Li-Al Layered Double Hydroxide Research Articles

Surfactant Intercalation in Li-Al-Based Binary and Ternary Layered Double Hydroxides by the Microwave-Assisted Rapid Ion-Exchange Process and Its Application in Iodine Adsorption

Recognizing the extreme speeds of reactions with microwaves, anionic forms of surfactants (sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS)) have been intercalated successfully by ion-exchange reactions in binary Li-Al and ternary Li-M-Al (M = Mg, Co, Ni, Cu, and Zn) layered double hydroxide (LDH) systems with the aid of microwaves. The samples have been characterized extensively. The basal spacings of 28.2 and 30.4 Å have been estimated for Li-Al-DS and Li-Al-DBS LDH samples, respectively, suggesting a perpendicular arrangement of DS− and DBS− anions in the interlayer space. The characteristic vibration bands of both LDH and the surfactant (DS− and DBS−) in the FTIR spectra confirmed the binding mode of surfactant molecules within the interlayers. DS−-intercalated Li-Al LDH showed lower thermal stability than the DBS−-intercalated sample. The nitrate-intercalated Li-M-Al (M = Mg, Co, Ni, Cu, and Zn) LDHs were ion-exchanged with SDS and SDBS to yield DS−-and DBS−-intercalated systems. The expanded basal spacings and a change in crystallite morphology confirmed the vertical intercalation of DS− and DBS− in Li-M-Al LDHs. ICP-AES and elemental analyses determined the metal contents and the surfactant content. FTIR spectra of intercalated samples confirmed the surfactant’s presence in the interlayer. The presence of Co, Ni, and Cu in Li-M-Al LDHs has been confirmed from UV-visible spectra. The Li-Al-DBS sample adsorbed iodine efficiently from methanol solutions, and the Langmuir model could explain the adsorption data in a better way. The adsorption followed pseudo-second-order kinetics.

Cerium-based conversion films developed on LiAl-layered double hydroxide coatings for corrosion protection of AA7075 aluminum alloys

The paper presents several experimental results regarding the influence of various procedures applied to incorporate Ce species in hydrotalcite–type chemical conver­sion coatings on the overall corrosion performance for AA 7075 aluminum alloy as a metallic substrate. Two routes were envisaged: (i) chemical incorporation of Ce by immersion in cerium nitrate solutions and (ii) electrochemical deposition of hydro­phobic Ce - based layer involving ethanolic solutions of stearic acid and cerium nitrate. The chemical route involving immersion in cerium nitrate solutions led to the incorpo­ration of 2.46 – 6.84 wt.% Ce in the composition of the porous conversion layer. The electrochemical process facilitated the formation of a hydrophobic cerium stearate layer on porous hydrotalcite conversion coating showing water contact angles of about 132o and a higher Ce content incorporated of 6.55 – 9.73 wt.%. The corrosion performance of the Ce-based conversion coatings is also discussed.

Electrodeposition of a Li-Al Layered Double Hydroxide (LDH) on a Ball-like Aluminum Lathe Waste Strips in Structured Catalytic Applications: Preparation and Characterization of Ni-Based LDH Catalysts for Hydrogen Evolution

A functionally structured catalyst was explored for ethanol steam reforming (ESR) to generate H2. Aluminum lathe waste strips were employed as the structured catalytic framework. The mixed metal oxide (Li-Al-O) was formed on the surface of Al lathe waste strips through calcination of the Li-Al-CO3 layered double hydroxide (LDH), working as the support for the formation of Ni catalyst nanoparticles. NaOH and NaHCO3 titration solutions were, respectively, used for adjusting the pH of the NiCl2 aqueous solutions at 50 °C when developing the precursors of the Ni-based catalysts forming in-situ on the Li-Al-O oxide support. The Ni precursor on the Al structured framework was reduced in a H2 atmosphere at 500 °C for 3 h, changing the hydroxide precursor into Ni nanoparticles. The titration agent (NaOH or NaHCO3) effectively affected the physical and chemical characterizations of the catalyst obtained by the different titrations. The ESR reaction catalyzed by the structured catalysts at a relatively low temperature of 500 °C was studied. The catalyst using NaHCO3 titration presented good stability for generating H2 during ESR, achieving a high rate of H2 volume of about 122.9 L/(gcat·h). It also had a relatively low acidity on the surface of the Li-Al-O oxide support, leading to low activity for the dehydration of ethanol and high activity to H2 yield. The interactions of catalysts between the Ni precursors and the Li-Al-O oxide supports were discussed in the processes of the H2 reduction and the ESR reaction. Mechanisms of carbon formation during the ESR were proposed by the catalysts using NaOH and NaHCO3 titration agents.

Synthesis of high-specific-surface-area Li-Al mixed metal oxide: Through nanoseed-assisted growth of layered double hydroxide

Li-Al layered double hydroxide (LDH) and LDH-derived mixed metal oxide (MMO) are promising solid base catalysts due to their instinct and strong surface basicity. Herein, nano Li-Al LDH was synthesized via the crystal growth from metal hydroxide nanoseeds with low crystallinities. The present Li-Al LDH possesses high specific surface area (326 m2 g−1), highly crystalline, and high purity. The present nano LDH undergoes a transformation to Li-Al MMO with a high specific surface area (349 m2 g−1) of abundant strong basic sites. Indeed, the present Li-Al MMO exhibits an enhanced catalytic activity for a transesterification reaction between methanol and soybean oil compared to one prepared through a co-precipitation method, thanks to the larger amount of active sites.

Effect of synthesis conditions and post-synthetic treatments of LiAl-LDH on the performance of sulfoaluminate cement

LiAl-layered double hydroxide (LiAl-LDH) has been reported as a potential hardening accelerator of calcium sulfoaluminate (CSA) cement. Until now, little has been known about the effect of synthesis conditions and post-synthetic treatments of LiAl-LDH on the performance of CSA cement. The present work shows two methods for the synthesis of LiAl-LDH – a solvothermal method and a separate nucleation and aging steps method (SNAS) – and two methods for the post-synthetic treatments of LiAl-LDH, with and without drying process. The effect of the resultant LiAl-LDH on the performance of CSA cement was studied in relation to the strength, hydration process and products. Results indicate that specimens containing LiAl-LDH showed a greatly enhanced performance with regard to setting time and compressive strength at early and later ages. Compared to LiAl-LDH prepared with the solvothermal method, LiAl-LDH from SNAS synthesis is more effective to increase the compressive strength and shorten setting time. Moreover, the post-synthetic treatments affect the performance of LiAl-LDH. LiAl-LDH without a drying process has better dispersion stability, higher compressive strength and a shorter setting time. Owing to the crystal seed effect, LiAl-LDH enhanced the hydration rate and improved the amount of hydration products, resulting in a higher compressive strength.

Cross-sectional characterization of the conversion layer formed on AA2024-T3 by a lithium-leaching coating

This work focuses on the cross-sectional characterization of the protective conversion layer formed on AA2024-T3 by lithium-leaching from a polyurethane coating in a corrosive environment. The layer shows a multi-layered arrangement comprising nanoscopic local phases. Transmission electron microscopy (TEM) and complementary high-resolution secondary ion mass spectroscopy (SIMS) were employed to observe the cross-sections of the entire layer formed at different locations of a 1-mm-wide scribe, in terms of morphology, structure and chemical composition. The conversion layer was comprised of two ubiquitous sublayers; a thin dense layer (i.e. 150 nm) adjacent the alloy substrate and a porous layer. The former represents an amorphous lithium-containing pseudoboehmite phase, Li-pseudoboehmite, whereas the latter is composed of amorphous and crystalline products; an outer columnar layer merely seen on the peripheral region is also crystalline. Through a sandwich structure and the d(003) basal spacing, the crystalline phases were identified as Li-Al layered double hydroxide. Although lithium was found uniformly spread within different regions, the local phases with no/low concentration of lithium were revealed with energy filtered TEM and confirmed with SIMS analysis.

Synthesis and Characterization of Aspartic Acid Modified LiAl Layered Double Hydroxide

Synthesis and Characterization of Aspartic Acid Modified LiAl Layered Double Hydroxide

Enhanced corrosion resistance of LiAl-layered double hydroxide (LDH) coating modified with a Schiff base salt on aluminum alloy by one step in-situ synthesis at low temperature

Disodium vanillin l-aspartic acid modified LiAl-layered double hydroxide (LDH) coating was fabricated on A6N01-T5 Al alloy by the one step in-situ synthesis at relatively low temperature. The characteristics of the modified LiAl-LDH (VLDH) coating were characterized by X-ray diffractometer (XRD), Flourier transformation infrared spectrometer (FT-IR), Scanning electron microscopy (SEM), Energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and Atomic force microscopy (AFM). The results showed that vanillin l-aspartic acid anions were successfully intercalated into the interlayer of LiAl-LDH to form the smoother and more compact surface of the VLDH coating. The corrosion resistance of the VLDH coating was investigated by Scanning electron microscopy (SEM), Energy dispersive spectrometer (EDS), Elemental analyzer (EA), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. These results indicated that the VLDH coating possessed the excellent ion-exchange property and the better corrosion resistance than the unmodified LiAl-LDH (NLDH) coating in 3.5 wt% NaCl solution. The corrosion resistance mechanism of the VLDH coating was proposed in this paper.

Gold-catalyzed conversion of lignin to low molecular weight aromatics.

A heterogeneous catalyst system, employing Au nanoparticles (NPs) and Li-Al (1 : 2) layered double hydroxide (LDH) as support, showed excellent activity in aerobic oxidation of the benzylic alcohol group in β-O-4 linked lignin model dimers to the corresponding carbonyl products using molecular oxygen under atmospheric pressure. The synergistic effect between Au NPs and the basic Li-Al LDH support induces further reaction of the oxidized model compounds, facilitating facile cleavage of the β-O-4 linkage. Extension to oxidation of γ-valerolactone (GVL) extracted lignin and kraft lignin using Au/Li-Al LDH under similar conditions produced a range of aromatic monomers in high yield. Hydrolysis of the Au/Li-Al LDH oxidized lignin was found to increase the degree of lignin depolymerization, with monomer yields reaching 40% for GVL extracted lignin. Based on these results, the Au/Li-Al LDH + O2 catalyst system shows potential to be an environmentally friendly means of depolymerizing lignin to low molecular weight aromatics under mild conditions.

Enhanced fluoride removal by La-doped Li/Al layered double hydroxides

In this study La intercalated Li/Al layered double hydroxide (LDH) was developed for efficient water defluoridation. The La-modified material, i.e., La doped Li/Al-LDH, exhibits more preferable fluoride adsorption than Li/Al-LDH in a broad pH range of 5–9, with the working capacity twice of the latter and seven times of magnitude higher than activated alumina. The fluoride removal kinetics is well fitted by pseudo-second order model, and the adsorption isotherm is well described by Freundlich model. Effect of pH and competing ions was examined during fluoride sequestration. The underlying mechanism for such enhanced adsorption of fluoride by La doped Li/Al-LDH was further revealed based on XPS and FTIR analysis. The presence of La and Al was found to be responsible for the satisfactory defluoridation of La doped Li/Al-LDH, and chloride replacement with fluoride occurred from both LDHs during fluoride adsorption. Also, the capacity of La doped Li/Al-LDH could be refreshed by alkaline solution (pH = 12) for cyclic runs. All the results implied that La doped Li/Al-LDH could serve asa potential adsorbent for efficient fluoride removal from water.

Self-healing Li-Al layered double hydroxide conversion coating modified with aspartic acid for 6N01 Al alloy

A self-healing Li-Al layered double hydroxide conversion coating (LCC) modified with aspartic acid (ALCC) was prepared on 6N01 Al alloy for corrosion protection. Scanning electron microscopy (SEM) showed that a compact thin film has been successfully formed on the alloy. X-ray diffraction (XRD) and FT-IR spectra proved that species of aspartic acid anions were successfully intercalated into LCC. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and neutral salt spray (NSS) testing showed that the resultant ALCC could provide effective corrosion protection for the Al alloy. During immersion of the ALCC-coated alloy in 3.5% NaCl solution, new film was formed in the area of artificially introduced scratch, indicating its self-healing capability. XPS results demonstrated that Cl- anions exchange partial Asp anions according to the change content of element on conversion coating. From the above results, the possible mechanism via exchange/self-assembly was proposed to illustrate the phenomenon of self-healing.

Mechano‐Hydrothermal Synthesis of Tetraborate Pillared Li–Al Layered Double Hydroxides

Tetraborate pillared Li–Al layered double hydroxide was synthesized for the first time by a mechano‐hydrothermal process in which gibbsite (Al(OH)3) sample was first activated by a ball milling, followed by hydrothermal treatment with Li2B4O7 in water at 95°C. Activation of gibbsite Al(OH)3 induced by mechanochemical process was essential for the formation of thin disk‐like Li–Al LDH intercalated with borate anion. When in excess the activated Al(OH)3 was transformed into bayerite phase during the hydrothermal process.

A facile approach to superhydrophobic LiAl-layered double hydroxide film on Al–Li alloy substrate

A highly oriented LiAl-layered double hydroxide (LDH) film was first fabricated via a facile in situ growth method on Al–Li alloy. The morphology and structure of the LDH film were characterized using scanning electron microscopy, atomic force microscopy, X-ray diffraction, and transmission electron microscopy. After chemical modification with 1H,1H,2H,2H-Perfluorodecyltrimethoxysilane, the chemical compositions and states of surface-modified film were analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results showed that the nest-like structure of LiAl-LDH film was composed of interconnected LiAl-LDH nanosheets, which oriented almost vertically to the substrate surface. After chemical modification, a superhydrophobic surface was obtained with water contact angle of 168°. The formation mechanism of the superhydrophobic film was also discussed.

Synthesis and Characterization of Poly(ethylene terephthalate)/Modified Lithium‐Aluminum‐Layered Double Hydroxide Nanocomposites Prepared Using In‐situ Polymerization

AbstractLayered double hydroxides are a type of layered stacked compound, which can be intercalated with organic‐molecule modifiers. An ion‐exchange process for layered double hydroxide (LDH) was used to intercalate water‐soluble sulfanilic acid salt (SAS) and dimethyl 5‐sulfoisopthalate (DMSI) into lithium aluminum layered double hydroxides (LiAl LDHs). In this work, a hydrothermal process was used to modify LiAl LDHs, and the modified LiAl LDHs were treated with either SAS or DMSI through an ion‐exchange process and were then intercalated using bis‐hydroxyethylene terephthalate (BHET). The results indicate that the modified LiAl LDHs improved the interlayer compatibility between the PET and LiAl LDH layers; thus, enabling the oligomer molecules to more easily enter the gallery of the LiAl LDH layers so that polymer chains could be included between the LDH layers during polymerization of the matrix. The better barrier, mechanical properties, and thermal stability of these new types of PET nanocomposites are discussed.

Preparation of a Thin Pd Membrane on a Modified Porous Stainless Steel by a Calcined Li–Al Layered Double Hydroxide Layer

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Synthesis of Li/Al LDH using aluminum and LiOH

The synthesis of Li/Al layered double hydroxide (LDH) within the ternary system of LiOH–Al–H2O was investigated to determine the feasibility of a one-step synthetic process and the optimal yield composition for the process. The dissolution of Al metal in LiOH solutions was spontaneous and resulted in the generation of H2 gas and heat. Pure Li/Al LDH precipitate was obtained when the Al/Li molar ratio was between 0.1 and 2 and was independent of the LiOH concentration. The yield of Li/Al LDH was correlated with the initial amounts of LiOH and Al in the system and inversely correlated to the quantity of water. However, the Al metal could not be completely dissolved if there was not enough water content due to its consumption in the reaction. The optimal yield of Li/Al LDH, as defined by the efficient conversion from Al and LiOH to Li/Al LDH, was obtained with a LiOH concentration=3molkg−1 and an Al/Li molar ratio=2. The reaction mechanism involves the dissolution of the Al metal in LiOH and the formation of aluminate ions in solution. The aluminate ion and the hydrated Li+ ion subsequently form an ion pair, and the polarizing effect of the Li+ on the water in its hydration shell leads to the acid hydrolysis of the aluminate ion and the formation of Li/Al LDH. This study demonstrated a synthetic process for Li/Al LDH with a high anion exchange capacity. This synthetic process will have additional economical and environmental benefits if recycled Al metal can be used in the synthesis and the evolved hydrogen gas and heat from the process can be further utilized.

Solution-processed Li–Al layered-double-hydroxide platelet structures for high efficiency InGaN light emitting diodes

High-oriented Li-Al layered double hydroxide (LDH) films were grown on an InGaN light-emitting diode (LED) structures by immersing in an aqueous alkaline Al(3+)- and Li+-containing solution. The stand upward and adjacent Li-Al LDH platelet structure was formed on the LED structure as a textured film to increase the light extraction efficiency. The light output power of the LED structure with the Li-Al LDH platelet structure had a 31% enhancement compared with a conventional LED structure at 20 mA. The reverse leakage currents, at -5V, were measured at -2.3 × 10(-8) A and -1.0 × 10(-10)A for the LED structures without and with the LDH film that indicated the Li-Al LDH film had the insulated property acted a passivation layer that had potential to replace the conventional SiO2 and Si3N4 passivation layers. The Li-Al LDH layer had the textured platelet structure and the insulated property covering whole the LED surface that has potential for high efficiency InGaN LED applications.

Structural Synthon Approach to the Study of Stacking Faults in the Layered Double Hydroxides of Lithium and Aluminum

AbstractA single layer of the Li‐Al layered double hydroxide (LDH) can be considered to be a structural synthon that can be stacked in a number of ways to give rise to the polytypes of the Li‐Al LDH family. The topotactic imbibition of lithium into gibbsite and bayerite precursors gives rise to crystalline 2H and 1M1 polytypes respectively. In contrast the sample formed through a gel to crystallite route is found to be a 1M1 polytype with stacking disorders whose local symmetry corresponds to the 1M2 polytype. On heating, a solid‐solid 1M1→1H polytype transformation is observed.

Rapid direct growth of Li–Al layered double hydroxide (LDH) film on glass, silicon wafer and carbon cloth and characterization of LDH film on substrates

This work presents a novel method for directly growing highly oriented Li–Al LDH films on substrates such as glass, Si wafer and carbon cloth in an aqueous alkaline Al3+- and Li+-containing solution. The substrate samples were each hanged and then respectively immersed in the solutions at 5–35 °C for 20 min or less than 6 h to form the LDH films. The Li–Al LDH film comprised of extra-high-density Li–Al LDH platelets, each standing almost perpendicularly on the surface of the substrate. The LDH film that was fabricated at 5 °C (∼1.4 μm thick) exhibits good UV shielding (with only 9.7% UV transparency) and a maximum of 56% transparency to visible light. A more rapid method (only 20 min needed) can be utilized to develop a Li–Al LDH film to cover both hydrophobic and hydrophilic carbon cloth surfaces. Despite the modification of these surfaces, the Li–Al LDH film on carbon cloths retained or enhanced their original surface properties (including hydrophobicity or hydrophilicity). The LDH film thickness increased with immersion time and/or solution temperature. The thickness reached a plateau during LDH formation. CO2 in the atmosphere dissolved in the alkaline Al3+- and Li+-containing solution, yielding CO32− ions for Li–Al LDH formation. The heterogeneous nucleation and growth of each LDH platelet on the substrate surface finally produced an LDH film.

The removal and recovery of Cr(VI) by Li/Al layered double hydroxide (LDH)

Hexavalent Cr has been identified as one of the toxic metals commonly present in industrial effluents. Among the treatment techniques developed for removing Cr(VI) from waste waters, sorption is most commonly applied, due to its simplicity and efficiency. However, few adsorbents can be recycled and reused cost-effectively. In this study, the removal and recovery of Cr(VI) from water using Li/Al LDH was investigated. The removal of Cr(VI) by Li/Al LDH was evaluated in a batch mode. The results demonstrated that Cr(VI) adsorption onto Li/Al LDH occurs by replacing the Cl − that originally exists in the interlayer of the adsorbent. The degree of Cr(VI) adsorption observed for Li/Al LDH was relatively high and the process occurred rapidly; however, a portion of adsorbed Cr(VI) was gradually desorbed, due to the Li de-intercalation of Li/Al LDH. Lithium de-intercalation from Li/Al LDH with interlayer Cl − and interlayer Cr(VI) follows the first order kinetics and has the activation energies of 76.6 and 41.5 kJ mol −1, respectively. The properties of thermal unstablility and the high adsorption capacity of Li/Al LDH may lead to the development of an innovative technique for the removal of Cr(VI) from Cr(VI)-containing wastewater. That is, Li/Al LDH may be used as an effective adsorbent for the adsorption of Cr(VI) in an ambient environment. Following the adsorptive process, the adsorbed Cr(VI) may be released, using heated water to treat the Cr(VI)-containing Li/Al LDH particles. Through this hydrothermal treatment of the used adsorbent, Cr(VI) can be recovered and the solid product (gibbsite) can be recycled for further use.