Use Of Layered Double Hydroxides Research Articles

Intercalation of olanzapine into CaAl and NiAl Layered Double Hydroxides for dissolution rate improvement: Synthesis, characterization and in vitro toxicity

The aim of this work was to develop and characterize different Layered Double Hydroxides (LDHs) loaded with of Olanzapine (OLZ), CaAl:OLZ and NiAl:OLZ, by thermogravimetry (TG), differential scanning calorimetry (DSC), Fourier Transform Infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), dissolution rate improvement, inhibition of AAPH-induced hemolysis and toxicity prospections with Artemia salina assay. No peaks of OLZ were found on diffractograms of both systems (5%) indicating amorphization of OLZ. This behavior was decreased with the increasing of drug. FT-IR spectra showed decreasing, displacements, suppressions and enlargements of bands in specific regions suggesting OLZ intercalation in both HDLs. No OLZ endothermic events was found in DSC curves indicating a decrease in the drug crystallinity, excepting for samples with 30% of OLZ. The dissolution profile evidenced that in 45 min CaAl:OLZ 5% and NiAl:OLZ 5% presented the maximum drug solubilization of 89.08 and 61.66%, respectively. In the inhibition of AAPH-induced hemolysis, both systems, showed significant inhibition (p ≤ 0.05) compared to the negative control, and Artemia salina assay evidenced that both HDLs (5%) did not cause the significant death of the specimens compared to OLZ in 24 h. The exposed results reinforced the proposed use of LDHs as functional excipients.

Application of layered double hydroxides for 99Tc remediation

The present study investigates possible use of Layered Double Hydroxides (LDH) for Tc(VII) remediation. Mg/Al– and Mg/Fe–LDH were obtained by a hydrothermal route and thermally activated at 450 °C, which was shown to significantly improve the Tc(VII) removal efficiency. Based on XRD investigation of Tc–LDH phases, the uptake Tc(VII) from the solution follows the restoring of a LDH structure. X-ray absorption spectroscopy demonstrates that Tc ions interact solely via the TcO bond, leaving no evidences of farther atomic interactions with, e.g., layers of LDH. The presence of competing anions, like NO3−, or CO32– in the solution decreases Tc(VII) uptake by LDH. Maximum uptake capacity of thermally activated Mg0.67/Al0.33-LDH and Mg0.75/Fe0.25–LDH were derived from fitting the experimental data into the modified Langmuir equation and correspondingly comprise 0.227 mol/kg and 0.213 mol/kg. In agreement with these findings, theoretical simulations predicted incorporation energies for Mg0.67/Al0.33–LDH and Mg0.75/Fe0.25–LDH of −128 kJ/mol and − 110 kJ/mol, respectively. Investigation of stability of Tc–LDH in different aqueous solutions demonstrated a rather low release Tc(VII) in contact with diluted solutions containing Cl− and OH−, however, in a high saline solution, like Q-brine a rather fast release of TcO4− occurs due to anion exchange with Cl−.

The Use of Layered Double Hydroxides in the Composition of Cement Compositions

The Use of Layered Double Hydroxides in the Composition of Cement Compositions

Development of horseradish peroxidase/layered double hydroxide hybrid catalysis for phenol degradation

Both photocatalytic and enzymatic degradation of phenol were studied in order to evaluate and to compare the catalytic potential of both methods. For this, solar-sensitive ZnMe (Me = Al, Cr) layered double hydroxides (LDHs) and their derived mixtures of mixed oxides (MMOs) were synthesized via co-precipitation and calcination at 750 °C, while the calcined LDH at 550 °C was used for horseradish peroxidase (HRP) immobilization through absorption. The structural, optical and thermal properties of catalysts were investigated by XRD, FTIR, TG/DTA, TEM and UV–Vis analyses. We approached here for the first time the use of LDH–HRP biohybrid for phenol degradation. Further, since HRP operates similarly as photocatalysts, we also investigated the ability of LDH–HRP to generate photo-enzymatic responses, when the biocatalyst is used under solar light. Both degradation methods are able to remove phenol from solution via different pathways, namely step-by-step phenol photodegradation and phenol enzymatic polymerization, when an insoluble product is obtained at the end of reaction. After 7 h of reaction, 95% of phenol was removed by a MMOs, while ZnAlLDH + light, ZnAlLDH–HRP and ZnAlLDH–HRP + light removed 20, 25 and 35% of phenol via photo-, enzymatic and photo-enzymatic catalysis, respectively.

Use of Layered Double Hydroxides to Create New Environmental Technologies

This review surveys recent advances in the applications of layered double hydroxides [LDHs] in sorption processes. By virtue of the flexible tunability and uniform distribution of metal cations in the brucite-like layers and the facile exchangeability of intercalated anions, LDHs-both as directly prepared or after thermal treatment or rehydrated have found many applications as stable and recyclable sorbents for environmental protection in industrial regions. This paper presents data on the structure and properties of LDHs, the production of sorbents with fixed and labile dimensions of interplanar spaces. Technologies for the removal of organic and inorganic substances using LDHs sorbents have been developed. Keywords: layered double hydroxides; sorbent; environmental protection;

Evaluation of antioxidant potencial of novel CaAl and NiAl layered double hydroxides loaded with olanzapine

Olanzapine (OLZ), is used in the treatment of bipolar disorder and schizophrenia, diseases that present oxidative stress in their physiopathology. It has low aqueous solubility, which may lead to low oral bioavailability. The search of new drug delivery systems (DDSs) that may increase dissolution rate of OLZ, associated with the investigation of the antioxidant potential of the loaded-systems become of major importance to understand improvement in bipolar disorder and schizophrenia therapy. Thus, this study aimed to evaluate the in vitro antioxidant potential of two different Layered Double Hydroxides (LDH) loaded with 5% of OLZ (CaAl and NiAl), by radical scavenging activity (2,2-Diphenyl-1-picrylhydrazyl and nitric oxid); radical cation scavenging activity (2,2′-azino-bis3-ethylbenzthiazoline-6-sulfonic acid ABTS) and evaluation of inhibition capacity of lipid peroxidation by thiobarbituric acid (TBARS). The results showed that both obtained LDH systems presented in vitro antioxidant capacity when associated with OLZ in all methods performed, and this activity is more pronounced with the systems containing OLZ compared to pure drug. The systems with CaAl was shown to have increased antioxidant potential, compared to NiAl, increasing the antioxidant activity up to 40,83%, 15,84% and 16,73%, as showed by the DPPH, nitric oxide and TBARS tests, respectively. The results revealed that the use of LDHs as a functional excipient may be promising in the pharmaceutical industry for bipolar disorder and schizophrenia therapy.

Preparation and characterization of polystyrene-MgAl layered double hydroxide nanocomposites using bulk polymerization

Abstract Polymer/mineral filler nanocomposites are more and more used for diverse applications. As mineral fillers, layered double hydroxides (LDHs) present a great advantage as flame retardants from an environmental point a view (reduction of smoke and toxic gases). This article deals with the use of LDH as flame retardants as compared to montmorillonite (MMT). In situ bulk polymerization of styrene was carried out in the presence of MgAl LDH modified with dodecyl sulfate (DDS) and dodecylbenzene sulfonate (DBS) surfactants. LDH concentrations used were lower than 10 wt.%. X-ray diffraction analysis of the LDH-styrene suspensions revealed the monomer intercalation into the DDS-LDH galleries and a slight decrease in the DBS-LDH basal spacing. Transmission electron microscopy analysis showed that the polymerization occurred outside the DBS-LDH galleries, leading to exfoliation of the layers on the outer surface of LDH platelets. DDS-LDH particles were trapped in the PS polymer. The thermal stability effect was observed for all LDH nanocomposites by thermogravimetric analysis. Cone calorimetry measurements revealed that only the DBS-LDH nanofiller resulted in a reduction of the peak heat released rate (PHHR) and a decrease of smoke released. DBS-LDH/PS exhibited fire properties close to those of clay-PS nanocomposite at 7 wt.% montmorillonite. The PHRR reduction remained small and the total heat release rate constant at 7 wt.% DBS-LDH loading.

Synergism between LDH and Nano-Zinc Phosphate on the Flammability and Mechanical Properties of Polypropylene

The synergistic effect of layered double hydroxide (LDH) and prepared nano-zinc phosphate was studied by melt compounding of polypropylene (PP) on a Brabender Plastograph. The obtained lumps of composites were grinded and injection molded to test the performance of nanocomposites with respect to their mechanical, physical, thermal, flame-retardant and morphological properties. The outcome of the present work revealed that the use of LDH and nano-zinc phosphate acted as synergistic fillers in PP nanocom-posites that improved the flammability, as well as other performance properties of PP substantially as compared to pristine PP.

Use of Layered Double Hydroxides to Remove Sunset Yellow FCF Dye from Aqueous Solution

The potential feasibility of layered double hydroxides for removal of sunset yellow dye FCF from aqueous solution was investigated. The effects of various experimental parameters such as contact time, solution pH, dye concentrations and adsorbent dosage were investigated. The extent of sunset yellow FCF dye removal increased with the increased in contact time and amount of layered double hydroxides used however the percentage removal was decreased with the increased in pH and dye concentrations. Adsorption data was better fitted to the Langmuir isotherm. The results in this study indicated that layered double hydroxide was an attractive adsorbent for removing sunset yellow FCF dye from aqueous solution.

Polytypism, Disorder, and Anion Exchange Properties of Divalent Ion (Zn, Co) Containing Bayerite-Derived Layered Double Hydroxides

Incorporation of Zn(2+) into bayerite results in the formation of a cation-ordered layered double hydroxide (LDH) of monoclinic symmetry in which about half the vacancies of Al(OH)(3) are occupied by Zn(2+) giving rise to positively charged layers. Charge compensation takes place by the incorporation of sulfate ions in the interlayer region. Structure refinement reveals that the adjacent layers in the crystal are related by a 2(1) axis (we call it 2M(1) polytype) with sulfate coordinating in the D(2d) symmetry in the interlayer region. Another polytype in which adjacent layers are related by a 2-fold axis (2M(2) polytype) can also be envisaged. Faulted crystals arising from intergrowths of the 2M(2) polytype within the 2M(1) structure were also obtained. These bayerite-based LDHs have a distinctly different interlayer chemistry when compared to the better known brucite-based LDHs, in that they have a strong affinity for tetrahedral ions such as SO(4)(2-), CrO(4)(2-), and MoO(4)(2-) and a poor affinity for CO(3)(2-) ions. These observations have implications for the use of LDHs in applications related to chromate sorption.

Recent Developments in the Use of Layered Double Hydroxides as Host Materials for the Storage and Triggered Release of Functional Anions

An extensive and systematic study of the intercalation of a number of commercially important anions into a range of layered double hydroxides (LDHs) has been undertaken. A pseudo-combinatorial approach was employed to determine rapidly the ideal reaction conditions for the intercalation of each guest. Over 50 LDH nanohybrids are reported, the vast majority of them having never previously been synthesized. Guest anions include key drugs, important agrochemicals, vitamins, fragrances, a dye, and a color fixant. The immense potential of LDH systems as reservoirs and to remove agrochemical pollutants from effluvium flows was demonstrated. The release of the guest anions was studied in representative conditions. Some of the thiosulfate intercalates show temperature programmable release characteristics which have not be observed previously.

Sorption of Pb(II) on Mg‐Fe Layered Double Hydroxide

AbstractMg‐Fe layered double hydroxide (LDH) with a Mg/Fe molar ratio of 3:1 was synthesized by using a coprecipitation method and the sorption removal of Pb(II) by the LDH sample from Pb(NO3)2 solution was investigated. It was found that Mg‐Fe LDH showed a good sorption ability for Pb(II) from Pb(NO3)2 solution, indicating that the use of LDH as a promising inorganic sorbent for the removal of heavy metal ions is possible. The sorption kinetics and the sorption isotherm of Pb(II) on the LDH sample obeyed the pseudo‐second order kinetic model and Aranovich‐Donohue equation, respectively. The sorption mechanism of Pb(II) on the LDH may be attributed to the surface‐induced precipitation and the chemical binding adsorption, and the removal ability arising from the surface‐induced precipitation is much higher than that from the chemical binding adsorption.

Synthesis and characterization of layered double hydroxides (LDHs) with intercalated chromate ions

Chromate intercalated layered double hydroxides (LDHs) having the formula M II 6M′ III 2(OH) 16CrO 4·4H 2O (M II = Ca, Mg, Co, Ni, Zn with M′ III = Al and M II = Mg, Co, Ni with M′ III = Fe) have been prepared by coprecipitation. The products obtained are replete with stacking disorders. DIFFaX simulations show that the stacking disorders are of three kinds: (i) turbostratic disorder of an originally single layered hexagonal (1H) crystal, (ii) random intergrowth of polytypes with hexagonal (2H) and rhombohedral (3R) symmetries and (iii) translation of randomly chosen layers by (2/3, 1/3, z) and (1/3, 2/3, z) leading to stacking faults having a local structure of rhombohedral symmetry. IR spectra show that the CrO 4 2− ion is incorporated either in the T d or in the C 3v symmetry. The interlayer spacing in the latter case is 7.3 Å characteristic of a single atom thick interlayer showing that the CrO 4 2− ion is grafted to the metal hydroxide slab. On thermal treatment, the CrO 4 2− ion transforms into Cr(III) and is incorporated into the spinel oxide or phase separates as Cr 2O 3. In the LDH of Mg with Al, Cr(III) remains in the MgO lattice as a defect and promotes the reconstruction of the LDH on soaking in water. In different LDHs, 18–50% of the CrO 4 2− ion is replaceable with carbonate anions showing only partial mineralization of the water-soluble chromate. The extent of replaceable chromates depends upon the solubility of the corresponding LDH, which in turn is determined by the solubility of the MCrO 4. These studies have profound implications for the possible use of LDHs for chromate amelioration in green chemistry.

An Approach towards Nano-size Crystals of Poly(acrylic acid): Polymerization Using Layered Double Hydroxides as Template

Abstract A new approach has been proposed and was shown to be a feasible method to produce nanosized polymer crystals of poly(acrylic acid). The new approach involves in situ polymerization of acrylic acid in the interlayers of a layered double hydroxides (LDHs) followed by exchange of the polymer anion for carbonate. The key is the use of LDHs as a template.

Adsorption of MCPA pesticide by MgAl-layered double hydroxides

In the present study, the adsorption characteristics of the herbicide MCPA (4-chloro-2-methylphenoxyacetic acid) on layered double hydroxides (LDHs) were evaluated under laboratory conditions with particular attention to the effect of layer charge, original interlayer anion and morphology. The final objective is the use of LDHs and modified LDH materials as recyclable adsorbents and heterogeneous catalysts for the treatment of contaminated waste waters. The anionic clays tested were [Mg 1− x Al x (OH) 2] x+ [X x/ m m− · nH 2O] materials. The MCPA adsorption capacity was determined from adsorption isotherms and a kinetic study. We looked at the influence of the pH, the Mg 2+/Al 3+ ratio, i.e. the anion exchange capacity, the nature of the intercalated anion X (CO 3 2−, NO 3 −, Cl −) and the morphology of the adsorbent on the extent of adsorption. The adsorption isotherms, described by Freundlich model, are of S-type with tendency to L-type for high MCPA equilibrium concentration. Furthermore, the adsorption capacity increases with the layer charge density. Hence, MCPA adsorption on LDHs occurs by anion exchange in two steps, an external exchange followed by an interlayer exchange, which explain these changes of type within the same isotherm. Besides, the adsorption capacity depends on the nature of the starting anions, following the affinity order (NO 3 −<Cl −<CO 3 2−) proposed by Miyata and increases with the specific surface area.