Layered Double Hydroxides Layers Research Articles

Design and in situ prepare a novel composite coating on Mg alloy for active anti-corrosion protection

In this paper, a novel composite coating combining Layered Double Hydroxides (LDH) film and Micro-arc Oxidation (MAO) ceramic layer was designed to further enhance anti-corrosion protection of coating. The MgFe-LDH/MAO composite coating was prepared through in situ synthesis MgFe-LDH nanoflakes on the surface of MAO coating. Subsequently, the active anti-corrosion mechanism of MgFe-LDH layer was revealed through microstructure characterization and electrochemical test. Furthermore, the interaction between LDH nanoflakes and original MAO coating was investigated, too. The results show that: LDH nanoflakes preferentially grow in the pores of original MAO coating, and form a dense layer on MAO coating. In situ prepared LDH layer gives a strong and stable adhesion on MAO coating, besides the dissolution of original MAO coating affects LDH growth. MgFe-LDH layer supplied an active anti-corrosion protection for Mg alloy, since LDH can effectively seal the inherent defects of MAO coating and absorb corrosive medium in environment. • A novel LDH/MAO composite coating was prepared through in situ synthesis. • Reveal the interaction between LDH layer and original MAO coating. • 3.LDH/MAO composite coating exhibits excellent anti-corrosion protection for Mg alloy. • 4.Reveal the anticorrosive protection mechanism of LDH layer.

Facile method for treating Zn, Cd, and Pb in mining wastewater by the formation of Mg–Al layered double hydroxide

Heavy metal pollution threatens aquatic systems worldwide, and mining activities are an important pollution source. Currently, the treatment of polluted water using a cost-effective technology that can purify multiple pollutants and is sustainable, environmentally friendly, and simple is a major challenge. The in situ preparation of Mg–Al layered double hydroxides (LDHs) and the concurrent treatment of Zn, Cd, and Pb from mining wastewater are important for preventing multiple steps and increasing adsorption sites. This study focused on mining wastewater containing high concentrations of Mg2+ and Al3+, with anion chemistry controlled by SO42−, which facilitates the formation of LDHs. The required amounts of Mg2+ and Al3+ ions were added to the wastewater, and the conditions for the creation of Mg–Al LDHs were controlled. The heavy metals in the experimental wastewater were effectively removed after the treatment via Mg–Al LDH formation. The X-ray diffraction of the post-treatment products suggested the formation of Mg–Al LDHs. The Mg/Al molar ratio (2.3:1) in the product approached the initial ratio (2:1), which meets the general limits of Mg–Al LDH formation. Scanning electron microscopy revealed that the products had a sheetlike stacked morphology, providing evidence for the formation of Mg–Al LDHs. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that SO42− might be the intercalated anion in the Mg–Al LDH layers. Consequently, SO42− was removed from the mining wastewater, as it was captured between the LDH layers during the formation reaction of Mg–Al LDHs.

Deterioration of anion-adsorption abilities of layered double hydroxides synthesized in agarose gel

With the goal of improving solid–liquid separability in wastewater treatment, Mg-Al layered double hydroxides (LDH) were synthesized in agarose gel, and the resulting LDH-containing hybrid hydrogels were dried. The anion-adsorption abilities of the dried hydrogels were compared with those of LDH synthesized by means of a conventional constant-pH coprecipitation method at low supersaturation. A surprising result was found: the adsorption abilities of the dried hybrid hydrogels decreased with storage time, whereas the adsorption abilities of the LDH synthesized by the conventional method remained essentially constant. Further investigation revealed that the adsorption abilities of LDH synthesized by rapid mixing of aqueous Mg-Al and aqueous NaOH at high supersaturation (i.e., a method similar to that used to prepare the hybrid hydrogel) also decreased over time. Therefore, only LDH synthesized by coprecipitation at high supersaturation showed deterioration during storage time in anion-adsorption abilities. Observed results that accompanied the deterioration suggest that the decrease was due to the formation of pockets of mutually adjacent Al-occupied cation sites in the metal hydroxide layers of the Mg-Al LDH as a result of rapid mixing of the starting solutions. The presence of mutually adjacent Al-occupied sites is thought to be in instability due to mutual repulsion. This instability may have led to gradual decomposition of hydroxide moieties containing mutually adjacent Al-occupied sites together with interlayer anions of OH– and Cl− to form aluminum hydroxide or basic aluminum chloride, as well as to separation of nearby Mg(OH)2 moieties from LDH structure.

Efficient activation of intercalated persulfate via a composite of reduced graphene oxide and layered double hydroxide

Efficient activation of peroxydisulfate (PDS, S2O82−) was achieved in this study by a hybrid of reduced graphene oxide (rGO) and layered double hydroxide (LDH). The peroxydisulfate was intercalated into the interlayers of LDH that was combined with rGO. This sample contributed to 92.4 % of phenol (PhOH) removal at 25 °C with a PDS loading amount of 0.4 mmol/g, which is better than its LDH-PDS counterpart. A high activation of PDS in rGO/LDH-PDS was also observed during the oxidation of 4-bromophenol (4-BrPhOH), 2,4-dibromophenol (2, 4-BrPhOH), 2,6-dibromophenol (2, 6-BrPhOH) and bisphenol A (BPA). As a redox reaction of PDS in LDH, this result determined that the composite of rGO/LDH caused more PDS to be activated than LDH. As the defective rGO sites activated the PDS on the surface or edges of LDH layers, the breaking of the OO bond in PDS generated SO4·− radicals from intercalated peroxydisulfate. This result was supported by the radical scavenger experiment, electron paramagnetic resonance measurements, and the increased number of oxygen functional groups in the reacted rGO. Our work thus provided a novel strategy for PDS activation to use in environmental remediation.

Enhancing the Desalination Performance of Capacitive Deionization Using a Layered Double Hydroxide Coated Activated Carbon Electrode

Capacitive deionization (CDI) is a promising desalination technology because of its simple, high energy efficient, and eco-friendly process. Among several factors that can affect the desalination capacitance of CDI, wettability of the electrode is considered one of the important parameters. However, various carbon materials commonly have a hydrophobic behavior that disturbs the ion transfer between the bulk solution and the surface of the electrode. In this study, we fabricated a layered double hydroxide (LDH) coated activated carbon electrode using an in-situ growth method to enhance the wettability of the surface of the carbon electrode. The well-oriented and porous LDH layer resulted in a better wettability of the activated carbon electrode, attributing to an enhanced capacitance compared with that of the uncoated activated carbon electrode. Furthermore, from the desalination tests of the CDI system, the LDH coated carbon electrode showed a higher salt adsorption capacity (13.9 mg/g) than the uncoated carbon electrode (11.7 mg/g). Thus, this enhanced desalination performance suggests that the improvement in the wettability of the carbon electrode by the LDH coating provides facile ion transfer between the electrode and electrolyte.

Preparation of tungstophosphoric acid intercalated MgAl layered double hydroxides with a tunable interlayer spacing and their catalytic esterification performance in the deacidification of model crude oil

This study demonstrates the synthesis of MgAl layered double hydroxides (LDHs) intercalated with tungstophosphoric acid (H3PW12O40, HPW) by an ion exchange method, and different interlayer spacings (d003) are obtained by adjusting the ion exchange temperature and time. The crystalline structures, molecular structures, compositions, acidity, and specific surface areas of the LDH samples are characterized. A relatively high ion exchange temperature is favorable for the formation of a large d003 value of around 1.46 nm, while a long exchange time is favorable for the formation of a small d003 value of around 1.05 nm. The different values of d003 are the result of different orientations of HPW anions within the interlayer space. Here, d003 around 1.46 nm is obtained when P2W18O6 − 62 and PW11O7 − 39 anions are arranged in the interlayer with their C2 axes respectively tilted toward and perpendicular to the LDH layer planes. In contrast, d003 around 1.05 nm is obtained when PW12O3 − 40 anions are grafted onto the LDH layers with their C2 axis perpendicular to the layer planes. Furthermore, the catalytic esterification performance of the samples is investigated for the deacidification of a model crude oil. Compared with PW12O3 − 40 anions, the presence of P2W18O6 − 62 and PW11O7 − 39 anions in the interlayer produces a higher proportion of acidic sites with medium acidity, which could act as catalytic sites. Moreover, the large d003 facilitates the diffusion of reactants into the interlayer, which enhances their contact with the catalytic sites, and thereby increases the catalytic esterification performance of the LDHs in the deacidification of model crude oil.

New electroactive and photosensitive polyamide/ternary LDH nanocomposite containing triphenylamine moieties in its backbone: synthesis and characterization

The new ternary (Mg–Zn–Al–) layered double hydroxide (LDH) with an organic modifier-containing azo group (LDH–SHDBS) as a guest anion was prepared by a co-precipitation through one-step synthetic method. The novel electroactive polyamide (EPA) was successfully prepared by direct polycondensation reaction of azelaic acid with a new synthetic diamine 4. The structure of diamine 4 was confirmed by FTIR and 1H NMR spectra. Also, polyamide/ternary LDH nanocomposites were prepared by resulting EPA and modified ternary LDH under ambient condition. The resulting data using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) showed ternary LDH were successfully distributed into the EPA matrix. Thermal behavior of the EPA and its nanocomposites were studied by thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG). The presence of LDH layers into EPA matrix improved thermal stability (T5, T10, char yield) in both air and nitrogen atmospheres. Also, photoisomerization and electrochemical behaviors of EPA and resulting nanocomposites were measured using UV–Vis spectroscopy and cyclic voltammetry (CV), respectively. The UV–Vis spectrum of the obtained nanocomposites showed two peaks at λmax = 422 and 480 nm related to π–π∗ and n–π∗ transitions of trans azobenzene. Moreover, trans to cis isomerization of azomoieties was studied by irradiation of the nanocomposites under 254 nm photons. The CV pattern of EPA exhibited a reversible anodic peak around 0.84 V, corresponding to the nitrogen atom of triphenylamine unit into polymer backbone that improved by incorporation of LDH–SHDBS into EPA matrix.

The influence of intercalated dye molecules shape and features on photostability and thermal stability between LDH layers

In the present work, an anionic azo dye, Orange G, was intercalated into the interlayer domain of Mg-Al layered double hydroxide (LDH) by co-precipitation route. The resulting hybrid material characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and thermal analysis, including thermal gravimetric analysis (TGA). The PXRD revealed the presence of host-guest interaction between the host matrix and interlayer anionic dye guest, with an expanded interlayer distance. The TGA studies showed that the dye-intercalated layered double hydroxides had higher thermal stability than the pristine dye. Scanning electron microscopy (SEM) method used to get information about the structure and morphology. Finally, photophysical properties of this intercalated hybrid measured by UV–visible diffuse reflectance (UV–VIS/DR) and photoluminescence spectroscopy (PL), which showed that intercalated dye to LDH had higher photostability than the pristine dye. Additionally, simulations studies were conducted using the Materials Studio software. There was a good agreement between calculated and measured X-ray diffraction patterns, and the results indicate that the dye molecules have vertical forms in the interlayer region. These values support to determine the relationship between the dye molecules translocation in the interlayer structure of LDH and thermal and photophysical stabilities of Orange G dye.

Photocatalytic removal of 4-chlorophenol present in water using ZrO2/LDH under UV light source

The influence of ZrO2 semiconductor content (0.3–5 wt%) supported on a Layered Double Hydroxides (LDH) system for photodegradation of 4-chlorophenol (4-CP) in water was studied. Complete removal of 4-CP is achieved in two stages: first, 4-CP was adsorbed on the photocatalyst in darkness, until equilibrium was reached. Afterwards, the light was turned on, and the photodegradation process started. Adsorption and photodegradation were analyzed both individually, and combined. The adsorption process of 4-CP on the synthesized samples is well described by fitting a pseudo-second-order equation. The UV photodegradation rates were 2.6 times higher than the 4-CP removal rates achieved by adsorption. The photodegradation process was analyzed by means of hydroxyl radical production displaying zeroth order behavior. The photocatalyst with 1 wt% ZrO2/LDH had the highest hydroxyl radical production rate, achieving 99 % of 4-CP degradation and 87 % of mineralization, while maintaining its photocatalytic activity during ten reaction cycles. At wt%ZrO2/ LDH higher than 1 wt%, clustering is observed, promoting charge recombination, hindering photodegradation efficiency and thus, decreasing mineralization rates. The monoclinic phase of ZrO2, identified by XRD, was responsible for the high photocatalytic activity. The distances between cations within the LDH layers were not modified after ZrO2 impregnation, thus suggesting that zirconia was supported on the external surface of LDH. Characterization was done by N2 physisorption, TGA, XRD, AAS, UV-DRS TEM, and SEM-EDS.

Highly efficient Ni nanotube arrays and Ni nanotube arrays coupled with NiFe layered-double-hydroxide electrocatalysts for overall water splitting

Novel nickel nanotube arrays (NTAs) on foamed nickel (NF) are developed by a facile electrochemical dealloying method to achieve a high hydrogen evolution reaction. Meanwhile, three dimensional heterostructure NiFe layered-double-hydroxide (LDH)@Ni NTAs electrode materials with strong interfacial interaction are prepared on NF by coupling ultrathin NiFe LDHs with Ni NTAs by electrochemical deposition, which demonstrate an excellent catalytic performance for oxygen evolution compared with NiFe LDH. Ni NTAs/NF require an overpotential of 101 mV to force the current density of 10 mA cm−2 for hydrogen evolution reaction because of the unique NTAs structure and the active sites for water dissociation provided by Ni2+ on the Ni NTAs surface. NiFe LDH@Ni NTAs/NF exhibit a low overpotential of 191 mV at a current density of 10 mA cm−2 for oxygen evolution reaction due to the reliable electron transfer from the intermediate metallic Ni NTAs to the external the NiFe LDH layer and more active sites that are exposed by highly dispersed ultrathin NiFe LDH nanosheets. The development of self-supporting NiFe LDH@Ni NTAs and Ni NTAs electrodes for efficient overall water splitting in an integrated alkaline electrolyzer is achieved a current density of 10 mA cm−2 at 1.51 V, accompanying excellent long-term durability.

2D layered double hydroxide membranes with intrinsic breathing effect toward CO2 for efficient carbon capture

2D material membranes with well-defined interlayer nanochannels hold great promise for precise molecular separation, where the size and surface chemical property of the channel determine the separation efficiency. The currently reported 2D material membranes for efficient CO2 separation are primarily built by introducing crosslinkers or intercalators into the interlayer channel. In this study, we demonstrate a novel 2D material membrane with inherent CO2-selective transport channels based on layered double hydroxide (LDH). The intrinsic breathing effect of LDH toward CO2 enables the spontaneous incorporation of CO2 molecules into the interlayer nanochannels and subsequent conversion/transport in the form of CO32− species which are released as CO2 at the downstream side of membrane. Moreover, the intercalated CO32− ions with an ionic radius of 0.136 nm narrow down the nanochannel size from 0.7 nm to 0.3 nm by electrostatic interaction with LDH layers, conferring the membrane a distinct molecular sieving ability for CO2/CH4 separation. The unique breathing effect and size-sieving effect jointly contribute to the high membrane separation performance with CO2 permeance of 150 GPU and CO2/CH4 selectivity of 33. This study is anticipated to extend the materials and strategies for design of the CO2 preferential transport channels in membranes.

Hierarchical In(OH)3/ZnAlIn-LDHs nanocomposite with extremely low detection limit for NO2 sensing

Layered double hydroxides (LDHs) have been acknowledged as potential gas sensing materials owing to their large specific surface area and compositional flexibility. In this work, highly sensitive LDHs-based nanocomposite of In(OH)3/ZnAlIn-LDHs was synthesized via hydrothermal growth of hierarchical ZnAlIn-LDHs and synchronous modification of single-crystalline nanoparticles of In(OH)3. The achieved In(OH)3/ZnAlIn-LDHs shows three-dimensional (3D) hierarchical architecture, with discrete In(OH)3 nanoparticles attachment on the nanosheet surface. The hierarchical ZnAlIn-LDHs forms loose 3D sensitive skeleton facilitating easy gas diffusion; additional In(OH)3 nanoparticles modification on LDHs nanosheets induces heterojunction effect capable of further enhancement of gas-sensing response. The gas-sensing measurements reveal that the achieved In(OH)3/ZnAlIn-LDHs nanocomposite is more sensitive to NO2 with rapid dynamic characteristic in comparison to the single components. At room temperature, the In(OH)3 modified ZnAlIn-LDHs can response ultra rarefied NO2 of 2.5 ppb with response of 35.4%. The significantly enhanced sensing response for the nanocomposite of In(OH)3/ZnAlIn-LDHs could attribute to the co-modulation of unique hierarchical microstructure, In-doping in LDHs layers and heterojunction effect between LDHs and the modified In(OH)3 nanoparticles.

Growth of cobalt-aluminum layered double hydroxide nanosheets on graphene oxide towards high performance supercapacitors: The important role of layer structure

Layered CoAl LDH (Cobalt-Aluminum layered double hydroxide) has been identified as a promising active electrode material for pseudocapacitors. However, some issues of CoAl LDH, such as poor conductivity and aggregation, limited its large-scale practical application. In addition, vague understanding of the role of the CoAl LDH's layer structure in pseudocapacitance process might mislead the research community on material modification. Herein, growth of CoAl LDH nanosheets with and without graphene oxide (GO) is prepared by hydrothermal method. To evaluate the role of layer structure in pseudocapacitance process, the CoOOH nanosheets with and without GO are also prepared by combining hydrothermal method with alkali etching treatment. As pseudocapacitance electrode material, the GO@CoAl LDH exhibits surpassing specific capacitance of 1725.71 F g−1 at a current density of 1 A g−1 and optimal 87.73% capacitance retention at 7 A g−1 which are much higher than the other as-obtained materials. The study provides not only a better perspective to explore the importance of LDH layered structure during the electrochemical process, but also a direction to subsequent design of the novel Co-based or LDH-based electrode materials.

Harvesting solar light on a tandem of Pt or Pt-Ag nanoparticles on layered double hydroxides photocatalysts for p-nitrophenol degradation in water

The quest to provide clean water has led to a tremendous boost in the synthesis of advanced photocatalysts that are able to decontaminate water by harvesting the solar energy. Herein, a tandem of Pt or both Pt-Ag nanoparticles on layered double hydroxides (LDH) photocatalysts were obtained via a green chemical procedure in which LDH serve a dual function of both facilitating the synthesis of nanoparticles of Pt and Ag and acting as a support. Detailed characterization showed that the LDH structure is well-retained, while small nanoparticles of Pt or Pt-Ag are formed and dispersed on the larger nanoparticles of the LDH. The effects of the heterometallic composition of the 2-D LDH layers (e.g. Zn2Al; Zn2FeAl) and the mono/bi-metal (Pt/Pt-Ag) identity on the solar-light-induced catalytic performances were investigated using p-nitrophenol (p-NPh) as a targeted pollutant. Pt-Ag synergistic activity was superior to Pt alone to promote p-NPh degradation and Pt-Ag/Zn2Al exhibited the best photocatalytic activity approaching 77% degradation and 71% mineralization of p-NPh, after 6 h under solar light, at room temperature. The introduction of Fe in the LDH layers caused a significant change in the degradation pathway of p-NPh and drastically decreased the catalytic response such that p-NPh mineralization was only 10% for Pt-Ag/Zn2FeAl. Even though UV–vis analysis showed that Pt-Ag/Zn2FeAl had a stronger absorption of the visible light than Pt-Ag/Zn2Al, the PL data indicated a significant increase in the photoluminescence signal for Pt-Ag/Zn2FeAl as compared to Pt-Ag/Zn2Al. This suggested a retard recombination of electrons-holes in Pt-Ag/Zn2Al and revealed the active role of the LDH multimetallic composition to establish an effective electronic coupling between the constituent nanounits. These findings may aid in the rational design of multimetallic heterostructures that can effectively harvest sunlight for environmental cleanup.

Effect of drying step on layered double hydroxides properties: Application in reactive dye intercalation

Freeze-dried sulfate intercalated layered double hydroxides (LDH) phase was synthetized by coprecipitation method via direct intercalation of sulfate anion. The effect of freeze-drying process on LDH properties was investigated. The resulting phase was evaluated for its efficiency in the intercalation of the reactive azo dye, Remazol Brilliant Red F3B (RR-F3B). The freeze-dried phase exhibited a low crystallinity and narrow particle size distribution compared to conventional LDH phases. The freezing step led to highly aggregated nanoparticles with a characteristic distance d003 of 8.12 Å. The preferential arrangement of the intercalated dye species was examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. The results showed that RR-F3B molecules were partially accommodated between the LDH layers as single-layer with horizontal orientation. The effect of drying on morphological and structural properties can be attributed to several stresses during freezing and drying steps.

Titanium Dioxide-Layered Double Hydroxide Composite Material for Adsorption-Photocatalysis of Water Pollutants.

Although adsorption has gained favor among numerous water treatment technologies as an effective pollutant removal method, its application is often hindered by challenges with its resource- and energy-intensive regeneration procedure once the available adsorption sites are exhausted. Herein, we present adsorption-photocatalysis composite materials combining layered double hydroxides (LDHs) and titanium dioxide (TiO2) for water treatment. Incorporation of the photocatalyst into the material opens opportunities to harness light from the sun or lamps for oxidative degradation of the adsorbed contaminants on the material surface, to free adsorption sites for material reuse. In addition to allowing photocatalytic regeneration, the addition of TiO2 to colloidal suspensions of delaminated LDH enabled the formation of TiO2-LDH composites with far superior adsorptive performances compared to their parent LDH compounds. During the material synthesis, positively charged LDH layers and negatively charged TiO2 particles combine through electrostatic attraction to yield composites with dramatically enhanced adsorption capacities toward model contaminants, methyl orange and 2,4-dichlorophenoxyacetic acid, by 16.0 and 76.7 times, respectively. Combining delaminated LDH with TiO2 allowed us to maximize the exposure of positively charged surfaces to the contaminants, in a form that can be used as a solid adsorbent. After regeneration, the material regained up to 92% of its adsorption efficiency toward model contaminants. In light of our findings showing significantly different kinetics of adsorption and photocatalytic regeneration, we propose a new scheme to utilize adsorption-photocatalysis systems, in which the two processes are separated to better utilize their unique strengths.

Effect of divalent metal ions on durability and anticorrosion performance of layered double hydroxides on anodized 2A12 aluminum alloy

Inhibitor-loaded layered double hydroxides (LDHs) sealing layers were prepared by hydrothermal co-precipitation method for anodic aluminum oxide (AAO) film on 2A12 aluminum alloy. Effects of different divalent metal ions (M2+ = Ni2+, Zn2+) on the LDHs structure and the anticorrosion behaviors of the corresponding sealing layer were investigated. Compared with the Zn-based LDHs, the Ni-based LDHs possesses a smaller basal spacing and a stronger interlayer interaction. The results revealed that the compact Ni-based sealing LDHs layer loaded with a large number of vanadate corrosion inhibitors exhibited high durability and excellent corrosion protection for an exposure time of 14 days in 3.5% NaCl solution. This study provides significant insights into understanding the anticorrosion effect of different divalent metal ions on the structure of the LDHs sealing layer.

Phosphate capture by ultrathin MgAl layered double hydroxide nanoparticles

Capture of phosphorus from runoff and wastewater is of high priority in order to reclaim phosphorus for food security and to prevent water pollution. Here we report an environmentally friendly method to synthesize ultrathin MgAl layered double hydroxide (LDH) nanoparticles for phosphorus adsorption. Fast co-precipitation of magnesium and aluminum at 25–80 °C in the presence of urea resulted in the desired LDH with variable admixtures of amorphous aluminum hydroxide (16–38%) quantified from solid state 27Al MAS NMR. Freshly synthesized particles appeared as exfoliated single layers that upon drying stacked to form particles with thickness of 3 to 5 nm (four to six LDH layers) and lateral sizes of ~30 nm, as seen by XRD, SEM, TEM, and AFM. Phosphate adsorption on LDH nanoparticles synthesized at room temperature (LDHns-U25) was very fast and reaction reached equilibrium within 15 min at pH 8.5. The freeze-dried LDHns-U25 nanoparticles exhibited phosphate sorption capacity of 98 ± 15 mg P·g−1, which is 55% higher than for conventional LDH. Phosphate was bound to LDH electrostatically and via inner-sphere surface complexation as evidenced from a combination of 31P MAS NMR spectroscopy, surface potential measurements, IR spectroscopy, and ionic strength effects on phosphate sorption. This study demonstrates that urea-facilitated synthesis of LDH nanoparticles provides high capacity phosphate sorbents with potentials for phosphate recovery from waste waters.

Corrosion Studies of 12-Aminododecanoate Modified Zn-Al LDH/Epoxy Coating

Addition of environmentally friendly layered double hydroxide (LDHs) to organic coatings can increase barrier properties within the coatings due to the platelet structure of the LDHs. A new approach combining silane coupling agents to enhance compatibility of the inorganic and organic matrix is used to form improved corrosion resistance coatings. For this work, Zn-Al-LDH are prepared via a co-precipitation method and modified by sodium 12-aminododecanoate through an anion exchange process. The organo-modified layered double hydroxide (LDH) is functionalized using 3-aminopropyltriethoxysilane (APTES) which is then incorporated into the epoxy matrix (EPON 828). The reaction between amine part of the amino dodecanoate as a strong nucleophilic group and epoxy ring part as an electrophilic group improves compatibility of LDHs layers and epoxy molecules in the composite. Differential scanning calorimetry is used to study this exothermic epoxy-amine ring opening reaction to determine the curing temperature of the coatings before and after modified LDH inclusion. The change in LDH structure, effect of incorporation of modified LDHs in the epoxy matrix, grafting of APTES on the LDH surface and elemental analysis are investigated respectively, by x-ray diffraction, thermogravimetric analysis, infrared spectroscopy and energy dispersive x-ray analysis. In the last step of preparation, Epikure 3571 as a curing agent, is added to the LDHs/epoxy system, then the coating is applied on steel substrates. After the thermal curing process, the anti-corrosion performance provided by this coating is assessed by multiple methods including, open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl aqueous solution. Further, scanning electron microscopy is used to study morphological changes on the coating before and after immersion test and to scan the localized corrosion spots. The results are compared with the coated steel samples with clear epoxy coating and none modified LDH/epoxy. Figure 1

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−.