Efficient removal of Cr (VI) from aqueous solution using memory effect property of layered double hydroxide material.

Treating wastewater containing pollutants with layered double hydroxide (LDH) material attracts excellent interest. LDH materials are known by the memory effect property, which leads to the reconstruction of the LDH structure after its calcination and rehydration. In this study, LDH material was prepared, calcined, and then rehydrated in an aqueous Cr(VI) solution. XRD, FTIR, and SEM-EDS analysis confirm the successful reconstruction of LDH-loading chromium on its surface and layered space. Response surface methodology (RSM) results showed that LDH mass, contact time, and chromium concentration are the main factors controlling the removal of Cr(VI). The heterogeneous sorption of chromium was described by fitting the equilibrium data to the Freundlich model. Analytical techniques, thermodynamic data, activation, and adsorption energies confirm that the removal process of Cr(VI) is endothermic, spontaneous, and physical nature. LDH exhibits good reusability performance with only a 7% reduction of initial adsorption capacity after five cycles of the calcination-rehydration process. These results show that the memory effect of LDH is helpful for the intercalation and the removal of emergent pollutants, especially for wastewater treatment.

Fe-Ce/Layered Double Hydroxide Heterostructures and Their Derived Oxides: Electrochemical Characterization and Light-Driven Catalysis for the Degradation of Phenol from Water.

Fe-Ce/layered double hydroxides (LDHs) were synthesized via a facile route by exploiting the "structural memory" of the LDH when the calcined MgAlLDH and ZnAlLDH were reconstructed in the aqueous solutions of FeSO4/Ce(SO4)2. XRD analysis shows the formation of heterostructured catalysts that entangle the structural characteristics of the LDHs with those of Fe2O3 and CeO2. Furthermore, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, TG/DTG, SEM/EDX and TEM results reveal a complex morphology defined by the large nano/microplates of the reconstructed LDHs that are tightly covered with nanoparticles of Fe2O3 and CeO2. Calcination at 850 °C promoted the formation of highly crystallized mixed oxides of Fe2O3/CeO2/ZnO and spinels. The photo-electrochemical behavior of Fe-Ce/LDHs and their derived oxides was studied in a three-electrode photo-electrochemical cell, using linear sweep voltammetry (LSV), Mott-Schottky (M-S) analysis and photo-electrochemical impedance spectroscopy (PEIS) measurements, in dark or under illumination. When tested as novel catalysts for the degradation of phenol from aqueous solutions, the light-driven catalytic heterojunctions of Fe-Ce/LDH and their derived oxides reveal their capabilities to efficiently remove phenol from water, under both UV and solar irradiation.

High efficient arsenic removal by In-layer sulphur of layered double hydroxide.

High-risk arsenic contamination found in aqueous system is reported across the world and causing severe environmental issues. In this study, the Mg-Al Layered Double Hydroxide (LDH) modified by sulphur species (LDH-S) was found exhibiting high effectivity and selectivity in As(V) removal owing to the strong interaction between embedded HS- and AsO43-. The LDH-S with Mg to Al ratio 2-1 give the best performance with As(V) adsorption capacity 40.8 mg/g, which is 715% higher than that of pristine LDH (2-1). The adsorbent exhibits a high tolerance to concentrated competitive anions. In the continuous flow test, the adsorbent can reduce the As(V) concentration from 20 ppm to below-ppb-level indicating the potential in industry application. The adsorption mechanism is experimentally investigated and examined by Density Function Theory (DFT) calculation. The result illustrates that, differ from the traditional ion exchange mechanism of LDH, the enhanced removal capacity and selectivity of LDH-S for As(V) is attributed to the strong affinity between H atom from HS- ion (in the interlayer region of LDH) and the O atom from AsO43-.

Synthesis, characterization, and comparative study of MgAl-LDHs prepared by standard coprecipitation and urea hydrolysis methods for phosphate removal.

Layered double hydroxides (LDHs), known as a class of anionic clays, have attracted considerable attention recently due to their potential applications in different areas as catalyst materials, energy materials, and adsorbent materials for environmental remediation, especially for anionic pollutant removal. In this study, magnesium aluminum layered double hydroxide (MgAl-LDH) was synthesized by two methods: standard coprecipitation and urea hydrolysis. Their textural properties and morphologies were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and differential (DTG) analysis, and point of zero charge (pHpzc). The specific surface area was calculated from BET adsorption equation. The results indicated that the crystallinity and the regularity of the samples prepared by urea hydrolysis were much preferable to those prepared by the coprecipitation method. Their sorption properties toward phosphate were investigated and the experimental evidence showed that, at the initial concentration of 100 mg L-1 and at room temperature, the LDH synthesized by urea hydrolysis had a percentage removal of 94.3 ± 1.12% toward phosphate ions while 74.1 ± 1.34% were uptaked by LDH synthesized by coprecipitation method, suggesting that the crystallinity affects the sorption capability. The sorption mechanism indicates that phosphate ions could be sorbed onto LDHs via electrostatic attraction, ligand exchange, and ion exchange.

Oleate-LDH hybrids by the successive use of the clay structural "memory effect".

Oleate/LDH composites have been obtain by calcination-reconstruction procedures by the successive uses of the anionic clay memory effect. XRD and FTIR analysis were used to study the structural characteristics of the hybrid samples. The amount of oleate in the hybrid formulation of the clay matrix is highest after the second calcination-reconstruction cycle. After the fourth cycle the clay structure is not recovered anymore. This result points out to the "short" structural "memory" of the LDH-like clays. Textural features of the samples were studied by N2 adsorption at 77 K, SEM and TEM analyses. The oleate/LDH hybrids, obtained by the successive uses of the clay "memory", are defined by different crystallinity and micromorphological characteristics.

Nanosized silver-anionic clay matrix as nanostructured ensembles with antimicrobial activity.

Nanostructured ensembles of silver nanoparticles/zinc-substituted anionic clay matrix (Ag/ZnLDH) were obtained by a simple synthetic route in which reconstruction of the layered clay, synthesis of the silver nanoparticles and their organisation on the clay surface took place in a single step at room temperature. The morphology, composition and phase structure of the prepared powders were characterised by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N(2) adsorption. Results showed that the silver-anionic clay nanoarchitecture consists of nanoparticles of silver (average size 7 nm) deposited on the larger nanoparticles of clay (average size 85 nm). The antimicrobial activity was examined by disk diffusion assay and minimal inhibitory concentration determination as a function of x, where x is a controlled variable parameter that represents the length of time since the sample was synthesised. Ag/ZnLDH showed more stable antimicrobial properties than the unsupported nanosized silver.

SEM and EDX studies of bioactive hydroxyapatite coatings on titanium implants.

This work presents a study on an alternative coating method based on biomimetic techniques which are designed to form a crystalline hydroxyapatite layer very similar to the process corresponding to the formation of natural bone. The HA formation on the surface of titanium alloy pretreated with NaOH solution is investigated. Two types of solutions such as supersaturated calcification solution (SCS) and modified SCS (M-SCS) were used to investigate bone-like apatite formation on alkali-treated titanium. The hydroxyapatite deposits are investigated by means of scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The data suggest that the method utilized in this work can be successfully applied to obtain deposition of uniform coatings of crystalline hydroxyapatite on titanium substrates.

New hybrid nanostructures based on oxacillin-hydrotalcite-like anionic clays and their textural properties.

New hybrid nanostructures based on inorganic matrices of hydrotalcite-like anionic clays (HT) incorporated with oxacillin are obtained by using calcinations-restructure method. XRD and TEM analyses are used to study the structural and textural characteristics of the clay containing hybrids. When nanoparticles of iron oxides are loaded on the layered anionic clay matrix a more effective delivery system of the drug is obtained. The results can be used to reduce the toxic side effects of oxacillin (e.g. upset stomach, diarrhea, cholestastic hepatitis), its aggregation process in aqueous solutions and also can open new perspectives for targeted the drug delivery.