Layered Double Hydroxide Nanosheets Research Articles

Deeply Reconstructed NiFe Layered Double Hydroxide Nanosheets for an Efficient Oxygen Evolution Reaction

Deeply Reconstructed NiFe Layered Double Hydroxide Nanosheets for an Efficient Oxygen Evolution Reaction

High electrochemical performance of MnCo2O4.5 nanoneedles/NiCo LDH nanosheets as advanced electrodes of supercapacitor

MnCo2O4.5@NiCo layered double hydroxides (LDHs) are synthesized on nickel foam (NF) using the hydrothermal-calcination-hydrothermal method. It retains MnCo2O4.5 nanoneedles and NiCo LDH nanosheets structures, improving its electrochemical performance. The composite has an excellent specific capacity (1266 C g−1 when current density is 2 A g−1) and deliver an outstanding initial capacity retention (96.8% when current density is 20 A g−1). Moreover, the self-assembled MnCo2O4.5@NiCo LDH/NF//AC (actived carbon) asymmetric supercapacitor (ASC) provides the highest energy density of 33.3 W h kg−1 when the power density is 798 W kg−1 and has a long cycle life of 81% at 5 A g−1 after 7000 cycles. The above results provide a useful strategy for new-generation energy storage devices with excellent properties.

NiCo Layered Double Hydroxide Nanoarrays Grown on an Etched Ni Foam Substrate for High-Performance Supercapacitor Electrode

Nickel foam (NF) with a desirable 3D open-pore structure is extensively adopted in developing integrated electrodes, and the enhanced interaction between the electrode materials and NF substrate is recognized as an effective method for a high-performance supercapacitor electrode with a low resistance nature and high stability. In this work, an etched NF (ENF) with residual nanosheets is adopted as a novel substrate to facilitate the capacitive activity of NiCo layered double hydroxide (NiCo LDH) nanowire arrays. NiCo LDH nanosheet arrays grown on a pristine NF substrate (NiCo LDH/NF) are synthesized initially and used as a precursor. Then, the ENF substrate with a residual nanosheet is obtained by partially removing NiCo LDH nanosheet arrays in a formamide/KOH mixed solution. Subsequently, NiCo LDH nanowire arrays are hydrothermally grown on ENF to form a NiCo LDH/ENF electrode. The role of the residual nanosheet on ENF is discussed in detail, in which the content of Ni3+/Co3+ and the resistance nature of NiCo LDH/ENF can be optimized with the amount of residual nanosheets. Hence, the ENF substrate with an optimal amount of residual nanosheets is beneficial for retaining the adhesion of nanoarrays and realizing the low resistance nature in a mild route. The NiCo LDH/ENF electrode shows a capacity of 976.6 C g–1 at 1 A g–1 with excellent cyclic stability. The as-assembled NiCo LDH/ENF//activated carbon hybrid supercapacitor delivers a high specific capacitance of 150.8 F g–1 at 1 A g–1 and achieves an energy density of 67.9 Wh kg–1 at a power density of 900 W kg–1 with an excellent cycle stability with a 90.6% capacity retention after 10,000 cycles, indicating high energy density and good stability.

Anticoagulation in Phototherapy to Inhibit the Cancer-Associated Hypercoagulable State

The hypercoagulable state has challenged the lives of cancer patients, which is related to the treatment and the cancer-secreted procoagulant factors. Herein, a phototherapy system based on heparin modified Fe/Co-layered double hydroxide loading IR783 (LDH-hep-IR783) is established, which prevents the side effects and prothrombotic defect of the traditional treatment. The Fe/Co LDH is applied not only as the carrier of the photosensitizer but also can catalyze the decomposition of H2O2 to overcoming the hypoxia of tumor microenvironment, enhancing the efficacy of photodynamic therapy (PDT) and decreasing the hypercoagulable state. The heparin plays as the stabilizer of the Fe/Co LDH nanosheet and also obviously inhibits the cancer associated hypercoagulable state of tumor-bearing mice. Therefore, the proposed strategy provides a promise insight for cancer therapy assisted by anticoagulated intervention.

Composites of Layered Double Hydroxides and ANA-Type Zeolite Synthesized from Hazardous Secondary Aluminum Dross for Cationic Dye Wastewater Treatment

This work first transformed hazardous aluminum waste into low-cost MgAl−layered double hydroxide@ANA zeolite (LDHs@ANA) composite for dye wastewater adsorption, which was meaningful for waste recovery and pollution control. Based on this strategy, the Al(OH)3 extracted from secondary aluminum dross (a hazardous waste in the aluminum industry) was used as an aluminum source to synthesize LDHs@ANA composite, which had more excellent adsorption capacity to methylene blue than MgAl−LDHs and ANA alone. The composite consisted of spherical ANA particles uniformly covered with LDH nanosheets, which effectively avoided a large amount of aggregation between nanosheets and increased specific surface areas and pore volumes. The kinetic results indicated that the adsorption process conformed to the pseudo-second-order kinetic model, and the adsorption site was the main factor affecting the adsorption process. The equilibrium studies showed the adsorption process was exothermic, and the Langmuir model best fitted for the adsorption process, with a maximum adsorption capacity reaching 65.27 mg/g. Meanwhile, the effects of pH, adsorbent concentration, initial methylene blue concentration, and adsorption time on the LDHs@ANA were analyzed. Overall, this work provides a fresh concept for the preparation of low-cost adsorbents from aluminum waste.

Magnetic two-dimensional Ca-Al layered double hydroxide/Fe3O4@dextran nanocomposites as drug delivery systems

Layered double hydroxides (LDHs) are one of the two-dimensional (2D) anionic clay materials that have received great attention for drug delivery applications due to their high surface-to-volume ratio and drug loading efficiency. In this research, Al-Ca layered double hydroxides (LDHs) were synthesized in situ in presence of Fe3O4@dextran nanoparticles through the co-precipitation method. X-ray diffraction (XRD) studies showed that by increasing the Fe3O4@dextran nanoparticles content, the peaks are broadened due to the intercalation. Field-emission electron microscopy (FESEM) images showed the LDH nanosheets are decorated with Fe3O4@dextran nanoparticles. The saturation magnetization for the sample LDH-Fe3O4@dextran was found to be 13.7 emu/g. The LDH-Fe3O4@dextran sample could load doxorubicin hydrochloride (DOX) with a loading efficiency of 69 %. The in vitro studies showed that the drug release from the synthesized nanocomposite is pH-sensitive. The accumulative release of DOX could reach 59 % in an environment with a pH of 7.4 and 71 % in an environment with a pH of 5.5 within 24 hrs. The synthesized magnetic nano-carrier is promising for its application as a drug delivery nanocarrier with a faster drug release in the tumor microenvironment.

Bridging Au nanoclusters with ultrathin LDH nanosheets via ligands for enhanced charge transfer in photocatalytic CO2 reduction

Au nanoclusters (NCs) bring new opportunities for constructing visible-light photocatalysts for solar-driven CO2 conversion, whereas the agglomeration under illumination and lack of catalytic sites severely hinder their application. One promising approach to address the limitations is the confinement of Au NCs on a heterogeneous substrate with efficient catalytic sites, in which a concomitant bottleneck originates from the electron transfer between Au NCs and catalytic sites determining the charge transfer dynamics. Herein, we develop an effective strategy for grafting Au NCs onto ultrathin layered double hydroxide (LDH) nanosheets via engineering bridging ligands. The bridging ligands function as both surface anchors and electron mediators, which confine and stabilize Au NCs on LDH, as well as facilitate electron transfer from Au NCs to catalytic sites. As a result, the durability and efficiency for photocatalytic CO2 reduction is significantly enhanced. This work provides a fresh hint for stabilizing ultrasmall nanoclusters and facilitating the electron transfer between light-harvesting nanoclusters and catalytic sites through bridging ligands.

In‐situ growth of layered double hydroxide on montmorillonite nanosheets to improve the flame retardant performance of ABS resin

AbstractLayered double hydroxide (LDH) is a widely used flame retardant in polymer materials; however, the poor dispersion due to its high hydrophilic nature results in disappointing thermal stability and fire safety. In this work, LDH was in‐situ grown on the disordered montmorillonite (MMT) nanosheets to obtain the hybrid of LDH and MMT nanosheets (LDH@MMT, simplified as LM). Various techniques, including X‐ray diffraction, Fourier‐transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscope were used to characterize the microstructure of LM. In addition, the acrylonitrile‐butadiene‐styrene (ABS) composite containing LM and intumescent flame retardant (IFR) was prepared, and its mechanical and flame‐retardant properties were also measured. The characterization results demonstrate that the LM exhibits a periodically alternating layered structure. The Limiting Oxygen Index (LOI) of the ABS composite reaches 27.2% with a V‐0 rating in the UL‐94 vertical burning test, while its flexural strength and tensile strength decrease by only 17.82% and 13.45%, respectively. Furthermore, the heat release rate, total heat release, smoke production rate, and carbon monoxide production rate of the ABS composite present a significant decline in cone calorimeter tests compared with those of pure ABS. The results further indicate that the hybridization could effectively improve the flame‐retardant performance of ABS composites and perform lesser impacts on their mechanical properties.

Dynamic Morphological Evolution of Co-Based Layered Double Hydroxide Nanosheets Investigated by In Situ Electrochemical-Atomic Force Microscopy

With excellent electrochemical activity, low consumption, and easy synthesis, Co-based layered double hydroxides (LDHs) have been applied to electrochemical energy conversion and storage devices. Understanding the mechanisms of morphological evolution and capacity changes under potential cycles is critical for the design of high-performance materials of Co-based LDHs. Here, we monitored the morphological evolution of two kinds of CoFe-LDH nanosheets and four kinds of CoAl-LDH nanosheets using in situ electrochemical-atomic force microscopy. The CoFe-LDH nanosheets present the growth of granular particles and the deterioration of capacity performances, which might be due to the irreversible conversion of hydroxide into oxyhydroxide under potential cycles. The CoAl-LDH nanosheets maintain more capacity and do not form granular particles under potential cycles, resulting from the electrochemical reaction reversibility of Co2+ and the stability of the host hydroxide layer enhanced by Al3+. The introduction of Al3+ into the Co-based LDH structure is conducive to cyclic stability of capacity compared to that of Fe3+. Additionally, the CoAl-LDH nanosheets with different Co/Al molar ratios present varying degrees of dissolution and variations of capacity under potential cycles. A moderate Co/Al molar ratio of CoAl-LDH nanosheets is beneficial to cyclic stability. These findings would provide a deep insight into the mechanisms of capacity changes based on in situ morphological evolution and support for the optimization of such material performance.

A hierarchical cactus-like nanostructure as a bifunctional catalyst for overall water splitting

In this study, a hierarchical cactus-like nanostructure with cobalt doped iron disulfide (Co-FeS2) needle nanowires as trunks and nickel-iron layered double hydroxide (NiFe-LDH) nanosheets as branches was constructed as a self-supporting electrode for overall water splitting in alkaline electrolytes. A low electron density NiFe-LDH derived from the strong electronic interaction between sulfides and NiFe-LDH is remarkably effective in facilitating the adsorption of H2O and OH−, while the presence of Co atoms in FeS2 facilitates the hydrogen adsorption. Such a synergetic effect improved the HER performance in alkaline electrolytes significantly. In terms of the OER process, the Fe/Co oxyhydroxides produced from in situ phase transition from Co-FeS2 in conjunction with NiFe-LDH endow the electrode with excellent OER activity. Furthermore, the Co-FeS2 needle nanowires with metal-like conductivity allow for rapid electron transfer during electrochemical processes, and the hierarchical structure exposes substantial active sites and facilitates electrolyte penetration. In alkaline media, the electrode demonstrated outstanding HER and OER catalytic activity, requiring small overpotentials of 131 mV and 220 mV to reach current densities of 10 mA cm−2 and 20 mA cm−2, respectively. Moreover, it only needed 1.58 V to drive 10 mA cm−2 when utilized simultaneously as both cathode and anode for overall water splitting.

Enhanced Carbon Monoxide Electroreduction to >1 A cm−2 C2+ Products Using Copper Catalysts Dispersed on MgAl Layered Double Hydroxide Nanosheet House‐of‐Cards Scaffolds

AbstractCu catalysts are most apt for reducing CO(2) to multi‐carbon products in aqueous electrolytes. To enhance the product yield, we can increase the overpotential and the catalyst mass loading. However, these approaches can cause inadequate mass transport of CO(2) to the catalytic sites, which will then lead to H2 evolution dominating the product selectivity. Herein, we use a MgAl LDH nanosheet ‘house‐of‐cards’ scaffold to disperse CuO‐derived Cu (OD‐Cu). With this support‐catalyst design, at −0.7 VRHE, CO could be reduced to C2+ products with a current density (jC2+) of −1251 mA cm−2. This is 14× that of the jC2+ shown by unsupported OD‐Cu. The current densities of C2+ alcohols and C2H4 were also high at −369 and −816 mA cm−2 respectively. We propose that the porosity of the LDH nanosheet scaffold enhances CO diffusion through the Cu sites. The CO reduction rate can thus be increased, while minimizing H2 evolution, even when high catalyst loadings and large overpotentials are used.

Enhanced Carbon Monoxide Electroreduction to >1 A cm-2 C2+ Products Using Copper Catalysts Dispersed on MgAl Layered Double Hydroxide Nanosheet House-of-Cards Scaffolds.

Cu catalysts are most apt for reducing CO(2) to multi-carbon products in aqueous electrolytes. To enhance the product yield, we can increase the overpotential and the catalyst mass loading. However, these approaches can cause inadequate mass transport of CO(2) to the catalytic sites, which will then lead to H2 evolution dominating the product selectivity. Herein, we use a MgAl LDH nanosheet 'house-of-cards' scaffold to disperse CuO-derived Cu (OD-Cu). With this support-catalyst design, at -0.7 VRHE , CO could be reduced to C2+ products with a current density (jC2+ ) of -1251 mA cm-2 . This is 14× that of the jC2+ shown by unsupported OD-Cu. The current densities of C2+ alcohols and C2 H4 were also high at -369 and -816 mA cm-2 respectively. We propose that the porosity of the LDH nanosheet scaffold enhances CO diffusion through the Cu sites. The CO reduction rate can thus be increased, while minimizing H2 evolution, even when high catalyst loadings and large overpotentials are used.

Interface strong-coupled 3D Mo-NiS@Ni-Fe LDH flower-cluster as exceptionally efficient electrocatalyst for water splitting in wide pH range

It is crucial to create a bifunctional catalyst with high efficiency and low cost for electrochemical water splitting under alkaline and neutral pH conditions. This study investigated the in-situ creation of ultrafine Mo-NiS and NiFe LDH nanosheets as an effective and stable electrocatalyst with a three-dimensional (3D) flower-cluster hierarchical structure (Mo-NiS@NiFe LDH). The strong interfacial connection between Mo-NiS and NiFe LDH enhances the formation of metal higher chemical states in the material, optimizes the electronic structure, increases OH– adsorption capacity improves electron transfer/mass diffusion, and promotes O2/H2 gas release. As a result, at 10 mA cm−2, Mo-NiS@NiFe LDH/NF demonstrates the outstanding bifunctional electrocatalytic activity of just 107 mV (HER, hydrogen evolution reaction) and 184 mV (hydrogen evolution reaction) (OER, oxygen evolution reaction). The catalytic performance is remarkably stable after 72 h of continuous operation in 1 M KOH at high current densities (300 mA cm−2). More interestingly, in the overall water splitting system, the cell voltages for anode and cathode in both alkaline and neutral electrolytes for Mo-NiS@NiFe LDH/NF are only 1.54 V (alkaline) and 2.06 V (neutral) at 10 mA cm−2. These results demonstrated that the bifunctional electrocatalyst design concept is a viable solution for water splitting in both alkaline and neutral systems.

Recent Advances on Transition-Metal-Based Layered Double Hydroxides Nanosheets for Electrocatalytic Energy Conversion.

Transition-metal-based layered double hydroxides (TM-LDHs) nanosheets are promising electrocatalysts in the renewable electrochemical energy conversion system, which are regarded as alternatives to noble metal-based materials. In this review, recent advances on effective and facile strategies to rationally design TM-LDHs nanosheets as electrocatalysts, such as increasing the number of active sties, improving the utilization of active sites (atomic-scale catalysts), modulating the electron configurations, and controlling the lattice facets, are summarized and compared. Then, the utilization of these fabricated TM-LDHs nanosheets for oxygen evolution reaction, hydrogen evolution reaction, urea oxidation reaction, nitrogen reduction reaction, small molecule oxidations, and biomass derivatives upgrading is articulated through systematically discussing the corresponding fundamental design principles and reaction mechanism. Finally, the existing challenges in increasing the density of catalytically active sites and future prospects of TM-LDHs nanosheets-based electrocatalysts in each application are also commented.

Al-Incorporated Cobalt-Layered Double Hydroxides for Enhanced Oxygen Evolution through Morphology and Electronic Structure Regulation.

Layered double hydroxides (LDHs) are promising electrocatalytic materials for the oxygen evolution reaction (OER) due to their tunable composition and low cost. Here, we construct ultrathin Al-incorporated Co LDH nanosheets on carbon cloth (CC) by a facile hydrothermal strategy. Compared to Co LDH/CC, the optimized Co2Al1 LDH/CC displays significantly improved OER performance, characterized by low overpotentials of only 171 and 200 mV to reach current densities of 10 mA cm-2 in alkaline and neutral media, respectively, as well as good stability over an extended period. The introduced Al3+ and CC support play a synergistic role in steering the morphology of Co2Al1 LDH/CC while also increasing the electrochemical active sites. X-ray absorption fine spectra (XAFS) analyses uncover the critical role of Al in regulating the coordination environment of Co atoms, with evidence affording highly active Co oxidation states. Moreover, density functional theory (DFT) calculations confirmed that the Al3+ incorporated into Co LDH/CC can efficaciously modulate the electronic density of states of the d-band center of Co atoms, optimize the Gibbs free energies of intermediates toward OER, and thus accelerate the O2 evolution rate.

Engineering layered double hydroxide-based sonocatalysts for enhanced sonodynamic-immunotherapy

Sonodynamic therapy (SDT) highly depends on O2 activation to generate desired reactive oxygen species (ROS), however, the deficiencies of sonocatalysts and the hypoxia tumor microenvironment (TME) limit the treatment effect. Herein, a local element rearrangement strategy is used to reconstruct Fe-based layered double hydroxide (LDH) nanosheets via substituting portions of Mg with Mn element (denoted as MMF NSs) for the first time as novel sonocatalysts for high performance SDT of cancer. The Mn substitution could tune the bond length of Fe-O to activate H2O2 for improving O2 generation yield, as well as decrease the band gap for promoting separation of excited electrons-holes and prolong the lifetime of electron-hole under ultrasound irradiation. Besides, the MMF NSs could immunostimulatory modulate TME including the ratio of M1 macrophage to M2 subtype and promote the maturation of dendritic cells (DCs) to reinforce high-efficient breast cancer therapy. Consequently, this study highlights novel LDH-based sonocatalysts constructed by a local element rearrangement strategy for improving the SDT-enhanced immunotherapy.

Novel Thin-Film Nanocomposite Forward Osmosis Membranes Modified with WS2/CuAl LDH Nanocomposite to Enhance Desalination and Anti-fouling Performance

Designing efficient membranes for desalination to help reduce the water shortage crisis has been the subject of various studies. In this study, first, CuAl LDH nanosheets were prepared and the surface of some thin-film composite (TFC) membranes was modified by them. Afterward, the novel heterostructure nanocomposite consisting of CuAl LDH and WS2 nanosheets was synthesized by hydrothermal method, and a new kind of thin-film nanocomposite (TFN) membranes were made using them. All the obtained membranes performance was studied in the forward osmosis (FO) process. The effects of the prepared compounds on the morphology, chemical structure, hydrophilicity, and topology of the polyamide (PA) active layer were evaluated by scanning electron microscopy (SEM), FT-IR spectroscopy, energy-dispersive X-ray (EDX), powder x-ray diffraction (XRD), water contact angle (WCA) goniometer and atomic force microscope (AFM) analysis. Finally, by comparing the results for both types of modified membranes, the membrane containing 0.025 wt% of the nanocomposite modifier showed the highest water flux (29.30 LMH) and selectivity (0.38 g/L) that was chosen as the optimal membrane. Also, the anti-fouling properties of this membrane were studied and the obtained results showed an increase in the fouling resistance compared to the membrane without filler.

Enhanced Carbon Monoxide Electroreduction to >1 A·cm-2 C2+ Products Using Copper Catalysts Dispersed on MgAl Layered Double Hydroxide Nanosheet House−of−Cards Scaffolds

Enhanced Carbon Monoxide Electroreduction to >1 A·cm-2 C2+ Products Using Copper Catalysts Dispersed on MgAl Layered Double Hydroxide Nanosheet House−of−Cards Scaffolds

Monolayer Iron and Iron-Rich Hydroxide Nanosheets Exfoliated from High-Quality Green Rust for Enhanced Electrocatalytic Oxygen Evolution Reaction

Ultrathin nanosheets of Ni-, Co-, and Fe-based (oxy)hydroxides exhibit promising catalytic activity for the oxygen evolution reaction (OER) in water electrolysis under alkaline conditions. It has been revealed that Fe may play a crucial role in the catalytic process of Ni- or Co-based catalysts. However, it lacks effective methods to prepare and study pure Fe hydroxide nanosheets. In the present work, we report a topochemical synthesis of mixed-valent Fe2+–Fe3+ layered double hydroxides (LDHs), i.e., Green Rust (GR), featured with much higher quality and crystallinity compared to the traditionally synthesized ones. Monolayer Fe2+–Fe3+ LDH nanosheets with a thickness of ∼0.8 nm were derived from the GR product. In addition, a series of Ni-bearing Fe-rich LDH nanosheets were successfully prepared by the same method. The OER catalytic performance of the obtained Fe-rich LDH nanosheets achieved a small overpotential with η = 290 mV@10 mA cm–2 in 1 M KOH, which either outperforms or is comparable to the most active Ni–Fe LDH catalysts. The monolayer Fe2+–Fe3+ LDH nanosheets may be ideal for exploring the fundamental physicochemical properties of iron hydroxides from a molecular-scale perspective as well as serving as a building block for the assembly with other functional materials to obtain hybrid nanocatalysts.

Cu2S@NiFe layered double hydroxides nanosheets hollow nanorod arrays self-supported oxygen evolution reaction electrode for efficient anion exchange membrane water electrolyzer

Herein, we prepared highly active self-supported Cu2S@NiFe layered double hydroxides nanosheets (LDHs) oxygen evolution reaction (OER) electrode (Cu2S@NiFe LDHs/Cu foam) with three-dimensional (3D) multilayer hollow nanorod arrays structure, which is composed of the outer layer (two-dimensional (2D) NiFe LDHs) and the inner layer (one-dimensional (1D) Cu2S hollow nanorod arrays). The unique structure of NiFe LDHs and Cu2S hollow nanorod composites can expose more active sites, and simultaneously promote electrolyte penetration and gas release during the water electrolysis process. Thus, the Cu2S@NiFe LDHs/Cu foam electrode exhibits a significant OER performance, with the overpotentials of 230 and 286 mV at 50 and 100 mA cm−2, respectively. Anion exchange membrane water electrolyzer (AEMWE) with the prepared electrode can attain a voltage of 1.56 V at the current density of 0.50 A cm−2, showing a good performance that is comparable to the-state-of-the-art AEMWE in 1 M KOH. In addition, the AEMWE can be run for 300 h at the current density of 0.50 A cm−2. The high performance and good stability of AEMWE are attributed to the special structure of the OER electrode, which can prevent the agglomeration of nanosheets and thus expose more active sites at the edge of the nanosheets.