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.

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.

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.

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.

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.

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.

Layered double hydroxides:Scale production and application in soil remediation as super-stable mineralizer

Soil contamination by heavy metals has presented severe risks to human health through food chain.As one of the most promising remediation technologies,in-situ immobilization strategy has been widely adopted in practice.However,considering the large quantities of contaminated soil,it is still a huge challenge to design low-cost amendments with strong and long-term immobilization ability.Layered double hydroxides(LDHs)have drawn tremendous attention in fundamental research and practical application because of their unique properties.Moreover,owing to its super-stable mineralization effect to heavy metal ions,LDHs have exhibited great potential in the field of soil remediation.In this work,we mainly focused on the scale production strategy of LDHs with low-cost,and its application in soil remediation.Besides,several key challenges in using LDHs as amendments for immobilization of heavy metal ions are presented.We hope that this mini-review could shed light on the sustainable development of LDHs as amendment for heavy metals in future research directions.

Design, synthesis, and nanoengineered modification of spherical graphene surface by layered double hydroxide (LDH) for removal of As (Ⅲ) from aqueous solutions

In this study, new nano spherical graphene modified with LDH(Layered Double Hydroxide) was prepared and used to remove As(Ⅲ) ion from aqueous solutions. At first, graphene oxide was synthesized from graphite using a well-known Hammer method. The obtained graphene oxide solution was sprayed in octanol solution under different temperatures and sprayed speed as influenced variables. The structure and physical characterization of synthesized spherical graphene oxide were determined by various techniques,including FT-IR, N_(2) adsorption–desorption, SEM, TEM, and EDX. In the next step, the hydrothermal method was applied to deposition LDH on the spherical graphene oxide. The synthesized spherical graphene modified by LDH was used to remove As(Ⅲ) as a toxic heavy metal ion. The effect of influenced variables including p H, contact time, amount of sorbent, and type eluent studied and the optimum values were as 8, 30, 50, and HCl(0.5 mol·L^(-1)), respectively. After optimization, the studied sorbent was shown a high adsorption capacity(149.3 mg·g^(-1)). The adsorption mechanism and kinetic models exhibited good agreement with the Langmuir isotherm and pseudo-second-order trends, respectively. Besides, the synthesized product was tested for seven times without significant loss in its sorption efficiency.

3D Hierarchical Co–Al Layered Double Hydroxides with Long-Term Stabilities and High Rate Performances in Supercapacitors

Three-dimensional(3D) flower-like Co–Al layered double hydroxide(Co–Al-LDH) architectures composed of atomically thin nanosheets were successfully synthesized via a hydrothermal method in a mixed solvent of water and butyl alcohol. Owing to the unique hierarchical structure and modification by butyl alcohol, the electrochemical stability and the charge/mass transport of the Co–Al-LDHs was improved. When used in supercapacitors, the obtained Co–Al-LDHs deliver a high specific capacitance of 838 Fg^(-1) at a current density of 1 Ag^(-1)and excellent rate performance(753 Fg^(-1) at 30 Ag^(-1) and 677 Fg^(-1) at 100 Ag^(-1)), as well as excellent cycling stability with 95% retention of the initial capacitance even after 20,000 cycles at a current density of 5 Ag^(-1). This work provides a promising alternative strategy to enhance the electrochemical properties of supercapacitors.

Synthesis of Ni/Mg/Al Layered Double Hydroxides and Their Use as Catalyst Precursors in the Preparation of Carbon Nanotubes

Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni)∶n(Mg)∶n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. Carbon nanotubes were produced in the catalytic decomposition of propane over the Ni/Mg/Al mixed oxide catalysts. The quality of as-made nanotubes was investigated by SEM and TEM. The nanotubes were multiwall with a high length-diameter ratio and appeared to be flexible. The catalytic activities of these mixed oxides increased with increasing the Ni content. The Ni/Mg/Al mixed oxide with the highest Ni content [n(Ni)/n(Mg)/n(Al)=1/1/1] showed the highest activity and the carbon nanotubes grown on its surface had the best quality.

Porous Cobalt Oxide@Layered Double Hydroxide Core-Shell Architectures on Nickel Foam as Electrode for Supercapacitor

The high performance of an electrode relies largely on a scrupulous design of nanoarchitectures and smart hybridization of electroactive materials.A porous core-shell architecture in which one-dimensional cobalt oxide(Co_3O_4)nanowire cores are grown on nickel foam prior to the growth of layered double hydroxide(LDH)shells is fabricated.Hydrothermal precipitation and thermal treatment result in homogeneous forests of 70-nm diameter Co_3O_4 nanowire,which are wrapped in LDH-nanosheet-built porous covers through a liquid phase deposition method.Due to the unique core-shell architecture and the synergetic effects of Co_3O_4and NiAl-LDH,the obtained Co_3O_4@LDH electrode exhibits a capacitance of 1 133.3F/g at a current density of 2A/g and 688.8F/g at 20A/g(5.3F/cm^(2 )at 9.4mA/cm^(2 )and 3.2F/cm^(2 )at 94mA/cm^2),which are better than those of the individual Co_3O_4nanowire.Moreover,the electrode shows excellent cycling performance with a retention rate of 90.4%after 3 000cycles at a current density of 20A/g.

Advances in Mg-Al-layered double hydroxide steam coatings on Mg alloys:A review

Layered double hydroxide(LDH)coatings on magnesium(Mg)alloys shine brightly in the field of corrosion protection because of their special ion-exchange function.State-of-the-art steam coating as a type of LDH film preparation technique has emerged in recent years because only pure water is required as the steam source and its environmentally friendly LDH coating fits the current need for green development.Moreover,this coating can effectively inhibit the corrosion of the Mg alloy substrate due to the chemical bonding between the coating and the Mg alloy substrate.This review systematically explains cutting-edge advancements in the growth mechanism and corrosion behavior of LDH steam coatings,and analyzes the advantages and limitations of the steam-coating method.The influencing factors including pressure,CO_(2)/CO_(3)^(2-),aluminum content of the substrate alloy,solution type,and acid-pickling pretreatment,as well as the post-treatment of steam-coating defects,are comprehensively elucidated,providing new insights into the development of the in situ steam-coating technique.Finally,existing issues and future prospects are discussed to further accelerate the widespread application of Mg alloys.

Recent advances in the detection and removal of heavy metal ions using functionalized layered double hydroxides:a review

Heavy metal pollution is one of the most severe environmental problems,possessing high ecotoxicity and health risk.Therefore,it is important to develop effective methods and corresponding materials for the detection and removal of heavy metals.Recent studies reveal the great potential of layered double hydroxides(LDHs)in detecting and removing heavy metals owing to their designable structure and tunable surface composition.In this review,we majorly discuss the recently adopted detection and removal of heavy metal ions based on LDHs.This review starts with an introduction of the structural characteristics and functionalization of LDHs.Then,the sensing tactics and mechanisms are introduced regarding LDHbased heavy metal ion detection.Based on the type of interaction,the removal of heavy metal ions with LDHs is summarized into two categories:reversible adsorption and irreversible mineralization.This review ends with a discussion on the challenges and future trends of LDH-based detectors and adsorbents for heavy metal ions.

Structure Engineering of Layered Double Hydroxides(LDHs)for Heterogeneous Catalysis

Layered double hydroxide(LDH)is regarded as an advanced platform material in catalysis and attracts vast attrition recently.As a kind of two-dimensional layered material,it exhibits great advantages including cation-tunability in layer,lattice limitation,topological transformation,ion exchange and intercalation characteristics.It also can be used as building blocks for composite catalytic materials.Over 100 years,a large number of works have been accomplished and researchers made great progress on investigating the LDH-based catalytic materials.In this review,we summarize representative achievements and significant progress in recent years,which mainly include constructing high entropy catalytic material,high dispersion/stability and interfacial supported catalytic material,composite catalytic materials and nano-reactor based on LDH.Furthermore,through collecting the excellent works,we conclude the future development potential of LDH and provide a perspective.

Disposal of wastewater containing Congo Red by synthesizing layer double hydroxide in-situ

Based on the principle of synthesis, a new method was put forward to dispose Congo Red anion-containing dyestuff from wastewater and its feasibility was also examined. The principle of the method is described as follows: Mg2+ and Al3+ are hydrolyzed to form Mg/Al-LDH by adding Mg2+, Al3+ and NaOH in wastewater containing anion dyestuff, which is selectively intercalated with the interlayer of LDH in order to balance positive structural charge. While Mg2+ and Al3+ are co-precipitated to form LDH, the anion dyestuff in wastewater will be removed by LDH synthesized in-situ, as is confirmed by X-ray diffraction analysis of settlings and chemical analysis of aqueous samples. In this work, we studied the influence of Mg/Al mole ratio, pH value, time and temperature of reaction on the removal of anion dyestuff and the use of Mg and Al. The experimental results showed the maximum removal efficiency of anion dyestuff could be attained when pH value was 9.0, and Mg/Al mol ratio was 2∶1, reaction duration was 2 hours, and the effect of temperature was not remarkable, and the removal efficiency could reach 100%. Meanwhile, the Mg and Al added could be made good use of. This technology has the advantage of extraordinary efficiency of wastewater disposal.

LDHs覆膜改性活性炭对水中磷的吸附特性研究

采用水热共沉淀法合成两种层状双金属氢氧化物(MgAl-LDHs和MgFe-LDHs)覆膜于活性炭,并研究了其对水中磷的吸附特性。结果表明,在pH=7、温度为298.15 K、吸附时间为4 h时,MgAl-LDHs和MgFe-LDHs改性基质对磷酸盐最大理论吸附容量分别为3.158 mg/g和4.557 mg/g。吸附过程更加符合Langmuir等温模型和拟二级动力学吸附模型,以均匀单分子层化学吸附为主。当磷酸盐初始浓度为0.5 mg/L和2 mg/L时,MgAl-LDHs改性基质的饱和吸附容量接近MgFe-LDHs改性基质的2倍,MgAl-LDHs改性基质更适合作为吸附剂。LDHs改性基质吸附磷酸盐的热力学参数ΔG_(0)<0、ΔH_(0)<0,说明吸附过程是自发的放热过程,低温更有利于提高吸附效果。

Catalytic applications of single-atom metal-anchored hydroxides:Recent advances and perspective

Developing isolated single atomic noble metal catalysts is one of the most effective methods to maximize noble metal atom utilization efficiency and enhance catalytic performances.Layered double hydroxides(LDHs)are two-dimensional nanoarchitectures in which M^(3+) and M^(2+) sites are atomically isolated due to static repulsions,providing special anchoring sites for single noble metal atoms and enabling the tuning of catalytic activity.Herein,a comprehensive review of the advances in LDHs supported single-atom catalysts(M/LDH SACs)is presented,focusing on the synthetic strategies,structure characterization,and application of M/LDH SACs in energy devices.Strong electronic coupling between single atomic noble metal atoms and corresponding anchoring sites of LDHs determines not only the catalytic activity of M/LDH SACs but also the stability during catalytic reactions.Furthermore,a perspective is proposed to highlight the challenges and opportunities for understanding the reaction mechanism and development of highly efficient M/LDH SACs.

层状双金属氢氧化物(LDHs)对SBS改性沥青抗老化性能的影响研究

为了增强SBS改性沥青(SMB)的抗老化性能,利用层状双金属氢氧化物(LDHs)的独特结构对SMB进行改性。研究了LDHs对SMB的物理性能、高低温流变性能和化学结构的影响规律。研究结果表明:LDHs的加入有助于提高SMB的弹性性能,提升SMB的高温稳定性能;老化后,沥青分子发生氧化反应导致SMB中含氧官能团(S=O和C=O)含量增加,同时SBS分子链发生断裂引起SMB中碳碳双键官能团(C=C)含量减少,这些变化使SMB的物理性能、高温抗车辙性能和低温抗疲劳开裂性能发生劣化,导致其变硬变脆;LDHs的加入可以阻止沥青分子的氧化反应和SBS分子链断裂,减缓沥青分子的老化和SBS老化降解,减轻老化对SMB物理性能和高低温流变性能的破坏,增强SMB的抗老化能力,为建设长寿命的SMB路面提供技术支持。

Selective photocatalytic CO2 reduction over Zn-based layered double hydroxides containing tri or tetravalent metals

Photocatalytic CO2 reduction holds promise as a future technology for the manufacture of fuels and commodity chemicals.However,factors controlling product selectivity remain poorly understood.Herein,we compared the performance of a homologous series of Zn-based layered double hydroxide(ZnM-LDH)photocatalysts for CO2 reduction.By varying the trivalent or tetravalent metal cations in the ZnM-LDH photocatalysts(M=Ti4+,Fe3+,Co3+,Ga3+,Al3+),the product selectivity of the reaction could be precisely controlled.ZnTi-LDH afforded CH4 as the main reduction product;ZnFe-LDH and ZnCo-LDH yielded H2 exclusively from water splitting;whilst ZnGa-LDH and ZnAl-LDH generated CO.In-situ diffuse reflectance infrared measurements,valence band XPS and density function theory calculations were applied to rationalize the CO2 reduction selectivities of the different ZnM-LDH photocatalysts.The analyses revealed that the d-band center(ed)position of the M3+or M4+cations controlled the adsorption strength of CO2 and thus the selectivity to carbon-containing products or H2.Cations with d-band centers relatively close to the Fermi level(Ti4+,Ga3+and Al3+)adsorbed CO2 strongly yielding CH4 or CO,whereas metal cations with d-band centers further from the Fermi level(Fe3+and Co3+)adsorbed CO2 poorly,thereby yielding H2 only(from water splitting).Our findings clarify the role of trivalent and tetravalent metal cations in LDH photocatalysts for the selective CO2 reduction,paving new ways for the development of improved LDH photocatalyst with high selectivities to specific products.

LDHs材料的结构、性质及其应用研究进展

LDHs(layered double hydroxides)是一类具有双金属氢氧化物层结构的新型无机材料,其酸碱性、热稳定性、层间阴离子可交换性以及结构记忆效应等特性在诸多领域中得到了广泛应用,成为当前研究的热点。针对国内外研究现状,本文综述了LDHs材料的基本性质、层间不同种阴离子及插层阴离子的化学作用。在此基础上,概括了LDHs材料的制备、表征方法和相关领域的应用,介绍了其在不同溶剂中进行剥离的研究进展,指出能否将其工业化扩大生产是制约其应用的重要因素,同时也分析了当前需要解决的相关问题,为今后LDHs材料的研究提供借鉴。