Synthetic Layered Double Hydroxides Research Articles

Leaching of iodide (I−) and iodate (IO3−) anions from synthetic layered double hydroxide materials

Several studies have previously demonstrated that layered double hydroxides (LDHs) show considerable potential for the adsorption of radioiodine from aqueous solution; however, few studies have demonstrated that these materials are able to store radioactive 131I for an acceptable period. The leaching of iodide (I−) and iodate (IO3−) form Mg/Al LDHs has been carried out. Contact time appeared to be a more significant variable for the leaching of iodate (IO3−) compared to that of iodide (I−). Experimental results are fitted to the pseudo second order model, suggesting that diffusion is likely to be the rate-limiting step. The presence of carbonate in the leaching solution appeared to significantly increase the leaching of iodide (I−) as did the presence of chloride to a lesser extent. The maximum amount of iodate (IO3−) leached using ultrapure water as the leaching solution was 21% of the iodate (IO3−) originally present. The corresponding result for iodide (I−) was even lower at 3%.

Heterocoagulated clay-derived adsorbents for phosphate decontamination from aqueous solution

A series of nanocomposite adsorbents were prepared by heterocoagulation of negatively charged delaminated montmorillonite (Mt) and positively charged synthetic layered double hydroxide (LDH) colloids with different LDH loading amounts. The mineralogy and physicochemical properties of the resulting nanocomposites were characterized. Their potential applications for phosphate (P) removal from aqueous solution, as a function of P concentration (2.5–200 mg/L), contact time (1 min–48 h) and pH (3–10), were evaluated by using batch adsorption modes. It was found that the adsorption data could be well described by both Freundlich and Langmuir isotherm models. The maximum adsorption capacity of three different LDH heterocoagulated montmorillonites (LDH-Mts) for P removal was found to increase with LDH loadings, reaching 12.6, 16.2 and 23.3 mg/g respectively; Adsorption kinetic data revealed that 90% of adsorption onto LDH-Mts was completed within 1 h (h) and the adsorption process could be well described by the pseudo-second-order model. These results demonstrated that heterocoagulation of Mt and LDH could preserve the adsorption capacity of LDH for P and enhance the stability of both clay minerals, and LDH-Mts could be effectively used as a potential promising filtration medium for P removal.

Structures of LDHs Intercalated with Ammonia and the Thermal Stability for Poly(vinyl chloride)

MgAl-NH3 LDHs (layered double hydroxides), ZnAl-LDHs and ZnAl-NH3 LDHs with different molar ratio of Al/ammonia were synthesized by co-precipitation method. The synthetic LDHs samples were characterized by XRD, FT-IR, TGA-DTG and SEM techniques and tested by Congo red method. In addition, after PVC (Poly vinyl chloride) and DOP (Dioctylphthalate) were added to LDHs, the thermal stability for PVC was characterized by TGA-DTG. The results indicated that LDHs intercalated with ammonia improved thermal stability for PVC significantly, MgAl-NH3 LDHs (Mg2+:Al3+: NH3·H2O = 3:1:0.5) and ZnAl-NH3 LDHs (Zn2+:Al3+:NH3·H2O=2:1:1.5) showed the best thermal stability for PVC, interlayered space of LDHs became larger by intercalating ammonia.

Cr(VI) removal from aqueous solutions by hydrothermal synthetic layered double hydroxides: Adsorption performance, coexisting anions and regeneration studies

Layered double hydroxide (LDH) materials comprising of Mg/Al, Ni/Al and Zn/Al with molar ratio (M2+/Al3+=3) were synthesized via a facile hydrothermal route. The microstructures, morphologies and textural properties of the LDH materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption–desorption techniques. It was found that the three LDHs with different divalent metal cations were constructed from nanosheets with well-defined shapes and sizes. Adsorption rates and isotherms of the LDH adsorbents for Cr(VI) were investigated in batch experiments. Desorption behaviors and regeneration of Cr(VI)-adsorbed LDHs at the solid liquid interface were also studied. The ZnAl-LDH exhibited excellent sorption capacity (68.07mg/g) for Cr(VI) and good regeneration performance. The effect of coexisting anions on the adsorption performance revealed that the anions (CO32−, HCO3−) greater impact on the adsorption process due to their larger laminate binding energy and closer affinity for hydrotalcite material.

Removal of boron from oilfield wastewater via adsorption with synthetic layered double hydroxides

Hydrotalcite is a layered double hydroxide (LDH) consisting of brucite‐like sheets of metal ions (Mg‐Al). In this work, hydrotalcites were synthesized, and boron removal from oilfield wastewater was evaluated. LDHs were synthesized using the co‐precipitation method. The calcined products (CLDHs) were obtained by heating at 500°C and characterized using X‐ray diffraction, X‐ray fluorescence, thermogravimetric analysis and the specific surface area (BET). The affinity of LDHs for borate ions was evaluated for calcined and uncalcined LDHs as a function of contact time, initial pH of the oilfield wastewater (pH ∼ 9) and the LDH surface area. The tests were conducted at room temperature (approximately 25ºC). The results indicated that 10 min were needed to reach a state of equilibrium during boron removal for calcined LDHs due to the high surface area (202.3 m2 g−1) regardless of the initial pH of the oilfield wastewater, which resulted from the high buffering capacity of the LDHs. The adsorption capacity increased as the adsorbents levels increased for the range studied. After treatment of the oilfield wastewater containing 30 mg L−1 of boron with Mg‐Al‐CO3‐LDHs, the final concentration of boron was within the discharge limit set by current Brazilian environmental legislation, which is 5 mg L−1. Pseudo–first‐order and pseudo–second‐order kinetic models were tested, and the latter was found to fit the experimental data better. Isotherms for boron adsorption by CLDHs were well described using the Langmuir and Freundlich equations.

Hidróxidos duplos lamelares como matrizes para fertilizantes de liberação lenta de nitrato

Diante do extensivo uso de fertilizantes nitrogenados na agricultura e elevado potencial de lixiviação do nitrato, há uma demanda por fertilizantes de liberação lenta ou controlada. Os hidróxidos duplos lamelares (HDLs) sintéticos reúnem características que os qualifica para o uso como matrizes para fertilizantes de liberação lenta de íons nitrato. Os objetivos deste trabalho foram focados na síntese, caracterização e investigação do processo de liberação lenta de nitrato em um HDL contendo íons Mg2+ e Al3+ em sua estrutura. O HDL com a fórmula Mg0,83Al0,17(OH)2(NO3)0,17.0,56H2O foi sintetizado pelo método de coprecipitação em pH alcalino constante, separado por centrifugação e seco em estufa a vácuo. As análises de difração de raios-X, de espectroscopia vibracional na região do infravermelho com transformada Fourier e as análises térmicas comprovam a obtenção do composto contendo o íon nitrato hidratado intercalado, além da fórmula proposta. O composto foi submetido a testes de liberação de nitrato em solução de NaHCO3 tamponado a pH 6,5 e em água destilada. As curvas obtidas evidenciaram dois eventos complementares de liberação de nitrato, um evento inicial rápido e um outro lento e gradativo. O composto investigado neste trabalho demonstrou potencial para ser utilizado como matriz para fertilizante de liberação lenta de nitrato.

Degradation by irradiation of an Acid Orange 7 on colloidal TiO2/(LDHs)

Abstract The photocatalytic efficiency of colloidal TiO2 was considerably improved after its immobilization using synthetic layered double hydroxides (LDHs) as support of the photocatalyst. Compared to conventional colloidal TiO2 nanoparticles (Q-TiO2), LDHs present the advantage to enhance the contact between an organic pollutant and TiO2. This work is focused at the same time on the synthesis of new materials (colloidal TiO2/LDHs) and to enhance their efficiency for photodegradation in aqueous solutions of selected dye. Q-TiO2/Mg2AlCO3 and Q-TiO2/Mg2FeCO3 composite photocatalysts were prepared by a direct coprecipitation method at constant pH and characterized by several analytical techniques including XRD, FTIR and BET. Subsequent to the dark adsorption studies, photocatalytic efficiency of the supported catalysts was evaluated using an azo dye, Acid Orange 7, as model compound in an aqueous medium. The supported catalysts exhibit good photodegradation efficiency of this dye and its removal was improved compared to bare colloidal TiO2.

Interactions of clay minerals and a layered double hydroxide with water stable, nano scale fullerene aggregates (nC 60)

The research presented details on specific interactions of underivatized C 60 as an aggregate suspension in water (termed nC 60) with clay minerals (montmorillonite and kaolinite), and a synthetic layered double hydroxide LDH. Batch and 1-D flow-through column interactions were analyzed via UV/Vis spectroscopy, X-ray diffraction analysis, and transmission electron microscopy. Results indicate that nC 60 suspended in water interacted with all the solid materials (‘clays’) studied. The LDH, with a net positive surface charge, has the greatest capacity to associate with the negatively charged nC 60, capable of adsorbing 18% w/w. Column studies support sorption isotherm data, with LDH retarding nC 60 transport > 30 times more, in relative terms, than montmorillonite or kaolinite. Findings suggest that specific material interactions are primarily dominated by available surface area and electrostatic interaction at charged surfaces. Intercalation was not observed. These results have implications not only for understanding fullerene transport in the subsurface, but also towards engineering effective barriers for safe storage and disposal.

Perchlorate uptake by synthetic layered double hydroxides and organo-clay minerals

The perchlorate uptake of hydrotalcite- and hydrocalumite-type layered double hydroxides (LDHs), and surfactant modified clay minerals were compared. Perchlorate uptake by both hydrotalcite- and hydrocalumite-type LDHs was in the range of 0.011 to 0.197meq/g from a 2mM perchlorate solution. The nitrate form of Mg:Al LDH had the highest uptake of 0.197±0.033meq/g, and the carbonate form of LDH the lowest uptake of 0.011±0.003meq/g. Octadecyltrimethylammonium (ODTMA), Dodecyltrimethylammonium (DoDTMA), and hexadecyltrimethylammonium (HDTMA) clay minerals removed perchlorate in the range of 0.025 to 0.348meq/g from a 2mM perchlorate solution. Synthetic HDTMA (5.0 CEC) Na-1-mica exhibited the highest adsorption of perchlorate with 0.348±0.011meq/g, while DoDTMA montmorillonite had the lowest adsorption with 0.025±0.009meq/g. Tested under the same conditions, a surfactant modified carbon showed an uptake of 0.303±0.005meq/g and this carbon is currently being used for filtration of drinking water.Hydrophobic organo-clay minerals with larger interlayer distance resulted in higher perchlorate uptake by exchange/adsorption on the residual charge of the cationic surfactants. The uptake by LDH was by anion exchange on the surfaces and, for the nitrate form of hydrotalcite, also from the interlayer spaces. The mechanisms of uptake were confirmed by X-ray diffraction (XRD) and scanning electron microscopy. This study indicated that cationic surfactant containing organo-clay minerals may be useful materials for the removal of perchlorate from water and could serve as alternatives to surfactant modified-activated carbons.

Cation Ordering and Superstructures in Natural Layered Double Hydroxides

Layered double hydroxides (LDHs) constitute an important group of materials with many applications ranging from catalysis and absorption to carriers for drug delivery, DNA intercalation and carbon dioxide sequestration. The structures of LDHs are based upon double brucite-like hydroxide layers [M(2+)(n)M(3+)(m)(OH)(2(m+n)](m+), where M(2+) = Mg(2+), Fe(2+), Mn(2+), Zn(2+), etc.; M(3+) = Al(3+), Fe(3+), Cr(3+), Mn(3+), etc. Structural features of LDHs such as cation ordering, charge distribution and polytypism have an immediate influence upon their properties. However, all the structural studies on synthetic LDHs deal with powder samples that prevent elucidation of such fine details of structure architecture as formation of superstructures due to cation ordering. In contrast to synthetic materials, natural LDHs are known to form single crystals accessible to single-crystal X-ray diffraction analysis, which provides a unique possibility to investigate 3D cation ordering in LDHs that results in formation of complex superstructures, where 2D cation order is combined with a specific order of layer stacking (polytypism). Therefore LDH minerals provide an indispensable source of structural information for modeling of structures and processes happening in LDHs at the molecular and nanoscale levels.

Crystal chemistry of natural layered double hydroxides. 2. Quintinite-1M: first evidence of a monoclinic polytype in M2+-M3+ layered double hydroxides

AbstractQuintinite-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, β = 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.

Utilization of a Selective Adsorbent for Phosphorus Removal from Wastewaters

In this study, a synthetic layered double hydroxide modified with chloride ions (LDH-Cl) was employed for the removal of phosphorus from wastewaters. A series of phosphate adsorption experiments demonstrated that the adsorption capacity of LDH-Cl was described well by the three-parameter isotherm model (Langmuir–Freundlich combination model). LDH-Cl was found to have ∼50 mg P/g of ion exchange capacity for phosphate, which was sufficient for phosphate recovery from wastewaters. Phosphate adsorption by LDH-Cl also followed pseudo-second-order reaction kinetics. Effective replacement of Cl− with PO43− during sorption was confirmed by X-ray diffraction and Fourier transform infrared analyses. Adsorption capacity varied with pH and reached a maximum value at pH 3. Anions commonly present in most wastewaters, such as nitrate, sulfate, and chloride, had a minimal effect on phosphate adsorption by LDH-Cl. On the contrary, the amount of phosphate ions removed by LDH-Cl decreased with increasing bicarbonate ion concentration. LDH-Cl also exhibited a sufficient chemical stability against adsorption/desorption repetitions and ∼80% of desorption rate was achieved at 5 M NaCl concentration. LDH-Cl exhibited a high phosphate removal capacity and a low sensitivity to the environmental conditions of wastewaters, supporting use as an effective means for the removal of phosphate.

Uptake of arsenite by synthetic layered double hydroxides

Two types of layered double hydroxides (LDHs), hydrotalcite and hydrocalumite with different composition of layers and interlayers were investigated for the removal of arsenite from solutions. The kinetics study showed that anion exchange process was very fast and apparently attained a steady-state in the range of 8–16 h. Arsenite removal was found to be 87.5% and 83.6% with the nitrate forms of hydrotalcite and hydrocalumite, respectively. Layered double hydroxides synthesized at room temperature showed higher uptake than those synthesized by hydrothermal method due to small crystal size (high surface area) of the former. As expected, calcined hydrotalcite showed higher uptake than uncalcined carbonate form of hydrotalcite. The uptake process was anion exchange in hydrotalcite-type LDH as confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) but possibly some dissolution–reprecipitation occurred with hydrocalumite-type LDH.

Adsorption of Aqueous Selenite [Se(IV)] Species on Synthetic Layered Double Hydroxide Materials

Layered double hydroxide materials (Zn/Al, Mg/Al, Zn/Fe) with varying composition (M2+:M3+ molar ratio, x = 3, 2, 1, and 0.33) were synthesized and evaluated for their selenium adsorption characteristics in aqueous medium. Zn/Al and Mg/Al LDHs with x = 3 and 2, exhibited very high selenite adsorption capacity. XRD patterns of the pristine LDHs, LDH after selenite adsorption, and chloride ion leaching studies revealed that adsorption of selenium on the LDHs occurred through both surface adsorption and ion-exchange mechanism. The adsorption data was fitted to Langmuir and Freundlich isotherm models. A pseudo second-order kinetic model was used to describe the adsorption kinetics of selenite on LDH materials. Desorption of selenite ions in water from the LDH−Se matrix was studied up to 5 h.

Removal of guar and humus from water by layered double hydroxides

Natural organic matter such as guar and humus are recalcitrant to conventional pretreatment technologies and can potentially foul processes such as membranes during water treatment. An innovative method of using synthetic layered double hydroxides (LDH) was investigated for removing common natural organic matter in the form of guar gum (GG) and humic acid (HA) from water. Adsorption isotherms were evaluated with Langmuir and Freundlich models. Results show the affinity of GG and HA to LDH to be 11.31 and 9.33 mg g(-1) LDH, respectively. Kinetic isotherms indicate that the sorbing rates of LDH to GG and HA increase with initial GG and HA concentrations, fitting a pseudo-second order model. This study demonstrate that LDH may be an effective material in removing GG and HA from waters and offer an alternative to conventional pretreatment technologies for the mitigation fouling of membrane and other systems in water treatment.

Perkalite as an Innovative Filler for Isotactic Polypropylene-Based Nanocomposites

Perkalite, an organically modified synthetic layered double hydroxide, was used as a filler in the preparation of nanocomposites based on isotactic polypropylene. The polymorphism of the polymer matrix was investigated, finding that Perkalite favors beta phase in certain conditions and is not a nucleant for the gamma polymorph. Perkalite promoted the formation of a dual population of lamellae, as evidenced by SAXS data. The dispersion of the filler was studied by WAXD, SAXS, and TEM. Perkalite was intercalated by the polymer and formed small, rather disordered tactoids, that determined an increase in physical mechanical properties, such as modulus, impact strength, thermal stability and heat deflection temperature. The Tm(0) of the materials was calculated by the method proposed by Marand, the kinetics of crystallization was evaluated by the Avrami analysis and also the Hoffman-Lauritzen theory of crystallization regimes was applied. Perkalite was found to depress Tm(0), to greatly enhance the rate of crystallization and to ease the chain folding of macromolecules.

Influence of high-pressure processing on the structure and memory effect of synthetic layered double hydroxides

We investigate the structural evolution of synthetic layered double hydroxides (LDH) samples, processed at room temperature and high-pressure (up to 7.7 GPa) in a toroidal chamber with two pressure-transmitting media, lead and graphite, using X-ray diffraction, thermogravimetry and N2-adsorption isotherms techniques. The X-ray patterns of compacted samples show a decrease in the peak intensities. For both pressure-transmitting media, our samples revealed a reduction of the basal d-spacing for the (003) plane when processed at 7.7 GPa. The expected high-pressure-induced amorphization was not observed. Surprisingly, we find high-pressure processing to have a strong influence on the memory effect of the LDH, due essentially to the reduction of the surface area and pore closing. Even when immersed in water, our samples did not recover the LDH structure, when either calcined at 450°C and compacted at 7.7 GPa, or calcined at 700°C and immediately compacted at 2.5 and 7.7 GPa.

Poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)]/layered double hydroxide nanocomposites

AbstractBACKGROUND: The thermomechanical performance of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (PHBV) is associated with its crystallization. Enhanced nucleation using a stearate‐functionalized synthetic layered double hydroxide (LDH) presents a potential solution.RESULTS: PHBV crystallization varied with concentration of LDH. At lower LDH concentration, thermal history‐induced cold crystallization was present. The extent of this order–disorder transition decreased with increasing LDH concentration and was completely eliminated at 7 wt% LDH. PHBV did not have a melt recrystallization peak but the introduction of LDH resulted in an increasingly pronounced melt recrystallization with increasing LDH concentration. Polarized optical microscopy coupled with differential scanning calorimetry and wide angle X‐ray diffraction (WAXD) analysis indicated increased lamella thickness in the nanocomposites compared to pure PHBV. WAXD and transmission electron microscopy showed that the nanocomposites had an intercalated but aggregated dispersion.CONCLUSION: The concentration of nanofiller provides unique effects in PHBV. Mechanical performance was found to scale with composition as determined using dynamic mechanical analysis and tensile testing. Copyright © 2008 Society of Chemical Industry

Synthesis and infrared spectroscopic characterization of selected layered double hydroxides containing divalent Ni and Co

Two new materials based upon layered double hydroxides with nickel and cobalt in the brucite-like layer with and without an anionic surfactant dodecylsulfonate (DS) have been synthesized and characterized by both near-infrared and infrared spectroscopy. This work shows that large anionic surfactants can be incorporated into the interlayer of the LDHs. The presence of the carbonate anions in the interlayer and the hydroxyl surface are readily analyzed by these techniques. The two materials of Ni3 and Co3Al-layered double hydroxides show different behaviour in the near-infrared and FT-IR spectra both in terms of position and band intensity. This is an indirect indication of the incorporation transition metal ions into the brucite-like layers. The nature of the observed reflectance bands in the near-infrared spectral region 12,000–8000 cm−1 is explained in terms of the d–d electronic transitions within the divalent nickel and cobalt brucite layers. The crystal field strengths of octahedral Ni2+ and Co2+ in the synthesized layered double hydroxides are close to but smaller than those in Ni-and Co-bearing carbonate minerals. The analysis of CO32− vibrational modes ν1, ν2, ν3 and ν4 in FT-IR spectra at 1045, 885, 1350 and 760 cm−1 reveals the presence of carbonate ion in the synthetic-layered double hydroxides.

Removal of bacteria and viruses from waters using layered double hydroxide nanocomposites

We have identified synthetic layered double hydroxides (LDH) nanocomposites as an effective group of material for removing bacteria and viruses from water. In this study, LDH nanocomposites were synthesized and tested for removing biological contaminants. LDH was used to remove MS2 and øX174 (indicator viruses), and Escherichia coli (an indicator bacterium) from synthetic groundwater and to remove mixed communities of heterotrophic bacteria from raw river water. Our results indicate that LDH composed of magnesium–aluminium or zinc–aluminium has a viral and bacterial adsorption efficiency ≥99% at viral concentrations between 5.9 × 106 and 9.1 × 106 plaque forming units (pfu)/L and bacterial concentrations between 1.6 × 1010 and 2.6 × 1010 colony forming units (cfu)/L when exposed to LDH in a slurry suspension system. Adsorption densities of viruses and bacteria to LDH in suspension ranged from 1.4 1010 to 2.1 1010 pfu/kg LDH and 3.2 × 1013–5.2 × 1013 cfu/kg LDH, respectively. We also tested the efficiency of LDH in removing heterotrophic bacteria from raw river water. While removal efficiencies were still high (87–99%), the adsorption capacities of the two kinds of LDH were 4–5 orders of magnitude lower than when exposed to synthetic groundwater, depending on if the LDH was in suspension or a packed column, respectively.