) were investigated using two synthetic methods for NAP intercalation. Full X‐ray diffraction profile refinement and a crystal‐geometrical reasoning were used to strengthen the results interpretation. Unlike coprecipitation, in which probably NAP complexation with FeIII hinders LDH‐NAP self‐assembling, topotactic ion exchange demonstrated to be a potential approach.
... The PDF curves were extracted from total X-ray scattering data and, to facilitate interpretation, and the same analysis was performed on Zn2Al-Cl55 sample and NAC salt. As reported elsewhere [72], the first peak observed on the PDF for LDH materials refers to the hydroxide layers. Thus, in the present case, the first peak around 2.0 Å is due to the closest OH shell around Zn, Al atoms while the peaks observed at about 3.07 Å (a), 5.3 Å (√3a), and 6.2 Å (2a) are attributed to the M−M bond distances The other peaks are due to multiple pairs of atoms. ...
... Indeed, NAC molecules can interact by intermolecular and intramolecular hydrogen bonds, as, for instance, the The PDF curves were extracted from total X-ray scattering data and, to facilitate interpretation, and the same analysis was performed on Zn 2 Al-Cl55 sample and NAC salt. As reported elsewhere [72], the first peak observed on the PDF for LDH materials refers to the hydroxide layers. Thus, in the present case, the first peak around 2.0 Å is due to the closest OH shell around Zn, Al atoms while the peaks observed at about 3.07 Å (a), 5.3 Å ( √ 3a), and 6.2 Å (2a) are attributed to the M−M bond distances The other peaks are due to multiple pairs of atoms. ...
N–acetyl–L–cysteine (NAC), a derivative of the L–cysteine amino acid, presents antioxidant and mucolytic properties of pharmaceutical interest. This work reports the preparation of organic-inorganic nanophases aiming for the development of drug delivery systems based on NAC intercalation into layered double hydroxides (LDH) of zinc–aluminum (Zn2Al–NAC) and magnesium–aluminum (Mg2Al–NAC) compositions. A detailed characterization of the synthesized hybrid materials was performed, including X-ray diffraction (XRD) and pair distribution function (PDF) analysis, infrared and Raman spectroscopies, solid-state ¹³carbon and ²⁷aluminum nuclear magnetic resonance (NMR), simultaneous thermogravimetric and differential scanning calorimetry coupled to mass spectrometry (TG/DSC–MS), scanning electron microscopy (SEM), and elemental chemical analysis to assess both chemical composition and structure of the samples. The experimental conditions allowed to isolate Zn2Al–NAC nanomaterial with good crystallinity and a loading capacity of 27.3 (m/m)%. On the other hand, NAC intercalation was not successful into Mg2Al–LDH, being oxidized instead. In vitro drug delivery kinetic studies were performed using cylindrical tablets of Zn2Al–NAC in a simulated physiological solution (extracellular matrix) to investigate the release profile. After 96 h, the tablet was analyzed by micro-Raman spectroscopy. NAC was replaced by anions such as hydrogen phosphate by a slow diffusion-controlled ion exchange process. Zn2Al–NAC fulfil basic requirements to be employed as a drug delivery system with a defined microscopic structure, appreciable loading capacity, and allowing a controlled release of NAC.
... Mg 2 Al and Zn 2 Al LDH batch of materials applied here were also subject of another studies. 29,30 However, in the present work the characterization of the materials was complemented, experimental parameters were carefully assessed and, as shown ahead, employed for the simulation of LDHÀ ÀCl and LDHÀ ÀNAP structures. XRD results were improved here for better peaks visualization, indexation, and determination of the cell parameters. ...
... LDH materials were prepared by the same methods previously reported. 29,30 Briefly, Mg 2 Al-Cl and Zn 2 Al-Cl LDH were prepared by the coprecipitation method at constant pH equal to 10.5 and 7.5 and at 50°C and room temperature, respectively. NAP intercalation was performed by ion exchange reaction from pristine LDHÀ ÀCl materials, with NAP/Al 3+ molar ratio equal to 1 and at room temperature for 24 h under magnetic stirring at 100 rpm. ...
In this work, Layered Double Hydroxide (LDH) materials carrying the worldwide administered non-steroidal anti-inflammatory drug naproxen (NAP), and the sodium naproxen salt for comparison, were studied by computational approaches aiming to model the structure of hybrid LDH-drug and shed light on NAP intercalation process. Atomic modelling calculations were performed at the quantum mechanical level based on Density Functional Theory and classical force fields based on empirical interatomic potentials. LDH-NAP materials were prepared by ion exchange reaction from Mg2Al(OH)6-Cl and Zn2Al(OH)6-Cl 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 LDH-NAP bands assignment. The employed theoretical models to represent the structure of LDH-NAP 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.
The diterpenoid abietate (ABI) ion, the conjugate base of the phytochemical abietic acid, was intercalated into a series of layered double hydroxides (LDH) with Mg2FeyAl(1-y) composition envisioning the preparation of drug delivery systems. Experimental parameters were evaluated to achieve organic-inorganic hybrid iron-based LDH as single-phases enriched with such endogenous metal, by coprecipitation method. A set of multiple physicochemical techniques was used for a detailed characterization of the hybrid materials. The assignment of ABI anions spectroscopic signals was inspected by density functional theory (DFT) calculations to address the ABI structural integrity after intercalation. Single-phase LDH-ABI materials having 41–48 wt% of the bioactive species were formed for compositions with y ≤ 0.5. Above the threshold Fe³⁺/Al³⁺ molar ratio equal to 1 (y > 0.5), multi-phases were observed in LDH-ABI samples, with the ABI amount corresponding to 33–22 wt%. Higher loading values were hindered by considering the steric constraint of ABI. Thermal analysis and spectroscopic data indicated that the chemical integrity of the sensitive abietic acid was preserved after its intercalation. These results should be inspiring for the design of delivery systems with multiple bio-functionalities based on iron-enriched LDH carriers.
This work developed an innovative membrane based on the high-performance PEBAX®2533 (PEBA) block copolymer and particles of iron-based layered double hydroxide (LDH) (Mg4FeAl layer composition) intercalated with phytotherapeutic abietate anions (ABI); both guest and host species are active in the promotion of wound healing. The presence of conjugated double bonds in the ABI structure promotes chemical reactions confronting its stability. Hence, LDH can protect the phytochemical species and promote its modified release. Aiming the development of wound dressings, LDH-ABI particles were immobilized in a biocompatible polymer (PEBA) by simple casting method. All samples were characterized by X-ray diffraction (XRD), vibrational (infrared and Raman) spectroscopies, thermogravimetry analysis coupled to mass spectrometry (TGA-MS), elemental chemical analyses and, in the case of polymer composites, by mechanical tests. Although the intercalation of organic anions into iron-based LDH materials is challenging, ABI intercalation was successful and using one-pot method (coprecipitation at constant pH value), according to XRD data. Additionally, spectroscopic techniques indicated the integrity of the ABI chemical structure after intercalation. The sodium abietate (NaABI) salt and the PEBA_NaABI membrane were also prepared to evaluate the effect of LDH in the formulations. In vitro release assays in saline solution at 32 °C showed the release (or solubilization) of around 3 and 5 wt./wt% of the ABI amount from LDH and salt, respectively, after 10 h. Comparatively, ABI release from the PEBA_Mg4FeAl-ABI and PEBA_NaABI formulations was improved to 20 and 22 wt%, respectively. The improvement in ABI release profiles from the membranes was related to the decrease in particles aggregation and improved media permeation. LDH particles released bioactive Mg²⁺ cations in the saline solution and, unlike NaABI particles, also improved the mechanical performance of the polymer. Thus, PEBA_Mg4FeAl-ABI showed promising as a component of wound dressings.
Hydroxyl groups are the cornerstone species driving catalytic reactions on mineral nanoparticles of Earth’s crust, water, and atmosphere. Here we directly identify populations of these groups on ferrihydrite, a key yet misunderstood iron oxyhydroxide nanomineral in natural sciences. This is achieved by resolving an enigmatic set of vibrational spectroscopic signatures of reactive hydroxo groups and chemisorbed water molecules embedded in specific chemical environments. We assist these findings by exploring a vast array of configurations of computer-generated nanoparticles. We find that these groups are mainly disposed along rows at edges of sheets of iron octahedra. Molecular dynamics of nanoparticles as large as 10 nm show that the most reactive surface hydroxo groups are predominantly free, yet are hydrogen bond acceptors in an intricate network formed with less reactive groups. The resolved vibrational spectroscopic signatures open new possibilities for tracking catalytic reactions on ferrihydrite, directly from the unique viewpoint of its reactive hydroxyl groups.
Ferrihydrite, a natural nanocrystal of iron, can adsorb and consequently eliminate contaminant ions when taken out of water at specific point-of-zero-charge. We propose to extract ferrihydrite clusters are wide range of pH and iron concentrations using zinc acetate coagulant. Added zinc is also removed due to strong chemical interaction between Fe and Zn leaving water free from both zinc and iron. This paper outlines a method of extraction of iron from water in form of iron oxyhydroxide natural nanoclusters at comparatively low concentrations and varied ranges of pH using zinc acetate salt. The zinc acetate salt dissociates into Zn 2+ and acetate ions in water where Zn 2+ interacts with the iron clusters present in a solution of given iron concentration and pH, while acetate ion helps in charge-neutralization based coagulation and consequent precipitation of such nanoclusters. The Zn 2+ ions may also lead to the growth of layered zinc hydroxide (LZH) nanosurfaces at pH ≥ 6 at sufficient loading. The advantage of this method is the active chemical interaction of Zn 2+ with Fe clusters, followed by growth, which ensures that only a part of the added Zn remains in the water while the rest precipitates out along with the residual iron oxyhydroxide, especially at higher pH. The solid precipitated under various different conditions, were successfully evaluated by XRD (formation of ferrihydrite-like nanoclusters (n-Fh)), FTIR (presence of acetate in the solid n-Fh), TEM (presence of zinc at higher pH), EXAFS (local structural characterization). ICP analysis of the obtained solid and the corresponding filtrate revealed the removal efficiency of iron and zinc from the solution under various initial concentrations and pH. This method of extracting soluble Fh-like nanoclusters by charge neutralization appears to be a suitable promising tool for water purification, because ferrihydrite is capable of isolating other adsorbed contaminants from water, along with itself.
Removal of zinc and cadmium from highly saline solutions by hydroxide precipitation is discussed. Experimental solubilities of zinc and cadmium in highly saline solutions were compared to modeled results obtained using Pitzer’s approach. An amphoteric character of zinc and cadmium and an influence of chloride ion on the concentration of dissolved metals were investigated. In order to avoid errors linked to pH measurements in concentrated aqueous solutions, the method of calibration of glass pH electrodes was developed and evaluated. The method uses easily prepared buffers whose pHs were determined with the Pitzer ion-interaction approach. The presented investigations address two issues of high significance in industrial wastewater treatment, namely: precise pH measurements and rigorous modeling of highly saline wastewaters. The results can be implemented in the treatment of hydrometallurgical wastewaters such as zinc refinery wastewater. Additionally, an implementation of the presented investigations is not limited to wastewater treatment but can easily be extended to other high-chloride metallurgical processes wherein the pH measurements in highly saline streams are required.
Graphical Abstract
Abstract Although, glyphosate (N-(phosphonomethyl) glycine) is one of the most widely used herbicides in the world, its interaction with poorly crystalline iron oxides, such as ferrihydrite, is not well studied. In this research, we examined the adsorption of glyphosate onto ferrihydrite using infrared spectroscopy (FT-IR), electron paramagnetic resonance spectroscopy (EPR), adsorption kinetic models and adsorption isotherm models. The effect of pH and sodium chloride concentration on the adsorption of glyphosate onto ferrihydrite as well as the effect of extractors (CaCl2 0.010 mol L−1 and Mehlich) on the desorption of glyphosate were also evaluated. There are two important findings described in this work. First, 84% of adsorbed glyphosate strongly interacted to ferrihydrite as an inner-sphere complex and phosphate and amine groups are involved in this interaction. Second, an increase of sodium chloride salt concentration increased the adsorption of glyphosate onto ferrihydrite. The non-linear Langmuir model and pseudo second order model showed a good agreement of theoretical limit of glyphosate adsorbed onto ferrihydrite, 54.88 µg mg−1 and 48.8 µg mg−1, respectively. The adsorption of glyphosate onto ferrihydrite decreased when the pH increased. Under the conditions used in this work, EPR spectra did not show dissolution of ferrihydrite. Surface area, pore volume and pHpzc of ferrihydrite decreased after adsorption of glyphosate.
This work explores the synthesis, physicochemical characterization, and in vivo biocompatibility of iron-based layered double hydroxides (LDHs) with molar ratio M²⁺/(Fe³⁺ + Al³⁺) equal to 2, Fe³⁺/Al³⁺ equal to 1, and chloride anions as charge-compensating ion (abbreviated Mg4FeAl-Cl and Zn4FeAl-Cl) prepared by the coprecipitation method. The higher structural organization of Zn4FeAl-Cl in comparison to Mg²⁺ analogous material was noticed by X-ray diffraction and scanning electron microscopy images. Biocompatibility of LDH was evaluated by intramuscular implantation in rats. Tablets of M4FeAl-Cl (M = Mg, Zn) were readily identified macroscopically after 7 and 28 days of implantation, denoting slow dissolution in the internal medium; adjacent to the tablets, blood flow was preserved without tortuosity or pathological dilatations, according to the Sidestream Dark Field Imaging technique. The histological analysis showed no inflammatory response and the presence of angiogenesis and tissue remodeling with the reconstruction of the extracellular matrix and cells around the tablets, besides the induction of collagen type-I formation. Prussian blue histochemical reaction suggested higher solubility of Mg4FeAl-Cl in the extracellular matrix compared to zinc LDH. Considering the positive biocompatibility results obtained for M4IIFeAl-LDH materials, experiments were conducted to intercalate the anti-inflammatory naproxen, as a model drug, into the iron-based LDHs (M4IIFeAl-NAP). The release profile of NAP in phosphate buffer showed 90% of the drug delivered after about 80 h. However, divalent metal leaching was verified mainly for Mg-LDH (around 50%) when compared to Zn²⁺ (around 1%). Iron-based LDHs have great potential for medical and technological applications as local drug delivery biomaterials exhibiting biocompatibility and biointegration properties.
We report the adsorption of dextranase on a Mg/Fe-layered double hydroxide (Mg/Fe-LDH). We focused the effects of different buffers, pH, and amino acids. The Mg/Fe-LDH was synthesized, and adsorption experiments were performed to investigate the effects. The maximum adsorption occurred in pH 7.0 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer, and the maximum dextranase adsorption uptake was 1.38 mg/g (416.67 U/mg); histidine and phenylalanine could affect the adsorption. A histidine tag could be added to the protein to increase the adsorption significantly. The performance features and mechanism were investigated with X-ray diffraction patterns (XRD) and Fourier transform infrared spectra (FTIR). The protein could affect the crystal structure of LDH, and the enzyme was adsorbed on the LDH surface. The main interactions between the protein and LDH were electrostatic and hydrophobic. Histidine and phenylalanine could significantly affect the adsorption. The hexagonal morphology of LDH was not affected after adsorption.
The patients with end-stage of renal disease (ESRD) need to take oral phosphate binder. Traditional phosphate binders may leave the disadvantage of aluminum intoxication or cardiac calcification. Herein, Mg-Fe-Cl hydrotalcite-like nanoplatelet (HTln) is for the first time characterized as potential oral phosphate binder, with respect to its phosphorus uptake capacity in cow milk and cellular cytotoxicity. A novel method was developed for synthesizing the Mg-Fe-Cl HTln powder in different Mg²⁺: Fe³⁺ ratios where the optimization was 2.8:1. Addition of 0.5 g Mg-Fe-Cl HTln in cow milk could reduce its phosphorus content by 40% in 30 min and by 65% in 90 min. In low pH environment, the Mg-Fe-Cl HTln could exhibit relatively high performance for uptaking phosphorus. During a 90 min reaction of the HTln in milk, no phosphorus restoration occurred. In-vitro cytotoxicity assay of Mg-Fe-Cl HTln revealed no potential cellular cytotoxicity. The cells that were cultured in the HTln extract-containing media were even more viable than cells that were cultured in extract-free media (blank control). The Mg-Fe-Cl HTln extract led to hundred ppm of Mg ion and some ppm of Fe ion in the media, should be a positive effect on the good cell viability.
Aluminium adjuvants remain the most widely used and effective adjuvants in vaccination and immunotherapy. Herein, the particle size distribution (PSD) of aluminium oxyhydroxide and aluminium hydroxyphosphate adjuvants was elucidated in attempt to correlate these properties with the biological responses observed post vaccination. Heightened solubility and potentially the generation of Al3+ in the lysosomal environment were positively correlated with an increase in cell mortality in vitro, potentially generating a greater inflammatory response at the site of simulated injection. The cellular uptake of aluminium based adjuvants (ABAs) used in clinically approved vaccinations are compared to a commonly used experimental ABA, in an in vitro THP-1 cell model. Using lumogallion as a direct-fluorescent molecular probe for aluminium, complemented with transmission electron microscopy provides further insight into the morphology of internalised particulates, driven by the physicochemical variations of the ABAs investigated. We demonstrate that not all aluminium adjuvants are equal neither in terms of their physical properties nor their biological reactivity and potential toxicities both at the injection site and beyond. High loading of aluminium oxyhydroxide in the cytoplasm of THP-1 cells without immediate cytotoxicity might predispose this form of aluminium adjuvant to its subsequent transport throughout the body including access to the brain.
Layered double hydroxides (LDHs) are versatile materials used for intercalating bioactive molecules in the fields of pharmaceuticals, nutraceuticals and cosmetics, with the purpose of protecting them from degradation, enhancing their water solubility to increase bioavailability and improving their pharmacokinetic properties and formulation stability. Moreover, LDHs are used in various technological applications to improve stability and processability. The crystal chemistry of hydrotalcite-like compounds was investigated by X-ray powder diffraction (XRPD), automated electron diffraction tomography (ADT) and thermogravimetric analysis (TGA)-GC-MS to shed light on the mechanisms involved in ion exchange and absorption of contaminants, mainly carbonate anions. For the first time, ADT allowed a structural model of LDH_NO3 to be obtained from experiment, shedding light on the conformation of nitrate inside LDH and on the loss of crystallinity due to the layer morphology. The ADT analysis of a hybrid LDH sample (LDH_EUS) clearly revealed an increase in defectivity in this material. XRPD demonstrated that the presence of carbonate can influence the intercalation of organic molecules into LDH, since CO3 -contaminated samples tend to adopt d spacings that are approximate multiples of the d spacing of LDH_CO3 . TGA-GC-MS allowed intercalated and surface- adsorbed organic molecules to be distinguished and quantified, the presence and amount of carbonate to be confirmed, especially at low concentrations (<2 wt %), and the different types and strengths of adsorption to be classified with respect to the temperature of elimination.
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Zn/Al- and Zn/Al/Sn-LDHs were prepared by the co-precipitation method at constant pH. The LDH structure and the local environment of the tin cations were investigated using XRD and UV-vis DR methods. Band component analysis of both infrared and Raman spectra has been used for the detailed characterization. Raman spectroscopy proved to be more useful to distinguish between the different metal-OH stretching modes than FT-IR spectroscopy. The carbonate anions were found to be in a lowered symmetry. Changes in the spectral profile were observed when part of Al 3+ was replaced by Sn 4+ in the brucite-like structure. The shift of a band and the appearance of a weak shoulder at 498 cm -1 in the Raman spectrum when the tin cations were involved indicated that small amounts of the tetravalent cations are segregated on the surface of the brucite-like sheets as very small regions of amorphous SnO 2.
The aim of this text is to show how the solubility (S) of metal hydroxides, oxide-hydroxides, and oxides can be calculated as function of the equilibrium pH of the solutions, taking into account the formation of various cationic and anionic species of metal aqua ions; however excluding all foreign ligands. The plots of log S versus pH are constructed and their applications to treat separations by consecutive precipitation are discussed.
Layered double hydroxides (LDHs) exhibit characteristic anion-exchange chemistry making them ideal carriers of negatively charged molecules like deoxyribonucleic acid (DNA). In this study, hydrotalcite (Mg−Al) and hydrotalcite-like compounds (Mg−Fe, Zn−Al, and Zn−Fe), also known as LDHs, were evaluated for their potential application as a carrier of DNA. LDHs were prepared by coprecipitation at low supersaturation and characterized by Powder X-ray diffraction (XRD), infrared (IR), Raman, and inductively coupled plasma—optical emission spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD patterns showed strong and sharp diffraction peaks for the (003) and (006) planes indicating well-ordered crystalline materials. TEM images yielded irregular circular to hexagonal-shaped particles of 50–250 nm in size. Varying degrees of DNA binding was observed for all the compounds, and nuclease digestion studies revealed that the LDHs afford some degree of protection to the bound DNA. Minimal toxicity was observed in human embryonic kidney (HEK293), cervical cancer (HeLa) and hepatocellular carcinoma (HepG2) cell lines with most showing a cell viability in excess of 80 %. All LDH complexes promoted significant levels of luciferase gene expression, with the DNA:Mg−Al LDHs proving to be the most efficient in all cell lines.
The coprecipitation method has been used to synthesize layered double hydroxide (Zn-Fe-LDH) nanostructure at different Zn2+/Fe3+ molar ratios. The structural properties of samples were studied using powder X-ray diffraction (PXRD). LDH samples were calcined at 600∘C to produce mixed oxides (ZnOand ZnFe2O4).Thecrystallite size of mixed oxide was found in the nanometer scale (18.1nm for ZnFe2O4 and 43.3 nm for ZnO). The photocatalytic activity of the calcination products was investigated using ultraviolet-visible-near infrared (UV-VIS-NIR) diffuse reflectance spectroscopy. The magnetic properties of calcined LDHs were investigated using a vibrating samplemagnetometer (VSM).Thecalcined samples showed a paramagnetic behavior for all Zn2+/Fe3+ molar ratios. The effect of molar ratio on magnetic susceptibility of the calcined samples was also studied.
Quintinite-1M, [Mg4Al2(OH)12](CO3)(H2O)3, is the first monoclinic representative of both synthetic and natural layered double hydroxides (LDHs) based on octahedrally coordinated di- and trivalent metal cations. It occurs in hydrothermal veins in the Kovdor alkaline massif, Kola peninsula, Russia. The structure was solved by direct methods and refined to R1 = 0.031 on the basis of 304 unique reflections. It is monoclinic, space group C2/m, a = 5.266(2), b = 9.114(2), c = 7.766(3) Å, = 103.17(3)°, V = 362.9(2) Å3. The diffraction pattern of quintinite-1M contains sharp reflections corresponding to the layer stacking sequence characteristic of the 3R rhombohedral polytype, and rows of weak superlattice reflections superimposed upon a background of streaks of modulated diffuse intensity parallel to c*. These superlattice reflections indicate the formation of a 2-D superstructure due to Mg-Al ordering. The structure consists of ordered metal hydroxide layers and a disordered interlayer. As the unit cell contains exactly one layer, the polytype nomenclature dictates that the mineral be called quintinite-1M. The complete layer stacking sequence can be described as ...=Ac1B=Ba1C=Cb1A=... Quintinite-1M is isostructural with the monoclinic polytype of [Li2Al4(OH)12](CO3)(H2O)3.
Layered double hydroxide (LDH)-ibuprofen (IBU) host-guest materials were prepared by in situ coprecipitation method for the purpose of drug controlled release. Three hosts containing different metal cations, MgAl-, ZnAl-, and MgFe-LDH, were studied. The results showed that the types of the metal cations had great influence on the structures of the host-guest materials and thus led to different drug release properities.
The naturally occurring layered double hydroxides (LDH, or anionic clays) are of particular interest in environmental geochemistry because of their ability to retain hazardous cations and especially anions. However, incorporation of these minerals into predictive models of water–rock interaction in contaminant environments, including radioactive-waste repositories, is hampered by a lack of thermodynamic and stability data. To fill part of this gap the present authors have derived properties of one of the complex multicomponent solid solutions within the LDH family: the hydrotalcite–pyroaurite series, Mg3(Al1−x Fex )(OH)8(CO3)0.5·2.5H2O.Members of the hydrotalcite–pyroaurite series with fixed MgII/(AlIII+FeIII) = 3 and various FeIII/(FeIII+AlIII) ratios were synthesized by co-precipitation and dissolved in long-term experiments at 23±2°C and pH = 11.40±0.03. The chemical compositions of co-existing solid and aqueous phases were determined by inductively coupled plasma-optical emission spectroscopy, thermogravimetric analysis, and liquid scintillation counting of 55Fe tracers; X-ray diffraction and Raman were used to characterize the solids. Based on good evidence for reversible equilibrium in the experiments, the thermodynamic properties of the solid solution were examined using total-scale Lippmann solubility products, ΣΠT. No significant difference was observed between values of ΣΠT from co-precipitation and from dissolution experiments throughout the whole range of Fe/Al ratios. A simple ideal solid-solution model with similar end-member ΣΠT values (a regular model with 0 W G−1) was sufficient to describe the full range of intermediate mineral compositions. In turn, this yielded the first estimate of the standard Gibbs free energy of the pyroaurite end member, G 298,Pyro = −3882.60±2.00 kJ/mol, consistent with G 298,Htlco = −4339.85 kJ/mol of the hydrotalcite end member, and with the whole range of solubilities of the mixed phases. The molar volumes of the solid-solution at standard conditions were derived from X-ray data. Finally, Helgeson's method was used to extend the estimates of standard molar entropy and heat capacity of the end members over the pressure–temperature range 0–70°C and 1–100 bar.
Phase transformation from Zn(OH)2 to ZnO has been studied by monitoring an intermediate growth stage. SEM observations reveal that the phase transformation takes place in three ways, i.e. dissolution–reprecipitation, in situ crystallization and solid–solid phase transformation.
Advanced oxidation process (AOPs) have attracted a special attention for high removal efficiency of recalcitrant organic contaminants. Recently, the use of Layered double hydroxides (LDHs) or LDHs composites as catalysts for AOPs (photocatalysis, Fenton reaction methods, and sulfate radical (SO4•−)-mediated oxidations) has received increasing attention and become a new research hotspot. This is due to its layered structure, flexible tunability, electronic properties, and high physicochemical stability. Herein, we provide a comprehensive review on the development and progress in the synthesis of pristine LDHs and modified LDHs catalysts for AOPs. Special attention has been paid to the design strategies of high-performance LDHs, including (1) rational design of pristine LDHs, such as binary and ternary LDHs, (2) calcination of LDHs at an appropriate temperature, (3) modification of LDHs with semiconductor or metal as a cocatalyst, (4) changing the compensating anions, and (5) controlling LDHs morphology. At last, some invigorating perspectives on the challenges and future research directions in LDHs-based AOPs are discussed. Keywords: Layered double hydroxides; Catalysts; Advanced oxidation; Pollutants; Design strategies.
Visible-blind ultraviolet (UV) photodetectors have achieved great attentions for realizing internet of things technologies as well as for monitoring the level of UV exposure to humans. To realize next-generation flexible and visible-blind UV photodetectors, new functional material systems with easy fabrication, selectively strong UV light absorption, environment friendliness, and high stability regardless of ambient conditions need to be developed. Herein, flexible visible-blind UV photodetectors are successfully fabricated based on two-dimensional ZnAl-layered double hydroxide (LDH) nanosheets with scroll structures grown on flexible substrates. The ZnAl-LDH nanosheet scrolls exhibit highly resistive semiconducting properties with a band gap of 3.2 eV and work function of 3.64 eV. The photodetector based on the ZnAl-LDH shows photoresponse in the UV spectral range below 420 nm, indicating visible-blind spectral response. In addition, the UV photodetector shows a maximum responsivity of 17 mA/W under illumination with 365 nm light. Moreover, the flexible photodetector shows reproducible photoresponse even after 1,000 bending cycles, which indicates the acceptable stability of the ZnAl-LDH nanosheet scrolls.
A supramolecular ferrofluid has been applied in air-assisted dispersive micro solid phase extraction method (SUPR-FF-AA-DMSPE) for the residual determination of two pesticides (diazinon and metalaxyl) prior to GC-FID. For this purpose, a magnetic calcined layered double hydroxide (CLDH(Zn-Fe)@Fe3O4) sorbent was modified with the tannic acid (TA) to produce a bio-sorbent. The ferrofluid was easily prepared through the combination of biosorbent and the supramolecular solvent as a carrier liquid. The ferrofluid was rapidly sucked up and injected 5 times using a syringe in the sample solution to improve the mass transfer of the analytes into the sorbent and achieve the fast extraction time. The characterization of CLDH (Zn-Fe)@Fe3O4@TA was investigated by XRD, FT-IR spectroscopy, FESEM and EDS. Influence parameters on the extraction of pesticides were investigated (pH 8; volume of supramolecula solvent 8 μL; amount of sorbent 10 mg; pulling and pushing numbers 5 times; volume of the eluent 100 μL). Under the optimized conditions, the calibration curves found to be linear in the range of 0.6–2000 and 2–2000 μg L⁻¹ with correlation coefficients > 0.9990 for diazinon and metalaxyl, respectively. The limits of detection (S/N = 3) and limit of quantification (S/N = 10) were obtained 0.2 and 0.8 μg L⁻¹ and 0.6 and 2 μg L⁻¹ for diazinon and metalaxyl, respectively. The intra-day and inter-day precisions (RSDs %) (50 μg L⁻¹, n = 6) were 6.5–7.1% and 7.7–8.5%, respectively. The preconcentration factors (PFs) were achieved to be 500. Finally, the proposed method was successfully applied to determine diazinon and metalaxyl in fruit juice and farm water samples with good recoveries in the range of 85–96.6%.
With the ability to host anions or neutral drugs, layered double hydroxide (LDH) are hot spots in the field of biomaterials. Intensive works so far only have focused on their application in surface modification or injectable medicine. Yet, little literatures report the potential of LDH as bone implants. In the present study, four types of LDH (Mg–Al, Mg–Fe, Zn–Al and Zn–Fe) were prepared via a coprecipitation method. Our results showed that the synthetic LDH powders can be pressed into discs in the absence of binder. The discs can maintain their shape after immersed in culture medium for 10 days, not including Mg–Al LDH disc. The elastic modulus of all discs was between 9 and 35 GPa, which was close to cortical bone (5–23 GPa). Zn–Al LDH and Zn–Fe LDH showed higher cytotoxicity than Mg–Al LDH and Mg–Fe LDH whether in the form of suspension or extract. Furthermore, even up to 10 mg/mL, the extract of Mg–Al LDH and Mg–Fe LDH showed no cytotoxicity, while cells were totally died in the extract of Zn–Al LDH and Zn–Fe LDH. Compared with cells, bacterial showed an even lower tolerance concentration to Zn–Al LDH and Zn–Fe LDH. This study indicates that Mg-containing LDH show better cytotocompatibility, while Zn-containing LDH show better antibacterial property. With proper elastic modulus and controllable biological effect, LDH are promising to be used as bone implants.
Hard tissue implant materials which can cause a suitable alkaline microenvironment are thought to be beneficial for stimulating osteoblasts differentiation while suppressing osteoclast generation. In order to make the local pH around the interface between materials and cells controllable, we prepared series of Mg-Fe layered double hydroxides (LDHs) films on acid-etched pure titanium surfaces via hydrothermal treatment. By adjusting the Mg/Fe proportion ratio, the interlayer spacing of Mg-Fe LDHs can be regulated, making their OH⁻ exchange abilities adjustable and ultimately results in a microenvironment with a controllable pH value. In vitro experiments demonstrated that the Mg-Fe LDHs films modified titanium surface possessed good biocompatibility and osteogenic activity, especially the Mg-Fe LDHs films with Mg/Fe proportion ratio of 4 which can form a suitable alkaline microenvironment for the growth and osteogenesis differentiation of stem cells, showing great potential application in enhancing the osteogenesis of implant materials and providing a new way into the design of the controllable alkaline environment.
Layered double hydroxides (LDH) which are one type of layered materials and are also known as anionic clays,
are promising layered materials due to some of their interesting properties, such as ease of synthesis, unique
structure, uniform distribution of different metal cations in the brucite layer, surface hydroxyl groups, flexible
tunability, intercalated anions with interlayer spaces, swelling properties, oxo-bridged linkage, and high chemical
and thermal stability, ability to intercalate different type of anions (inorganic, organic, biomolecules, and
even genes), delivery of intercalated anions in a sustained manner and also high biocompatibility. Considering
the previous work on LDH as novel biomaterials, research on this particular materials has become one of the
most interesting topic of today's research. LDH has become an important class of layered materials having
prospects in the field of biomaterials, wherein great attention has been paid to the biocompatibility nature,
exchange of the existing anion with the target anion, holding of guest species in between the interlayer space and its controlled release of the anion in a particular medium. This article, after deliberating the recent significant evolution in the structure and different methods of synthesis of different LDH materials and its applications in various extents especially its biological applications through their structural and functional properties, considers many typical examples. In particular, recent progress on the emerging strategies of LDH to improve their antimicrobial activity is also presented.
Currently, energy storage devices draw considerable attention owing to the growing need for clean energy. The depletion of fossil fuels and the generation of greenhouse gases have led to the development of alternative, environmentally friendly energy storage devices. Supercapacitors with high power densities are excellent devices for energy storage. Although widely used in such devices, the non-faradic behavior of carbon-based materials in electrical double layer capacitors (EDLCs) limits the maximum power density that can be generated. In contrast, the faradaic mechanism of transition metal hydroxides results in better capacitance rates along with good stability during cycling. This review is confined to nickel cobalt layered double hydroxides (NiCoLDHs) classified based on the fabrication of electrodes for application in supercapacitors. We discuss growth of the active LDH material in situ or ex situ on the current collector and how the synthetic can affect the crystal structure as well as the electrochemical performance of the electrode.
Cellular behaviors, such as differentiation, are regulated by complex ligation processes involving cell surface receptors, which can be activated by various divalent metal cations. The design of nanoparticle for co-delivery of ligand and ligation activator can offer a novel strategy to synergistically stimulate ligation processes in vivo. Here, we present a novel layered double hydroxide (LDH)-based nanohybrid (MgFe-Ado-LDH), composed of layered MgFe hydroxide nanocarriers sandwiching the adenosine cargo molecule, maintained through an electrostatic balance, to co-deliver the adenosine (Ado) ligand from the interlayer spacing and the Mg(2+) ion (ligation activator) through the dissolution of the MgFe nanocarrier itself. Our findings demonstrate that the MgFe-Ado-LDH nanohybrid promoted osteogenic differentiation of stem cells through the synergistic activation of adenosine A2b receptor (A2bR) by the dual delivery of adenosine and Mg(2+) ions, outperforming direct supplementation of adenosine alone. Furthermore, the injection of the MgFe-Ado-LDH nanohybrid and stem cells embedded within hydrogels promoted the healing of rat tibial bone defects through the rapid formation of fully integrated neo-bone tissue through the activation of A2bR. The newly formed bone tissue displayed the key features of native bone, including calcification, mature tissue morphology, and vascularization. This study demonstrates a novel and effective strategy of bifunctional nanocarrier-mediated delivery of ligand (cargo molecule) and activation of its ligation to receptor by the nanocarrier itself for synergistically inducing stem cell differentiation and tissue healing in vivo, thus offering novel design of biomaterials for regenerative medicine.
Simonkolleite is a zinc-layered hydroxide salt with the formula Zn5(OH)8Cl2·H2O. It has a platelet morphology and can be used for many applications, owing to both its layered structure and its nature as a hydroxide salt. It can be prepared via a simple precipitation from ZnCl2 and NaOH in water thermostated at 50 °C. Depending on the synthesis conditions, we could obtain different sizes and a hybrid containing parts of ZnO. We studied the influence of the OH:Zn molar ratio, the addition order, and the maturation time after the reaction was completed. With the support of pH profiles, kinetic studies, and thermodynamic equilibrium data, we were able to propose a global synthesis mechanism explaining the influence of those three parameters and identify the range of conditions in which simonkolleite can be formed. Depending on the desired application, we were able to synthesize bigger or smaller layered crystals of simonkolleite, in the presence of absence of ZnO.
Abstract With rapidly growing industrial development worldwide, the need for a new class of nanoparticles and techniques for treating wastewater remains a major concern to protect the environment. Layered double hydroxides and particularly LDH-containing hybrids are emerging as potential nano-sized adsorbents for water treatment. Recent studies have demonstrated LDH-containing hybrids as promising multifunctional materials for potential utilization in various applications such as, photo-catalysis, energy storage, nanocomposites and water purification. This article reviews the recent applications of LDH-containing hybrids as adsorbents for water remediation. The maximum adsorption capacities of various toxic heavy metals and dyes on different LDH hybrids were reported as 483 mg/g for Pb2 +, 95 mg/g for Cd2 +, 181 mg/g for Cu2 +, 649 mg/g for Cr6 +, 180 mg/g As5 +, 813 mg/g for Hg2 +, 450 for Ag+, 277 mg/g for U6 +, 1062 mg/g for methyl orange, 185 mg/g for methylene blue, and 1250 mg/g for Congo red, which is comparatively higher than other commercial adsorbents. This review discusses the adsorption performance of manifold LDH-containing hybrids for treating various pollutants such as heavy metals and dyes. The mechanisms of interaction of LDH-containing hybrids with pollutants and the influence of key adsorption parameters such as pH, contact time, adsorbent dose and temperature have been comprehensively discussed. Moreover, the regeneration potential and reuse of spent LDH-containing hybrids and its toxicity effects have also been reviewed.
Layered double hydroxides comprise a stacking of positively charged metal hydroxide layers with anions and water molecules included in the interlayer galleries. Among the anions, the carbonate ion is the most ubiquitous in both mineral and laboratory synthesized phases. Taylor (1973) suggested that the carbonate ion (molecular symmetry D3h) prefers a trigonal prismatic interlayer site (local symmetry D3h), whereby the hydrogen bonding with the metal hydroxide layer is maximized. However, the cation ordered structure models of hexagonal symmetry include interlayer sites which are exclusively trigonal antiprisms (local symmetry D3d). In keeping with Taylor's criterion, a hexagonal stacking of metal hydroxide layers does not permit the inclusion of carbonate ions in the interlayer. In this work, a crystal chemical approach is adopted based on the translationgleiche subgroups of hexagonal and cubic summits to arrive at a structure model based on the space group C2/m. In this structure, not only is the 3-fold symmetry of metal coordination retained, but also interlayer sites of ∼D3h symmetry are generated to host the intercalated carbonate ions. Using this model, the structures of a cohort of carbonate-intercalated layered double hydroxides are refined.
Facile and simple processes to get Zn-Fe layered double hydroxide (LDH) with nitrate as the interlayer anion are reported. The method of co-precipitation produced high crystallinity LDH that is marked by XRD, SEM, TEM and FT-IR. Results showed that 99.8% of Cd+ 2 removals were at pH 11 and 4 h. To get the adsorption isotherms, the concentration of metal ions extending from 6 to 18 mg/L was utilized. Results supported the Langmuir adsorption model. In contrary, the adsorption process followed the pseudo-second-order reaction kinetics. Interestingly, the prepared LDH shows durable antimicrobial activities against Gram-negative (Proteous vulgaris, Klebsiellapneumoniae, Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus pyogenes and MRSA) and fungi (Candida albicans, Aspergillus fumigatus, Geotricumcandidum, and Trichophyton mentagrophytes). The minimum inhibitory concentration (MIC) of Zn-Fe LDH varied from 0.49 to 15.60 μg/mL according to the types of microorganisms. The prepared LDH achieved 90% at pH 8.50 which is the pH of wastewater and at the same time exhibited durable antimicrobial activities against MRSA, Gram-negative, Gram-positive and fungi. Results have significant implications in the field of bioremediation of water with little cost, simple operation, high productivity and easiness of the equipment.
Thermal decomposition of layered zinc hydroxide double salts provides an interesting alternative synthesis for particles of zinc oxide. Here, we examine the sequence of changes occurring as zinc hydroxide chloride monohydrate (Zn5(OH)8Cl2·H2O) is converted to crystalline ZnO by thermal decomposition. The specific surface area of the resultant ZnO measured by BET was 1.3 m(2) g(-1). A complicating and important factor in this process is that the thermal decomposition of zinc hydroxide chloride is also accompanied by the formation of volatile zinc-containing species under certain conditions. We show that this volatile compound is anhydrous ZnCl2 and its formation is moisture dependent. Therefore, control of atmospheric moisture is an important consideration that affects the overall efficiency of ZnO production by this process.
The syntheses of Mg-Fe(III) layered double hydroxides with different compositions at varied temperature through a co-precipitation method were attempted. The well-crystallized and white colored layered double hydroxides with chloride anions were obtained from the samples adjusted to the composition of Mg/Fe. =. 4 and aged at higher temperature. The Fe species in the white colored Mg-Fe layered double hydroxides were evaluated as all Fe(III) species by a Mössbauer measurement. The synthesized Mg-Fe(III) layered double hydroxide was treated with a sugar alcohol at temperature above its melting point in order to reduce Fe(III) incorporated into the hydroxide layers. The Mg-Fe layered double hydroxide resulting from a sugar alcohol treatment showed the reduction property in an aqueous solution.
An enormous research effort is currently being directed towards the development of efficient visible-light-driven photocatalysts for renewable energy applications including water splitting, CO2 reduction and alcohol photoreforming. Layered double hydroxide (LDH)-based photocatalysts have emerged as one of the most promising candidates to replace TiO2-based photocatalysts for these reactions, owing to their unique layered structure, compositional flexibility, controllable particle size, low manufacturing cost and ease of synthesis. By introducing defects into LDH materials through the control of their size to the nanoscale, the atomic structure, surface defect concentration, and electronic and optical characteristics of LDH materials can be strategically engineered for particular applications. Furthermore, through the use of advanced characterization techniques such as X-ray absorption fine structure, positron annihilation spectrometry, X-ray photoelectron spectroscopy, electron spin resonance, density-functional theory calculations, and photocatalytic tests, structure-activity relationships can be established and used in the rational design of high-performance LDH-based photocatalysts for efficient solar energy capture. LDHs thus represent a versatile platform for semiconductor photocatalyst development with application potential across the energy sector.
Use of layered double hydroxides (LDHs) in the environmental field is gaining popularity due to their potential to sorb toxic anions, attributed to their large surface area, high anion exchange capacity, and good thermal stability. In this study, four different LDHs (i.e., Cu-Al-, Mg-Al-, Mg-Fe-, and Zn-Al-LDH) were synthesized to select one or more efficient sorbents, capable of removing arsenite [As(III)] from contaminated waters. In particular, we studied the following: (1) X-ray diffraction patterns and specific surface area of the synthesized LDHs; (2) sorption isotherms of As(III) at pH 7.0; and (3) sorption of As(III) on LDHs, in the presence of inorganic anions [carbonate (CO3), chloride (Cl), fluoride (F), phosphate (PO4), sulfate (SO4)] commonly present in aquatic environments. The poorly crystalline LDHs (i.e., Cu-Al-LDH and Mg-Fe-LDH) sorbed greater amounts of As(III) than the well-crystalline LDHs (i.e, Mg-Al-LDH and Zn-Al-LDH). The efficiency of the competing anions at inhibiting As(III) sorption by the LDHs was Cl ≤ F < SO4 << CO3 << PO4, regardless of initial ligand/As(III) molar ratios (R) or LDH. Although Cu-Al-LDH sorbed lower amounts of As(III) than the Mg-Fe-LDH, it showed, surprisingly, a higher affinity for As(III). This surprising behavior puts this LDH in the forefront as a potential sorbent for the treatment of arsenic-contaminated waters.
Layered double hydroxide (LDH) nanoparticles have excellent anion-intercalating property, and their potential as theranostic nanovectors is high. However, understanding of the control of the mean particle size (MPS) and achievement of monodispersed particle size distribution (PSD) remains elusive. Herein, with the aid of statistical design of experiments on a model system of Cl(-)-intercalated (Zn, Al)-LDH, controlled synthesis of single crystalline nanoparticles using the coprecipitation method followed by hydrothermal treatment (HT) was achieved in three steps. First, a 2(4-1) design enabled the identification of influential parameters for MPS (i.e., salt concentration, molar ratio of carbonate to aluminum, solution addition rate, and interaction between salt concentration and stirring rate) and PSD (i.e., salt concentration and stirring rate), as well as the optimum coprecipitation conditions that result in a monodispersed PSD (i.e., low salt concentration and high stirring rate). Second, a preliminary explanation of the HT was suggested and the optimum HT conditions for obtaining ideal Gaussian PSD with chi-squared (χ(2))<3 were found to be 85°C for 5h. Third, using a central composite design, a quantitative MPS model, expressed in terms of the significant factors, was developed and experimentally verified to synthesize nearly monodispersed LDH nanoparticles with MPS ∼200-500nm.
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The total hip arthroplasty is one of the most common artificial joint replacement procedures. Several different surface coatings have been shown to improve implant fixation by facilitating bone ingrowth and consequently enhancing the longevity of uncemented orthopaedic hip prostheses. In the present study, two different layered double hydroxides (LDHs), Mg-Fe- and Mg-Al-LDH, were investigated as potential magnesium (Mg)-containing coating materials for orthopaedic applications in comparison to Mg hydroxide (Mg(OH)2 ). In vitro direct cell compatibility tests were carried out using the murine fibroblast cell line NIH 3T3 and the mouse osteosarcoma cell line MG 63. The host response of bone tissue was evaluated in in vivo experiments with nine rabbits. Two cylindrical pellets (3 × 3 mm) were implanted into each femoral condyle of the left hind leg. The samples were analyzed histologically and with μ-computed tomography (μ-CT) 6 weeks after surgery. An in vitro cytotoxicity test determined that more cells grew on the LDH pellets than on the Mg(OH)2 -pellets. The pH value and the Mg(2+) content of the cell culture media were increased after incubation of the cells on the degradable samples. The in vivo tests demonstrated the formation of fibrous capsules around Mg(OH)2 and Mg-Fe-LDH. In contrast, the host response of the Mg-Al-LDH samples indicated that this Mg-containing biomaterial is a potential candidate for implant coating. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2015.
© 2015 Wiley Periodicals, Inc.
We studied a series of NiAl–CO3 layered double hydroxides (LDHs) of various degrees of crystallinity prepared by a glycine-assisted hydrothermal method. The structures and the microstructures were determined by Rietveld refinement with a spherical harmonic-implemented algorithm using high-resolution synchrotron powder X-ray diffraction (XRD) data. These XRD results combined with transmission electron microscopy (TEM) observations indicate that the broadening of 00l diffraction lines is mainly due to size effects, while both size and strain effects contribute to the anisotropic broadening of the other hkl reflections. The in-plane TEM dimensions of LDH platelets are found larger than the coherent lengths in the 110 direction, indicating a noncoherent coalescence of domains during crystal growth. The DIFFaX program was also used to model structural defects, i.e., CO32–/SO42– interstratification and intergrowth between rhombohedral 3R1 and hexagonal 2H1 polytypes. Furthermore, the distribution of the cations within the hydroxide layers has been determined by the atomic pair distribution function technique, indicating a disordered distribution of the cation in all samples with absolutely identical cationic coordination spheres. The electrochemical characterization of these samples as thin-film modified electrodes, by means of cyclic voltammetry and electrochemical impedance spectroscopy measurements, reveals complex behaviors which are the result of competing effects between the coherent domain size and the particle size, the aggregation state of LDH particles, the Ni bulk concentration, and the presence of structural defects. Remarkably, the presence of the 2H1 stacking motifs in the 3R1 LDH matrix results in an increased electrochemical signal. Either the location of metal cations exactly on top of the others in the 2H1 polytype or the defects associated with the intergrowth of 2H1–3R1 polytypes may be responsible for the enhanced electroactivity of Ni centers.
In this highlight, attempts have been made to focus on the effect of physico-chemical properties of nanoparticles, such as chemical composition, solubility, particle size, and specific surface area, on the toxicity. Among various inorganic particles, layered double hydroxides on nano scales were especially studied in terms of the toxicity in cell culture systems and in animal models as well. Important major issues and challenges in toxicity evaluation of nanomaterials are also described to answer key questions about their toxicity potential. Understanding the interrelationship between the physico-chemical properties and toxicity of nanoparticles will provide new insights into development of novel materials for biological and medical applications with minimized side effects.
Synthetic Mg-, Ni- (takovite), and Co-hydrotalcite are characterized by FT-IR and FT-Raman spectroscopy. Changes in the composition brought about by changing the divalent metal result in small but significant changes in band positions of the modes related to the hydroxyl groups, as each hydroxyl group in the hydrotalcite structure is coordinated to three metal cations. It has also a similar effect on the interlayer water and carbonate band positions as evidenced by small shifts in band positions and the occurrence of doublets, especially for the interlayer carbonate ions. The carbonate doublets are due to site symmetry lowering.