Recent advances in flat sheet mixed matrix membrane modified by Mg-based layered double hydroxides(LDHs)for salt and organic compound separations

Magnesium(Mg)is a widely used and attractive metal,known for its unique physical and chemical properties,and it has been employed in the manufacture of many practical materials.Layered Double Hydroxides(LDHs),particularly Mg-based LDHs,rank among the most prevalent two-dimensional materials utilized in separation processes,which include adsorption,extraction,and membrane technology.The high popularity of Mg-based LDHs in separation applications can be attributed to their properties,such as excellent hydrophilicity,high surface area,ion exchangeability,and adjustable interlayer space.Currently,polymer membranes play a pivotal role in semi-industrial and industrial separation processes.Consequently,the development of polymer membranes and the mitigation of their limitations have emerged as compelling topics for researchers.Several methods exist to enhance the separation performance and anti-fouling properties of polymer membranes.Among these,incorporating additives into the membrane polymer matrix stands out as a cost-effective,straightforward,readily available,and efficient approach.The use of Mg-based LDHs,either in combination with other materials or as a standalone additive in the polymer membrane matrix,represents a promising strategy to bolster the separation and anti-fouling efficacy of flat sheet mixed matrix polymer membranes.This review highlights Mg-based LDHs as high-potential additives designed to refine flat sheet mixed matrix polymer membranes for applications in wastewater treatment and brackish water desalination.

Deprotonated of layered double hydroxides during electrocatalytic water oxidation for multi-cations intercalation

Aqueous rechargeable batteries using abundant multi-ion cations have receivedincreasing attention in the energy storage field for their high safety and low cost.Layered double hydroxides(LDHs)possess a two-dimensional structure andexhibit great potential as cathodes for multi-ion intercalation.However,theinsufficient active sites of LDHs result in low capacities in the discharging process.Interestingly,the LDHs after the deprotonation process exhibit favorable electrochemicalperformance of multi-cation intercalation.The deprotonation process ofLDHs has been widely found in the oxygen evolution reaction and energy storagefield,where LDHs lose H in laminates and converts to deprotonatedγ-phaseMOOHs(MOOs).Herein,we take a comprehensive overview of the dynamicsstructure transformation of the deprotonation process of LDHs.Furthermore,thedevelopment of advanced aqueous battery cathode and metal battery anode basedon deprotonated LDHs for energy storage is explored and summarized.Finally,theperspective of deprotonated LDHs in the energy storage field is discussed.

Balancing loading mass and gravimetric capacitance of NiCo-layered double hydroxides to achieve ultrahigh areal performance for flexible supercapacitors

Delivering high areal capacitance(CA)at high rates is crucial but challenging for flexible supercapacitors.CA is the product of areal loading mass(MA)and gravimetric capacitance(CW).Finding and understanding the balance between MA and CW of supercapacitor materials is significant for designing high-CA electrodes.Herein,we have systematically studied the correlation between MA and CW of the nanosheet arrays of NiCo-layered double hydroxide(NiCo-LDH),which were electrodeposited on carbon cloth with different heights to adjust the MA,accompanied by the interlayer distance regulation to improve the CW.The optimal CW performance is achieved at the best charge transfer kinetics for each of MA series.The NiCo-LDH electrode with the suitable MA(2.58 mg cm^(-2))and the relatively high CW(1918 F g^(-1) at 5 A g^(-1) and 400 F g^(-1) at 150 A g^(-1))present a high CA of 4948 mF cm^(-2) at 12.9 mA cm^(-2) and a record-high 1032 mF cm^(-2) among LDHs-based flexible electrodes at an ultrahigh current density of 387 mA cm^(-2).The corresponding flexible supercapacitor coupled with activated carbon delivers a high energy density of 0.28 mWh cm^(-2) at an ultrahigh power density of 712 mW cm^(-2),showing great potential applications.

Adsorption of Cd（II） on Zn-AI LDHs （Layered Double Hydroxides） Intercalated with Chelating Agents EDTA

The hydrotalcite-like compound [Zn2AI（OH）6]NO3-mH20 （shorted as ZnAI-NO3） was intercalated with the chelating agent EDTA （ethylene diamine tetraacetic acid） by anion exchange to uptake cadmium ion from aqueous solutions. The materials synthesized in this work were characterized by chemical analysis, FT-IR （fourier transform infrared spectroscopy）, XRD （X-ray powder diffraction） to confirm their properties. In order to investigate the optimum conditions for Cd（II） adsorption, the amount of Cd（ll） adsorbed by Zn-AI LDHs intercalated with EDTA （ZnAI-EDTA） under different conditions （i.e., adsorbent dosage, temperature and contact time） were determined by ICP-AES （inductively coupled plasma-atomic emission spectrometry）. Adsorption isotherms of Cd（II） onto ZnA1-EDTA were measured at varying initial Cd concentrations （0.05 mg/L to 1 mg/L） under optimized conditions. The data were applied to Langmuir and Freundlich isotherms model, and well fitted by the Freundlich isotherms model. The pseudo-second-order kinetic model was more adequate to describe the kinetic in this case.

Synthesis and Characterization of LDHs （Layered Double Hydroxides） Intercalated with EDTA （Ethylenediaminetetracetic Acid） or EDDS （N, N＇-1, 2-Ethanediylbis-l-Aspartic Acid）

The hydrotalcite-like compound [Zn2Al·（OH）6] NO3·nH2O and [Mg2Al·（OH）6] NO3·nH2O （shorted as ZnA1-NO3 and MgAl-NO3） was intercalated with the chelating agent EDTA （Ethylenediaminetetraacetic Acid） and EDDS （N, N＇-1, 2-Ethanediylbis-1-Aspartic Acid） by anion exchange. The materials synthesized in this work were characterized by chemical analysis, FT-IR （Fourier Transform Infrared Spectroscopy）, SEM （Scanning Electron Microscopy） and XRD （Powder X-ray Diffraction） to confirm their properties. In order to discuss the adsorption capacity of LDHs （Layered Double Hydroxides）, the adsorption experiment was investigated under the optimum condition （10 mg, 25℃ and 100 μg·L-1）. The amount of metallic ions adsorbed by LDHs intercalated with EDTA and precursor LDHs were determined by ICP-AES （Inductively Coupled Plasma-Atomic Emission Spectrometry） and AAS （Atomic Absorption Spectrometry）. The intercalation of EDTA leads to improve the adsorption capacity of LDHs. LDHs intercalated with chelating agents have generally high affinity for removing metallic ions, and they can be efficient adsorbents for metallic ions.

Self-assembling organomodified Co/Al based layered double hydroxides (LDH) via one-step route

The preparation of self-assembling organomodified Co/Al-layered double hydroxide(LDH)via one-step route was studied. A common surfactant,sodium dodecylbenzenesulfonate(DBS),was employed as an organic modifier.The behavior and structure of self-assembled intercalated organic Co/Al-LDH were investigated by FTIR,SEM,WAXS,element analysis and TGA.Based upon the WAXS results and calculation by Bragg equation,the interlayer distance(d value)for organic Co/Al-LDH is enlarged from 0.75 nm to 3.10 nm,showing that the self-assembling behavior has been carried out successfully.Considering the observation from SEM, the product shows the morphology of organic Co/Al-LDH of a layered structure.In addition,FTIR,element analysis and TGA analysis show that the modifier is intercalated into the gallery of the Co/Al-LDH.Since organic modification for nanofiller is deemed to be necessary before applying it into polymer,the successful preparation of organomodified Co/Al-LDH will be significantly beneficial to the preparation and investigation of novel polymer/LDH nanocomposite.

Synthesis and highly efficient photocatalytic activity of mixed oxides derived from ZnNiAl layered double hydroxides

ZnO/NiO/ZnAl2O4 mixed-metal oxides were successfully synthesized through a hydrotalcite-like precursor route, in which appropriate amounts of metal salts solutions were mixed to obtain a new series of ZnNiAl layered double hydroxides（LDHs） as precursors, followed by calcination under different temperatures. The as-obtained samples were characterized by SEM, HRTEM, TEM, XRD, BET, TG-DTA, and UV-Vis spectra techniques. The photocatalytic activities of the samples were evaluated by degradation of methyl orange（MO） under the simulated sunlight irradiation. The effects of Zn/Ni/Al mole ratio and calcination temperature on the composition, morphology and photocatalytic activity of the samples were investigated in detail. The results indicated that compared with ZnNiAl-LDHs, the mixed-metal oxide showed superior photocatalytic performance for the degradation of MO. A maximum of 97.3% photocatalytic decoloration rate within 60 min was achieved from the LDH with the Zn/Ni/Al mole ratio of 2：1：1 and the calcination temperature of 500 ℃, which much exceeded that of Degussa P25 under the same conditions. The possible mechanism of photocatalytic degradation over ZnO/NiO/ZnAl2O4 was discussed.

Enhancing the stability of Ni Fe-layered double hydroxide nanosheet array for alkaline seawater oxidation by Ce doping

Electrocatalytic hydrogen production from seawater holds enormous promise for clean energy generation.Nevertheless,the direct electrolysis of seawater encounters significant challenges due to poor anodic stability caused by detrimental chlorine chemistry.Herein,we present our recent discovery that the incorporation of Ce into Ni Fe layered double hydroxide nanosheet array on Ni foam(Ce-Ni Fe LDH/NF)emerges as a robust electrocatalyst for seawater oxidation.During the seawater oxidation process,CeO_(2)is generated,effectively repelling Cl^(-)and inhibiting the formation of Cl O-,resulting in a notable enhancement in the oxidation activity and stability of alkaline seawater.The prepared Ce-Ni Fe LDH/NF requires only overpotential of 390 m V to achieve the current density of 1 A cm^(-2),while maintaining long-term stability for 500 h,outperforming the performance of Ni Fe LDH/NF(430 m V,150 h)by a significant margin.This study highlights the effectiveness of a Ce-doping strategy in augmenting the activity and stability of materials based on Ni Fe LDH in seawater electrolysis for oxygen evolution.

Colloid of Delaminated Layered Double Hydroxides:a Novel Type of LDH-based Catalyst

The colloid of delaminated layered double hydroxides(LDHs), a new LDH-based catalyst, is described. The semi-heterogeneous delaminated colloidal MgPdA1-LDH, in which the total surface of catalytic site-bearing lamellae was rendered accessible for chemical reactivity, showed excellent catalysis toward Suzuki reaction. The turnover frequency of this catalyst for Suzuki reaction between bromobenzene and phenylboronic acid is about 8000 h^-1.

Defective Nickel-Iron Layered Double Hydroxide for Enhanced Photocatalytic NO Oxidation with Significant Alleviation of NO2 Production

Photocatalysis offers a sustainable means for the oxidative removal of low concentrations of NOx(NO,NO2,N2O,N2O5,etc.)from the atmosphere.Layered double hydroxides(LDHs)are promising candidate photocatalysts owing to their unique layered and tunable chemical structures and abundant surface hydroxide(OH)moieties,which are hydroxyl radical(OH)precursors.However,the practical applications of LDHs are limited by their poor charge-separation ability and insufficient active sites.Herein,we developed a facile N_(2)H_(4)-driven etching approach to introduce dual Ni^(2+)and OHvacancies(Niv and OHv,respectively)into NiFe-LDH nanosheets(hereafter referred to as NiFe-LDH-et)to facilitate improved charge-carrier separation and active Lewis acidic site(Fe^(3+)and Ni^(2+)exposed at OHv)formation.In contrast to inert pristine LDH,NiFe-LDH-et actively removed NO under visible-light illumination.Specifically,Ni_(76)Fe_(24)-LDH-et etched with 1.50 mmol·L^(-1)N_(2)H_(4)solution removed 32.8%of the NO in continuously flowing air(NO feed concentration:500 parts per billion(ppb))under visible-light illumination,thereby outperforming most reported catalysts.Experimental and theoretical data revealed that the dual vacancies promoted the production of reactive oxygen species(O_(2)·^(-)andOH)and the adsorption of NO on the LDH.In situ spectroscopy demonstrated that NO was preferentially adsorbed at Lewis acidic sites,particularly exposed Fe^(3+)sites,converted into NO+,and subsequently oxidized to NO3without the notable formation of the more toxic intermediate NO2,thereby alleviating risks associated with its production and emission.

Effective multifunctional coatings with polyvinylpyrrolidone-enhanced ZIF-67 and zinc iron layered double hydroxide on microarc oxidation treated AZ31 magnesium alloy

Modulating metal-organic framework’s(MOF)crystallinity and size using a polymer,in conjunction with a high surface area of layered double hydroxide,yields an effective strategy for concurrently enhancing the electrochemical and photocatalytic performance.In this study,we present the development of an optimized nanocomposite,denoted as 0.5PVP/ZIF-67,developed on AZ31 magnesium alloy,serving as an efficient and durable multifunctional coating.This novel strategy aims to enhance the overall performance of the porous coating through the integration of microarc oxidation(MAO),ZnFe LDH backbone,and ZIF-67 formation facilitated by the addition of polyvinylpyrrolidone(PVP),resulting in a three-dimensional,highly efficient,and multifunctional material.The incorporation of 0.5 g of PVP proved to be effective in the size modulation of ZIF-67,which formed a corrosion-resistant top layer,improving the total polarization resistance(R_(p)=8.20×10^(8)).The dual functionality exhibited by this hybrid architecture positions it as a promising candidate for mitigating environmental pollution,degrading 97.93%of Rhodamine B dye in 45 min.Moreover,the sample displayed exceptional degradation efficiency(96.17%)after 5 cycles.This study illuminates the potential of nanocomposites as electrochemically stable and photocatalytically active materials,laying the foundation for the advancements of next-generation multifunctional frameworks.

Exploring the role of solvents in structural regulation during ultrasonic synthesis of Co/Ni-layered double hydroxide for oxygen evolution reaction

Cobalt-based layered double hydroxides(LDHs)are highly sought after by researchers due to their low-cost,high efficiency and stability for oxygen evolution reaction(OER)in water electrolysis.The OER performance of these LDHs is closely related to their morphology and electronic structure.However,there is a lack of theory on how to control reaction conditions to regulate the morphologies.In this paper,the growth mechanism of LDH prepared in different solvents is thoroughly studied.Consequently,the Co/Ni-LDHs exhibiting a 3D hierarchical flower-like structure were synthesized with normal alcohol as a solvent,meanwhile,the thickness of the LDHs can be controlled by the molecular weight of the normal alcohol.By adjusting the suitable Co/Ni ratio and solvent,the Co/Ni0.050-LDH-Me was synthesized and exhibited excellent OER performance.At 10 mA cm^(-2),the overpotential of Co/Ni0.050-LDH-Me is 307 mV,and the Tafel slope is 76.5 mV dec^(-1).

Long-lasting growth regulation on cotton using mepiquat chloride adsorbed layered double hydroxide

Mepiquat chloride(1,1-dimethyl piperidinium chloride,DPC)is a representative plant growth regulator which can regulate the source-sink relationship for yield increase and shape ideal plant type for mechanical cultivation.Here we show a DPC adsorbed layered double hydroxide(DPC-LDH)architecture with enhanced controlled release property and soil distribution.By drip irrigation on cotton,it makes total dosage of DPC reduced from 270 to 90 g/ha,while the frequency decreased from 5 to 2 times.The unique supramolecular interaction is confirmed as the basis of controlled release behavior.Moreover,except for the physical resistance to the sedimentation brought by the lamellar LDH,the enhanced electrostatic interaction makes DPC-LDH the dominant distribution in soil.It improves the efficiency of DPC molecules absorbed by cotton plants and greatly saves the inputs in labor and chemicals.This method is expected to achieve the yield increase and agricultural sustainability by energy saving and emission reduction.

Synthesis and characterization of colored layered double hydroxides for thermal stabilizer

Colored layered double hydroxides （LDHs） can be synthesized by introducing colored cations such as Fe^3＋ and Cr^3 ＋, which call be used as thermal stabilizers for polyvinyl chloride （PVC）. The yellowish Mg/Fe and bluish Mg/Cr LDHs are prepared by the co-precipitation method. The results show that the MgsCr_ CO3 and Mg3Fe_ CO3 colored layered double hydroxides can stabilize PVC for more than 30 min under the thermal aging temperature of 180 ℃. The preparation can use cheap Mg（OH） 2 instead of MgCl2, which produces a much smaller amount of the by-product NH4Cl. It is known that NH4Cl is a cheap fertilizer that is difficult to sell; therefore, the preparation is much greener and more economic than the one using magnesium salt.

Advances in efficient electrocatalysts based on layered double hydroxides and their derivatives

The explore and development of electrocatalysts have gained significant attention due to their indispensable status in energy storage and conversion systems, such as fuel cells, metal–air batteries and solar water splitting cells. Layered double hydroxides（LDHs） and their derivatives（e.g., transition metal alloys, oxides, sulfides, nitrides and phosphides） have been adopted as catalysts for various electrochemical reactions, such as oxygen reduction, oxygen evolution, hydrogen evolution, and COreduction, which show excellent activity and remarkable durability in electrocatalytic process. In this review, the synthesis strategies, structural characters and electrochemical performances for the LDHs and their derivatives are described. In addition, we also discussed the effect of electronic and geometry structures to their electrocatalytic activity. The further development of high-performance electrocatalysts based on LDHs and their derivatives is covered by both a short summary and future outlook from the viewpoint of the material design and practical application.

Recent progress in functionalized layered double hydroxides and their application in efficient electrocatalytic water oxidation

Layered double hydroxides (LDHs), a class of anionic clays consisting of brucite-like host layers and interlayer anions, have been widely investigated in the last decade due to their promising applications in many areas such as catalysis, ion separation and adsorption. Owing to the highly tunable compositi on and uniform distribution of metal cations in the brucite-like layers, as well as the facile exchangeability of intercalated anions, LDHs can be modified and functionalized to form various nanostructures/composites through versatile processes such as anion intercalation and exfoliation, decoration of nanoparticles, selfassembly with other two-dimensional (2D) materials, and controlled growth on conductive supports (e.g., nanowire arrays, nano tubes, 3D foams). In this article, we briefly review the recent advances on both the LDH nano structures and functionalized composites toward the applications in energy conversion, especially for water oxidation.

Layered double hydroxide(LDH)-based materials:A mini-review on strategies to improve the performance for photocatalytic water splitting

The high energy demand we currently face in society and the subsequent large consumption of fossil fuels cause its depletion and increase the pollution levels.The quest for the production of clean energy from renewable and sustainable sources remains open.The conversion of solar energy into hydrogen via the water-splitting process,assisted by pho tores pons ive semiconductor catalysts,is one of the most promising technologies.Significant progress has been made on water splitting in the past few years and a variety of photocatalysts active not only under ultra-violet(UV) light but especially with the visible part of the electromagnetic spectrum have been developed.Layered double hydroxides(LDH)-based materials have emerged as a promising class of nanomaterials for solar energy applications owing to their unique layered structure,compositional flexibility,tunable bandgaps,ease of synthesis and low manufacturing costs.This review covers the most recent research dedicated to LDH materials for photocatalytic water-splitting applications and encompasses a range of synthetic strategies and post-modifications used to enhance their performance.Moreover,we provide a thorough discussion of the experimental conditions crucial to obtaining improved photoactivity and highlight the impact of some specific parameters,namely,catalysts loading,cocatalysts,sacrificial agents,and irradiation sources.This review provides the necessary tools to select the election technique for adequately enhancing the photoactivity of LDH and modified LDH-based materials and concludes with a critical summary that outlines further research directions.

Effect of Layered Double Hydroxides on Ultraviolet Aging Resistance of SBS Modified Bitumen Membrane

Layered double hydroxides （LDHs）/styrene-butadiene-styrene （SBS） eopolymer modified bitumen was prepared by melt blending. The effect of LDHs on the ultraviolet （UV） aging behavior of SBS modified bitumen was investigated. The changes of chemical structures of modified bitumen before and after UV aging were characterized by Fourier transform infrared spectroscopy （FTIR）. The results show that LDHs obviously reduce the variation of softening point and low temperature flexibility of SBS modified bitumen under different UV radiation intensities, which indicates that the UV aging resistance performance of SBS modified bitumen is improved effectively by LDHs. Compared with SBS modified bitumen, the changes of carbonyl, sulfoxide and butadienyl of LDHs/SBS modified bitumen decrease significantly after UV aging according to FTIR analysis, demonstrating that the oxidation and degradation reactions of SBS modified bitumen were restrained effectively by adding LDHs.

Recent advance on VOCs oxidation over layered double hydroxides derived mixed metal oxides

Catalytic oxidation is regarded as one of the most promising strategies for volatile organic compounds(VOCs)purification.Mixed metal oxides(MMOs),after topological transformation using layered double hydroxides(LDHs)as precursors,are extensively used as catalysts for VOCs oxidation due to their uniformity advantage.This review summarizes the developments in the LDH-derived VOCs heterogeneous catalytic oxidation over the last 10 years.Particularly,it addresses the VOCs abatement performance over MMO,noble metal/MMO,core-shell structured MMO,and integral MMO film catalysts originating from LDHs.Moreover,it highlights the water vapor effect and oxidation mechanism.This review indicates that LDH-based catalysts are a category of important VOCs oxidation materials.

Selenium(Ⅵ) removal from caustic solution by synthetic Ca-Al-Cl layered double hydroxides

To extract selenium(Ⅵ)from the highly caustic leachate of copper anode slime,the Ca-Al-Cl layered double hydroxides(Ca-Al-Cl-LDHs)with a formula of Ca2 Al(OH)6 Cl·2 H2 O by three co-precipitation methods were synthesized.A plate-like morphology and hexagonal crystal structure with typical mineral phases and functional groups were identified by the FESEM,XRD,FTIR,BET and XPS analysis.The forward feeding sample exhibits the best adsorption capacity of Se(Ⅵ).The factor experiments then reveal a favorable adsorption process with low temperature,low NaOH concentration and high adsorbent dosage.Furthermore,the adsorption kinetics and isotherm parameters can be well described by the Langmuir isotherm and the pseudo-second-order models,respectively.Accordingly,the maximum adsorption amount of Se(Ⅵ)onto Ca-Al-Cl-LDHs reaches188.6 mg/g at 50 ℃.