Interlayer Anions Research Articles

Systematic screening of layered double hydroxides for phosphate removal and mechanism insight

To optimize the chemical composition of layered double hydroxides (LDH) as phosphate adsorbents and further discuss the adsorption mechanism, 14 LDH were synthesized from theoretically feasible, inexpensive and innoxious (or low noxious) precursors through the coprecipitation method. The morphology, chemical composition and nanostructure of LDH were confirmed by scanning electron microscopy equipped with energy dispersive spectrometer, X-ray diffraction and Fourier transform infrared spectroscopy. Then their adsorption performance were evaluated and compared. Phosphate adsorption by the selected LDH as a function of pH and competing anions were subsequently studied. In a 20 mg-P/L phosphate solution at pH 5.5, LDH with trivalent cation Al3+ had a better performance than Fe3+-based LDH. Phosphate adsorption kinetics of the as-synthesize LDH fitted well with the pseudo-second-order model. Mg2-Al1-Cl-LDH (corresponding to LDH with cations of Mg2+ and Al3+ in Mg2+/Al3+ molar ratio of 2.0 and interlayer anion of Cl−) had a higher phosphate removal and faster kinetics than others did. The isotherm data of Mg2-Al1-Cl-LDH showed a good compliance with Langmiur model, and the maximum adsorption capacity reached 76.1 mg/g under 25 °C. The phosphate adsorption mechanisms were deduced as ion exchange, electrostatic attraction, physical adsorption and ligand exchange. Specifically, ion exchange was the main mechanism.

Effect of interlayer anion on the CO2 capture capacity of hydrotalcite-based sorbents

A series of hydrotalcites (HTCs) samples with different compensating anions was prepared (several anions never used before). The physicochemical characterization of these materials was realized through several techniques (including XRD and SEM/EDS). The CO2 sorption capacities of the HTCs were assessed using a magnetic suspension balance (static tests) and CO2 breakthrough runs in a packed column (dynamic tests). The HTC-CO3 sample presents the highest CO2 sorption capacity (1.05 mmol·g−1, @ pCO2 = 1 bar and 300 °C) in comparison with the other materials. The sorption kinetics were analyzed from CO2 uptake measurements and two distinct contributions were observed. Besides, the effect of temperature on the CO2 sorption capacity was studied for HTC-CO3. The efficiency of the column (in the breakthrough tests) was higher for the HTC-CO3 formulation (20%).

Adsorption mechanism of hexavalent chromium onto layered double hydroxides-based adsorbents: A systematic in-depth review.

An attempt has been made in this review to provide some insights into the possible adsorption mechanisms of hexavalent chromium onto layered double hydroxides-based adsorbents by critically examining the past and present literature. Layered double hydroxides (LDH) nanomaterials are typical dual-electronic adsorbents because they exhibit positively charged external surfaces and abundant interlayer anions. A high positive zeta potential value indicates that LDH has a high affinity to Cr(VI) anions in solution through electrostatic attraction. The host interlayer anions (i.e., Cl-, NO3-, SO42-, and CO32-) provide a high anion exchange capacity (53-520 meq/100 g) which is expected to have an excellent exchangeable capacity to Cr(VI) oxyanions in water. Regarding the adsorption-coupled reduction mechanism, when Cr(VI) anions make contact with the electron-donor groups in the LDH, they are partly reduced to Cr(III) cations. The reduced Cr(III) cations are then adsorbed by LDH via numerous interactions, such as isomorphic substitution and complexation. Nonetheless, the adsorption-coupled reduction mechanism is greatly dependent on: (1) the nature of divalent and trivalent salts utilized in LDH preparation, and the types of interlayer anions (i.e., guest intercalated organic anions), and (3) the adsorption experiment conditions. The low Brunauer-Emmett-Teller specific surface area of LDH (1.80-179 m2/g) suggests that pore filling played an insignificant role in Cr(VI) adsorption. The Langmuir maximum adsorption capacity of LDH (Qomax) toward Cr(VI) was significantly affected by the natures of used inorganic salts and synthetic methods of LDH. The Qomax values range from 16.3 mg/g to 726 mg/g. Almost all adsorption processes of Cr(VI) by LDH-based adsorbent occur spontaneously (ΔG° <0) and endothermically (ΔH° >0) and increase the randomness (ΔS° >0) in the system. Thus, LDH has much potential as a promising material that can effectively remove anion pollutants, especially Cr(VI) anions in industrial wastewater.

Understanding the Ion Exchange Process in LDH Nanomaterials by Fast In Situ XRPD and PCA-Assisted Kinetic Analysis

Layered double hydroxides (LDHs) are nanomaterials with interesting properties finding applications in many fields, such as catalysis, environmental chemistry, and pharmaceuticals. They are anionic clays with positively charged layers and anions within the layers to reach neutrality. Their properties are defined by both composition and morphology. The composition can be tuned by exchanging the interlayer anion. The far more stable, common, and highly prevalent among natural LDHs is the carbonate anion thanks to its double negative charge. To adapt the properties of LDHs for technological applications, the challenge is to exchange the carbonate with the functionalizing monovalent anions in an effective and cheap way. In this study, the exchange of carbonate with nitrate ions is studied by in situ X-ray powder diffraction (XRPD). The exchange is carried out by a liquid-assisted grinding approach, inserting the mechanically ground dry sample in a capillary and then wetting it with a drop of nitric acid, while measuring the XRPD pattern. The kinetics of the process was investigated by the Avrami-Erofe’ev method; the reaction mechanism was determined using the advancing interface model and by analyzing the XRD peak shapes, which evidentiate changes in the crystallinity during the reaction. The reaction starts from the faces perpendicular to the layers and occurs along the channels, increasingly limited by diffusion when approaching the internal part of the crystals.

Pros and cons of coating layered double hydroxide nanoparticles with polyacrylate

Preventing the aggregation of layered double hydroxide nanoparticles (LDH-NP) and producing additional functionality are two important objectives for their applications as drug nanocarriers, among others. Adsorption of polyelectrolytes like polyacrylate (PA) is a promising approach to produce protective, functional coatings, but the effect of factors such as chain length, as well as the pros and cons of this strategy, have not been described. In this work, these aspects were studied using LDH-NP intercalated with chloride and benzoate as interlayer probes. The interaction between LDH-NP and PA, as well as the effect in the aggregation of the former, was studied as a function of the molecular weight (MW = 1.2, 8.0 and 450 kDa) and the PA concentration. High MW were more effective for preventing LDH-NP aggregation as well as for minimizing the PA intercalation between the layers. Thus, the 8.0 kDa PA allowed obtaining benzoate intercalated LDH-NP with a particle size around 200 nm that maintained 40% of the exchange sites occupied by benzoate anions. PA coating not only hindered aggregation and changed the particle charge, but also provided new functionality, such as a protective layer towards proton diffusion and, consequently, dissolution of LDH-NP. PA coating is then an effective tool for LDH-NP stabilization and customization, if interlayer anion loss is controlled.

Silica-layered double hydroxide nanoarchitectured materials

This work shows the viability for assembling layered double hydroxides (LDH) containing surfactant anions in its interlayer region, with silicon alkoxides through a sol-gel processes, leading to SiO2-LDH nanoarchitectured materials consisting in delaminated LDH particles assembled to silica nanoparticles. Tetrametoxysilane (TMOS) has been used as silica precursor being hydrolyzed and polycondensed in presence of MgAl-, NiAl- and NiCoFe-LDH containing dodecylsulphate ions as interlayer anions. The resulting materials were further heated to remove the organic matter and to consolidate the final nanoarchitecture, being the LDH re-constructed in a final step in the presence of a salt solution (e.g., Na2CO3, sodium dodecysulphate, …), producing LDH-SiO2 materials. These resulting materials have being characterized using XRD, FTIR, 29Si and 27Al NMR spectroscopy, N2 adsorption-desorption isotherms, FE-SEM and TEM amongst other physical-chemical characterization techniques. The obtained results confirm the formation of silica nanoparticles within the nanosheets generated by delamination of the pristine LDH, producing functional materials of elevated specific surface area of potential interest in diverse fields of applications.

Ultrasonically-assisted mechanochemical synthesis of zinc aluminate spinel from aluminium-rich layered double hydroxide

An ultrasonically-assisted mechanochemical method was further improved to increase the yield of high-quality ZnAl2-LDH with carbonate interlayer anions. In the LDH formation, the rarely studied temperature, power and pulse character of ultrasound irradiation were investigated to determine the optimal parameters for the synthesis. The as-prepared samples were milled with varying the grinding frequency in order to convert the layered hydroxide structure into ZnAl2O4 spinel. This was the first time that ZnAl2O4 spinel formation was induced mechanochemically. The main method to identify the effects of ultrasonic and mechanochemical treatments was X-ray diffractometry; however, infrared spectroscopy, scanning electron microscopy, and thermal analysis were also applied to follow and compare the mechanochemically induced spinel formation to the more frequently used heat treatment.

Preparation and Properties of F-Substituted Layered Double Hydroxides (LDHs):Anion-Intercalation Material

Introduction: There have been increasing attention to anion-intercalation behavior and materials. In lithium ion battery field, intercalation property of PF6 − into graphitic carbon was studied for a hybrid capacitor. In ion-exchange field, selective removal of toxic anionic species by anion-exchangeable layered compounds has been focused. Layered double hydroxides (LDHs) was representative of anion-exchangeable layered compounds, represented by a general formula of [M2+ 1−x M3+ x (OH)2] x +[A nx /n ] x − mH2O consisting of octahedral brucite-like host-layers (M2+/M3+: divalent and trivalent metal cations), charge-balancing anions (A n −) and interlayer water molecules. Their ion-exchange properties, selectivity and capacity, have been widely studied. Miyata previously reported the order of affinity of various anions to Mg-Al LDHs; OH− > F− > Cl− > Br− > NO3 − > I−. Although other researchers have tried to control the affinity by changing composition of metal cations (M2+/M3+) to control charge density of host layers, significant change in the order was hardly achieved. Looking back to intrinsic crystalline structure of LDHs, host-layers, optimal positions of interlayer anions, and water molecules is supposed to be determined with hydrogen-bonding interaction among them. In other words, the affinity of anion to LDHs should be controlled by tuning strength of hydrogen-bonding in addition to charge density of host layers. In this presentation, we tried to prepare F-substituted Mg-Al LDHs (F-LDHs), OH groups belonging to host layer of LDHs was substituted by F atoms, and anion-exchange selectivity was investigated. Experiment: Based on traditional co-precipitation method with solution pH = 10, F-LDHs was prepared by using AlCl3, NaAlF6, and MgCl2·6H2O as a precursor. Mg/Al ratio was controlled as 2.5，3.0，3.5，and 4.0 by changing ([AlCl3]+[NaAlF6])/[MgCl2] ratio and F-substitution ratio was controlled by changing [AlCl3]/[NaAlF6] ratio. Crystal structure, morphology, chemical composition, local structure of Al and F atoms of obtained samples were analyzed by XRD, FE-SEM (EDS), XPS, solid-state NMR. Next, anion-exchanging properties of obtained F-LDHs was tested. Firstly, as a pre-treatment, LDHs samples was immersed in acidic NaCl aqueous solution for 24 hours at room temperature and interlayer “contaminated” carbonate was exchanged by chloride ions as much as possible. Seconds, by using chloride-exchanged samples, anion-exchange test was carried out with 1.2~1.5 mM NaNO3, Na2SO4, Na2HPO4, NaF, and NaI aqueous solutions for 24 h, where solid to liquid ratio was fixed to 1.0 gL-1. After 24 h, exchanged amount was analyzed by ion-chromatography. Results and discussion: XRD patterns of all samples exhibit successful formation of LDHs without byproducts even after chloride-exchange treatment. Successful inclusion of F atoms into host-layer of LDHs was confirmed by solid-state NMR and, in all samples, 80% of interlayer anions was exchanged by chloride ions, which is confirmed by compositional analysis with EDS and XPS. XRD patterns also revealed that the basal spacing, d 003, of F-LDHs tend to decrease comparing to original LDHs, which implies that host-layers strongly interacts with interlayer anions and water molecules. In addition, F-substitution amount was found out to be limited by about 10%, LDHs can be obtained without byproducts. Next, distribution coefficient, useful indicator of the affinity of respective anions to LDHs, was calculated from the result of ion-exchange test. It clarified that the order of affinity was NO3 − > HPO4 2− > Br− > F− > SO4 2− > I−, which is totally different from previous reports. Furthermore, the affinity of NO3 − ions comparing to SO4 2− ion and F− ions was increased depending on F-substitution amount. In conference, detailed formation mechanism of F-LDHs and anion-exchanging mechanism was presented.

A novel magnetic biochar/MgFe-layered double hydroxides composite removing Pb2+ from aqueous solution: Isotherms, kinetics and thermodynamics

An absorbent, magnetic biochar supporting MgFe-Layered double hydroxides (MgFe-LDH) composites was synthesized to remove Pb2+ from the aqueous solution. The results of SEM, EDS, XRD, FT-IR, XPS, VSM and BET determinations showed that MgFe-LDH was successfully loaded on the magnetic biochar by hydrothermal synthesis. These characterizations also indicated that the adsorption of Pb2+ resulted from co-precipitation between interlayer anions, surface hydroxyl groups and Pb2+. The isotherms study revealed that the adsorption of Pb2+ on magnetic biochar/MgFe-LDH was well fitted to Langmuir model. The maximum adsorption capacity was 476.25 mg g−1 at 25 °C. Kinetic and thermodynamic studies indicated that the adsorption process was a spontaneous endothermic reaction and limited by chemisorption. Owing to the simple synthesis, superior adsorption capacity, good magnetic properties and cyclic utilization, the magnetic biochar/MgFe-LDH is a promising adsorbent for removing Pb2+ from aqueous solution.

Enhanced adsorption of Cr(vi) on BiOBr under alkaline conditions: interlayer anion exchange

The first time to explore the adsorption of Cr(vi) on BiOBr in alkaline solutions, and propose an original adsorption mechanism.

A comparative study and optimization of corrosion resistance of ZnAl layered double hydroxides films intercalated with different anions on AZ31 Mg alloys

Layered double hydroxides (LDHs) have great potential as protective coatings on magnesium alloys due to their nanolamellar structure and exchangeability of interlayer anions. ZnAl layered double hydroxides films intercalated with nitrate anions (ZnAl-NO3−-LDHs) was synthesized on the AZ31 magnesium alloy by hydrothermal method. In order to obtain better corrosion resistance, ZnAl-X-LDHs (X = Cl−, VO43−, PO43−, or MoO42−) were prepared by using ZnAl-NO3−-LDHs as a precursor, and Cl−, VO43−, PO43−, and MoO42− anions intercalated into the LDHs interlayers to replace NO3− through anion-exchange reaction. X-ray diffraction (XRD), scanning electronic microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy were used to investigate structure, morphology and composition of the ZnAl-LDHs. The corrosion resistance of ZnAl-LDHs intercalated with different anions was compared by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results show that the corrosion resistance of ZnAl-LDHs films is ranged in order as follows: ZnAl-VO43−-LDHs > ZnAl-MoO42−-LDHs > ZnAl-PO43−LDHs > ZnAl-Cl−LDHs > ZnAl-NO3−LDHs. ZnAl-VO43−-LDHs has the largest basal spacing distances d(003) value and strongest ability to release anions and absorb chloride ions, so ZnAl-VO43−-LDHs films has the optimal corrosion resistance and can provide enhanced anticorrosion protection for magnesium alloys substrate.

Anion intercalated layered-double-hydroxide structure for efficient photocatalytic NO remove

Due to the easily controllable interlayer anions, metal cation composition proportion and thickness, which is beneficial to modify surface chemical state and tune bandgap, layered double hydroxides (LDHs) have great promising potential for photocatalytic applications. In this study, we have successfully synthesized the ZnAl–LDH intercalated the single anion between ZnAl cationic interlayer without anionic impurities by using a facile calcining and reconstructing routes. The electron structure and surface chemical state of the prepared products have been investigated by combining the DFT calculation and experimental characterization methods. UV–vis DRS was used to certify the light absorption of the prepared products, and we performed the DFT calculation to demonstrate the density of state and activation of reactant. These results suggested that the ZnAl–LDH–CO3 possessed the more proper band structure and superior ability to activate NO and O2 for accelerating the photocatalytic NO oxidation activity. Moreover, the in situ DRIFTS with dynamically monitoring intermediates and products over the ZnAl–LDH–CO3 was adopted to declare the photocatalytic NO oxidized process during the photocatalytic reaction process. This work illustrated the influence of different interlayer anions to the electron structure and surface chemical state of ZnAl–LDH structure through the experimental verification combined DFT calculation and the photocatalytic NO oxidized process via in situ DRIFTS analyzing, which would provide a novel way to design and fabricate the efficient photocatalysis, and understand the reaction process.

Assembling biochar with various layered double hydroxides for enhancement of phosphorus recovery.

Highly efficient and cost-effective adsorbents for phosphate (P) recovery are the key to control eutrophication and recover phosphorus from waste streams to enhance food production. This study assembled corn stalk-derived biochar (BC) with various forms of layered double hydroxides (LDHs) (B-M-LDH) through simultaneous pyrolysis of waste biomass and metal (i.e., Zn/Al, Mg/Al, and Ni/Fe) hydroxide precipitates. Batch sorption experiments evaluated the kinetics and isotherms of phosphate adsorption as well as the influence of pH value and co-existing anions. Morphological characterization showed that crystalline LDH flakes were impregnated within the framework of fabricated B-M-LDH composites. Superior P adsorption capacity (152.1 mg (P) g-1) and fast Elovich kinetics (5925 mg g-1 h-1) could be achieved by the B-Zn/Al-LDH composite at pH 5. The P adsorption onto BC-LDHs was pH dependent and subjected to adverse influence of co-existing anions. Interlayer anion exchange and surface complexation were probably the predominant adsorption mechanisms at the studied phosphate concentration. Therefore, BC can be functionalized as mineral composites for enhancing P recovery and wastewater treatment.

Solid-state speciation of interlayer anions in layered double hydroxides

Layered double hydroxides (LDH) have been proposed for phosphate (PO4) recovery and recycling from waste streams due to their high anion exchange capacity, good stability and high affinity towards PO4. The high affinity towards PO4 strongly relates to the electrostatic interaction with PO4, and thus the charge of PO4. However, the anion speciation of intercalated PO4, i.e. either H2PO4−, HPO42− or PO43− is often overlooked. This study was set up to measure solid phase PO4 speciation through ion exchange stoichiometry, X-ray diffraction (XRD), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and modelling. Six phase pure Mg/Al LDH materials were synthesized using co-precipitation of metal nitrate (NO3−) solutions with varying M2+/M3+ ratio at pH 12 and pH 10. The LDHs synthetized at pH 12 contained larger equivalent fractions of intercalated OH−, smaller fractions of NO3− and smaller interlayer distance than those prepared at pH 10, likely because of the higher OH− concentration in the more alkaline synthesis solutions. Two high charge LDHs prepared at pH 12 or 10 were selected, exchanged with PO4 (0–20 mM initial PO4, 24 h) at one starting pH (7.20); desorption was subsequently performed with carbonate (3 mM, initial pH 8.4) during 480 h. The resulting solution concentrations of NO3, PO4 and CO3 and the pH allowed the identification of the anion exchange stoichiometry. The LDH synthesized at pH 12, which had a large fraction of exchangeable OH−, adsorbed PO4 as HPO42−/PO43−, in exchange for both NO3− and OH− anions. The material synthesized at pH 10 containing a lower fraction of exchangeable OH−, therefore, adsorbed mainly HPO42− in exchange for NO3− anions. The carbonate exchange was consistent with adsorption of divalent CO32−. The pH dependent speciation modelling showed that the exchanged PO4 ions have higher charge compared to those in the contacting solution. This study suggests that the highest P content of LDH is obtained in high charge materials holding divalent PO4 anions, i.e. materials synthesized at lower pH and/or exchanged in solutions with low alkalinity.

Intercalation of Bioactive Molecules into Nanosized ZnAl Hydrotalcites for Combined Chemo and Photo Cancer Treatment

Hydrotalcites-like compounds, also known as anionic clays or layered double hydroxides, represent the only example of lamellar solid with positively charged layers and exchangeable interlayer anions. In this study, a nanostructured HTlc with formula [Zn0.72Al0.28(OH)2] Br0.28·0.69 H2O was used as inorganic drug delivery system for anticancer therapy. Two different molecules were selected for being separately intercalated into ZnAl-HTlc: the anticancer drug norcantharidin, known for inducing cell cycle arrest at G2/M phase, and the tetra-sulfonated aluminum phthalocyanine, a photosensitizer used in anticancer photodynamic therapy. The obtained hybrid ZnAl-HTlc, were characterized in terms of X-ray powder diffraction pattern, thermogravimetric analysis, scanning electron microscopy, drug release profile, in vitro cytotoxicity, and ability to produce ROS and 1O2 upon light irradiation. Our results clearly indicate that the two selected compounds are efficiently intercalated within HTlc layers. Moreover, in v...

Application of a novel, efficient and recyclable photo redox catalyst (Zn–Al layered double hydroxide/eosin) for the synthesis of substituted pyridine derivatives under visible light irradiation

Layered double hydroxides (LDHs) are a class of anionic clays with brucite‐like layers and interlayer anions and varying in composition and morphology. LDHs show potential as supports for the immobilization of catalytically active species, to synthesize recyclable catalysts, in which catalytic sites can be preferentially orientated, highly dispersed and stabilized to afford high catalytic efficiency and recyclability in reaction media. Redox active organic dyes such as eosin Y with strong absorption in the visible region of the spectrum have been successfully used. In this work, an intercalated photo redox catalyst (Zn–Al LDH/eosin) was synthesized by co‐precipitation of an aqueous solution of zinc nitrate and aluminium nitrate simultaneously with eosin Y as anionic dye. Zn–Al LDH/eosin as a recyclable catalyst was used in the reaction of various aryl ketones and benzylamines under molecular oxygen and visible light, giving good yields of substituted pyridines at room temperature. Also, the Zn–Al LDH/eosin catalyst could be reused three times without any significant changes in the reaction yields.

Layered Double Hydroxide‐Based Catalysts: Recent Advances in Preparation, Structure, and Applications

AbstractLayered double hydroxides (LDHs) are a class of functional anionic clays, which consist of positively charged host layers (brucite‐like M(OH)6 octahedra) and interlayer anions. By virtue of their unique combination of structural features (including the tunability of both host layers and interlayer guest anion, exfoliation property, structure topological transformation, confinement effect), LDHs have many potential applications in heterogeneous catalysis—as catalysts themselves, catalyst supports, or catalyst precursors. In addition, the properties of LDH‐based catalysts can be tailored for specific purposes by facile modulation of their surface/interface defect structure (e.g., oxygen vacancy defects or metal defects), controlling the concentration/strength of surface acid/base sites, tuning the geometric/electronic structure of active sites, or by taking advantage of the confinement effect intrinsic to 2D materials. In addition, by utilizing the topological structural transformation of LDH precursors, supported metal catalysts can be obtained (as single metals, bimetallic alloys or heterostructures, and intermetallic compounds) with tunable particle size/morphology and intriguing electronic properties. The main focus of this review is on recent advances in structure design, preparation, and catalytic applications of LDH‐based heterogeneous catalysts. In addition, future challenges and development strategies are discussed from the viewpoints of modulation of intrinsic active sites and establishment of scalable fabrication processes.

Insights into phosphate adsorption behavior on structurally modified ZnAl layered double hydroxides

Abstract The present study focuses on the phosphate uptake by synthetic ZnAl-layered double hydroxides having different charge density due to the modification of the cationic ratio (Zn2+/Al3+) within the brucite-like sheets. The structure of the as-synthesized ZnAl-LDH was confirmed by X-ray diffraction and 27Al NMR and micro-Raman spectroscopy characterization techniques. The materials were applied for sorption of phosphate anions in aqueous media under relevant conditions. Parameters affecting the sorption process were thoroughly investigated, such as the layer cationic ratio, the exchangeable interlayer anion, thermal treatment and competitive sorption in the presence of co-existing anions. The sorption data provided information regarding the relationship between the phosphate uptake and the physical-chemical properties of these materials. The phosphate adsorption onto the non-calcined LDH occurred via the anionic exchange mechanism while both structural reconstruction and precipitation mechanisms were observed for the calcined materials. The obtained results suggest that the Zn containing LDH are suitable candidates for the phosphate recovery or removal from aqueous media in wastewater treatment processes.

Fabrication of Ni-Al LDH/nitramine-N-doped graphene hybrid composites via a novel self-assembly process for hybrid supercapacitors

The ingenious synthesis strategies have been highly desired to construct hybrid composites with intriguing properties for supercapacitors. Herein, Ni-Al LDH (layered double hydroxide)/NNDG (nitramine-N-doped graphene) hybrid composites with a layered structure were fabricated via a novel self-assembly process. Nitramine-N dopants anchored to graphene framework allow the self-immobilization of delaminated Ni-Al LDH nanolayers onto the surface of two-dimensional carbonaceous scaffolds and boost the abundance of Ni3+ within hybrid composites along with the removal of interlayer anions within Ni-Al LDH-NO3. Remarkably, the combination of Ni-Al LDH with NNDG can not only enhance the utilization of electrochemically active matrixes in dependence on the increase of electrolyte accessible active sites, but also maximize the electrochemically active contact between inorganic macromolecules and carbonaceous matrixes in favor of the establishment of conductive architectures. Furthermore, Ni-Al LDH/NNDG hybrid composites achieve a specific capacity of 975 C g−1 at a specific current of 1.0 A g−1 with a capacity retention of 75% as the increase of specific currents to 10 A g−1, superior to Ni-Al LDH-NO3 and Ni-Al LDH/rGO hybrid composites. The hybrid supercapacitor comprised of Ni-Al LDH/NNDG hybrid composites as a positive electrode and activated carbon as a negative electrode attains a high energy density of 59 Wh kg−1 with a power density of 1991 W kg−1 at a specific current of 2.5 A g−1 and retains 95% of the initial capacitance after 10 000 cycles at a specific current of 10 A g−1. The excellence electrochemical performance demonstrates clearly the potential application of self-assembled Ni-Al LDH/NNDG hybrid composites for hybrid supercapacitors.

Delamination and self-assembly of layered double hydroxides for enhanced loading capacity and corrosion protection performance

Layered double hydroxides (LDHs) nanocontainers intercalating with corrosion inhibitors are considered as a great platform to deliver corrosion inhibitors to the corroding sites. However, the small interlayer spacing and strong interaction between hydrotalcite laminates and interlayer anions impede the loading of macromolecular species into LDHs via a conventional anion-exchange process. This work devises a new paradigm for the preparation of LDHs in corrosion protection. A new method combining delamination and self-assembly to increase the loading of the organic corrosion inhibitor —5-Methyl-1,3,4-thiadiazole-2-thiol (MTT) into LDHs is applied and exhibits remarkable corrosion protection effects. The SEM, EDS, TEM, XRD, XPS and FT-IR were used to characterize the LDHs and LDH nanosheets. UV–vis absorption spectra and thermogravimetric analysis (TGA) experiments indicate an enhanced loading of MTT which is slowly released to the chloride media. The electrochemical experiments indicate that the release of MTT from their LDHs host can efficiently inhibit the corrosion on the surface of mild steel in 3.5 wt% NaCl solution. Furthermore, surface analysis experiments were carried out to probe into the anticorrosion mechanism of LDHs.