Layered double hydroxides: an attractive material for electrochemical biosensor design

Electrochemical biosensors for phenol determination were developed based on the immobilization of polyphenol oxidase (PPO) within two different clay matrixes, one anionic (layered double hydroxide, LDH) and the other cationic (Laponite). The biosensor based on the enzyme immobilized in [Zn-Al-Cl] LDH shows greater sensitivity (7807 mA M(-1) cm(-2)) and maximum current (492 microA cm(-2)). Biosensor characteristics, such as Michaelis-Menten constant, recycling constant, activation energy, and permeability highlight the advantages of LDH matrixes to immobilize PPO. It appears that LDH provides a favorable environment to PPO activity. The best PPO/[Zn-Al-Cl] configuration was used to determine five different phenol derivatives reaching extremely sensitive detection limits (< or = 1 nM).     

层状双金属氢氧化物活化过硫酸盐降解有机污染物研究进展

近代工业的快速发展造成大量难降解的新型有机污染物进入水体,亟需经济、高效的难降解有机污染物污染控制和削减技术。近年来,基于硫酸根自由基(SO₄^·–)的高级氧化技术（SR-AOPs）具有强氧化性、宽pH耐受性以及方便操作性等优势而备受关注。不同种类的金属氧/硫化物、碳基材料、金属-非金属复合材料以及有机金属材料等被用来活化过硫酸盐产生活性氧,从而实现对有机污染物的氧化降解和进一步矿化。其中,层状双金属氢氧化物（Layered double hydroxides, LDHs）因其独特的层状结构优势、阴离子可交换性和客体分子可调节性,在活化过硫酸盐方面表现出优良的反应活性和催化优势。本论文从催化剂类型、催化性能与机制以及降解体系影响因素等方面,综述了LDHs及其复合材料作为非均相催化剂活化过硫酸盐的研究现状,并对催化体系持续改进以及未来发展提出相关展望。     

Layered double hydroxides intercalated with EDTA as effective sorbents for U(VI) recovery from wastewater

The performance of the synthetic hydrotalcite-like sorbents, initial {[Zn₄Al₂(OH)₁₂]CO₃·nH₂O} and heat-treated (Zn₄Al₂O₇) forms and the form intercalated with EDTA and prepared in a nitrogen atmosphere from [Zn₄Al₂(OH)₁₂]Cl₂·nH₂O, was evaluated and compared. Increased concentrations of hydrocarbonate and carbonate ions do not noticeably affect the degree of U(VI) recovery from wastewaters with pH 8, which is due to tight binding of U(VI) with EDTA anions in the interlayer space of layered double hydroxides. [Zn₄Al₂(OH)₁₂]EDTA·nH₂O is one of the most effective and cheapest synthetic sorbents for recovering from aqueous media not only cationic but also anionic U(VI) species, which is particularly important. Therefore, the sorbent can be recommended for practical use.     

水滑石作为药物载体--萘普生的插层和缓释

水滑石(LDHs)是由带正电荷类水镁石层和层间的可交换阴离子组成的阴离子型粘土化合物,由于它的生物适应性,能够以它为主体,以药物为客体,插层组装成超分子结构复合物.抗炎药萘普生采用共沉淀法一步插层进入LDHs,用X射线衍射、红外光谱及热分析方法表征了超分子结构,表明层间距离扩大了,即萘普生已经插层组装成功,并且以单层、垂直作用在层间.萘普生柱撑水滑石的药物释放度在模拟肠液(pH7.4的缓冲液)条件下测定,结果表明萘普生柱撑水滑石释放速度降低,具有缓释作用,说明药物--无机混合物材料能够用作有效的药物传输系统.     

基于NiMoCo层状双金属氢氧化物的电催化剂和超级电容器电极

本文通过调控Ni,Mo,Co三种元素的摩尔比得到一系列高效双功能电催化剂.其中,Co元素特定的氧吸附位点(Co^2+-O-Co^3+)可有效提高催化剂的活性.Mo元素在温和反应条件下具有较好的氧化还原能力.Ni是另一种高活性过渡金属.与其他材料结合可有效增强催化剂的氧化还原活性和储氧能力.所制备的NiMoCo层状双金属...     

Corrosion inhibition of layered double hydroxides for metal-based systems

Layered double hydroxide(LDH),a kind of 2D layered materials,has been recognized as the promising anticorrosion materials for metal and its alloy.The microstructure,physical/chemical properties,usage in corrosion inhibition and inhibition performance of LDH have been studied separately in open literature.However,there is a lack of a complete review to summarize the status of LDH technology and the potential R&D opportunities in the field of corrosion inhibition.In addition,the challenges for LDH in corrosion inhibition of metal-based system have not been summarized systematically.Herein,we review recent advances in the rational design of LDH for corrosion inhibition of metal-based system(i.e.Mg alloy,Al alloy,steel and concrete)and high-throughput anticorrosion materials development.By evaluating the physical/chemical properties,usage in metal-based system and the corrosion inhibition mechanism of LDH,we highlight several important factors of LDH for anticorrosion performance and common features of LDH in applying different metal alloys.Finally,we provide our perspective and recommendation in this field,including high-throughput techiniques for combinatorial compositional design and rapid synthesis of anticorrosion alloys,with the goal of accelerating the development and application of LDH in corrosion inhibition of metal-based system.     

Phosphorus oxoanion-intercalated layered double hydroxides for high-performance oxygen evolution

Rational design and controlled fabrication of efficient and cost-effective electrodes for the oxygen evolution reaction (OER) are critical for addressing the unprecedented energy crisis.Nickel-iron layered double hydroxides (NiFe-LDHs) with specific interlayer anions (i.e.phosphate,phosphite,and hypophosphite) were fabricated by a co-precipitation method and investigated as oxygen evolution electrocatalysts.Intercalation of the phosphorus oxoanion enhanced the OER activity in an alkaline solution;the optimal performance (i.e.,a low onset potential of 215 mV,a small Tafel slope of 37.7 mV/dec,and stable electrochemical behavior) was achieved with the hypophosphite-intercalated NiFe-LDH catalyst,demonstrating dramatic enhancement over the traditional carbonate-intercalated NiFe-LDH in terms of activity and durability.This enhanced performance is attributed to the interaction between the intercalated phosphorous oxoanions and the edge-sharing MO6 (M =Ni,Fe) layers,which modifies the surface electronic structure of the Ni sites.This concept should be inspiring for the design of more effective LDH-based oxygen evolution electrocatalysts.     

Synthesis of layered double hydroxides from eggshells

Ca-Al and Ca-Fe layered double hydroxides (LDHs) were successfully synthesized from chicken eggshells by an ultrasonic wave assistant method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. XRD and TEM analyses showed that the 4Ca-Al LDHs were of high purity but other samples were not. The present study provides a simple, efficient and environmental friendly method to obtain LDHs from biowaste eggshells, in which additional alkaline solution is not required for synthesis. Moreover, eggshells provide all the requisite bivalent metal ions, which are needed to form layered double hydroxides.     

Layered double hydroxides as efficient drug delivery system of ciprofloxacin in the middle ear: an animal study in rabbits

Chronic otitis media is a common disease often accompanied by recurrent bacterial infections. These may lead to the destruction of the middle ear bones such that prostheses have to be implanted to restore sound transmission. Surface coatings with layered double hydroxides (LDHs) are evaluated here as a possibility for drug delivery systems with convenient advantages such as low cytotoxicity and easy synthesis. Male New Zealand White rabbits were implanted with Bioverit^® II middle ear prostheses coated with the LDH Mg₄Al₂(OH)₁₂(SO₄)₂·6H₂O impregnated with ciprofloxacin. 12 (group 1) were directly infected with Pseudomonas aeruginosa and another 12 (group 2) 1 week after the implantation. Clinical outcome, blood counts, histological analyses and microbiological examination showed an excellent antimicrobial activity for group 1, whereas this effect was attenuated in animals where infection was performed 1 week after implantation. This is the first study to demonstrate an efficient drug delivery system with an LDH coating on prostheses in the middle ear.     

层状双氢氧化物析氧催化剂的研究进展

层状双氢氧化物具有制备简单,层间客体可调节,合成成本较低,稳定性较好等优点,因此成为析氧催化剂的研究热点,但仍存在电荷传输速率低,过电位相对较高等问题,因此需要对其改性来加快其大规模应用。首先介绍了层状双氢氧化物的结构特点,简述了其析氧反应的催化机理,然后总结了不同种类的优化改性策略来增强其催化活性。优化改性方法分别包括:与导电基材复合;合成超薄纳米片法;与石墨烯复合法;杂化改性法。重点探讨了层状双氢氧化物析氧催化剂在电解水制氢方面的应用,提出了不同改性方法的优缺点,阐明将其适当结合,有利于制备更高效的析氧催化剂,最后指出了这类催化剂仍面临的问题:回收率较低,催化剂稳定性和可实现的电流密度尚未达到工业化需求,无法实现大规模制备等难点。     

Surfactant-assisted fatty acid intercalation of layered double hydroxides

Surfactant-mediated intercalation of aliphatic carboxylic acids into a commercial layered double hydroxide (LDH) with approximate composition ] was explored. The reaction was conducted at elevated temperatures with the LDH powder as a suspension in a stearic acid oil-in-water emulsion. The acidic fatty acid, e.g., stearic acid, reacts with the basic carbonate anions, CO₂ is released and the fatty acid is intercalated as a bilayer. High-concentration anionic or nonionic surfactants, i.e., sodium dodecylsulfate or Tween 60, aid the intercalation process by emulsifying the molten acid and dispersing the hydrotalcite particles. X-ray diffraction, thermal analysis, and infrared spectroscopy confirmed that a bilayer-intercalated hydrotalcite was formed and that the surfactant is not co-intercalated. The method is convenient, economical, and environmentally friendly: It employs the readily available carbonate form as starting reagent; water is used as medium rather than organic solvents; low reaction temperatures suffice, i.e., calcinations of the clay are superfluous and there is no need for working under a CO₂-free atmosphere.     

Crystal face specificity of double layer structure and electrocatalysis

Experimental data for single crystal faces of transition and non-transition metals are examined to appraise the applicability of the approaches thus far proposed for polycrystalline surfaces to the analysis of the experimental response obtained with single crystals. The topics reviewed are zero charge potential, metal-water interaction, adsorption from the gas phase, adsorption from solution, electron and proton exchange reactions and hydrogen evolution. The electron work function has been used as the parameter on which predictions for the behaviour of single crystal faces have been based. It is shown that conclusions based on the behaviour of polycrystalline surfaces maintain their validity as regards double layer structure and physical adsorption. The picture becomes much more varied and complex when chemisorption bonds are involved.     

Topotactic reduction of layered double hydroxides for atomically thick two-dimensional non-noble-metal alloy

Layered double hydroxides (LDHs) have been widely used as catalysts owing to their tunable structure and atomic dispersion of high-valence metal ions; however, limited tunability of electronic structure and valence states have hindered further improvement in their catalytic performance. Herein, we reduced ultrathin LDH precursors in situ and topotactically converted them to atomically thick (~2 nm) two-dimensional (2D) multi-metallic, single crystalline alloy nanosheets with highly tunable metallic compositions. The as-obtained alloy nanosheets not only maintained the vertically aligned ultrathin 2D structure, but also inherited the atomic dispersion of the minor metallic compositions of the LDH precursors, even though the atomic percentage was higher than 20%, which is far beyond the reported percentages for single-atom dispersions (usually less than 0.1%). Besides, surface engineering of the alloy nanosheets can finely tune the surface electronic structure for catalytic applications. Such in situ topotactic conversion strategy has introduced a novel approach for atomically dispersed alloy nanostructures and reinforced the synthetic methodology for ultrathin 2D metal-based catalysts.

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Electronic spectra of anions intercalated in layered double hydroxides

Transition metal complexes intercalated in layered double hydroxides have a different electronic structure as compared to their free state owing to their confinement within the interlayer gallery. UV–Vis absorptions of the intercalated complex anions show a significant shift as compared to their free state. The ligand to metal charge transfer transitions of the ferricyanide anion show a red shift on intercalation. The ferrocyanide ion shows a significant blue shift of d–d bands due to the increased separation between t _2g and e _g levels on intercalation. MnO $_{4}^{{-}}$ ion shows a blue shift in its ligand to metal charge transfer transition since the non-bonding t ₁ level of oxygen from which the transition arises is stabilized.     

The construction and characterization of layered double hydroxides as delivery vehicles for podophyllotoxins

The aim of this study was to construct PPT-LDH nanohybrids and compare their tumor inhibition effects with that of free PPT. Anticancer drug podophyllotoxin (PPT) was encapsulated in the galleries of Mg-Al layered double hydroxides (LDHs) by a two-step approach. Tyrosine (Tyr) was first incorporated into the interlayer space by co-precipitation with LDH, prop-opening the layers of Mg-Al/LDH and creating an interlayer environment inviting drug molecules. PPT was subsequently intercalated into the resulting material lamella by an ion exchange process. The intermediate and final products, which can be termed drug-inorganic nanocomposites, have been characterized by powder X-ray diffraction (XRD), UV-VIS spectrophotometer, transmission electron microscopy (TEM) and in cell culture. Our results demonstrate that the interlayer spacing distance of the PPT-LDH nanohybrids (34% w/w of drug/material) is 18.2 A. LDHs do not harm normal cells (293T) based on toxicity tests. Ex-vivo anticancer experiments reveal that the PPT-LDH nanohybrids have higher tumor suppression effects than intercalated PPT. We conclude that the higher tumor inhibition effects of PPT-LDH hybrids result from the inorganic drug delivery vehicle, LDHs.     

Study of bi-enzyme immobilization onto layered double hydroxides nanomaterials for histamine biosensor application

In this work, we present the development of a hybrid biomembrane based on the immobilization of diamine oxidase (DAO) into LDH thin films for histamine detection. The LDHs preselected as host matrixes are: hydrotalcites (Mg2Al(CO3)0.5(OH)6), lowaite (Mg4Fe(OH)10Cl) and hydrocalumite (Ca2Al(OH)6Cl). The immobilized probes were characterized by atomic force microscopy (AFM) and attenuated total reflection infrared spectroscopy (IR-ATR mode). The analysis of these results shows that the immobilization of DAO occurs with all type of selected LDH and is stable after a 7 day-immersion in phosphate buffer solution. The LDH incorporating magnesium or calcium divalent cations present high-quality surface topology for DAO immobilization and the ability to keep the enzyme in a well conformation for biogenic amines catabolism and histamine detection.     

Evolution of structure and performance of Cu-based layered double hydroxides

A new series of Cu/Zn/Mn/Fe/Al hydrotalcite-like layered double hydroxides (LDHs) with the Cu/(Zn + Mn)/(Fe + Al) atomic ratios of 1/1/1 in synthesis mixture were synthesized by the coprecipitation method. The chemical composition of multicomponent precursors was identified by chemical analyses. The thermal stability, structure, and texture changes of these as-synthesized LDHs were studied by in situ high-temperature X-ray diffraction (HT-XRD), thermogravimetric-differential thermal analysis combined with mass spectrometry (TG-DTA-MS) in different atmosphere, transmission electron microscopy (TEM), and N₂ adsorption–desorption experiments. The results exhibit that the incorporation of Fe³⁺ and Mn²⁺ into the lattices of Cu-containing LDHs in sequence decreases the crystallinity, water content, and thermal stability of corresponding compounds, and the thermal treatment of LDHs results in the formation of thermodynamically stable composite metal oxide associated with a small amount of simple metal oxide and also changes in texture of calcined solid. Under mild experimental conditions (atmospheric pressure and 25 °C), the catalytic liquid-phase oxidation of aqueous phenol solutions is related to the composition, oxidation states, composite forms and synergy of transition metal cations in calcined LDHs, and calcined LDH with Cu/Zn/Mn/Fe/Al atomic ratio of 1/1/0/0.3/0.7 at 500 °C achieves the highest conversion of phenol mainly owing to the formation of a larger amount of composite metal oxide with some residual carbonate in the solid.     

Surface control of layered double hydroxides by in-situ initiating&terminating polymerization

Appropriate surface modification or functionalization is prerequisite for the application of inorganic nanoparticles.And surface control between organic and inorganic interface plays an important role in constructing organic-inorganic composites.In-situ polymerization has been extensively studied to improve the compatibility and dispersibility of inorganic nanoparticles,but the polymerized nanoparticles tend to concatenate and form large composites,restricting further applications.Herein,uniform and dense polyacrylic acid(PAA)membranes have been grafted on layered double hydroxide(LDH)nanosheets via an in-situ initiating and terminating radical graft polymerization method.With initiating and terminating on the same particle,the size,morphology and density of grafted PAA onto the surface of LDHs can be controlled by adjusting the ratio of initiated sites to terminated sites,the amount of redox initiator or monomer.As a result,with only 17.33%organic grafting ratio,PAA@LDHs with largely improved compatibility can be monodispersed in polyethylene(PE)and polyvinyl chloride(PVC)matrices,which is determined by a fluorescence microscope technique.