Recent advances in layered double hydroxides-based electrochemical sensors: Insight in transition metal contribution

Among the nanomaterials reported in the literature, layered double hydroxides (LDHs) are considered promising for the electrochemical sensor technology. Transition metal-based layered double hydroxides (TM-LDHs) show excellent electrocatalytic properties that facilitate redox reactions with analytes, e. g. H₂O₂, glucose or glyphosate. Elaboration of porous nano-structures with TM-LDHs nanosheets on the electrode surface allows a rapid diffusion of the analytes and a good accessibility of the TM active sites. An association of TM-LDHs with conductive materials, e. g. graphene or metal nanoparticles (M-NPs), improves the electronic conductivity in the LDH-based composites and also the electrocatalytic activity. With a selection of recent publications, the present mini-review aims to discuss about the specific electrocatalytic role played by TMs (Ni, Co, Cu, Mn and Fe) present in the LDH layers on the performance (sensitivity and detection limit) of these TM-LDHs-based sensors.     

石墨烯/钴镍双金属氢氧化物复合材料的制备及电化学性能研究

采用微波辐射与高温裂解相结合的二步还原法制备石墨烯。二步还原使氧化石墨被充分还原和剥离,所得到的石墨烯有较好的传导性,其比表面达675.4 m2.g-1。以此石墨烯为原料,水热法合成出石墨烯/钴镍双金属氢氧化物复合材料,并考察了复合材料作为超级电容电极材料的电化学性能。研究发现,褶皱的石墨烯纳米片均匀分散在钴镍双金属氢氧化物中,这改善了钴镍双金属氢氧化物的传导性和结构稳定性。在0.25 A.g-1电流密度下,复合材料的比电容量是800.2 F.g-1。当电流密度增加至10 A.g-1,比电容量为386.5 F.g-1,恒电流充-放电500次后比电容量仍能保持99%以上,这些呈示该复合材料具有优良的电化学性能。     

层状双金属氢氧化物/石墨烯复合材料及其在电化学能量存储与转换中的应用

高效的电化学能量存储与转换功能材料及其器件近年来受到了人们的广泛关注。层状双金属氢氧化物/石墨烯（LDH/G）复合物就是一类重要的能源材料。它们兼具LDH和石墨烯的优异的物理、化学性能,同时克服了LDH导电性差和石墨烯片易于团聚的问题;在超级电容器和电化学催化分解水等方面具有广泛应用。本文综述了LDH与化学修饰石墨烯（氧化石墨烯,还原氧化石墨烯及其衍生物）的有效复合的方法及其在电化学能量存储与转换领域中的应用,特别是关于基于该类材料的超级电容器及电化学析氧反应催化的研究;对LDH/G复合材料研究领域中的挑战和未来发展方向做了展望。     

Water Molecules in Hydrotalcite‐like Layered Double Hydroxides: Interplay between the Hydration of the Anions and the Metal Hydroxide Layer

Layered double hydroxides comprise positively charged metal hydroxide layers and intercalated anions. These materials are obtained from aqueous medium both in nature and in the laboratory. Consequently the layered double hydroxides include a considerable amount of water. The presented study was designed to determine the proportion of water associated with the hydration sphere of the anion as opposed to that of the metal hydroxide slab. Among the two differently bound water species observed in all layered double hydroxides, the weakly bound water is associated with the metal hydroxide layer and is lost at 100 °C, whereas the strongly bound water is in the hydration sphere of the anion and is lost at higher temperatures (100 °C ≤ T ≤ 250 °C). This is in contrast to the better known cationic clays, wherein all the intercalated water is generally found to be in the hydration sphere of the cations. Further the water molecules in layered double hydroxides also bond to each other, leading to the incorporation of water in excess of what is predicted by the Miyata formula (Miyata, 1975) based on crystal chemical considerations. The excess water is one of the reasons for the poor crystallinity of layered hydroxides.     

On the possible discovery of intercalated carbonate anions via the analysis of 13C NMR spectra of graphite-like carbon materials

Analysis of ¹³C NMR spectra of graphite-like carbon materials shows that pyrolytic carbon, being a part of carbon-carbon composites, contains carbonate ions that are probably intercalated between the graphite-like layers of composites as in the case of layered double hydroxides.     

石墨烯/钴镍双氢氧化物复合材料的制备及其超电容特性

采用氧化石墨(GO)还原法制备石墨烯(GNS),以氨水为沉淀剂,在石墨烯存在的情况下,通过Co²⁺和Ni²⁺化学共沉积的方法合成了石墨烯/钴镍双氢氧化物复合电极材料,采用红外光谱(FT-IR)、X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)、比表面积测试(BET)等技术手段表征了产物的组成、结构和形貌,用循环伏安、恒电流充放电等测试方法对复合材料的电化学性能进行了研究。 研究发现,石墨烯纳米片均匀分散在钴镍双氢氧化物中,改善了钴镍双氢氧化物的传导性和结构稳定性。 电化学测试表明,在1 A/g的电流密度下,复合材料比电容高达2770 F/g,且循环500次后,比电容仍能保持93.4%,呈示该复合材料具有优异的电化学性能。     

Montmorillonite-Based Two-Dimensional Nanocomposites: Preparation and Applications

Montmorillonite (Mt) is a kind of 2:1 type layered phyllosilicate mineral with nanoscale structure, large surface area, high cation exchange capacity and excellent adsorption capacity. By virtue of such unique properties, many scholars have paid much attention to the further modification of Mt-based two-dimensional (2D) functional composite materials, such as Mt-metal hydroxides and Mt-carbon composites. In this review, we focus on two typical Mt-2D nanocomposite: Mt@layered double hydroxide (Mt@LDH) and Mt@graphene (Mt@GR) and their fabrication strategies, as well as their important applications in pollution adsorption, medical antibacterial, film thermal conduction and flame-retardant. In principle, the prospective trend of the composite preparation of Mt-2D nancomposites and promising fields are well addressed.     

Synthesis and release behavior of composites of camptothecin and layered double hydroxide

A simple method, reconstruction of calcinated layered double hydroxides (CLDH) in an organic (ethanol)-water mixed solvent medium containing drug, was developed to intercalate partially a non-ionic and poorly water-soluble drug (camptothecin) into the gallery of layered double hydroxides (LDHs) to form the drug-LDH composites. The purpose of choosing organic-water mixed solvent is to increase remarkably the solubility of camptothecin (CPT) in the reconstruction medium. A probable morphology of CPT molecules in the gallery of LDHs is that CPT molecules arrange as monolayer with the long axis parallel to the LDH layers. The in vitro drug release from the composites was remarkably lower than that from the corresponding physical mixture, which shows these drug-inorganic composites can be used as a potential drug delivery system.     

Flammability and thermal degradation behavior of ethylene‐vinyl acetate/layered double hydroxides/zinc borate composites

Mg‐Al‐Fe ternary‐layered double hydroxides (LDHs) were synthesized by a calcination‐rehydration method using Bayer red mud. The products were characterized using X‐ray diffraction and thermogravimetric analysis. The flammability and thermal degradation of ethylene‐vinyl acetate/layered double hydroxides/zinc borate (EVA/LDHs/ZB) composites were studied with limiting oxygen index, UL 94, cone calorimeter test, smoke density test, and thermogravimetry‐Fourier transform infrared spectrometry. Although limiting oxygen index value of the composites decreased with increasing ZB amount, a suitable addition of ZB can apparently improve the UL 94 rating of the material. The heat release rate of the 5% ZB containing ternary composites decreased compared with the EVA/LDHs composites. It is obtained from smoke density test that ZB could help smoke suppression. The ternary composites possessed a higher thermal stability than the EVA/LDHs composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Mild Mechanochemical Synthesis of Nanodispersed Composites Magnetite@M(II)-Fe Layered Double Hydroxides (M = Mg,Ni)

Russian Journal of Applied Chemistry - The possibility of synthesis of nanodispersed composites Fe3O4@M(II)-Fe layered double hydroxides (M = Mg, Ni) is shown by mechanical processing a mixture of...     

Novel Zn-Fe LDH/MWCNTs and Graphene/MWCNTs Nanocomposites Based Potentiometric Sensors for Benzydamine Determination in Biological Fluids and Real Water Samples

Two sensitive and selective potentiometric sensors based on zinc-iron layered double hydroxides/multiwalled carbon nanotubes (Zn−Fe LDH/MWCNTs) (sensor I) and graphene/multiwalled carbon nanotubes (Gr/MWCNTs) (sensor II) nanocomposites were developed for benzydamine hydrochloride (Benz) determination. The investigated sensors displayed excellent Nernstian slopes 58.5±0.7 and 59.5±0.5 mV decade⁻¹, detection limits 8.3×10⁻⁷ and 1.9×10⁻⁷ mol L⁻¹, long lifetimes, adequate selectivity, high chemical, and thermal stability within pH range of 2.4–8.5 for sensors І and ІІ, respectively. The surface morphology of sensors was analyzed using a Transmission Electron Microscope (TEM). The analytical method was efficiently implemented for Benz determination in biological fluids and surface water samples.     

Flower‐like layered double hydroxide‐modified stainless‐steel fibers for online in‐tube solid‐phase microextraction of Sudan dyes

Layered double hydroxides are a family of inorganic crystals that have gained a lot of attention due to its special structure and properties such as high porosity, large specific area, and excellent anion exchange ability. In this work, flower‐like NiAl‐layered double hydroxides with high specific area were in situ immobilized onto the stainless steel fibers by bioinspired polydopamine modification method and packed into poly (ether ether) ketone tube for online solid‐phase microextraction with high performance liquid chromatography analysis. Thanks to the high specific surface area and excellent extraction ability of the NiAl‐layered double hydroxides, the fibers showed excellent extraction performance to three Sudan dyes with enrichment factors between 260 to 650 folds. After optimization of the reaction and extraction conditions, an online solid‐phase microextraction method was developed for determination of Sudan dyes in water samples and chili samples. The method has limits of detection of 0.01 to 0.02 ng/mL, good linearity and good reproducibility (≤1.45%).     

The role of the trivalent metal in an LDH: Synthesis, characterization and fire properties of thermally stable PMMA/LDH systems

Two layered double hydroxides (LDHs), calcium aluminum undecenoate (Ca₃Al) and calcium iron undecenoate (Ca₃Fe), have been prepared by the co-precipitation method. XRD analysis of these LDHs reveals that they are layered materials and FT-IR and TGA confirmed the presence of the undecenoate anions in the material produced. The PMMA composites were prepared by bulk polymerization and the samples were characterized by XRD, TEM, TGA and cone calorimetry. Both additives greatly enhance the thermal stability of PMMA, while the calcium aluminum LDH gives better results when the fire properties were examined using the cone calorimeter.     

Immobilization of anionic iron(III) porphyrins into ordered macroporous layered double hydroxides and investigation of catalytic activity in oxidation reactions

The first generation anionic iron(III) porphyrin [Fe(TSPP)] and the second generation anionic complexes [Fe(TDFSPP)], [Fe(TCFSPP)], and [Fe(TDCSPP)] were immobilized into three-dimensionally macroporous layered double hydroxide (3DM-LDH), using the direct reconstruction of 3DM-LDH from macroporous mixed oxides MOX or the anionic exchange on DDS intercalated 3DM-LDH. The macroporous layered double hydroxides were obtained at the surface of nanometric polystyrene spheres, which were synthesized by an inverse opal method. Polystyrene was removed after calcination in oxidizing atmosphere, nanostructured mixed oxides (3DM-MOX) were obtained, which after reconstruction give origin to macroporous layered double hydroxide (3DM-LDH). Following metalloporphyrin immobilization, the resulting materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), UV–vis (glycerin mull) spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FTIR), and electron paramagnetic resonance (EPR). Results revealed that the complexes are either immobilized at the surface of the macroporous layered double hydroxide or intercalated between the layers, displacing some dodecylsufate anions. The obtained materials were investigated as catalysts for oxidation reactions, to find out whether they function as cytochrome P-450 models.     

Synthesis and characterisation of alkaline earth-iron(III) double hydroxides

Double hydroxides containing alkaline earth and iron(III) ions were synthesised by the co-precipitation method. The solid materials obtained were characterised by a range of instrumental methods (powder X-ray diffractometry, thermogravimetry, scanning electron microscopy, energy dispersive X-ray fluorescence spectrometry, elemental maps, and infrared spectroscopy). It was found that the Ca(II)Fe(III), Mg(II)Fe(III), and Ba(II)Fe(III) double hydroxides had layered structures, while Sr(II)Fe(III) had not. The optimum conditions for synthesis of Ca(II)Fe(III)-layered double hydroxides (materials to be used in further studies) were also elaborated.     

2020 Roadmap on two-dimensional nanomaterials for environmental catalysis

This roadmap demonstrates a series of two-dimensional nanomaterials, such as graphene, black phosphorus, oxides, layered double hydroxides, chalcogenides, bismuth-based layered compounds, MXenes, metal organic frameworks, covalent organic frameworks, and others, for environmental catalysis.     

Combustion behavior and thermal stability of TPU composites based on layered yttrium hydroxides and graphene oxide

Journal of Thermal Analysis and Calorimetry - Layered yttrium hydroxides (LYH)- and graphene oxide (GO)-supported layered yttrium hydroxides (GO–LYH) were synthesized by a co-precipitation...     

A Novel Thermotropic Elastomer based on Highly‐filled LDH‐SSB Composites

Elastomeric composites are prepared based on solution styrene butadiene elastomer and zinc‐aluminium layered double hydroxides (LDH), using a conventional sulphur cure system. Up to 100 parts per hundred rubber of LDH are incorporated into the elastomer matrix. The composites exhibit an interesting phenomenon of thermoreversible transparency, i.e. the transparent sample becomes opaque at warm condition and restores the transparency at room temperature. The transparency is found to be increased as the amount of LDH was increased. The addition of LDH gradually improved the mechanical, dynamic mechanical performance and thermal stability of the base elastomer. These developped elastomers could be utilised as smart materials in different applications.     

Determination of haloacetic acids in water using layered double hydroxides as a sorbent in dispersive solid‐phase extraction followed by liquid chromatography with tandem mass spectrometry

In the present study, highly efficient and simple dispersive solid‐phase extraction procedure for the determination of haloacetic acids in water samples has been established. Three different types of layered double hydroxides were synthesized and used as a sorbent in dispersive solid‐phase extraction. Due to the interesting behavior of layered double hydroxides in an acidic medium (pH?4), the analyte elution step was not needed; the layered double hydroxides are simply dissolved in acid immediately after extraction to release the analytes which are then directly introduced into a liquid chromatography with tandem mass spectrometry system for analysis. Several dispersive solid‐phase extraction parameters were optimized to increase the extraction efficiency of haloacetic acids such as temperature, extraction time and pH. Under optimum conditions, good linearity was achieved over the concentration range of 0.05–100 μg/L with detection limits in the range of 0.006–0.05 μg/L. The relative standard deviations were 0.33–3.64% (n = 6). The proposed method was applied to different water samples collected from a drinking water plant to determine the concentrations of haloacetic acids.     

Unveiling the Occurrence of Co(III) in NiCo Layered Electroactive Hydroxides: The Role of Distorted Environments

Co- and Ni-based layered hydroxides constitute a unique class of two-dimensional inorganic materials with exceptional chemical diversity, physicochemical properties and outstanding performance as supercapacitors and overall water splitting catalysts. Recently, the occurrence of Co(III) in these phases has been proposed as a key factor that enhance their electrochemical performance. However, the origin of this centers and control over its contents remains as an open question. We employed the Epoxide Route to synthesize a whole set of α-NiCo layered hydroxides. The PXRD and XAS characterization alert about the occurrence of Co(III) as a consequence of the increment in the Ni content. DFT+U simulation suggest that the shortening of the Co−O distance promotes a structural distortion in the Co environments, resulting in a double degeneration in the octahedral Co 3d orbitals. Hence, a strong modification of the electronic properties leaves the system prone to oxidation, by the appearance of Co localized electronic states on the Fermi level. This work combines a microscopic interpretation supported by a multiscale crystallochemical analysis, regarding the so-called synergistic redox behavior of Co and Ni, offering fundamental tools for the controllable design of highly efficient electroactive materials. To the best of our knowledge, this is the first computational–experimental investigation of the electronic and structural details of α-NiCo hydroxides, laying the foundation for the fine tuning of electronic properties in layered hydroxides.