Morphology Of Layered Double Hydroxides Research Articles

(Invited) Layered Double Hydroxides with Enhanced Interlayer Space for Electrochemical Energy Storage and Deionization

Layered double hydroxides (LDHs) have been extensively studied as promising functional nanomaterials owing to their excellent electrochemical activity and tunable chemical composition. In this work, we presented a series of investigations on enhanced interlayer space of LDHs for electrochemical energy and deionization.Firstly, using acetate anions (Ac-) as an intercalating element, NiCo-LDH nanosheets arraying on Ni Foam with different amounts of Ac- anions intercalation or volumes of hydrothermal solution were prepared by a simple hydrothermal method. The optimized amount of Ac- anions expanded the interlayer space of LDH nanosheets from 0.8 to 0.94 nm. An ultrahigh specific capacity of 1200 C g-1 at 1 A g-1 (690 C g-1 without Ac- anions), outstanding rate capability of 72.5% at 30 A g-1 and cycle stability of 79.90% after 4500 cycles, which were mainly attributed to the higher interlayer spacing of Ac- anions intercalation.Moreover, CoAl-LDH nanosheets intercalated by sodium dodecyl sulfate (SDS) with an enhanced interlayer spacing from 0.76 to 1.33 nm are synthesized and used as an anode of electrosorption. The enlarged interlayer spacing provides an enhanced ion diffusion channel and improves the utilization of the interlayer electroactive sites, while heat treatment transferring LDHs to layered metal oxides offers additional active oxidation reaction sites to facilitate the electro-sorption rate, contributing to the high salt adsorption capacity (31.78 mg g-1) and average salt adsorption rate (3.75 mg g-1 min-1) at 1.2 V in 500 mg L-1 NaCl solution. In addition, the excellent long-term cycling stability (92.9%) after 40 cycles proves the strong electronic interaction between SDS and the host layer, which is validated by density functional theory calculations later on.In addition, ionic surfactants like SDS and cetyl trimethyl ammonium bromide (CTAB) can be used to modify the morphology of LDH. The original LDH shows microspheres formed by nanorods, and LDH-CTAB is similar, yet more tangled, while LDH-SDS is like micro flowers consisting of interwoven nanosheets. LDH-SDS achieved better electrochemical performance (1003.6 C g-1 at 1 A g-1 and 73.84% after 3500 cycles) than LDHs-CTAB (430.54 C g-1, 57.3%), and both higher than the original LDH (278.5 C g-1, 54.3%), while the electrocatalytic performance like Tafel slope follows an opposite trend owing to the difficulty of bubbles detachment from the nanosheets or nanorods, clearly showing the importance of morphology regulation in the synthesis of nanomaterials.

Synthesis of calcium-bismuth layered double hydroxide (LADH) nanoparticles: Applications as photo-catalyst and fuel additive

The development of calcium-bismuth layered double hydroxide [(Ca-Bi) LADH] microflowers for catalyzing degradation of Congo red (CR) and combustion of fuel is significant and highly desirable. Ca-Bi LADH microflowers are prepared by hydrothermal method with intercalated nitrates ions in inter lamellar spaces with 3–4 µm diameter and exposed active sites. After hydrothermal heating, the product is calcined at 400 °C for 4 and 7 hr to study the effect of calcination time on morphology of LADH. Prepared LADH is characterized by X-Ray diffraction and scanning electron microscopy (SEM). It is clear from XRD pattern that product is consist of hexagonal unit cell and highly crystalline. Synthesized LADH is used as catalyst for degradation of dye and combustion of fuel. The values of apparent rate constant (kapp) of catalytic degradation of CR are 0.0528, 0.0550, 0.0550 and 0.0557 min−1 for 1.0, 1.5, 2.0 and 2.5 mg/mL catalyst dosage respectively. Different parameters like flash point, fire point, kinematic viscosity and cloud point of fuel are increased by increasing additive dosage due to high surface area of LADH. LADH degrades dye in aqueous medium due to large number of adsorption sites. Synthesis of Ca-Bi LADH microflowers involves low cost and environmental friendly materials that can be used for different applications.

(Cu3-x Nix)Co2-Layered Double Hydroxide Nanosheets for Enhanced Electrocatalytic Activity Towards Overall Water Splitting

The exploration of transition metal based electrocatalyst for overall water splitting is becoming important as hydrogen becomes integral part of energy landscape. Recently, a new class of compounds i.e. layered double-hydroxides (LDHs), also known as anionic clays, are have shown tremendous promise for use as electrocatalyst. The lamellar morphology of LDHs accommodates higher active sites, that contributes to the facile electron transfer and thus attracts a great deal of interest in catalysis application. Moreover, the high catalytic activity of LDHs are also linked to their facile anion exchange, specific electronic structures, and versatile chemical compositions.Herein, we have developed a series of ternary layered double hydroxide (LDH) using pH-adjusted co-precipitation method with varying ratio of Cu, Ni and Co, which are used as an electrocatalyst for overall water splitting. (CuxNi1)Co1-LDHs (x = 0.5 1, 1.5, and 2 ) were systematically characterized using XRD, XPS, SEM, FTIR, TEM and BET techniques. The synergistic contributions from the electrocatalytically active metals and lamellar morphology of LDHs promotes water dissociation, facilitates faster release of H2-O2 gas bubbles, ameliorate electrolyte ion diffusion and improves electron transfer rate. It is further observed that the (CuxNi1)Co1-LDHs showed excellent electrocatalytic activity for both hydrogen evolution (HER) and oxygen evolution reaction (OER) with an overpotential of 147 and 218 mV for HER and OER, respectively at 10 mA cm-2. Tafel slope was found to be lowest for (Cu1Ni1)Co1-LDH. Further, the durability of the materials was also analysed by performing chronoamperometry for over 12 h. The overall water electrolytic cell using (Cu1Ni1)Co1-LDH as both electrodes can reach 50 mA cm−2 at 1.9V with outstanding durability.

Effect of Zn2Cr layered double hydroxide on photocatalytic hydroxylation of terephthalic acid and photodegradation of sodium diclofenac

Titanium dioxide has been widely used in traditional photocatalysis but layered double hydroxides (LDHs) based on Zn/Cr have attracted interest due to their semiconducting properties and tunable bandgap. The typical layered particle morphology of LDHs can result in interesting physicochemical properties, like the properties of traditional bulk semiconductors. The present manuscript describes the synthesis, characterization, and photocatalytic investigation of Zn2Cr LDHs intercalated with Ac-, I-, Br-, F-, Cl- and NO3-. Samples containing SO42-/Na+ were also obtained by coprecipitation at constant and increased pH. The photocatalytic activity was initially investigated using terephthalic acid as a model reaction, and only the LDHs intercalated with SO42-/Na+ could promote the formation of 2-hydroxy terephthalic acid. The two selected photocatalysts intercalated with SO42-/Na+, prepared under different conditions, were investigated regarding photocatalytic degradation of the emerging organic contaminant sodium diclofenac. Promising results were obtained specially after the recycling of the photocatalysts, which kept almost the same catalytic activity after six cycles of use.

(Invited, Digital Presentation) Maximizing the Layered Structure and Interlayer Anion Exchange Characteristics of Nico-Based Layered Double Hydroxides for Battery-Type Supercapacitors

The transition metal-based layered double hydroxides (LDHs) have been extensively studied as promising electrode materials for battery-type supercapacitors owing to their excellent electrochemical activity and tunable chemical composition. In our work, we firstly built a novel three-dimensional composite with a core-shell structure by self-assembling NiCo-LDHs nanosheets on dual surface-modified halloysite nanotubes (D-HNTs) via in-situ electrodeposition and hydrothermal method (NiCo-LDH/D-HNTs). HNTs were pretreated by a dual surface modification for the first time including a carbonization process and cobalt doping to enhance electrical conductivity and chemical stability. This multicomponent hierarchical nanocomposite, NiCo-LDH/D-HNTs, has a specific capacity of 1401.4 C g-1 at 1 A g-1, a rate capability of 52.9% increasing the current density to 30 A g-1, and cycling stability of 80.8% after 2000 cycles. Moreover, using acetate anions (Ac-) as intercalating element, the NiCo-LDH nanosheets arraying on Ni Foam were prepared with the optimized amount of Ac- anions expanding the interlayer space of LDH nanosheets from 0.8 to 0.94 nm. An ultrahigh specific capacity of 1200 C g-1 at 1 A g-1 (690 C g-1 without Ac- anions), outstanding rate capability of 72.5% at 30 A g-1 and cycle stability of 79.90% after 4500 cycles were achieved. The enlarged interlayer spacing was beneficial for stabilizing the α-phase of LDH and accelerating the electron transport and electrolyte penetration in the electrochemical reaction. In addition, ionic surfactants like sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) were introduced to regulate the morphology of LDHs and alter the electrochemical performance. The original NiCo-LDHs shows microspheres formed by nanorods, and NiCo-LDHs-CTAB is similar, yet more tangled, while NiCo-LDHs-SDS is like microflowers consisting of interwoven nanosheets. NiCo-LDHs-SDS achieved better electrochemical performance (1003.6 C g-1 at 1 A g-1 and 73.84% after 3500 cycles) than NiCo-LDHs-CTAB (430.54 C g-1, 57.3%), and both higher than original NiCo-LDHs (278.5 C g-1, 54.3%), clearly showing the importance of morphology regulation in the synthesis of nanomaterials. Our work offers a promising strategy to synthesize functional nanomaterials with excellent electrochemical performance via integrating its unique layered structure and interlayer anion exchange characteristics.

SYNTHESIS, PROPERTIES AND PRACTICAL APPLICATIONS OF DOPED AND UNDOPED, ZINC-CONTAINING LAYERED DOUBLE HYDROXIDES – A BRIEF REVIEW

Recently, layered double hydroxides (LDHs) have been developed for more potential applications in various industry fields. Many synthesis methods of LDHs in the literature have been considered and classified by changing properties. However, the property change by the synthesis method does not happen in the same way in all LDHs. Also, when LDH with the same composition is synthesized by the same synthesis method, it is possible to obtain LDHs with the same composition but different properties due to the change of reaction parameters. Recently, the doping of semiconductor nanocomposites with different element atoms has led to new properties. The effect of the elements used in the doping process on the properties of zinc-containing LDHs was investigated and explained in the review article. The synthesis's techniques differ from each other by the reaction parameters and they impact the crystal structure, physicochemical properties, and morphology of LDHs. Finding more additional effects of doping processes and doping elements' nature on the zinc-containing LDHs' properties, the synthesis procedures, and the determination of reaction parameters are shown in this review article. It was revealed that rare earth elements are not selected as three valence metals for the main structure of LDHs, they are mainly used as a doping element which is replaced by three valence metals (Al, Cr, Ti, Fe(III)) as dopants because of the ionic radius and various factors.

Insight into the Preparation of MgAl-Layered Double Hydroxide (LDH) Intercalated with Nitrates and Chloride Adsorption Ability Study

In recent years, layered double hydroxide (LDH) has attracted extensive attention of researchers in the field of corrosion protection due to its unique structure and anion exchange characteristics. However, its chloride adsorption capacity remains to be further optimized to increase its corrosion protection ability. In this work, the influence of reactant concentration on the prepared MgAl-LDH intercalated with nitrates was investigated, and the morphology, composition, and structure were characterized by scanning electronic microscopy/energy dispersive spectrometer (SEM/EDS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), respectively. The results indicate that the reactant concentration did not have an obvious influence on the particle size and morphology of LDH, while the composition and crystalline structure were changed to some extent. The corresponding reasons were interpreted deeply. The chloride absorption behavior was investigated, and the powder after immersion in NaCl solutions with different concentrations was characterized by XRD to explain the difference in chloride adsorption amounts. The MgAl-LDH powder synthesized at higher concentrations presented excellent chloride adsorption ability with a Qm value of 155.88 mg/g, which was much better than that reported in the literature. This work demonstrated the superior chloride adsorption of the synthesized MgAl-LDH, and it is of great significance for providing a solid foundation and guidance for the industrial application of LDH in the field of corrosion protection in the future.

Advances and Challenges in Industrial-Scale Water Oxidation on Layered Double Hydroxides

A substantial effort is devoted to the development of efficient electrolyzers made of earth-abundant elements for low-temperature industrial-scale water electrolysis. However, a large current density leads to the decline of the reaction kinetics that result from the decrease of local pH, the irreversible redox states of active metal sites, and the structure and composition collapse. Currently, the transition metal layered double hydroxides (LDHs) are proven as efficient alkaline oxygen evolution catalysts and demonstrate promising current density, generally at the scale of 10 mA cm–2 for the potential solar-driven catalysis concerning 10% solar-to-fuels efficiency. However, there is very limited progress in understanding the activity and stability degradation mechanism of LDHs at high current density, for instance above 100 mA cm–2. Here we introduce the current advances in achieving activity enhancement by tuning the composition, structure, and morphology of LDHs and present the degradation mechanism during the electrolysis under oxidative alkaline environments, long-term operation, and voltage fluctuations. Finally, we present the state-of-the-art approaches to stabilize the overall performance of LDHs for water oxidation and provide an outlook in this field.

Activation of peroxymonosulfate by MgCoAl layered double hydroxide: Potential enhancement effects of catalyst morphology and coexisting anions

The morphology and specific surface area of layered double hydroxide (LDH) are of great significance for optimizing the application of LDH in sewage treatment. Herein, we present a study of the relation between the catalytic property and the morphology of LDH via activating peroxymonosulfate (PMS) for degradation of organic pollutants. The results demonstrated that LDH nanoscrolls possessed a superior performance for methylene blue (MB) degradation, which achieved almost 100% removal in 40 min and the calculated apparent rate constant was about 2.1, 4.5 and 11.5 times higher than that of LDH nanosheets, Co2+ and Co3O4, respectively. According to the results of X-ray photoelectrons spectroscopy (XPS) and electron paramagnetic resonance (EPR), 1O2 was confirmed to play a dominant role in the MB degradation, where the redox cycle of Co3+/Co2+ provided the impetus for the reaction. Moreover, the pH and ion tolerance abilities of LDH nanoscrolls in PMS activating process were determined as well. Remarkably, CO32− and H2PO4− could even promote the generation of •OH and 1O2 to facilitate the progress of reaction. Overall, these findings in the study may provide more opportunities in the preparation of high-efficiency catalysts and give insight into the accelerated degradation of refractory contaminants with surrounding anions.

The photothermal stability of CNFs/ZnAl-LDHs composited films: Influence of the crystal morphology of ZnAl-LDHs

The existence of hydroxyl and carboxyl groups makes the photothermal stability of cellulose nanofibers (CNFs) poor and thus limits its scale application. This problem could be solved by doping layered double hydroxides (LDHs) nanopowders with opposite charge on the surface of CNFs. This work mainly focused on investigation of the influence of the crystal morphology of the inorganic ultraviolet shielding agent (i.e. ZnAl-LDHs) on the thermal stability of CNFs/ZnAl-LDHs composited films. The results showed that the morphology of LDHs was positively correlated with the photothermal stability of CNFs-based films. Specially, the ZnAl-LDHs with uniform crystal morphology could be prepared by controlling the molar ratio of Zn/Al at 3:1 and thus enhance the photothermal stability of CNFs-based films without any serious light transmittance deteriorating after doping. This work provided a practical and effective way for preparation of photothermal-stable CNFs-based transparent films for industrial application in the fields of photonics and electronics.

Synthesis of glutamate intercalated Mg-Al layered double hydroxides: influence of stirring and aging time

An Mg-Al layered double hydroxides (LDHs) intercalated by glutamate ions (Glu/LDH) was obtained using co-precipitation processing. The influence of stirring and aging time on LDH morphology was investigated. The morphology of LDH was characterized by means of XRD, FT-IR, FE-SEM and XPS. The thermal stability, pore volume and specific surface area were probed through thermal gravimetric (TG) analysis and automatic specific surface area analyzer, respectively. The results showed that the stirring and aging time had an insignificant influence on the interlayer distance of Glu/LDH; while it had a critical impact on the crystallinity degree of the Glu/LDH structure. TG analysis designated that the thermal stability of glutamate ion intercalated in LDH layers was higher than that of glutamate ion before intercalation. Glu/LDH exhibited the best adsorption performance at a stirring and aging time of 12 h. A schematic molecular structure model of Glu/LDH was proposed.

In-situ intercalation of 8-hydroxyquinoline in Mg-Al LDH coating to improve the corrosion resistance of AZ31

Mg-Al based layered double hydroxide (LDH) coating intercalated with 8-hydroxyquinoline (8HQ) was successfully prepared on AZ31. The influence of concentrations of 8HQ on the morphology and corrosion resistance is reported first time. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra confirm the intercalation of 8HQ. Furthermore, scanning electron microscopy (SEM) reveals concentration dependence of morphology of LDH. The enhancement in corrosion resistance is a function of morphological change, adsorption of 8HQ and chelation with Mg2+. The optimum amount of 8HQ enhances corrosion resistance of LDH coating. The deductions of this study deliver valuable understandings of corrosion protection mechanism of Mg-Al-LDH coatings.

Multiscale structural modulation of layered double hydroxide nanosheets and their application in solar-driven catalysis

Due to the high photocatalytic efficiency in activating chemical bonding under mild reaction conditions, photocatalysis has been acted as a green and promising technology. However, how to improve the quantum efficiency and solar energy utilization to further enhance the photocatalytic performance remains a challenge, and it is highly desirable to rational synthesize photocatalyst with suitable energy band structure, and efficient active sites. Layered double hydroxides (LDHs) is a kind of two-dimensional materials, with molecular formula [M12-+ x M x 3+(OH)2] x + [A x / n ] n -·mH2O. The layered structure of LDHs is similar to brucite Mg(OH)2, which is connected by the octahedral MO6 sites. The substitution of divalent metal cations (M2+) with trivalent metal cations (M3+) makes the layers positively charged, in which M2+, M3+ can be as one or more of the elements such as Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, In, etc. M2+, M3+ ions alternately arrange in the main layers at a high atomic level to form the planar structure ( a , b axis direction), and the alternation of the positively charged layers and the negatively charged anionic layers ( c axis direction) constitute the three-dimensional structure of LDHs. There are many unique structural characteristic of LDHs, such as the high dispersion of the metal elements in the layers, the controllable particle size and thickness, topological transformation and so on. The above properties have provide LDH as photocatalysts as the followings reason. Firstly, the metal elements of LDHs are arranged in an alternating order at the atomic level with flexible compositions (such as Fe, Co, Ni, Ti, etc.), and can be directly used as photocatalysts due to the tunable band gap. Secondly, the topological transformation property can turn LDH materials into heterogeneous mixed metal oxides or highly supported metal-containing catalysts, which are not easily agglomerated even under reaction condition. Thirdly, based on the tunable particle size and thickness of LDHs, it is possible to adjust the morphology of LDHs into nanoscale, which can fully expose the active sites and enhance the catalytic performance. Based on the abundant adjustable properties of LDHs, the following structures can be well optimized, such as their composition, particle sizes, defects, abundant interfaces, the high dispersion characteristics, and tunable energy band structures, etc. by using LDHs as catalysts for the potential enhanced catalytic efficiency. In this review, in order to activate H ˗ O, C = O, NN and C ˗ C bonds under mild condition, a series of LDH-based photocatalysts have been finely synthesized (like NiTi-LDH nanosheets, ZnAl-LDH, CoFe alloy derived from LDH, Co/Fe-hetrostructure derived from LDH, Cr-containing LDH, etc.), and widely applied in solar-driven water splitting, CO2 reduction, CO hydrogenation to high carbon hydrocarbons, ammonia synthesis, degradation and so on. Collectively, with the multiscale structural regulation of the microstructure, mesoscopic interfacial structure and highly dispersed metal-supported structure, the following properties such as the band gap, defect and the interface of LDH-based photocatalysts can be well modulated, and the solar-driven catalytic performance are demonstrated to be comprehensively facilitated. Furthermore, the relationship among the preparation, structure and catalysis has been well discussed, which will provide a strategy for the rational design of efficient photocatalysts.

Flower-like Surface of Three-Metal-Component Layered Double Hydroxide Composites for Improved Antibacterial Activity of Lysozyme.

Microbes play an important function in our lives, while some pathogenic bacteria are responsible for many infectious diseases, food safety, and ecological pollution. Layered double hydroxide (LDH) is a kind of natural two-dimensional material and has been applied in many fields. Lysozyme is a green natural antibacterial agent, while the antimicrobial activity of lysozyme is not as good as antibiotics. We use a different ratio of cations to tune the morphology of LDH covered with lysozyme to enhance the antibacterial ability of lysozyme. We synthesize MgAl-LDH, ZnAl-LDH, and ZnMgAl-LDH covered with lysozyme, characterize the structure and morphology, test the antibacterial in culture media, and evaluate the biotoxicity in vitro and in vivo. The flower-like structure of ZnMgAl-LDH has a rough surface, covered with lysozyme with a perfect ring, and presents good antibaterial properties and promotes wound healing of mice. The bloom flower structure of ZnMgAl-LDH can enhance the loading rate of lysozyme; meanwhile, the rougher surface can adhere more bacteria, so lyso@ZnMgAl-LDH presents better antibacterial activity than the binary LDHs.

Recycling of LCW produced form water plants for synthesizing of nano FeO(OH), Al(OH)3, and layered double hydroxide: Effect of heat-treatment

Liquid concentrate waste (LCW) is a high concentrated liquid produced as a by-product from water plants. It contains huge amounts of aluminum and iron residues. Its disposal causes many environmental problems, so it is significant to recycle this waste for production of interested nano materials such as FeO(OH) or Fe2O3·H2O, Al(OH)3 and layered double hydroxide (LDH) to be used for different applications. In the present work, these materials were chemically prepared using suitable chemicals and under appropriate conditions to get nano powders. The synthesized Al(OH)3 was utilized for preparation of Mg-Al-LDH in the presence of magnesium salt. The synthesized nano powders were investigated by X-ray diffraction (XRD), fourier transform infrared (FTIR), transmission electron microscope (TEM) and scanning electron microscope (SEM). The crystallite size was also calculated using XRD data by Scherrer equation. Effect of temperature up to 1000 °C on the phase composition and morphology of LDH was also studied. The results revealed that well crystalline Al(OH)3 and weak crystalline FeO(OH) nano powders were successfully synthesized by the suggested chemical method. Al(OH)3 exhibited ultrafine, fiber-like crystalline forms consisted of tiny hexagonal-like plates with size of about 30 nm, whileas FeO(OH) exhibited hexagonal prism particles with size of about 60 nm. Well crystalline hexagonal plate LDH having size of 80 nm was obtained after precipitation at 75 °C; its crystallinity was increased after hydrothermally treated at 140 and 180 °C. LDH having gel structure with very small particles was obtained at 180 °C. Heat treatment of LDH up to 1000 °C led to dissociation with the formation MgAl2O4 spinel. Grain growth was happened after heat treatment but the size was still in the nano range.

Quaternized polysulfone‐based nanocomposite membranes and improved properties by intercalated layered double hydroxide

Two anions (dodecylbenzenesulfonate anion and stearate anion) are employed to synthesize intercalated layered double hydroxides (LDH) by co‐precipitation method. Then the intercalated LDHs are incorporated in the casting solutions of chloromethylated polysulfone (CMPSF) for fabricating quaternized polysulfone/LDH nanocomposite membranes. Fourier transform infrared, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and mastersizer laser particle size analysis are used to characterize the structure and morphology of LDHs and membranes. The properties of the composite membranes including water uptake, mechanical property, thermal stability, and ionic conductivity are investigated. Compared with other anion exchange membranes, both nanocomposite membranes containing 5% LDH sheets displayed better balanced performance. They exhibit the ionic conductivity of 3.58 × 10−2 S cm−1 and 3.86 × 10−2 S cm−1 at 60°C, respectively. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Anion-exchange membranes derived from quaternized polysulfone and exfoliated layered double hydroxide for fuel cells

Layered double hydroxides (LDH) are prepared by controlling urea assisted homogeneous precipitation conditions. Morphology and crystallinity of LDHs are confirmed by X-ray diffraction and scanning electron microscope. After LDHs are incorporated into quaternized polysulfone membranes, transmission electron microscope is used to observe the exfoliated morphology of LDH sheets in the membranes. The properties of the nanocomposite membranes, including water uptake, swelling ratio, mechanical property and ionic conductivity are investigated. The nanocomposite membrane containing 5% LDH sheets shows more balanced performances, exhibiting an ionic conductivity of 2.36×10−2Scm−1 at 60°C.

Effect of modified layered double hydroxide on the flammability and mechanical properties of polypropylene

Abstract Copper-aluminum layered double hydroxides (Cu-LDHs) and nickel-aluminum layered double hydroxides (Ni-LDHs) were synthesized using co-precipitation method. LDHs were organically modified by long chain sodium stearate. Polypropylene (PP)/layered double hydroxides (LDHs) and polypropylene (PP)/organically-modified layered double hydroxides (m.Cu-LDHs or m.Ni-LDHs) were prepared through the melt bending of the PP with either nanosized LDHs or m.LDHs without any other additives. The effect of stearate on the dispersibility of LDHs was investigated by X-ray diffraction (XRD). The surface morphology of LDHs was also studied using scanning electron microscope (SEM), and the thermal stability properties of PP/LDHs composites were studied by thermogravimetric analysis (TGA). The mechanical properties of the PP/LDH composites, tensile strength, and modulus of elasticity were investigated. The flammability properties were investigated using the cone calorimeter test. The intercalation of modified LDHs was determined by XRD in the presence of stearate. Results showed that modified LDHs presented good disperasbility in the PP matrix. The thermal stability of PP has been improved by up to 6% using m.Ni-LDHS. Unmodified and modified nanosized LDHs decreased the fire growth rate of PP from 10.8 kW/m2.s to 4.1 kW/m2.s and 4.5 kW/m2.s, respectively.

Preparation of Hierarchically Structured Layered Double Hydroxide Microspheres and Their Application in BSA Separation

Hierarchically structured layered double hydroxides (LDHs) are being actively investigated due to their potential applications in adsorption and catalysis that result from their special surface structures and positively charged nanosheets. However, a control over the structure and morphology of LDHs is essential to achieve the diverse structures and desirable properties. In this work, hierarchically porous LDH microspheres are successfully fabricated in a large scale by combining the hydrothermal method and in situ growth method, and the calcined LDH microspheres are further applied to separate bovine serum albumin (BSA) from solution. The prepared LDH microspheres are characterized by scanning electron microscopy (SEM), transmission electron microscopy, powder x-ray diffraction, and surface area analyzer. The SEM results demonstrate that microspheres have a coral-like hierarchical architecture comprised of oriented LDH nanoplatelets. The high specific surface areas (143.82 m2/g) of calcined LDH microspheres are demonstrated to be beneficial for the adsorption of BSA. To obtain better insights into the separation processes, the adsorption and desorption of BSA on LDH microspheres are investigated by solution temperature and BSA concentration. The results indicated that the adsorption process of BSA is an exothermic process and desorption process of BSA is endothermic process.

Isomorphous substitution of divalent metal ions in layered double hydroxides through a soft chemical hydrothermal reaction

We have successfully incorporated Co(2+) ions into layered double hydroxides (LDHs) comprising Mg and Al hydroxides via isomorphous substitution utilizing a soft chemical hydrothermal reaction. The inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis showed that the incorporation of Co(2+) into an LDH was highly dependent on the dissolution of Mg(2+). The X-ray diffraction (XRD) patterns showed that the crystalline phase, as well as the crystallinity of pristine LDH, was well preserved without the evolution of impurities during the substitution reaction. It was notable that the size (~250 nm) and hexagonal plate-like morphology of LDHs did not change significantly upon Co(2+) substitution. Transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) exhibited homogeneous distribution of Co(2+) in the LDH particles obtained by this substitution reaction. Solid-state UV-vis and X-ray absorption spectroscopy (XAS) verified that the incorporated Co(2+) ions were well stabilized in the octahedral sites of an LDH, which were formerly occupied by Mg(2+) ions.