Layered Double Hydroxide Nanoplates Research Articles

LDH@MgSiO3 multi-core@shell catalyst for dry reforming of methane

In this paper, LDH@SiO2 catalyst was prepared via coating a layer of silica over LDH (Layered Double Hydroxide) nanoplates. Then it was calcined and further treated by hydrothermal method with magnesium acetate to convert silica layer into MgSiO3. After H2- reduction, a layer of branch-like MgSiO3 was observed as the shell and nickel nanoparticles with average diameter around 10 nm were encapsulated within the shell, which was called as LDH@MgSiO3 multi-core@shell catalyst. This catalyst was then tested in dry reforming of methane (DRM) at 675 °C and the CH4 conversion was kept stable around 25% for 30 h time on stream at GHSV of 360 L/gcat/h. Besides, the H2/CO ratio in the product gas was 0.85, much higher than that of LDH@SiO2 catalyst, indicating its superb selectivity. Characterization revealed that the formation of MgSiO3 was beneficial to reduce the nickel particle size, modify the porosity and improve the surface alkalinity, which enhanced the DRM activity and selectivity. More importantly, it enhanced the hydrothermal stability, thus preventing the reconstruction of the shell.

2D/2D NiAl LDH integrated graphitic carbon nitride with robust interfacial contact for driving photocatalytic hydrogen production

Photocatalytic hydrogen production is promising for generating carbon-free energy through water splitting. Efficient photocatalytic materials with high photochemical efficiency are crucial for creating well-structured photocatalytic systems. Layered Double Hydroxides (LDHs) have gained significant scientific attention due to their unique electronic structure, compositional flexibility, and tunable band gap, which make them highly active for photocatalytic hydrogen evolution. However, the high surface energy of LDHs can lead to layer deactivation and reduce their efficiency as standalone photocatalysts. Herein, a novel design of two-dimensional (2D) g-C3N4 with 2D NiAl LDH to construct morphologically 2D/2D binary heterojunction composite with strong electrostatic interactions has been investigated. Different characterization techniques, such as XRD, FESEM, EDX, UV–Vis spectra, and PL were conducted to assess its photo-physical properties. The introduction of 15% NiAl LDH led to a significant increase in hydrogen production, reaching 28.13 µmol h−1, which is 3.75 and 9 times higher than pure g-C3N4 and NiAl LDH, respectively. The improved photocatalytic performance was attributed to the efficient charge transfer facilitated by the formation of Type-II heterojunction system. The interface junction observed in 2D/2D g-C3N4/NiAl LDH restricts charge recombination and extends its lifetime to carry out photocatalytic reactions. Furthermore, the effective integration of NiAl LDH onto g-C3N4 observed from FESEM and EDX prevents the deactivation of LDH nanoplates, supplying abundant reaction-active sites to expedite the photo-redox reaction. Significantly, the incorporation of transition metals, such as Ni and Al, into the LDH brucite layer enhances the optical properties, allowing for better utilization of light and further improving photocatalytic hydrogen production. This work provides valuable insights into the development of 2D/2D morphologically-engineered nanohybrids for driving photocatalytic hydrogen production.

Lattice oxygen-mediated Ni[sbnd]O[sbnd]O[sbnd]M formation for efficient oxygen evolution reaction in MOF@LDH core–shell structures

Two-dimensional (2D) layered double hydroxides (LDHs) are promising as an effective electrocatalyst towards oxygen evolution reaction (OER), but their poor conductivity and tendency to stack together limits their activity and durability as an electrocatalyst. Herein, a three-dimensional (3D) core–shell catalyst, in which numerous LDH nanoplates are vertically grown on cuboidal metal organic framework (MOF) structures, is synthesized through a facile one-pot reaction strategy. The representative electrocatalyst (CoNi-BDC@LDH) achieves an excellent OER performance (with an overpotential of 282 mV at 100 mA cm−2) and stability. A series of quasi-operando and ex-situ characterization reveals a lattice oxygen-mediated mechanism where Ni and its neighboring metal site collaboratively forms Ni-O-O-M (M = Ni, Co) bridges, and the high valence state of Ni facilitates O2 desorption from the bridges. The high OER performance is additionally attributed to γ-NiOOH and CoOOH phases, and a large electrochemically active surface area.

Multi-core@Shell catalyst derived from LDH@SiO2 for low- temperature dry reforming of methane

In this paper, a multi-core@shell catalyst LDH@SiO2 was fabricated by coating a silica layer over hexagonal Ni–Mg–Al LDH nanoplates. After calcination and H2-reduction, Ni nanoparticles were well dispersed on the support, as well as encapsulated within the mesoporous silica shell. The multi-core@shell catalyst was then tested in low temperature dry reforming of methane (DRM) at 600 °C and showed a stable CH4 conversion of 27% for 16 h time on stream. Characterizations of the spent catalyst indicated that there was almost no carbon formation and the multi-core@shell structure was well preserved. While the pristine layered double hydroxide (LDH) catalyst exhibited a severe carbon formation as 68%. The confinement effect conveyed by the unique multi-core@shell structure effectively suppressed metal sintering and carbon deposition. Besides, the thickness of the silica shell was tuned and it made a great difference to the catalytic activity due to the diffusion resistance.

Corrosion-resistant Mg(OH)2/Mg-Fe layered double hydroxide (LDH) composite films on magnesium alloy WE43

BackgroundA new synthesis approach was developed for Mg-Fe layered double hydroxide (LDH) film on oxidised magnesium (Mg) alloy WE43 surface by cathodic electrodeposition. MethodsThe synthesised Mg(OH)2 surface layer provides essential divalent cations and a foundation for the direct growth of an Mg-Fe LDH film through the electrodeposition process with trivalent cations containing solution. FindingsThe cross-section analysis results disclosed that the Mg(OH)2 layer altered the typical morphology of LDH film, leading to structured LDH nanoplates with a thickness of approximately 3.5 µm. The formation of structured LDH nanoplates resulted from the perpendicular arrangement of the ab-faces of the crystallites to the WE43 surface, as seen from Field Emission Scanning Electron Microscopy (FE-SEM) images. Electrochemical tests in Hank's Balanced Salt Solution (HBSS) report the Ecorr value increased by 0.24 V and a decrease in icorr by one order of magnitude of Mg(OH)2/Mg-Fe LDH composite films against its substrate. Furthermore, the impedance modulus values of Mg(OH)2/Mg-Fe LDH composite films can achieve a magnitude of three times greater than its substrate. These results indicate that the Mg-Fe LDH film can effectively capture the corrosion anions during corrosion through the anion-exchange process, making it a promising surface modification for Mg alloy.

Synthesis, characterization and protective functioning of surface decorated Zn-Al layered double hydroxide with SiO2 nano-particles

In this paper, ZnAl layered double hydroxide particles surface were decorated with SiO2 nanoparticles to investigate the influence of SiO2 nanoparticles presence on molybdate anion loading and release behavior as a corrosion inhibitor. For this purpose, we have synthesis a carbonate-based layered double hydroxide (LDH). Nano SiO2 particles were used to decorate the surface of carbonate-based LDH nano-plates. Molybdate was then intercalated into LDH interlayer space through an ion exchange process. Characterization of the synthesized nano-plates was done by XRD, FTIR, FE-SEM, and ICP tests. The decorated nano-plates were employed in silane coating to investigate and compare their corrosion protective properties using EIS and polarization tests. The results illustrated that the protective functioning enhanced after SiO2 decoration. Moreover, molybdate loaded in SiO2 decorated LDH had a better protective functioning, and provided more extended protection due to its higher loading, and controlled release of molybdate anions.

An analytical method to characterize the crystal structure of layered double hydroxides: synthesis, characterization, and electrochemical studies of zinc-based LDH nanoplates

Due to their unique soft and complex structure, it has been difficult to analyze the exact crystal structure of layered double hydroxides (LDHs), which has been a major obstacle to understanding and improving the catalytic properties of LDHs.

A Three-Dimensional ZnO/CdS/NiFe Layered Double Hydroxide Photoanode Coupled with a Cu2O Photocathode in a Tandem Cell for Overall Solar Water Splitting

An integrated tandem photoelectrochemical (PEC) cell, composed of a three-dimensional (3D) ZnO/CdS/NiFe layered double hydroxide (LDH) core/shell/hierarchical nanowire arrays (NWAs) photoanode and a [Formula: see text]-Cu2O photocathode, was designed for unassisted overall solar water splitting in this study. The optical and photoelectrochemical characteristics of ZnO-based photoanodes and Cu2O photocathode were investigated. The results show that ZnO/CdS/NiFe LDH nanostructures offer significantly enhanced performances with a photocurrent density reaching 5.8[Formula: see text]mA[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text] at 0.9[Formula: see text]V and an onset potential as early as 0.1[Formula: see text]V (versus RHE). The enhancement can be attributed to the existence of CdS nanoparticles (NPs) which boosts the light absorption in visible region and enhances charge separation. Moreover, the introduction of NiFe LDH nanoplates, with unique hierarchical mesoporous architecture, promotes electrochemical reactions by providing more active sites as co-catalyst. On the above basis, the ZnO/CdS/NiFe LDH–Cu2O two-electrode tandem cell system was established. At zero bias, the device shows a photocurrent density of 0.4[Formula: see text]mA[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text] along with the corresponding solar-to-hydrogen (STH) conversion efficiency reaching 0.50%. Our results indicate that the tandem PEC cells consisting of metal–oxide–semiconductor photoelectrodes based on Earth-abundant and low-cost materials hold promising application potential for overall solar water splitting.

Acid Susceptible Ultrathin Mesoporous Silica Coated on Layered Double Hydroxide Nanoplates for pH Responsive Cancer Therapy.

Bioresponsive drug delivery systems that can modulate drug release profiles according to different tumor microenvironment are highly desired for improving cancer therapy. In this work, a pH-responsive nanocarrier, layered double hydroxide (LDH) nanoplates coated with ultrathin mesoporous silica layer (LDH@MS), was fabricated with total thickness of around 9 nm. The coating of ultrathin porous silica significantly improved the stability of nanoplates. Moreover, the LDH@MS exhibited pH responsive functionality due to the degradation of silica shell and LDH under moderately acidic pH condition. Notably, the curcumin loaded LDH@MS displayed nearly five-fold greater antitumor efficacy against human breast cancer cells in vitro and marked tumor inhibition in vivo compared to free curcumin under the same drug dosage, most likely due to high dispersibility of the nanocarrier, as well as responsive and steady release of drug molecules. This study opens new avenues to design safer and more effective drug delivery systems with improved therapeutic outcomes.

Cobalt-doped Ni–Mn layered double hydroxide nanoplates as high-performance electrocatalyst for oxygen evolution reaction

Abstract Active, stable and low-cost electrocatalysts are in high demand to replace the traditional noble metal catalysts towards efficient water splitting. Here we report a type of nickel-manganese (Ni–Mn) layered double hydroxide (LDH) with controllable doping content of cobalt as an oxygen evolution reaction (OER) electrocatalyst with excellent performance in alkaline media. Co-doped Ni–Mn LDH nanoplates were synthesized via a facile hydrothermal method. It was found that the doping content of cobalt significantly affected the OER activities. The best electrocatalyst was based on a doping ratio of 21.1% Co, exhibiting a low overpotential of ~310 mV at a current density of 10 mA cm−2, a Tafel slope of ~59 mV dec−1 as well as excellent stability. This work demonstrates a facile synthetic method of rationally doping transition-metal hydroxides to develop new OER electrocatalysts with remarkable performance in water splitting.

NiCo-layered double hydroxides vertically assembled on carbon fiber papers as binder-free high-active electrocatalysts for water oxidation

Building nanocomposite architectures made of carbon materials and layered double hydroxides (LDHs) materials as high-efficiency and low-cost catalysts for oxygen evolution reaction (OER) is one of potential strategies for sustainable and clean water splitting. Nevertheless, conventional powder samples, mixed with polymer binders and immobilized on a matrix, suffer from the limited specific surface area and poor conductivity. Herein, a carbon fiber paper (CFP)-assisted strategy is presented to mediate vertical in situ growth and assembly of NiCo-LDH nanoplates, and their catalytic activities as binder-free high-active electrocatalysts for water oxidation were investigated. The CFP is capable of modulating the assembly of NiCo-LDH nanoplates, yielding the vertically oriented nanoarrays on CFP. The as-made hybrids indicate a dramatically increased catalytic activity and long-term stability towards OER in comparison to that of micro-sized LDHs spheres derived from the self-assembly of LDHs nanoplates. A relatively low overpotential of 307 mV is achieved at 10 mA cm−2 and a low Tafel slope of 64 mV dec−1 is delivered in basic medium. The vertically oriented LDHs nanoarrays featuring large specific surface areas, open structure and rich active sites, together with the highly conductive CFP substrate are synergistically responsible for the enhanced electrochemical performance.

Facile synthesis of LDH nanoplates as reinforcing agents in PVA nanocomposites

In the present study, layered double hydroxide (LDH) nanoplates with high crystallinity and uniform size were facilely synthesized to act as reinforcing agents in polymer materials. The structure of the synthesized LDH nanoplates was characterized by X‐ray diffraction, Fourier transform infrared spectra, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy measurements. Subsequently, the LDH nanoplates were incorporated into poly(vinyl alcohol) (PVA) matrix as reinforcing agents based on a solution casting method. The LDH nanoplates were well dispersed in PVA matrix and formed strong interfacial interactions with PVA chains, leading to remarkable improvements of thermal stability, flame retardancy, and mechanical properties. With the incorporation of 1 wt% LDH nanoplates into PVA, the Tonset and T50% increased by 11°C and 57°C, respectively. Moreover, the presence of LDH nanoplates decreases the decomposition rates of PVA and increases the amount of char residues. Compared with pure PVA, the peak heat release rate value of the PVA/5 wt% LDH nanocomposites is decreased by 52%. The tensile strength and the elongation at break increased by 71% and 187%, respectively, when incorporating with 3 wt% LDH nanoplates. Copyright © 2016 John Wiley & Sons, Ltd.

Co-Fe layered double hydroxides nanosheets vertically grown on carbon fiber cloth for electrochemical capacitors

We demonstrate the fabrication of a core-shell structure composite of Co–Fe layered double hydroxides (LDHs) on the surface of carbon fiber cloth (CFC). The Co–Fe LDHs nanoplates are vertically anchored onto the surface of electrical conductive CFC via a simple hydrothermal process followed by an I2 oxidation process. The hexagonal Co–Fe LDHs nanoplates on the surfaces of carbon fibers form a porous network film. The carbon fibers with high conductivity can act as conductive cores to support a large number of Co–Fe LDHs nanoplates to deliver a high specific capacitance of 774 F g−1 at the current density of 1 A g−1. An assembled asymmetric capacitor by using Co–Fe LDHs-CFC as positive electrode material and activated carbon as negative electrode material can deliver an energy density of 16.1 Wh kg−1 at the power density of 399.7 W kg−1 with a good cycling stability. This study provides a way to combine Co–Fe LDHs with carbon materials to obtain a composite that can deliver an improved performance for electrochemical capacitor application.

Growth Behaviors of Layered Double Hydroxide on Microarc Oxidation Film and Anti-Corrosion Performances of the Composite Film

Microarc oxidation (MAO) film has been widely used as an anti-corrosive film for Al alloys. However, it is still a big challenge to further improve its anti-corrosion performance due to the defects that form during the MAO process. In this study, for the first time, Ni-Al layered double hydroxide (LDH) was in-situ synthesized on the MAO film to seal its defects, which contributes to the corrosion resistance enhancement of MAO treated 6061 Al alloy. The growth of the LDH on MAO film is largely determined by the specific area, chemical composition, and crystalline structures of the alumina phase of the MAO film. More importantly, LDH nanoplates can grow into the micropores and microcracks in MAO film, and then gradually seal these structural defects. The anti-corrosion performance of MAO film during long-term immersion in NaCl solution also can be improved greatly via LDH treating because the defect-sealing effects of LDH can enhance the barrier property of both the porous and dense layers of MAO film, and then restrain the penetration of corrosive agents through the MAO film to the metal substrate.

Controlled synthesis of layered double hydroxide nanoplates driven by screw dislocations.

Layered double hydroxides (LDHs) are a family of two-dimensional (2D) materials with layered crystal structures that have found many applications. Common strategies to synthesize LDHs lead to a wide variety of morphologies, from discrete 2D nanosheets to nanoflowers. Here, we report a study of carefully controlled LDH nanoplate syntheses using zinc aluminum (ZnAl) and cobalt aluminum (CoAl) LDHs as examples and reveal their crystal growth to be driven by screw dislocations. By controlling and maintaining a low precursor supersaturation using a continuous flow reactor, individual LDH nanoplates with well-defined morphologies were synthesized on alumina-coated substrates, instead of the nanoflowers that result from uncontrolled overgrowth. The dislocation-driven growth was further established for LDH nanoplates directly synthesized using the respective metal salt precursors. Atomic force microscopy revealed screw dislocation growth spirals, and under transmission electron microscopy, thin CoAl LDH nanoplates displayed complex contrast contours indicative of strong lattice strain caused by dislocations. These results suggest the dislocation-driven mechanism is generally responsible for the growth of 2D LDH nanostructures, and likely other materials with layered crystal structures, which could help the rational synthesis of well-defined 2D nanomaterials with improved properties.

Hydrothermal continuous flow synthesis and exfoliation of NiCo layered double hydroxide nanosheets for enhanced oxygen evolution catalysis.

We report the controlled synthesis of NiCo layered double hydroxide (LDH) nanoplates using a newly developed high temperature high pressure hydrothermal continuous flow reactor (HCFR), which enables direct growth onto conductive substrates in high yield and, most importantly, better control of the precursor supersaturation and, thus, nanostructure morphology and size. The solution coordination chemistry of metal-ammonia complexes was utilized to synthesize well-defined NiCo LDH nanoplates directly in a single step without topochemical oxidation. The as-grown NiCo LDH nanoplates exhibit a high catalytic activity toward the oxygen evolution reaction (OER). By chemically exfoliating LDH nanoplates to thinner nanosheets, the catalytic activity can be further enhanced to yield an electrocatalytic current density of 10 mA cm(-2) at an overpotential of 367 mV and a Tafel slope of 40 mV dec(-1). Such enhancement could be due to the increased surface area and more exposed active sites. X-ray photoelectron spectroscopy (XPS) suggests the exfoliation also caused some changes in electronic structure. This work presents general strategies to controllably grow nanostructures of LDH and ternary oxide/hydroxides in general and to enhance the electrocatalytic performance of layered nanostructures by exfoliation.

Controllable synthesis of Mg–Fe layered double hydroxide nanoplates with specific Mg/Fe ratios and their effect on adsorption of As(v) from water

Layered double hydroxides (LDHs) have been studied comprehensively for adsorptive application due to their outstanding ability to exchange anions. An easy thermal method is presented to synthesize Mg–Fe LDH nanoplates with the controlled Mg/Fe molar ratios (3 : 1, 4 : 1, 5 : 1). Their ability to remove arsenate from water is investigated. Through comparative analysis, the results indicate that the Mg/Fe molar ratio strongly affects adsorption of As(V) on the as-prepared LDHs. The LDHs with a Mg/Fe molar ratio of 4 : 1 exhibited the fastest adsorption rate and the highest adsorption capacity among the LDHs with three different Mg/Fe molar ratios, which was attributed to the higher BET surface area and metastable iron ions in the brucite-like sheets of the LDHs.

Synthesis of ultrafine layered double hydroxide (LDHs) nanoplates using a continuous-flow hydrothermal reactor

We report a novel continuous-flow hydrothermal method for the synthesis of layered double hydroxide (LDH) nanoplates. The precursor solutions may be fed to the reactor so that the production of LDHs occurs in a continuous mode. By control of the synthesis temperature, pressure and contact time, the synthesis of LDH nanoplates can be tuned with constant and consistent product quality. This very general and simple approach shows high potential for commercial scale-up.

A new method for preparation of nanoplates of Zn-Al layered double hydroxides

Methods for preparation of nanoplates of layered double hydroxides (LDHs) have been intensively investigated for the purpose of making nanocomposites. The present study provides a new simple method of nanoplate preparation for Zn-Al LDHs. Zn-Al LDHs containing lactate or combinations of lactate and simple inorganic anions were synthesized by a coprecipitation method, and water-washed and undried LDHs were dispersed in water. Among them, suspensions of Zn-Al LDHs containing both lactate and bicarbonate were unique in that they rapidly became translucent colloidal dispersions when the molar ratio of added bicarbonate to added Al was ≤ 0.5. The resulting LDH nanoplates in the dispersions were delaminated single layers or nanoplates with a thickness of several layers, depending on the amount of bicarbonate.

Water-dispersible magnetite-graphene-LDH composites for efficient arsenate removal

A composite material, containing magnetite particles, graphene and layered double hydroxides (LDHs) was fabricated through a simple two-step reaction. Graphene was used as the matrix for supporting magnetite particles and LDH nanoplates. The synthesized magnetite-graphene-LDH (MGL) composites were characterized by field emission scanning electron microscopic (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transformed infrared (FTIR) spectroscopy, N2adsorption-desorption, and X-ray photoelectron spectroscopy (XPS). The MGL composites were applied to remove arsenate from aqueous solutions and could be easily separated by magnetic separation process. The results showed enhanced adsorption capacity of arsenate on the MGL as compared to that of pure Mg/Al LDHs. The surface area of MGL is greatly enhanced through the incorporation of magnetite particles and graphene, which provides more active sites for arsenate uptake. Moreover, LDHs were hybridized with mechanically and chemically stable graphene materials, providing an accessible diffusion pathway in the macropore domain, and therefore their adsorption capacity was enhanced. The fast and efficient adsorption of arsenate from solution to MGL suggests that the MGL composites are potential and suitable materials in the preconcentration of arsenate from large volumes of aqueous solutions in wastewater treatment.