Layered Double Hydroxide Nanosheets Research Articles

Graphene quantum dots/NiTi layered double hydroxide heterojunction as a highly efficient De-NOx photocatalyst with long persistent post-illumination action

Persistent photocatalysis is an attractive process to broaden the spectrum of environmental applications. Herein, blue luminescent graphene quantum dots (GQD) are incorporated into NiTi-based layered double hydroxide nanosheets (NiTi-LDH) by a facile impregnation method. The enhanced performance of GQD/NiTi-LDH leads to excellent NO photo-removal activity (61 %) and insignificant NO2 release (< 0.6 %), beating the standard TiO2 P25 (48 % and 14.2 %, respectively). Interestingly, after the end of light irradiation period, GQD/NiTi-LDH maintained a NO removal efficiency higher than 20 % for up to 75 min regardless of the previous irradiation time. This De-NOx post-photocatalytic process is the most effective reported at present. The dark/light mechanism is explained by the electron storage capacity of NiTi-LDH under light excitation, which is assisted by the electron migration from GQD to NiTi-LDH. Once the light is shut off, electrons are released and take part in the superoxide radical generation.

Two-Dimensional Chiroptically Active Copper Oxide Nanostructures

Induction of chirality in colloidal nanomaterials has been of great interest in recent years due to the broad range of potential applications for these materials, including in biomedicine, sensing, and photocatalysis. However, the investigation of chirality induction in two-dimensional (2D) nanomaterials is currently at a very early stage, despite their potential unique properties and important applications. Here, we report the synthesis and characterization of chiroptically active 2D copper(II) oxide (CuO)-based nanomaterials for the first time. In our studies we demonstrate that postsynthetic treatment of copper- aluminium carbonate intercalated layered double hydroxide (CuAl-CO3 LDH) nanosheets with phenylalanine at room temperature under basic conditions results in the formation of two-dimensional chiral CuO nanosheets exhibiting strong circular dichroism signals, far beyond the onset of the characteristic signals of the initial ligands.

Ultra-thin CoAl layered double hydroxide nanosheets for the construction of highly sensitive and selective QCM humidity sensor

To achieve real-time monitoring of humidity in various applications, we prepared facile and ultra-thin CoAl layered double hydroxide (CoAl LDH) nanosheets to engineer quartz crystal microbalances (QCM). The characteristics of CoAl LDH were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), Brunauer–Emmett–Telle (BET), atomic force microscopy (AFM) and zeta potential. Due to their large specific surface area and abundant hydroxyl groups, CoAl LDH nanosheets exhibit good humidity sensing performance. In a range of 11.3% and 97.6% relative humidity (RH), the sensor behaved an ultrahigh sensitivity (127.8 Hz/%RH), fast response (9.1 s) and recovery time (3.1 s), low hysteresis (3.1%RH), good linearity (R2 = 0.9993), stability and selectivity. Besides, the sensor can recover the initial response frequency after being wetted by deionized water, revealing superior self-recovery ability under high humidity. Based on in-situ Fourier transform infrared spectroscopy (FT-IR), the adsorption mechanism of CoAl LDH toward water molecules was explored. The QCM sensor can distinguish different respiratory states of people and wetting degree of fingers, as well as monitor the humidity in vegetable packaging, suggesting excellent properties and a promising application in humidity sensing.

Construction of 0D/1D/2D MXene nanoribbons-NiCo@NC hierarchical network and their coupling effect on electromagnetic wave absorption

The construction of MXene-based composites with rational hierarchical structures and networks has emerged as a promising candidate for high-performance electromagnetic wave (EMW) absorption, stemming from the unpredictable formation of multiple components and multiple interfaces. Herein, a stable and porous 0D/1D/2D MXene nanoribbons (NRs)-NiCo@NC hierarchical network consisting of 0D NiCo alloy embedded in nitrogen (N)-doped carbon (NiCo@NC), 1D Ti3C2Tx MXene nanoribbons, and 2D N-doped carbon nanosheets is rationally constructed for EMW absorption. The “shearing effect” of alkaline KOH can induce the formation of 1D MXene nanoribbons with staggered-connected nanoribbon network and macroporosity, which greatly increases the attenuation of multiple reflections of EMW. Meanwhile, MXene nanoribbons can serve as a structural network for the subsequent growth of 2D NiCo layered double hydroxide (LDH) ultrathin nanosheets as well as a conductive network for conduction loss. The 0D NiCo@NC derived from NiCo LDH nanosheets inherit excellent eddy current losses that contribute to magnetic loss and abundant N heteroatoms that contribute to dipole polarization. Furthermore, thanks to the coupling effect, 0D/1D/2D hierarchical network provides numerous interfaces that contribute to interfacial polarization and considerable exchange resonances that contribute to magnetic loss. As a result, 0D/1D/2D MXene nanoribbons-NiCo@NC hierarchical network exhibits robust EMW absorption performance with a reflection loss (RL) value of −57.1 dB at a thickness of 4.82 mm and a RL value of −33.19 dB at a thickness of only 1.4 mm. This study provides new inspiration for the future construction of EMW absorbers with hierarchical networks.

Facile construction of well-defined hierarchical NiFe2O4/NiFe layered double hydroxides with a built-in electric field for accelerating water splitting at the high current density

Interfacial charge redistribution induced by a strong built-in electric field can expertly optimize the adsorption energy of hydrogen and hydroxide for improving the catalytic activity. Herein, we develop a well-defined hierarchical NiFe2O4/NiFe layered double hydroxides (NFO/NiFe LDH) catalysts, exhibiting superior performance due to the strong interfacial electric field interaction between NiFe2O4 nanoparticle layers and NiFe LDH nanosheets. In 1 M KOH, NFO/NiFe LDH needs 251 mV and 130 to drive 50 and 10 mA cm−2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Moreover, only 1.517 V cell voltage is needed to reach 10 mA cm−2 towards overall water splitting. Notably, under simulated industrial electrolysis conditions, NFO/NiFe LDH only needs 289 mV to drive 1000 mA cm−2. This work puts a deep insight into the role of the built-in electric field in transition metal-based catalysts for accelerating water splitting and scalable industrial electrolysis applications.

(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.

Chemiresistive gas sensors based on layered double hydroxides (LDHs) structures: A review

A wide range of materials and nanomaterials have been considered gas sensors due to the growing needs of developed and developing societies. It has been more than six decades since Taguchi introduced the first commercial gas sensor, yet the development of sensors has grown exponentially and has not slowed down. Researchers always look for new materials with more efficient morphologies. It can probably be said that one of the newest materials discussed is LDH nanosheets, which has been discussed for less than two decades. Thus, in this review, after defining the general structure of LDH and giving a general description of nanomaterials, we have discussed the relevant terms and various methods of synthesis. The film preparation of nanomaterial sensor is then discussed in detail as a scalable approach in line with the various methods of nanomaterial synthesis (especially with a focus on LDH nanosheets). The following is discussed the unique properties of LDH nanosheets and their effect on the detection of various contaminants. Since LDH nanomaterials fall into both n- and p-type categories, the pollutant (gas) measurement approach has been investigated in both categories. This creates a specific comparative approach for the reader. Concisely, this study describes the use of LDH nanosheets in the field of gas sensors and may provide the idea for more extensive and practical research on LDHs.

Layered double hydroxides nanosheets for capturing chloride ions in magnesium oxychloride cement

As an alternative inorganic cementitious material, the application of magnesium oxychloride cement (MOC) is often limited due to its poor water resistance, which caused by the migration of Cl- to the surface. In this research, magnesium aluminum layered double hydroxides (Mg2Al-LDH) nanosheets were used to capture the free Cl- in MOC paste taking advantage of the enormous specific surface area of the Mg2Al-LDH nanosheets with ultrathin structure. The Cl- adsorption capacity of Mg2Al-LDH nanosheets in KCl solution was one order of magnitude higher than that of LDH particles prepared traditionally. The scumming of the MOC cube under high humidity was efficiently avoided at the optimum dosage of 2.0% Mg2Al-LDH nanosheets. The compressive strength of the MOC cured under sealed conditions increased by 13–118% over the control sample at various dosages in the range of 0.5–2.0%, and the maximum value of compressive strength was obtained at optimum Mg2Al-LDH dosage of 2.0%. The morphology of MOC under high humidity curing showed that more rod-like hydration products were formed by adding LDH nanosheets into MOC paste. The results demonstrated a suitable dosage of LDH nanosheets not only increased the efficiency of capturing Cl-, but also stimulated the formation of rod-like crystals and enhanced the compressive strength of the MOC cube.

Influence of Mg[sbnd]Al layered double hydroxide nanosheets on the structure and properties of Ni[sbnd]Fe[sbnd]P composite coatings

NiFeP/MgAl layered double hydroxide (LDH) composite coatings with high corrosion and wear resistance were prepared by electroless deposition. A series of test methods was used to comprehensively evaluate the crystal structure, surface morphology, element composition, roughness of the composite coating. The anti-wear and anti-corrosion performances of NiFeP/MgAl LDH (the following are all expressed as NiFeP/LDH) composite coatings were investigated. The deposition mechanism of the NiFeP/LDH alloy was rationalised. The results show that the MgAl LDH nanosheets were uniformly distributed in the NiFeP coating due to ion adsorption. The corrosion potential of NiFeP coatings in 3.5 wt% NaCl solution at 25 °C was −0.458 V vs. SCE, while the corrosion potential of NiFeP/LDH (0.4 g L−1) was −0.334 V vs. SCE. The coating shows adhesive wear during the friction test. The wear resistance of the NiFeP/LDH composite coating was much higher than that of the NiFeP coating. The two-dimensional lamellar nanomaterial LDH was good reinforcement phases for the NiFeP matrix.

MOF-derived Mo-CoP@NiFe LDH hierarchical nanosheets for high-performance hybrid supercapacitors

The well-designed hierarchical nanosheets composed of different components can enhance specific capacitances and cycling stabilities of electrode materials. Herein, [email protected] layered double hydroxide (LDH) hierarchical nanosheets were prepared by growing NiFe LDH nanosheets on MOF-derived ultrathin Mo-CoP nanosheets fabricated by etching Co-MOF with Mo ions. The hierarchical nanosheet structure can facilitate the transport of electrons/ions and provide numerous electroactive sites. Furthermore, the synergistic effects between the active materials provided more oxidation states for redox reactions. Owing to the hierarchical nanosheets and the synergistic effects between Mo-CoP and NiFe LDH, the [email protected] LDH electrode exhibited a large specific capacity of 1655 C g−1 (2796 F g−1) and good long-term stability with 79.6 % capacity retention after 8000 cycles. Additionally, the hybrid supercapacitor (HSC) delivered an energy density of up to 48.6 Wh kg−1 at 800 W kg−1 and outstanding cycling stability (90.6 % retention of the initial capacitance over 20,000 cycles).

One-pot preparation of La(OH)3 nanoparticles and NiMn LDH nanosheets with mutual support structure as cathode for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion battery (ZIB) is a promising electrochemical energy storage device, which combines high safety and low cost of water-based batteries, as well as the advantages of high theoretical capacity and low redox potential. In this work, a transition metal hydroxide material (La(OH) 3 /NiMn LDH) with a composite structure of nanosheets and nanoparticles has been synthesized by a simple hydrothermal reaction. In the electrochemical process, different structures support and restrict each other, which improves the stability of the structure while also buffering the volume shrinkage/expansion during the electrochemical process. The combination of NiMn LDH and La(OH) 3 is also in favor of material’s conductivity. Used as ZIBs cathode material, the La(OH) 3 /NiMn LDH composite structure achieves a better electrochemical performance than the single structure of other hydroxides. It’s specific capacity of the La(OH) 3 /NiMn LDH electrode can reach 284.2 mA h g -1 at the current density of 1 A g -1 . Furthermore, at higher current density of 5 A g -1 , 106.3 mA h g -1 of specific capacity is retained. At the same time, the hydroxyl on hydroxide surface and water molecules in the aqueous electrolyte will undergo surface remodeling, stabilize H + at the electrode and electrolyte interface, and promote the diffusion of H + into the material, thereby the electrochemical performance can be enhanced. • Multiple metal hydroxides are compounded together by one-pot hydrothermal method. • La(OH) 3 /NiMn LDH has a composite structure of nanosheets and nanoparticles. • The capacity of La(OH) 3 /NiMn LDH is 284.2 mA h g -1 at 1 A g -1 . • The La(OH) 3 /NiMn LDH cathode displays high energy density of 411.5 Wh kg -1 .

Enhance methanol-sensing properties based on Ag functionalized monolayer LDH nanosheet: A combined experimental and theoretical calculation investigation

Layered double hydroxides has been greatly explored for gas sensor applications due to their highly tunable chemical composition and unique layer structure. In this work, an investigation combined experimental and theoretical on Ag functionalized monolayer ZnAl-LDH (Ag/LDH) is performed for excellent methanol sensing performance. The monolayer ZnAl-LDH nanosheets was firstly prepared via an inverse-microemulsion method to reduce the stacking of LDHs. Then Ag nanoparticles (NPs) were successfully introduced on the surface of monolayer LDH by glucose reduction method. The Ag/LDH nanocomposite shows Ag NPs uniformly attached on the monolayer LDH nanosheet with large specific surface area. Benefiting from the unique microstructure of monolayer LDH and Ag functionalization, the Ag/LDH gas sensor exhibits about 23-fold enhancement in response value to 25 ppm methanol at room temperature compared with multilayer LDHs sensor. Meanwhile, the as-prepared sensor can detect 500 ppb methanol and exhibits extremely fast response-recovery characteristics upon 10–200 ppm methanol. Further gas adsorption calculations based on first principles were performed to clarify the key contribution of Ag NPs to methanol adsorption and the corresponding gas mechanism is also proposed. Above all, the present work indicates that the functionalization of Ag NPs is highly potential for enhancing the response LDH towards methanol vapor. • Combination of experiment and first-principles calculations. • Monolayer LDH nanosheets with uniformly attached Ag NPs were prepared. • The Ag/LDH sensor shows rapid response and recovery characteristic to methanol at room temperature. • The as-fabricated gas sensor could detect as low as 500 ppb methanol with a response of 3.35% at room temperature.

Inducing the SnO2-based electron transport layer into NiFe LDH/NF as efficient catalyst for OER and methanol oxidation reaction

• Introduce the electron transport layer SnO 2 between NiFe LDH and conductive substrate NF was first reported. • SnO 2 nanosheets are interwoven to form a sponge-like 3D structure, which promotes the formation of relatively smaller and thinner NiFe LDH nanosheets, thereby generating more active sites and reducing electron transmission resistance. • It was verified that the electronic structure of Ni and Fe was optimizing via the introduction of SnO 2 . • NiFe LDH@SnO 2 /NF possesses a low overpotential of 234 mV at 10 mA cm −2 for OER and 1.396 V at 10 mA cm −2 for methanol oxidation reaction. In an electrocatalyst with a heterointerface structure, the different interfaces can efficiently adjust the catalyst's conductivity and electron arrangement, thereby enhancing the activity of the electrocatalyst. Ultrathin and smaller NiFe LDH was successfully constructed on the surface of SnO 2 nanosheet supported NF by layer by layer assembly, and exhibits lower overpotential of 234 mV at a current density of 10 mA cm −2 , which only increases by 6.4% even at a high current density of 100 mA cm −2 . The excellent OER activity of catalyst is attributed to the contribution of the semiconductor SnO 2 electron transport layer. Through experiments and characterization, 3d structure SnO 2 nanosheets control the growth of ultra-thin nickel-iron, the hierarchical interface between SnO 2 and NiFe LDH can change the electron arrangement around the iron and nickel active centers at the interface, resulting the valence states of iron slightly increased and Ni 3+ content increased. The result will promote the oxidation of water. Meanwhile, the SnO 2 semiconductor as electron transport layer is conducive to trapping electrons generated in oxidation reaction, promoting electrons transferring from the NiFe LDH active center to the Ni substrate more quickly, and enhance the activity of NiFe LDH. It also shows excellent activity in an electrolyte solution containing 0.5 M methanol and 1 M KOH, and only 1.396 V (vs. RHE) is required to drive a current density of 10 mA cm −2 .

Dynamic Changes of Ni-Al LDH Nanosheets under Potential Cycling Investigated by In Situ Electrochemical Atomic Force Microscopy

Nickel-aluminum layered double hydroxides (Ni-Al LDHs) are widely used in energy storage and conversion devices, and the impact of the Ni/Al molar ratio on the structural evolution and kinetic process is of great significance for improving reaction kinetics and efficiency. In this paper, the morphological evolutions and nanomechanical property changes of Ni-Al-n LDH (n is the Ni/Al molar ratio) nanosheets during potential cycling were explored by in situ electrochemical atomic force microscopy. The conversion of Ni2+ into Ni3+ and the amphoteric properties of Al3+ during potential cycling resulted in the dissolution of Ni-Al-n LDH nanosheets. The dissolution rate of Ni-Al-2 LDH nanosheets was slower than those of Ni-Al-2.5 LDH and Ni-Al-3 LDH nanosheets. Meanwhile, the Young’s modulus value of the dissolved area was much larger than that of the undissolved area, and the dissolved area exhibited a harder property. It was attributed to the different microcrystalline structures of Ni-Al LDH nanosheets affected by the Ni/Al molar ratio and the rearrangement of Ni2+ and Al3+ during the reaction. The slow dissolution of Ni-Al-2 LDH nanosheets was beneficial to improving the electrochemical performance, while the fast dissolution of Ni-Al-2.5 LDH and Ni-Al-3 LDH nanosheets was not conducive to the electrochemical performance. Understanding the effect of the Ni/Al molar ratio on the morphological evolutions and nanomechanical property changes of Ni-Al LDH nanosheets during potential cycling has important guiding significance for the subtle compositional modification and structural design of Ni-Al LDHs as an electrode material.

Multi-hierarchy heterostructure assembling on MnO2 nanowires for optimized electromagnetic response

One-dimensional (1D) nanomaterials allow reflection of electromagnetic (EM) waves due to large anisotropy and aspect ratio. It is still a challenge to optimize the impedance matching characteristic for strong EM dissipation of 1D nanomaterials. Herein, we propose a strategy of incorporating two-dimensional (2D) layered double hydroxides (LDHs) sheets with 1D nanowires to reinforce interactions with EM waves. Wherein, 1D MnO2 nanowires are used to support the LDH nanosheets, which facilitates the EM waves capture and impedance matching characteristics. Moreover, the heterogeneous interfaces and vacancies contributes to the polarization loss as well. As a consequence, the minimum reflection loss (RLmin) of MnO2@ZnCoNi-LDHs demonstrates −56.3 dB at 2.4 mm and the broad effective absorption bandwidth (fE) reaches 4.56 GHz at 2.1 mm. This heterogeneous structure assembly strategy can be served as a reference for refining the absorption performance of 1D EM absorbers.

Triethanolamine-assisted synthesis of NiFe layered double hydroxide ultrathin nanosheets for efficient oxygen evolution reaction

Water electrolysis is a promising technique for producing high-quality hydrogen, the application of which is impeded by the sluggish oxygen evolution reaction (OER) process. In this study, ultrathin nickel–iron layered double hydroxide (NiFe LDH) nanosheets were successfully synthesized through a facile hydrothermal reaction with the assistance of triethanolamine (TEA). Morphological and structural characterizations revealed that the presence of TEA modified the morphology of NiFe LDH, facilitated the synthesis of high-purity NiFe LDH, improved the crystallinity of NiFe LDH and resulted in a slight decrease in specific surface area. X-ray photoelectron spectroscopy (XPS) analysis demonstrated the modulation of the electronic structure engendered by the addition of TEA, with nickel and iron appearing in high valence state in the resulting NiFe LDH nanosheets. The as-prepared NiFe LDH nanosheets possessed outstanding OER activity with fast kinetics, exhibiting a low overpotential of 261 mV to achieve a current density of 10 mA cm−2 and a small Tafel slope of 32.5 mV dec−1 in 1 M KOH. The excellent OER performance and rapid OER kinetics are mainly attributed to the high-valence Ni and Fe rather than the modification in the morphology and microstructure.

NiFe Layered Double Hydroxide Nanosheets Anchored on Cobalt Nanocrystal Matrixes as Electrocatalysts for Oxygen Evolution

NiFe Layered Double Hydroxide Nanosheets Anchored on Cobalt Nanocrystal Matrixes as Electrocatalysts for Oxygen Evolution

MnCo-Layered double hydroxides nanosheets supported Pd nanoparticles for complete catalytic oxidation of formaldehyde at room temperature

Removal of gaseous formaldehyde by room-temperature catalytic oxidation has promising applications. The rational design of the structure of catalyst to improve the ability of activated key species (adsorbed oxygen and hydroxyl) through understanding the reaction mechanism can improve the catalytic activity. In this paper, Pd nanoparticles were deposited on pre-reduction uniform LDH nanosheets to prepare Pd-decorated sodium borohydride-reduced Mn/Co layered double hydroxides (Pd/LDH-NaBH4). The transition metal (Mn and Co) doping of Pd improved the catalyst's ability to activate oxygen and formaldehyde, and the support of LDHs increased the hydroxyl concentration of the catalyst. Pd/LDH-NaBH4 showed reduced valence of Pd, improved dispersion of Pd NPs, and retention of abundant hydroxyl groups on LDH. Characterizations revealed that the synergistic effect of the supported Pd NPs and LDH, as well as many oxygen vacancies, was responsible for the effective removal of HCHO by Pd/LDH-NaBH4 catalyst at ambient temperature. This study further developed a new catalyst for HCHO oxidation, which may provide a new idea for the removal mechanism of oxidized HCHO.

VO4 -Modified Layered Double Hydroxides Nanosheets for Highly Selective Photocatalytic CO2 Reduction to C1 Products.

The conversion of CO2 into high-value added chemicals driven by solar energy is an effective way to solve environmental problems, which is, however, largely restricted by the competition reaction of the hydrogen evolution reaction (HER) and easy electron-hole recombination, etc. Herein, VO4 -supported ultrathin NiMgV-layered double hydroxide (V/NiMgV-LDH) nanosheets are successfully fabricated, and the extended X-ray absorption fine structure (EXAFS) and density function theory (DFT) calculations reveal that VO4 species are located on the top of V atoms in the NiMgV-LDH laminate. The V/NiMgV-LDH is proved to be highly efficient for the photocatalytic CO2 reduction reaction (CO2 PR) with high selectivity of 99% for C1 products and nearly no HER (<1%) takes place under visible light. Contrast experiments using NiMgV-LDH as the catalyst for CO2 PR show a CO selectivity of 71.40% and a H2 selectivity of 28.11%. Such excellent performance of V/NiMgV-LDH can be attributed to the following reasons: 1) the V/NiMgV-LDH modulates the band structure and promotes the separation of electrons and holes; 2) strong bonding between V/NiMgV-LDH and CO* and H* facilitates the hydrogenation to form CH4 and inhibits the formation of by-product H2 at the same time.

Mechanochemical synthesis of ZIF(Zn, Co)/NixCoyAlz-LDH composite by solid state ion exchange as advanced materials for pseudocapacitor electrode

Metal-organic frameworks (MOFs), and layered double hydroxides (LDHs) as worthy hot-spot materials have gained substantial attention for electrochemical energy storage and conversion applications as a result of their structural diversities, excellent physical properties, and promising electrochemical performance. In this work, we synthesized composite materials comprised of ZIF-8 and NiCoAl-LDHs via a mechanochemical method and in-situ solid state ion exchange. The findings have shown that the synergetic effects between ZIF-8 and LDHs in composite materials and tuning of the percentages of Ni and Co in LDHs have a positive contribution to enhancing electrochemical performance in supercapacitors. In this regard, among pure LDHs and ZIF-8\\NixCoyAl0.33 LDHs, ZIF-8\\Ni(17%)Co(50%)Al(33%)-LDH indicated higher specific capacitance of 256 F g−1 and higher rate of performance. In ZIF-8/Ni(17%)Co(50%)Al(33%)-LDH, LDH nanosheets’ structure improves the conductivity of ZIF-8, and optimized bimetal Ni-Co provides more active sites. In addition, the asymmetric supercapacitor (ASC) assembled by ZIF-8/Ni(17%)Co(50%)Al(33%)-LDH as the cathode and activated carbon (AC) as the anode achieved a good performance in terms of specific capacity, energy density, and cyclic stability. For instance, the ASC delivered a maximum energy density of 184 Wh kg−1 at 1291 W kg−1 and outstanding capacitance retention of 91% after 5000 cycles. This study demonstrates that the interaction between different element ratios in LDHs and the composition of LDHs with ZIFs (porous and redox-active MOFs) has significant effects on using ZIFs/LDHs electrode materials in advanced supercapacitor applications.