Article

Liquid Exfoliation of Layered Materials

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Abstract

Not all crystals form atomic bonds in three dimensions. Layered crystals, for instance, are those that form strong chemical bonds in-plane but display weak out-of-plane bonding. This allows them to be exfoliated into so-called nanosheets, which can be micrometers wide but less than a nanometer thick. Such exfoliation leads to materials with extraordinary values of crystal surface area, in excess of 1000 square meters per gram. This can result in dramatically enhanced surface activity, leading to important applications, such as electrodes in supercapacitors or batteries. Another result of exfoliation is quantum confinement of electrons in two dimensions, transforming the electron band structure to yield new types of electronic and magnetic materials. Exfoliated materials also have a range of applications in composites as molecularly thin barriers or as reinforcing or conductive fillers. Here, we review exfoliation—especially in the liquid phase—as a transformative process in material science, yielding new and exotic materials, which are radically different from their bulk, layered counterparts.

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... Next, bulky intercalation species such as tetrabutylammonium hydroxide (TBAOH) are used to react with the protons through a fast acid-base reaction, intercalating the amphiphilic cations like TBA + between the layers, weakening the interlayer Van der Waals interactions so as to complete the chemical exfoliation, as schematically shown in Fig. 17 (d). [140,143,155]. The intercalated ions often provide interplanar electrostatic interactions that are too strong for simple sonication or other mechanical exfoliation to be effective for delamination, showing the need for these chemical exfoliation techniques [51]. ...
... (a) mechanical exfoliation via adhesive tape, adapted from[129]. (b) sonication-assisted mechanical exfoliation, adapted from[143]. (c) electrochemical exfoliation, adapted from[144]. (d) chemical exfoliation via ion intercalation and exchange, adapted from[143]. ...
... (c) electrochemical exfoliation, adapted from[144]. (d) chemical exfoliation via ion intercalation and exchange, adapted from[143]. ...
Article
Today, the atmospheric carbon dioxide (CO2) concentrations have reached an unprecedented record high of almost 420 ppm since the industrial revolution, resulting in an increase of the average global temperature by 1.5 ◦C. Tremendous efforts are being made to reduce carbon emission e.g. at stationary point sources such as fossil fuel-based power plants via CO2 capture and utilization (CCU) technologies. Pilot demonstrations of carbon capture using amine-based solvent have shown potential, but suffer from high operational costs and low thermodynamic efficiency, motivating researchers towards more cost-effective measures, such as integrated carbon capture and utilization (ICCU) systems. Here, a solid, dual-functional material (DFM) is used to capture CO2 and convert it into value-added chemicals/fuels in-situ. Such integrated systems eliminate the most energy & capitaldemanding upstream operations, such as stripping, compression, and transportation. ICCU technologies also possess a much higher energy efficiency through effective heat utilization by leveraging the high temperature of the flue gas to supply the reaction enthalpies. The graduation of ICCU technology from academia to commercial applications requires the development of stable and high-performance DFMs that are not only capable of selectively capturing CO2, but also catalyzing CO2 into value-added products at reasonable temperatures. Most DFMs explored to date are characterized by a physical combination of CO2 adsorbers and catalysts, however such ensembles intrinsically contain limitations from the diffusion of CO2 from the adsorptive sites to the catalytic ones. In the present review, we present an emerging class of 2 dimensional (2D) materials, transition metal oxides (TMOs), to be explored as potential high-performance DFMs, where the adsorptive and catalytic sites are in close proximity. 2D TMOs have been extensively studied in both CO2 capture and catalysis fields, but their utilization as DFMs for ICCU applications are just starting to be studied. We provide a comprehensive summary of typical 2D TMOs and their composites with specific synthetic strategies and unique features for CCU related applications. Although research on 2D TMOs as DFMs is still in an early stage, we hope that this review will inspire more demonstrations of 2D TMOs utilized in ICCU systems, with the ultimate goal to reduce CO2 emissions.
... Immense efforts have been devoted to discover new 2D materials and studying their physico-chemical properties, since the breakthrough discovery of graphene. [1][2][3] Recently, 2D tellurium (Te) nanostructures are emerging as potential candidates for optoelectronics, [4] energy-conversions, [5][6][7][8] and chemical sensor [9] applications due to its striking features, like tunable thickness-dependent band gap, [10,11] excellent on-state current density, [12] and decent carrier mobility with superior airstability. [12][13][14] Elemental Te has a bulk trigonal (t) crystal lattice with a space group P3 1 21 and an anisotropic helical structure in which helical chains of Te remain stacked via weak van der Waals forces, spiraling around the axis parallel to the c-axis. ...
... [1][2][3] Recently, 2D tellurium (Te) nanostructures are emerging as potential candidates for optoelectronics, [4] energy-conversions, [5][6][7][8] and chemical sensor [9] applications due to its striking features, like tunable thickness-dependent band gap, [10,11] excellent on-state current density, [12] and decent carrier mobility with superior airstability. [12][13][14] Elemental Te has a bulk trigonal (t) crystal lattice with a space group P3 1 21 and an anisotropic helical structure in which helical chains of Te remain stacked via weak van der Waals forces, spiraling around the axis parallel to the c-axis. [15,16] Due to the inherent structural anisotropy, earlier reported synthesis approaches predominantly produced several onedimensional (1D)-nanostructures e. g., nanorods, nanowires, nanobelts, and nanotubes, etc. [17,18] Very recently the work on morphology switching from 1D to 2D started with the motivation from theoretical predictions of several quasi-stable structural phases of 2D Te, also known as tellurene. ...
Article
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Mechanical stirring of bulk Te in N‐methyl‐2‐pyrrolidone (NMP) solution at room temperature resulted in the formation of free‐standing few‐layer (~1.2‐2.8 nm) crystalline ultrathin nanosheets of tellurene with a large lateral thickness (~1‐1.6 μm) as confirmed by atomic force microscopy (AFM). High‐resolution transmission electron microscopy (HRTEM) confirms the presence of α‐ and β‐phases of tellurene. First‐principle density functional theoretical (DFT) based electronic structure calculations demonstrate the indirect band gap of bi‐layer β‐tellurene. The band gap decreases with increasing number of layers in the tellurene nanosheet.
... Liquid exfoliation is another versatile technique that is being extensively used to produce atomically thin 2D nanosheets of layered materials [122,123]. In this technique, the final materials are produced in liquid dispersions with a large amount of 2D nanosheets. ...
... In liquid exfoliation, ultrasound waves create microscopic bubbles in the liquid, and the average size of bubbles can be optimized with the ultrasound waves' frequency and power. These microscopic bubbles contract at a high-pressure cycle, expand at low pressure, and further explode violently during the pressure change, leading to the cavitation effect [122]. The cavitation effect instantaneously generates a very high pressure of more than 100 MPa within a hotspot. ...
Article
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Two-dimensional (2D) materials are the focal point of intensive research efforts due to their unique properties and ability to reveal fascinating new phenomena. As an analog to graphene, phosphorene is a monolayer of black phosphorus crystals. Phosphorene obtained a special place among the family of 2D semiconducting materials because of its fascinating features such as high optical absorption, high carrier mobility, and several other attractive features having an exceptional interest in electronic and optoelectronic applications. The anisotropic orthorhombic crystal structure of phosphorene provides remarkable mechanical, electronic, optical, and transport properties. This review summarizes phosphorene's chemical and physical properties and highlights the recent progress made in the synthesis. The application of phosphorene-based devices in high-speed electronics and optoelectronics has been surveyed. Also, sufficient emphasis has been given to emerging biomedical applications. Finally, phosphorene's remaining challenges and potential applications are outlined.
... Zeng and co-workers [100] successfully synthesized WO 3 nanosheets with enriched O vacancies by liquid exfoliation methods [110,111]. Electron transport measurements revealed the nature of the semiconductor degenerate for O vacancies embedded in WO nanosheets. DFT calculations showed that the introduction of O vacancies transforms the conventional WO semiconductor into a degenerate semiconductor, with higher conductivity and a preferential DGH* to enhance the activity of HER. ...
Article
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As a form of clean and renewable energy, hydrogen has received much attention recently. However, industrial hydrogen production is primarily via conversion of natural gas, which consumes a large amount of energy and emits large volumes of greenhouse gases. Electrochemical water electrolysis is a promising, pollution-free method for the production of hydrogen from water. Efficient, cost-effective, stable and abundant catalysts that can drive hydrogen production in water with minimal electrical bias are a major goal towards achieving electrolysis on a large scale. Recently, tungsten oxide-based materials have emerged as one of the most promising electrocatalytic compounds, due to their activity, low cost and durability in both acid and base conditions. There are often oxygen vacancies in metal oxides, whether intentional or not, which can potentially promote the water electrolysis. In this review, we provide an overview of tungsten oxide-based materials used for electrocatalytic water splitting. In addition, mechanisms to improve the electrocatalytic activities of oxygen vacant tungsten oxide are summarized and discussed, with proposals for future research. This review article will provide a valuable resource for scientists pursuing materials for electrochemical water splitting.
... From then on, the studies of 2D materials are being entered a high-speed developing period, which is attributed to the adoption of mechanical exfoliation providing a convenient method to obtain 2D nanoflakes. However, the studies about how to improve mechanical exfoliation for high-quality nanoflakes are still lacking, more attentions have been paid to scale-selective growth techniques (such as chemical vapor deposition, CVD) [15] and wet chemical synthesizes (such as ion exchange-assisted intercalation, liquid phase epitaxial and interfacial assembly) [16][17][18]. The CVD technology has been proved to be a time-and powerconsuming process. ...
Article
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Mechanical exfoliation is a facile way for the preparation of two-dimensional (2D) nanoflakes. However, the quality of obtained flakes still needs to be further improved, e.g., the exfoliated size and production yield, which plays a crucial role in practical applications. Here, solvent-assisted method is proposed by introducing chemical solvents in the exfoliations. The impacts of wrinkles and defects existed in the outmost layer of bulk MoS2 crystal are overcome due to the capillary and diffusion forces driven by solvent molecules underlying flakes. Hence, the size and yield of nanoflakes are promoted manifestly. The MoS2 nanoflakes are obtained with the largest area of ~ 1.5 mm² that is three orders of magnitude bigger than conventional mechanical exfoliation. In addition, the characterizations verify the existence of monolayer which may exhibit intrinsic properties of the MoS2 flakes. Subsequently, MoS2 field-effect transistors are conveniently fabricated by one-step mechanical shadow-mask process. The field-effect mobility of ~ 26 cm²V⁻¹ s⁻¹ and on/off ratio of ~ 10⁶ are achieved. All results indicate that the solvent-assisted exfoliations provide a universal path in the preparation of 2D nanoflakes, which is a fundamental support for the studies of 2D materials and devices. Graphical abstract
... 2D materials and properties 2D materials share a series of advantages that arise solely from their near-atomic thickness, which endows them with an extremely high surface area, excellent mechanical strength and easy regulation of their properties by surface modification and functionalization; these properties are advantageous for applications driven by surface reactions, such as catalysis, energy storage and sensing 16 . Furthermore, it is relatively simple to build heterostructures out of several types of 2D materials, obtaining new properties and overcoming some of the individual limitations of each material 1 . ...
Article
The development of new and more accurate fabrication technologies has, in the past few years, boosted interest in advanced device manufacturing. 2D materials, thanks to their diverse properties and dispersibility in liquid carriers, constitute a rich toolbox for ink-based applications. However, the lack of standardized production methods offering a good compromise between performance and affordability has so far been a limiting factor for the application of 2D inks. In this Review, we provide a comprehensive description of the steps involved in device fabrication for different applications, from material selection and ink formulation to printing strategies and device assembly. We conclude with a critical overview of the main scientific and technical limitations currently faced by 2D inks and the related printing technologies, and discuss their market penetration and implementation stage.
... Zhu et al. used MoS 2 to detect DNA and small molecules (Zhu et al. 2013), Our group took advantage of photoluminescence properties of MoS 2 for biological applications related to ions (Ou et al. 2014), while other teams focused on applications of MoS 2 in the area of drug delivery (Chou et al. 2013;Yin et al. 2014), biomedical imaging , and cancer treatment (Liu et al. 2014Yu et al. 2015 ). Among methods used for production of the two-dimensional nanomaterials, one of the most widely used is liquid phase exfoliation (LPE) (Bourlinos et al. 2009;Nicolosi et al. 2013) that involves sonication (Hernandez et al. 2008), shearing (Varrla et al. 2015), or mixing of the two methods (Tkachev et al. 2021). The solvent used in the process of exfoliation is one of the challenges to be addressed (Backes et al. 2017). ...
... With the rise of layered materials [1][2][3][4][5][6][7], intercalation [8][9][10] and exfoliation [11][12][13][14][15] became two of the most commonly used methods to alter their structural and electronic properties. Such intercalation with elements or molecular moieties changes the separation between layers, screening environment and electronic structure, including Fermi surface properties. ...
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Bulk FeSe becomes superconducting below 9\,K, but the critical temperature (T$_{c}$) is enhanced almost universally by a factor of $\sim$4-5 when it is intercalated with alkali elements. How intercalation modifies the structure is known from in-situ X-ray and neutron scattering techniques, but why T$_{c}$ changes so dramatically is not known. Here we show that the enhancement originates mainly from modifications of the pairing vertex in the particle-particle channel. Thus, intercalated FeSe provides an archetypal example of superconductivity where information derived from the single-particle electronic structure is not sufficient to account for the origins of superconductivity, even when they are computed including correlation effects.
... A good matching of surface tension between the 2D material and the solvent molecule enables the solvent to be intercalated into the layers of 2D material, enlarging the vdW gap between the layers thereby yielding the exfoliation of 2D nanosheets from bulk materials. [86] Solvent molecules should not be considered as inert liquids. In Chapter 5 and Chapter 6 of this thesis, we will show that organic solvent molecules are able to influence the electronic and optical properties of the 2D monolayer and few-layer semiconductors. ...
Thesis
This thesis mainly studies the mechanism of interactions between molecules and two-dimensional (2D) semiconducting materials, and the related applications in electronics. The research works begin with studying the effect of organic solvents on the optical and electronic properties of 2D transition metal dichalcogenides (TMDs) and black phosphorus, followed by functionalizing 2D indium selenide (InSe) with ionic surfactant molecules and the applications in photodetectors. The research is ended with creating periodic potentials using axially functionalized pyridinic ligands on metal phthalocyanines that are physisorbed onto 2D TMDs. These ligands include simply functionalized pyridine and the pyridines with photochromic azobenzene to induce doping on 2D materials.The interdisciplinary projects involves physical chemistry, solid state physics, supramolecular chemistry, materials science, nanoelectronics, computational chemistry and photochemistry.
... In addi tion, this method requires a qualified operator and further processing methods to transfer and stabilize the 2D mate rial produced. [28] The use of ultrasound [29] and shearbased [30] mechanical exfoliation processes enables the production of highquality 2D materials with fewer defects. ...
Article
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In the modern age of nanotechnology, the discovery of graphene has opened up the way to study and develop of several novel 2D materials. The unique physical and chemical properties of 2D materials have enhanced their research, making them superior to the commercial bulk materials used in various applications. Efforts have been made in the current study to present an overview of the intrinsic properties of these materials. Furthermore, synthesis and applications are also reviewed and discussed. Finally, the future outlook of 2D materials is discussed to enhance the research and performance of these materials, which can result in broader applications benefitting the electrical and electronics industries and society. Intensive research into 2D materials is expected to lead to the discovery of new materials with enhanced properties that will benefit the industry and society at large. 2D materials have unique intrinsic properties. The properties of 2D materials are tunable. Layer size produces significant variation in properties. Ductile failure in 2D materials is very rare. Transition metal‐dichalcogenides are superior to graphene.
... Typically, liquid exfoliation techniques are divided into ion intercalation, ion exchange, and sonication-assisted liquid exfoliation [ 28 ]. Sonication-assisted exfoliation method: directly ultrasonically treat hexagonal boron nitride (h-BN) in a liquid medium to prepare BNNSs. ...
Article
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In recent years, graphene has been widely employed in the field of metal corrosion protection owing to its outstanding impermeability and chemical stability, with examples of such metal protection including pure graphene coatings and graphene-based composite coatings. But the conductive graphene could promote the electrochemical reaction at the interface and accelerate the corrosion of metal substrates. More emerging graphene-like 2D nanosheets are attracting research attention for the application of metal anticorrosion, because of their barrier properties and poor conductivity, mainly including boron nitride (BN), molybdenum disulfide (MoS2), zirconium phosphate (ZrP), and titanium carbide (MXene). In this review, the application of these graphene-like 2D nanosheets to metal protection is comprehensively reviewed. First, the general preparation methods of 2D nanosheets are briefly introduced. Second, surface functionalization of 2D nanosheets, including covalent and non-covalent modification, is described in detail. Third, the anticorrosion performance and optimization measures of pure 2D nanosheets coatings are summarized. Next, the protection performance, anticorrosive mechanism, and optimizations of 2D nanosheets composite coatings are presented. Finally, the future development of 2D nanosheets-based anticorrosive coatings has been prospected, and the challenges in the industrial application are discussed.
... This process often produces high quality 2D materials by exfoliation (textural intermolecular forces) of solids with ultrasonication or mechanical stimuli. The multiple layer of exfoliation reduces the intermolecular attraction between the layers and produces exfoliated sheets, liquid-liquid interfaces, polymers etc. [143] ...
Article
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Being cognizant of modern electronic devices, the scientists are continuing to investigate renewable green‐energy resources for a decade. Amid different energy harvesting systems, the triboelectric nanogenerators (TENGs) have been found to be the most promising mechanical harvesting technology and have drawn attention to generate electrical energy. Thanks to its instant output power, choice to opt for wide‐ranging materials, low maintenance cost, easy fabrication process and environmentally friendly nature. Due to numerous working modes of TENGs, it is dedicated to desired application at ambient conditions. In this review, an advance correlation of TENGs have been explained based on the variety of nanostructures, including 0D, 1D, 2D, 3D, metal organic frameworks (MOFs), coordination polymers (CPs), covalent organic frameworks (COFs), and perovskite materials. Moreover, an overview of previous and current perspectives of various nanomaterials, synthesis, fabrication and their applications in potential fields have been discussed in detail. Desirable TENGs application based on various materials including 0D to 3D that consummate robust structures such as MOFs, CPs, COFs, and Perovskites.
... For example, van der Waals layered compounds like graphite, h-BN and layered metal dichalcogenides (e.g., MoS 2 ) have strong covalent bonding in the host layer (i.e., in the ab plane) but very weak van der Waals interaction between layers (i.e., in the c direction). [25][26] Their highly anisotropic structure allows such type of compounds to exfoliate through a solventassisted sonication. By comparison, exfoliating layered metal oxides with charged host layers is more difficult because of strong ionic interactions between host layers and interlayer cations. ...
Article
Ir-based perovskite oxides show great promise for next-generation oxygen evolution reaction (OER) electrocatalysts in acidic medium, but they are generally stuck with their uncontrollable surface amorphization and thus structural instability (e.g., serious Ir leaching) during OER. Herein, we report the high-yield chemical exfoliation of Ruddlesden-Popper layered perovskite Sr2IrO4 into protonated, colloidal nanosheets with undamaged perovskite framework. We further demonstrate the potential of protonated perovskite nanosheets to evade the trade-off between OER activity and structural stability. The 2D morphological benefit and nice monodispersity of these protonated perovskite nanosheets enable the facile fabrication of ultralow-Ir-loading catalyst film (30 µg cm-2), which exhibits about ten times higher activity than the IrO2 catalyst film, and undergoes almost as much Ir leaching during OER. Our joint experimental and theoretical results also reveal that structural hydroxyl groups on the surface of protonated nanosheets participate in the catalytic cycle of OER, and the protonated layered perovskite framework represents an example of OER electrocatalyst that works with a nontraditional adsorbate evolution mechanism.
... Growth methods to obtain uniform 2D layers on large areas could be based either on chemical methods (for example, CVD) or on physical deposition such as MBE, PLD and sputtering 114,115,147,[164][165][166][167][168][169][170][171] (Fig. 3a). Chemical routes are arguably the most promising owing to their low cost and compatibility with large-wafer processing but progress so far is limited to a few selected materials. ...
Article
Non-volatile magnetic random-access memories (MRAMs), such as spin-transfer torque MRAM and next-generation spin–orbit torque MRAM, are emerging as key to enabling low-power technologies, which are expected to spread over large markets from embedded memories to the Internet of Things. Concurrently, the development and performances of devices based on two-dimensional van der Waals heterostructures bring ultracompact multilayer compounds with unprecedented material-engineering capabilities. Here we provide an overview of the current developments and challenges in regard to MRAM, and then outline the opportunities that can arise by incorporating two-dimensional material technologies. We highlight the fundamental properties of atomically smooth interfaces, the reduced material intermixing, the crystal symmetries and the proximity effects as the key drivers for possible disruptive improvements for MRAM at advanced technology nodes. Developments, challenges and opportunities in using two-dimensional materials for the next generation of non-volatile spin-based memory technologies are reviewed, and possible disruptive improvements are discussed.
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Naturally occurring van der Waals crystals have brought unprecedented interest to nanomaterial researchers in recent years. So far, more than 1800 layered materials (LMs) have been identified but only a few insulating and naturally occurring LMs were deeply investigated. Phyllosilicate minerals, which are a class of natural and abundant LMs, have been recently considered as a low-cost source of insulating nanomaterials. Within this family an almost barely explored material emerges: phlogopite [KMg3(AlSi3)O10(OH)2]. Here we carry out a high throughput characterization of this LM by employing several experimental techniques, corroborating the major findings with first-principles calculations. We show that monolayers (1L) and few-layers of this material are air and temperature stable, as well as easily obtained by the standard mechanical exfoliation technique, have an atomically flat surface, and lower bandgap than its bulk counterpart, an unusual trend in LMs. We also systematically study the basic properties of ultrathin phlogopite and demonstrate that natural phlogopite presents iron impurities in its crystal lattice, which decreases its bandgap from about 7 eV to 3.6 eV. Finally, we combine phlogopite crystals with 1L-WS2 in ultrathin van der Waals heterostructures and present a photoluminescence study, revealing a significant enhancement on the 1L-WS2 optical quality (i.e., higher recombination efficiency through neutral excitons) similarly to that obtained on 1L-WS2/hBN heterostructures. Our proof-of-concept study shows that phlogopite should be regarded as a good and promising candidate for LM-based applications as a low-cost layered nanomaterial.
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Exploiting the full potential of layered materials for a broad range of applications requires delamination into functional nanosheets. Delamination via repulsive osmotic swelling is driven by thermodynamics and represents the most gentle route to obtain nematic liquid crystals consisting exclusively of single-layer nanosheets. This mechanism was, however, long limited to very few compounds, including 2:1-type clay minerals, layered titanates, or niobates. Despite the great potential of zeolites and their microporous layered counterparts, nanosheet production is challenging and troublesome, and published procedures implied the use of some shearing forces. Here, we present a scalable, eco-friendly, and utter delamination of the microporous layered silicate ilerite into single-layer nanosheets that extends repulsive delamination to the class of layered zeolites. As the sheet diameter is preserved, nematic suspensions with cofacial nanosheets of ≈9000 aspect ratio are obtained that can be cast into oriented films, e.g., for barrier applications.
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Naturally occurring van der Waals crystals have brought unprecedented interest to nanomaterial researchers in recent years. So far, more than 1800 layered materials (LMs) have been identified but only a few insulating and naturally occurring LMs were deeply investigated. Phyllosilicate minerals, which are a class of natural and abundant LMs, have been recently considered as a low-cost source of insulating nanomaterials. Within this family an almost barely explored material emerges: phlogopite [KMg3(AlSi3)O10(OH)2]. Here we carry out a high throughput characterization of this LM by employing several experimental techniques, corroborating the major findings with first-principles calculations. We show that monolayers (1L) and few-layers of this material are air and temperature stable, as well as easily obtained by the standard mechanical exfoliation technique, have an atomically flat surface, and lower bandgap than its bulk counterpart, an unusual trend in LMs. We also systematically study the basic properties of ultrathin phlogopite and demonstrate that natural phlogopite presents iron impurities in its crystal lattice, which decreases its bandgap from about 7 eV to 3.6 eV. Finally, we combine phlogopite crystals with 1L-WS2 in ultrathin van der Waals heterostructures and present a photoluminescence study, revealing a significant enhancement on the 1L-WS2 optical quality (i.e., higher recombination efficiency through neutral excitons) similarly to that obtained on 1L-WS2/hBN heterostructures. Our proof-of-concept study shows that phlogopite should be regarded as a good and promising candidate for LM-based applications as a low-cost layered nanomaterial.
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Two-dimensional semiconductors with suitable indirect band gaps, excellent light absorption capacity, and oxidation resistance are particularly suitable for material applications. Here based on first-principle calculations, we report that the FeP2 monolayer, which is isoelectronic with MoS2, has novel electronic properties and an ultra-low diffusion energy barrier of K on the surface, indicating its potential as an anode material of K-ion batteries. The calculated phonon dispersion curves, molecular dynamics, and elastic constants showed that it has high structural stability and oxidation resistance. The monolayer was a semiconductor with an indirect band gap of 0.68 eV. In addition, the FeP2 monolayer had obvious light absorption in the infrared, visible, and ultraviolet regions, which can be widely used in optoelectronic devices. Bonding analysis showed that there were multicenter bonds inside every hexagonal ring. As the anode material of K-ion batteries, the FeP2 monolayer had a capacity of 456.84 mA h g-1, low diffusion energy barrier, and open-circuit voltage. All these characteristics suggest that the FeP2 monolayer is a potential anode material for K-ion batteries, which needs to be further verified by experiments.
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Magnetic, dielectric, and structural investigations of Cu(Cr y ,In 1− y )P 2 (Se x ,S 1− x ) 6 mixed crystals have revealed bunch of interesting semiconducting properties which are different as found for well‐known graphene. Ferrielectric CuInP 2 S 6 and CuInP 2 Se 6 , and antiferroelectric CuCrP 2 S 6 were investigated for several concentrations of Cr/In and S/Se. Once antiferroelectric is mixed with ferroelectric, dipolar glass phase appears in the middle of the phase diagram. As Cr concentration is higher (>70%), antiferromagnetic spin ordering and antiferroelectricity coexist. Higher In concentration increases phase transition temperature, but still some dipolar glass behavior is observed at low temperatures. The dipole freezing results a broad distribution of the relaxation times. The parameters of the double‐well potentials, the local polarization distribution function, and glass order parameter have been extracted from the dielectric measurements. From these results the complete phase diagram has been constructed. Single‐crystal XRD investigations were used to clarify the structure of CuInP 2 Se 6 at various temperatures. The material exhibits ferrielectric ordering, similar to that of CuInP 2 S 6 .The potential relief for copper ions in CuInP 2 Se 6 was found to be shallower than for its sulfide analog. The large family of chalcogen phosphate layered crystals is enriched by consideration of Mn 2 P 2 S 6 with antiferromagnetic ordering and SnP 2 S 6 ‐type compounds with polar metal state.
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The study presents the novel design and potential function of a two-dimensional nanosheet formed at the liquid-liquid interface between FeII,IIIoxide nanoparticles (IONPs) and [Zn²⁺]:[Insulin]. Under thermal stress, the supramolecular organization of [Zn²⁺]:[Insulin] shifted from hydrophilic phase to hydrophobic, which gradually dissolved with the IONP hydrophobic layer. As a consequence, insulin monomers assembled into two-dimensional nanosheets by intercalating Zn²⁺-bridges, whereas, the IONPs (18-20 nm) were oxidized from Fe3O4 to Fe2O3 crystals, and decomposed into ultra-small crystallites of 2-5 nm. These tiny crystallites were found adsorbed on the nanosheet surface, creating IONP-decorated insulin nanosheet. To our knowledge, the ability of insulin to form nanosheet-structure has never been reported earlier. Adding to its uniqueness, the IONP-insulin nanosheets formed ordered arrays of superimposed surface wrinkles, giving rise to geometrically arranged channels. These surface properties have been previously demonstrated with graphene, but the ability of proteins to exhibit such material properties has not been reported earlier. Thus, the study demonstrates an entirely new potential of proteins, in this case insulin, and is believed to be a new advancement in protein-based bio-nanomaterials. Further, cellular uptake of these nanosheets was observed when BHK-21 cells were cultured on its layer, thereby displaying cell-targeting potential.
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In liquid-based material processing, hydrodynamic forces are known to produce severe bending deformations of two-dimensional (2D) materials such as graphene. The non-linear rotational and deformation dynamics of these atomically thin sheets is extremely sensitive to hydrodynamic particle-particle interactions. To investigate this problem, we developed a computational model of the flow dynamics of elastic sheets suspended in a linear shear flow, solving the full fluid-solid coupling problem in the two-dimensional, slender-body, Stokes flow regime. Both single and pairs of sheets in close proximity are analyzed. Despite the model being two-dimensional, the critical non-dimensional shear rate yielding single-particle buckling is comparable in order of magnitude to that reported for fully three-dimensional, disk-like sheets. For pairs of interacting sheets, hydrodynamic interactions lead either to parallel sliding or bending, depending on the value of an elasto-viscous number based on particle length. For sufficiently low bending rigidity or large shear rates, large deformations of initially stacked sheets lead to sheet reattachment after separation, unlike for the rigid case. A peeling-like dynamics where lubrication provides a viscous bonding force is observed for sheet pairs when one of the two sheets is more rigid than the other. Practical implications for graphene processing and exfoliation are discussed.
Article
Two-dimensional (2D) materials have garnered significant attention due to their ultrathin 2D structures with a high degree of anisotropy and functionality. Reliable manipulation of interfaces between 2D materials and biomaterials is a new frontier for biomedical nanoscience and combining biomaterials with 2D materials offers a promising way to fabricate innovative 2D biomaterials composites with distinct functionality for biomedical applications. Here, we focus exclusively on a summary of the current work in the interface investigation of 2D biomaterials. Specifically, we highlight extraordinary features that make 2D materials so desirable, as well as the molecular level interactions between 2D materials and biomaterials that have been studied thus far. Furthermore, the approaches for investigating the interface characteristics of 2D biomaterials are presented and described in depth. To capture the emerging trend in mass manufacturing of 2D materials, we review the research progress on biomaterial-assisted exfoliation. Finally, we present a critical assessment of newly developed 2D biomaterials in biomedical applications.
Chapter
In today's rapidly evolving technology-centric society, many aspects of our everyday lives hinge on the ready availability of energy-storage devices such as batteries to meet the tremendous energy demands of portable and consumer systems. The lithium-ion battery (LIB) is one of the most widely adopted energy-storage platforms based on the lithium-ion intercalation mechanism. Although LIBs have been studied extensively over the years, major materials-related issues nonetheless arise and have limited their applicability in high-performance commercial systems. Some of the challenges discussed in this work can be alleviated using two-dimensional (2-D) layered materials to enhance electrical conductivity and improve electrochemical properties within galvanic LIB cells. We discuss using some of these 2-D materials, such as graphene, molybdenum disulfide (MoS2), tungsten disulfide (WS2), hexagonal-boron nitride (h-BN), and MXenes, to form solution dispersions for flexible electronics and additive manufacturing platforms, where such manufacturing approaches can also be applied to the development of conformable batteries.
Article
In this article, we present a fab-compatible metal–organic chemical vapor deposition growth process, realized in a hydrogen ambience, of two-dimensional (2D) layered GaSe on 200 mm diameter Si(111) wafers. Atomic scale characterization reveals initial stages of growth consisting of passivation of the H–Si (111) surface by a half-monolayer of GaSe, followed by nucleation of 2D-GaSe from the screw dislocations located at the step edges of the substrate. We, thus, demonstrate that by using a Si wafer that is slightly misoriented toward [Formula: see text], the crystallographic orientation of 2D-GaSe can be step-edge-guided. It results in a coalesced layer that is nearly free from antiphase boundaries. In addition, we propose a sequential process to reduce the density of screw dislocations. This process consists in a subsequent regrowth after partial sublimation of the initially grown GaSe film. The local band bending in GaSe near the antiphase boundaries measured by Kelvin probe force microscopy emphasizes the electrical activity of these defects and the usefulness of having a nearly single-orientation film. Such a low defectivity layer opens up the way toward large-scale integration of 2D-optical transceivers in Si CMOS technology.
Article
Two‐dimensional (2D) polymer nanonets have demonstrated great potential in various application fields due to their integrated advantages of ultrafine diameter, small pore size, high porosity, excellent interconnectivity, and large specific surface area. Here, a comprehensive overview of the controlled constructions of the polymer nanonets derived from electrospinning/netting, direct electronetting, self‐assembly of cellulose nanofibers, and nonsolvent‐induced phase separation is provided. Then, the widely researched multifunctional applications of polymer nanonets in filtration, sensor, tissue engineering, and electricity are also given. Finally, the challenges and possible directions for further developing the polymer nanonets are also intensively highlighted. This article is protected by copyright. All rights reserved
Article
A two-dimensional (2D) high-temperature ferromagnetic half-metal whose magnetic and electronic properties can be flexibly tuned is required for the application of new spintronics devices. In this paper, we predict a stable Ir 2 TeI 2 monolayer with half-metallicity by systematical first-principles calculations. Its ground state is found to exhibit inherent ferromagnetism and strong out-of-plane magnetic anisotropy of up to 1.024 meV per unit cell. The Curie temperature is estimated to be 293 K based on Monte Carlo simulation. Interestingly, a switch of magnetic axis between in-plane and out-of-plane is achievable under hole and electron doping, which allows for the effective control of spin injection/detection in such 2D systems. Furthermore, the employment of biaxial strain can realize the transition between ferromagnetic and antiferromagnetic states. These findings not only broaden the scope of 2D half-metal materials but they also provide an ideal platform for future applications of multifunctional spintronic devices.
Conference Paper
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The production of energy by using renewable energy sources are going depth of the earth. Production energy by using a traditional blade wind has many advantages and disadvantages one of them, the cost of the capital and maintenance cost and friction loss represents a negative point. At the present, a new approach of capturing wind energy by using bladeless windmill find a low-priced and safe replacement to conventional windmills. Vortex-Bladeless is new concept of a wind turbine without blades called vorticity wind turbine which uses the VIV. The vortex design aims to eliminate and reduce many of the existing problems in conventional generators and represents a new paradigm of wind energy. Vortex can be able to operate efficiently at lower wind speeds, so runtime increases. The purpose of this is study to provide a basic comparison between the conventional wind turbine and vortex paradigm in harvesting wind energy.
Article
Confined electronic states and optical transitions in 3D topological insulator nanoparticles have been studied in the literature, assuming idealized geometries such as spheres or infinitely long cylinders, that allow to obtain analytical solutions to the corresponding eigenvalue equation within such geometries. In contrast, in this article we consider triangular-shaped nanoplates as a more realistic approximation to the experimentally observed morphologies of topological insulator nanoparticles. In this particular geometry, we obtain analytical expressions for the confined eigenstates and the corresponding energy spectrum. Moreover, by a spatial representation of the probability density distribution, we further identify the conditions leading to the emergence of topologically trivial surface states, i.e. those arising as a result of morphological-dependent quantum confinement of the bulk that nonetheless project onto the surface, in contrast with topologically protected surface states. Finally, we also study the optical transitions and the corresponding selection rules imposed by the nanoparticle size and morphology.
Chapter
Given their unique helical-chain crystal structure, tellurium (Te) and selenium (Se) can present in both two-dimensional (2D) form such as layered-thin films and one-dimensional (1D) configuration such as nanowires. These two elemental materials have attracted more and more attention due to their excellent physical properties, including the tunable bandgaps, high carrier mobilities, good thermoelectric properties, ambient stability, and strong and angle-dependent photoresponse. Especially, Te has started to show potential to be a new-generation electronic material for future device applications beyond Moore’s law by overcoming the fundamental challenges that graphene, transition metal dichalcogenides, and black phosphorus encountered. In the past few years, reliable growth methods have been reported, including not only their 2D configuration (termed tellurene and selenene) down to monolayer but also their 1D form down to single atomic chain limit. These synthesis routes provide well-grounded access to the materials, benefiting more property investigation and application exploration.
Article
Recently, layered double hydroxides (LDHs) have gathered vast interest due to overall positive charge, unique crystallinity, and biocompatibility for diverse applications. Despite the advantageous attributes, these hydrotalcites often result in several limitations concerning the application requirements, such as aggregation, as well as poor chemical and thermal stabilities, hindering their scale‐up progress and practical utilization. In addressing these issues, the recent advancements in the fabrication of intelligent LDHs nanocomposites based on organically (polymer/polyelectrolyte)‐modified and inorganic (metal)‐composited architectures are systematically presented. Initially, a brief note on the shortcomings in various fields and the chemistry of these pristine LDHs is given. Then, various synthetic strategies used to fabricate these emerging LDH nanocomposites are comprehensively emphasized, focusing on the advancements in their structure and applicability. In addition, the effects of various attractive physicochemical attributes of LDHs and their nanocomposite forms are discussed, including their applicability in adsorption, biomedicine, catalysis, energy, and environment‐related applications. In summary, this article is concluded with an outlook concerning the positioning of LDH‐based nanocomposites compared to other innovative materials, as well as the current challenges and future requirements for scale‐up.
Chapter
Magnetism is emerging as a key property of two-dimensional (2D) materials and heterostructures. 2D magnetism engenders new quantum and topological phases, endows materials with unexpected functionalities, and inspires new device concepts. The family of Xenes and their derivatives—materials at the core of 2D research—present an important constituent to the library of 2D magnets. Here, we trace out the development of Xene magnetism from general theoretical guidelines to experimental realization of intrinsic 2D magnets in a class of Xene compounds. In particular, we review the synthesis and properties of silicene and germanene coupled with rare earths which evolve from antiferromagnets in multilayer structures to 2D ferromagnets in the monolayer (ML) limit. Unconventional transport properties accompany magnetism in Xene materials to exhibit high carrier mobility in multilayers, colossal exponential negative magnetoresistance in one ML, and layer-controlled laws of electron transport. Furthermore, we demonstrate that the general approach developed for Xenes is applicable to graphene, making it ferromagnetic. Finally, we outline the potential future developments in Xene magnetism.
Article
The outstanding chemical and physical properties of 2D materials, together with their atomically thin nature, make them ideal candidates for metaphotonic device integration and construction, which requires deep subwavelength light-matter interaction to achieve optical functionalities beyond conventional optical phenomena observed in naturally available materials. In addition to their intrinsic properties, the possibility to further manipulate the properties of 2D materials via chemical or physical engineering dramatically enhances their capability, evoking new science on light-matter interaction, leading to leaped performance of existing functional devices and giving birth to new metaphotonic devices that were unattainable previously. Comprehensive understanding of the intrinsic properties of 2D materials, approaches and capabilities for chemical and physical engineering methods, the resulting property modifications and novel functionalities, and applications of metaphotonic devices are provided in this review. Through reviewing the detailed progress in each aspect and the state-of-the-art achievement, insightful analyses of the outstanding challenges and future directions are elucidated in this cross-disciplinary comprehensive review with the aim to provide an overall development picture in the field of 2D material metaphotonics and promote rapid progress in this fast emerging and prosperous field.
Article
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In recent years, 2D oxides have attracted considerable attention due to their novel physical properties and excellent stability. With the efforts of researchers, significant progress has been made in the synthesis and electronics and optoelectronics application of 2D oxides. Herein, a systematic review focusing on the preparation of 2D oxides and their applications in electronics and optoelectronics is provided. First, 2D oxides are summarized and classified according to their elements. Then, common preparation methods to synthesize 2D oxides including exfoliation, liquid‐phase synthesis, vapor deposition, surface oxidation of metal, and so on are introduced. Further, the applications of 2D oxides in electronics and optoelectronics are presented. Finally, the current challenges and envisioned development of 2D oxides are commented and prospected. Due to the excellent properties and air stability, 2D oxides show promising application prospects in optoelectronics and electronics, which are expected to promote the development of the semiconductor industry together with common other 2D materials. Herein, the preparation and application in optoelectronics and electronics of 2D oxides in recent years are summarized.
Article
Recently, the 1D ternary transition metal chalcogenide Nb2Pd3Se8 has been reported as a promising channel material for the field‐effect transistors (FETs) with high performance transport behavior. Its structural characteristic of weak van der Waals (vdW) forces between unit ribbons allows for the isolation of high quality Nb2Pd3Se8 nanowires from the bulk crystal that are similar to typical layered 2D materials. This study reports on the liquid phase exfoliation (LPE) of 1D vdW Nb2Pd3Se8 to predict the optimal solvent in terms of the total surface tension and polar/dispersive component ratio. Among the various test solvents, N‐methyl‐2‐pyrrolidone and dimethylformamide are found to be the best solvents for the exfoliation and stabilization of the Nb2Pd3Se8 nanowires due to their well‐matched total surface tensions and polar/dispersive component ratios. Additionally, FETs are fabricated on the LPE‐processed Nb2Pd3Se8 nanowires, and the charge transport behavior is characterized at room temperature. The FETs exhibit n‐type characteristics with an Ion/Ioff ratio and field‐effect mobility up to ≈103 and 15 cm2 V−1 s−1. This study on the LPE of novel Nb2Pd3Se8 nanowires is an important step toward various practical applications in nanoelectronics. Liquid phase exfoliation of 1D ternary transition metal chalcogenide Nb2Pd3Se8 is studied. The N‐methyl‐2‐pyrrolidone and dimethylformamide are found to be the best solvents for the exfoliation and stabilization of the Nb2Pd3Se8. The field‐effect transistors fabricated by exfoliated Nb2Pd3Se8 exhibit n‐type characteristics with an Ion/Ioff ratio and field‐effect mobility up to ≈103 and 15 cm2 V−1 s−1.
Article
Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.
Article
Currently, hydrogen is mainly produced by conversion from natural gas via steam methane reforming (SMR), generating massive amounts of CO2. Here, we present a novel production scheme that can neutralise the CO2 from natural gas-based hydrogen productions by direct deposition of 2-dimensional carbon as cement-nanoadditive. Our tests demonstrated that cement-compatible particles can be used effectively as substrates to grow carbon nanosheets. Our analysis showed that the scheme, bridging hydrogen and cement industries, translates a ~268.7 tons cement reduction per ton of produced hydrogen with >99% reduction of carbon nanosheets costs. Correspondingly, 375.5 Mt CO2 generated from the current SMR-based hydrogen production in the USA, China, and Australia could be neutralised by adopting this approach. We showed that combining CO2 capture in SMR and 5% replacement by our scheme can produce carbon-neutral hydrogen to meet the predicted global demand in 2045.
Article
Flexible electronics require elastomeric and conductive biointerfaces with native tissue-like mechanical properties. The conventional approaches to engineer such a biointerface often utilize conductive nanomaterials in combination with polymeric hydrogels that are cross-linked using toxic photoinitiators. Moreover, these systems frequently demonstrate poor biocompatibility and face trade-offs between conductivity and mechanical stiffness under physiological conditions. To address these challenges, we developed a class of shear-thinning hydrogels as biomaterial inks for 3D printing flexible bioelectronics. These hydrogels are engineered through a facile vacancy-driven gelation of MoS2 nanoassemblies with naturally derived polymer-thiolated gelatin. Due to shear-thinning properties, these nanoengineered hydrogels can be printed into complex shapes that can respond to mechanical deformation. The chemically cross-linked nanoengineered hydrogels demonstrate a 20-fold rise in compressive moduli and can withstand up to 80% strain without permanent deformation, meeting human anatomical flexibility. The nanoengineered network exhibits high conductivity, compressive modulus, pseudocapacitance, and biocompatibility. The 3D-printed cross-linked structure demonstrates excellent strain sensitivity and can be used as wearable electronics to detect various motion dynamics. Overall, the results suggest that these nanoengineered hydrogels offer improved mechanical, electronic, and biological characteristics for various emerging biomedical applications including 3D-printed flexible biosensors, actuators, optoelectronics, and therapeutic delivery devices.
Article
Biomaterials have provided promising strategies towards improving the functions of injured tissues of the nervous system. Recently, 2D nanomaterials, such as graphene, layered double hydroxides (LDHs), and black phosphorous, which are characterized by ultrathin film structures, have attracted much attention in the fields of neural repair and regeneration. 2D nanomaterials have extraordinary physicochemical properties and excellent biological activities, such as a large surface-area-to-thickness ratio, high levels of adhesion, and adjustable flexibility. In addition, they can be designed to have superior biocompatibility and electrical or nano-carrier properties. To date, many 2D nanomaterials have been used for synaptic modulation, neuroinflammatory reduction, stem cell fate regulation, and injured neural cell/tissue repair. In this review, we discuss the advances in 2D nanomaterial technology towards novel neurological applications and the mechanisms underlying their unique features. In addition, the future outlook of functional 2D nanomaterials towards addressing the difficult issues of neuropathy has been explored to introduce a promising strategy towards repairing and regenerating the injured nervous system.
Article
We have recently demonstrated that coated exfoliated Egyptian blue powder is effective for detecting latent fingermarks on a range of highly-patterned non-porous and semi-porous surfaces. In this extension of that work, we present our studies into an alternative approach to prepare exfoliated Egyptian blue coated with cetrimonium bromide and Tween® 20 using a simpler technique. The quality of the latent fingermarks developed with these exfoliated powders and the commercial powder were compared in a comprehensive study. Depletion series of natural fingermarks from a wide range of donors (12 males and females) deposited on non-porous (glass slides) and semi-porous (Australian banknotes) surfaces were used in this study. Enhancement in the performance of the coated exfoliated particles compared to the commercial powder was observed, particularly in the case of aged fingermarks and polymer banknotes as challenging substrates.
Conference Paper
Humboweyne dam structure is a dam that located north east in Hargeisa city of Somaliland (unrecognized sovereign state in the Horn of Africa.), The dam is built for keeping the flood water from hills which used to go directly into the sea without the benefits. The main aims of this study are to identify the possible impacts of sedimentation on the Humbo-weyne reservoir and measuring the technique to assess and to choose the suitable management strategy to control the sedimentation based the two technical reports from Hargeisa Water Agency. Humbo-weyne dam structure project funded by United Arab of Emirates UAE, starting time of the project was 28-12-2015 and the completion time was April 24, 2017 The Reservoir capacity design of the dam was 500,000 m3 . The main purposes of project were water supply and livestock demand [3]. After two year of completion time the Sustainability of Humboweeyne reservoir was severely threatened by sedimentation resulting from design errors, deforestation of the catchment, climate change effects and natural geomorphologic processes of the Humboweeyne catchment. the reservoir began to loss of water-storage capacity due to Sediments from the floods which eventually leads the reduction reliability of the project purposes.
Article
The development of two-dimensional (2D) nanomaterials for cancer therapy has attracted increasing attention due to their high specific surface area, unique ultrathin structure, electronic and photonic properties. For biomedical applications, investigations into the family of 2D materials have been sparked by graphene and its derivatives. Many 2D nanomaterials, including layered double hydroxides, transition metal dichalcogenides, nitrides and carbonitrides, black phosphorus nanosheets, and metal-organic framework nanosheets, are extensively explored as cancer theranostic platforms. In addition to the high drug loading, 2D nanomaterials are featured with improved physiological properties of drugs, prolonged blood circulation, and increased tumor accumulation and bioavailability. As a consequence, 2D nanomaterials have been widely examined in pre-clinical tumor therapy, particularly through the tumor microenvironment (TME) modulation. This review summarizes recent progresses in developing 2D nanomaterials for TME modulating-based cancer diagnosis and therapy. It is anticipated that this review will benefit researchers to obtain a deeper understanding of interactions between 2D nanomaterials and TME components and develop rational and reliable 2D nanomedicines for pre/clinical cancer theranostics.
Article
The ordered coassembly of mixed-dimensional species—such as zero-dimensional (0D) nanocrystals and 2D microscale nanosheets—is commonly deemed impracticable, as phase separation almost invariably occurs. Here, by manipulating the ligand grafting density, we achieve ordered coassembly of 0D nanocrystals and 2D nanosheets under standard solvent evaporation conditions, resulting in macroscopic, freestanding hybrid-dimensional superlattices with both out-of-plane and in-plane order. The key to suppressing the notorious phase separation lies in hydrophobizing nanosheets with molecular ligands identical to those of nanocrystals but having substantially lower grafting density. The mismatched ligand density endows the two mixed-dimensional components with a molecular recognition-like capability, driving the spontaneous organization of densely capped nanocrystals at the interlayers of sparsely grafted nanosheets. Theoretical calculations reveal that the intercalation of nanocrystals can substantially reduce the short-range repulsions of ligand-grafted nanosheets and is therefore energetically favorable, while subsequent ligand-ligand van der Waals attractions induce the in-plane order and kinetically stabilize the laminate superlattice structure.
Chapter
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The production of energy by using renewable energy sources are going depth of the earth. Production energy by using a traditional blade wind has many advantages and disadvantages one of them, the cost of the capital and maintenance cost and friction loss represents a negative point. At the present, a new approach of capturing wind energy by using bladeless windmill find a low-priced and safe replacement to conventional windmills. Vortex-Bladeless is new concept of a wind turbine without blades called vorticity wind turbine which uses the VIV. The vortex design aims to eliminate and reduce many of the existing problems in conventional generators and represents a new paradigm of wind energy. Vortex can be able to operate efficiently at lower wind speeds, so runtime increases. The purpose of this is study to provide a basic comparison between the conventional wind turbine and vortex paradigm in harvesting wind energy.
Article
The advent of graphene and other two-dimensional van der Waals materials, with their unique electrical, optical, and thermal properties has resulted in tremendous progress for fundamental science. Recent developments suggest that taking one more step down in dimensionality — from mono-layer atomic sheets to individual atomic chains — can bring exciting prospects in fundamental science and practical applications. The atomic chain is the ultimate limit in material downscaling, a frontier for establishing an entirely new field of one-dimensional quantum materials. Here, we review this emerging area of one-dimensional van der Waals quantum materials and anticipate its future directions. We focus on quantum effects associated with the charge-density-wave condensate, strongly-correlated phenomena, topological phases, and other unique physical characteristics, which are attainable specifically in van der Waals materials of lower dimensionality. Possibilities for engineering the properties of quasi-one-dimensional materials via compositional changes, vacancies, and defects, as well as their potential applications in composites are also discussed.
Article
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Two-dimensional (2D) nanomaterials such as graphene, boron nitride (BN), and molybdenum disulfide (MoS2) have been attracting increasing research interest in the past few years due to their unique material properties. However, the lack of a reliable large-scale production method is an inhibiting issue for their practical applications. Here we report a facile, efficient, and scalable method for the fabrication of monolayer and few-layer BN, MoS2, and graphene using combined low-energy ball milling and sonication. Ball milling generates two forces on layered materials, shear force and compression force, which can cleave layered materials into 2D nanosheets from the top/bottom surfaces, and the edge of layered materials. Subsequent sonication would further break larger crystallites into smaller crystallites. These fabricated 2D nanosheets can be well dispersed in aqueous solutions at high concentrations, 1.2 mg mL−1 for BN, 0.8 mg mL−1 for MoS2, and 0.9 mg mL−1 for graphene, which are highly advantageous over other methods. These advantages render great potential in the construction of high-performance 2D material-based devices at low cost. For example, a prototype gas sensor is demonstrated in our study using graphene and MoS2, respectively, which can detect several ppm of ammonia gas.
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Layered hydroxide zinc benzoate compounds with structure of layered basic metal salt (LBMS) were prepared by a hydrothermal reaction in a temperature range of 110–180 °C. The structure, chemical composition, and exfoliation reaction in alcohol solvents of the layered compounds were investigated by using XRD, TG-DTA, SEM, and TEM. Two kinds of layered phases with a basal spacing of 1.93 and 1.47 nm were obtained by the hydrothermal reaction. The chemical formulas for the 1.93 and 1.47 nm layered phases can be written as Zn(OH)1.66(C6H5COO)0.34·0.24H2O and Zn(OH)1.14(C6H5COO)0.86, respectively. The 1.93 and 1.47 nm layered phases show plate-like and fibrous particle morphology, respectively. Both of the layered phases can be exfoliated in alcohol solvents. The exfoliated nanosheets of the 1.93 nm layered phase can be curled into the nanotubes of Zn(OH)2. Nanobelt-like and nanoflower-like particles of Zn(OH)2 were formed by exfoliating the 1.47 nm layered phase.
Article
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This perspective covers the use of molybdenum disulfide and related compounds, generally termed MoSx, as electro- or photoelectrocatalysts for the hydrogen evolution reaction (HER). State of the art solutions as well as the most illustrative results from the extensive electro- and photoelectrocatalytic literature are given. The research strategies currently employed in the field are outlined and future challenges pointed out. We suggest that the key to optimising the HER activity of MoS2 is divided into (1) increasing the catalytic activity of the active site, (2) increasing the number of active sites of the catalyst, and (3) improving the electrical contact to these sites. These postulations are substantiated by examples from the existing literature and some new results. To demonstrate the electrocatalytic properties of a highly conductive MoS2 hybrid material, we present the HER activity data for multi-wall MoS2nanotubes on multi-wall carbon nanotubes (MWMoS2@MWCNTs). This exemplifies the typical data collected for the electrochemical HER. In addition, it demonstrates that the origin of the activity is closely related to the amount of edges in the layered MoS2. The photoelectrocatalytic HER is also discussed, based on examples from literature, with an emphasis on the use of MoSx as either (1) the co-catalyst providing the HER activity for a semiconductor, e.g. Mo3S+4on Si or (2) MoS2 as the semiconductor with an intrinsic HER activity. Finally, suggestions for future catalyst designs are given.
Article
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The remarkable properties of graphene have renewed interest in inorganic, two-dimensional materials with unique electronic and optical attributes. Transition metal dichalcogenides (TMDCs) are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Although TMDCs have been studied for decades, recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics. TMDCs such as MoS(2), MoSe(2), WS(2) and WSe(2) have sizable bandgaps that change from indirect to direct in single layers, allowing applications such as transistors, photodetectors and electroluminescent devices. We review the historical development of TMDCs, methods for preparing atomically thin layers, their electronic and optical properties, and prospects for future advances in electronics and optoelectronics.
Book
Materials with layered structures remain an extensively investigated subject in current physics and chemistry. Most of the promising technological applications however deal with intercalation compounds of layered materials. Graphite intercalation compounds have now been known for a long time. Intercalation in transition metal dichalcogenides, on the other hand, has been investigated only recently. The amount of information on intercalated layered materials has increased far beyond the original concept for this volume in the series Physics and Chemistry of Materials with Layered Structures. The large size of this volume also indicates how important this field of research will be, not only in basic science, but also in industrial and energy applications. In this volume, two classes of materials are included, generally investigated by different scientists. Graphite intercalates and intercalates of other inorganic com­ pounds actually constitute separate classes of materials. However, the similarity between the intercalation techniques and some intercalation processes does not justify this separation, and accounts for the inclusion of both classes in this volume. The first part of the volume deals with intercalation processes and intercalates of transition metal dichalcogenides. Several chapters include connected topics necessary to give a good introduction or comprehensive review of these types of materials. Organic as well as inorganic intercalation compounds are treated. The second part includes contributions concerning graphite intercalates. It should be noted that graphite intercalation compounds have already been mentioned in Volumes I and V.
Book
This new volume in the series Physics and Chemistry of Materials with Layered Structures satisfies the need for a comprehensive review of the progress made in the decade 1972-1982 in the field of the electronic properties of layer compounds. Some recent theoretical and experimental developments are highlighted by authori­ tative physicists active in current research. The previous books of this series covering similar topics are volumes 3 and 4. The present review is mainly intended to fulfill the gap up to 1982 and part of 1983. I am indebted to all the authors for their friendly co-operation and continuous effort in preparing the contributions in their own fields of competence. I am sure that both the expertise scientists and the beginners in the field of the electronic properties of layered materials will find this book a valuable tool for their research work. Warm thanks are due to Prof. E. Mooser, General Editor of the series, for his constant and authoritative advice. * * * This book has been conceived as a tribute to Prof. Franco Bassani to whom the Italian tradition in the field of layer compounds, as well as in other fields of solid­ state physics, owes much. The authors of this review have all benefited at some time of their professional life from close cooperation with him. Istituto di Struttura della Materia, VINCENZO GRASSO Universitd di Messina IX V Grasso (ed.). Electronic Structure and Electronic Transitions in Layered Materials. ix.
Article
The transition metal dichalcogenides are about 60 in number. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to less than 1000 Å and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of electrical and structural data available to yield useful working band models that are in accord with a molecular orbital approach. Several special topics have arisen; these include exciton screening, d-band formation, and the metal/insulator transition; also magnetism and superconductivity in such compounds. High pressure work seems to offer the possibility for testing the recent theory of excitonic insulators.
Article
This review reports recent advances in the field of polymer–layered silicate nanocomposites. These materials have attracted both academic and industrial attention because they exhibit dramatic improvement in properties at very low filler contents. Herein, the structure, preparation and properties of polymer–layered silicate nanocomposites are discussed in general, and detailed examples are also drawn from the scientific literature.
Article
Solvent exfoliation of inorganic layered compounds is likely to be important for a range of applications. However, this method generally gives dispersions of small nanosheets at low concentrations. Here we describe methods, based on sonication of powdered MoS2 in the solvent N-methyl-pyrrolidone, to prepare dispersions with significantly increased lateral nanosheet size and dispersed concentration. We find the concentration to scale linearly with starting MoS2 mass allowing the definition of a yield. This yield can be increased to 40% by controlling the sonication time, resulting in concentrations as high as 40 mg/mL. We find the nanosheet size to increase initially with sonication time reaching 700 nm (for a concentration of 7.5 mg/mL). At longer sonication times the nanosheets size falls off due to sonication induced scission. The nanosheets produced by such methods are relatively thin and have no observable defects. We can separate the dispersed nanosheets by size using controlled centrifugation. This allows us to produce dispersions with mean flake size of up to 2 μm. However, such large flakes are noticeably thicker than the standard nanosheets. We demonstrate that such nanosheets can be mixed with polymers to form composites. While standard nanosheets result in no improvement in composite mechanical properties, addition of size-selected nanosheets results in significant improvements in composite modulus and strength.
Article
Hildebrand and Hansen solubility parameters are commonly used to identify suitable solvents for the dispersion or dissolution of a range of solutes, from small molecules to graphene. This practice is based on a number of equations, which predict the enthalpy of mixing to be minimized when the solubility parameters of solvent and solute match. However, such equations have only been rigorously derived for mixtures of small molecules, which interact only via dispersive forces. Herein, we derive a general expression for the enthalpy of mixing in terms of the dimensionality of the solute, where small molecules are considered zero‐dimensional, materials such as polymers or nanotubes are one‐dimensional (1D) and platelets such as graphene are two‐dimensional (2D). We explicitly include contributions due to dispersive, dipole–dipole, and dipole‐induced dipole interactions. We find equations very similar to those of Hildebrand and Hansen so long as the solubility parameters of the solute are defined in a manner which reflects their dimensionality. In addition, the equations for 1D and 2D systems are equivalent to known expressions for the enthalpy of mixing of rods and platelets, respectively, as a function of surface energy. This agreement between our expressions and those commonly used shows that the concept of solubility parameters can be rigorously applied to extended solutes such as polymers, nanotubes, and graphene. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Article
A simple and environmentally friendly method was proposed to prepare high barrier graphene oxide nanosheet (GONS)/poly(vinyl alcohol) (PVA) nanocomposite films. Transmission electrical microscope and two-dimensional wide angle X-ray diffraction techniques showed that GONSs in PVA matrix were fully exfoliated, uniformly dispersed and highly oriented along the surface of nanocomposite films. Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) measurements investigated the strong H-bonding interactions between GONSs and PVA matrix. A remarkable improvement on barrier properties of GONS/PVA nanocomposite films was achieved. Both O2 and water vapor permeability coefficients of PVA film declined by about 98% and 68% at a low GONS loading of 0.72 vol%. This was attributed to excellent impermeable property of GONSs, their full exfoliation, uniform dispersion and high alignment in the PVA matrix and the strong interfacial adhesion between GONSs and PVA matrix. These results demonstrate that such a plate-like nanofiller blending method is an effective strategy to design and fabricate high barrier polymer-based nanocomposite films and it will dramatically promote the application of polymer film in the packaging industry.
Article
Transition-metal trichalcogenides have been investigated as cathode materials in the lithium electrochemical cell. Three lithium ions per TiS3 molecule have been found to be marginally reversible, while only one lithium is reversible in TaSe3. This difference may be related to exfoliation of these substances due to the progress of lithium intercalation.
Article
There has been a lot of confusion about the nature of restacked MoS{sub 2} and WS{sub 2}. The structure has been proposed to be trigonal TiS{sub 2} type with octahedral M{sup 4} and called 1T-MoS{sub 2}. The presence of a distortion in the metal plane that gives rise to a superstructure has been suggested. Electron crystallographic studies on small (submicron) single crystal domains of restacked WS{sub 2} and MoS{sub 2} have been performed to solve their superstructure. It was shown that what initially seems to be a trigonal crystal is actually a triplet of three individual orthorhombic crystals. Using two-dimensional hk0 data from films for both triple and single crystals the authors calculated corresponding Patterson projections, which reveal a severe distortion in the Mo/W plane, forming infinite zigzag chains. The projection of the structure suggests M-M distances of 2.92 and 2.74 {angstrom} for MoS{sub 2} and Ws{sub 2}, respectively. Least-squares refinement from the single-crystal data gives R{sub 1} = 13.3% for WS{sub 2} and R{sub 1} = 15.3% for MoS{sub 2}. Therefore, it is proposed that restacked MoS{sub 2} and WS{sub 2} are not 1T form but rather WTe{sub 2} type.
Article
The performance of photovoltaic cells using as semiconductor a film of layered γ-zirconium phosphate (γ-ZrP) containing Ru(bpy)3 and bipyridinium ions (viologens) as electron relays has been studied. The materials are easily prepared by intercalation of Ru complexes and the bipyridinium ions into preformed γ-ZrP nano sheets as colloidal solutions in the appropriate solvent and concentration. High loading of these two guests has been obtained as determined by elemental analysis. Inclusion of Ru(bpy)3 complex and bipyridinium in the intergallery spaces of γ-ZrP can be assessed by powder XRD monitoring of the d100 peak. A dyad was also synthesized where the Ru(bpy)3 and the 4,4′-bipyridinium were covalently connected by a four-methylene tether. The semiconducting behavior of layered γ-ZrP was supported by cyclic voltammetry (reversible reduction peak at −0.6 V), observation of photocurrent and Mott-Schottky measurements (flat band potential −1.3 V vs. NHE) of thin films of this material supported on FTO electrode. Photovoltaic cells based on γ-ZrP containing Ru(bpy)3, exhibited similar VOC (0.5 V) and fill-factor values (0.3–0.4), differing in the current density and therefore in their efficiency. The maximum efficiency was obtained for the material containing high loading of the dyad (JSC = 0.383 mA/cm2, efficiency 0.1%). The photo response spectrum shows that the main limitation of these materials is still the inefficient photo sensitization of the semiconductor by the dye, probably due to the high negative flat band potential of γ-ZrP.
Article
This paper discusses a derivative of FeOCl chemically prepared by ion exchanging Cl⁻ ions with OH⁻ ions. This modification was made in order to improve the discharge and charge characteristics of a secondary lithium battery made with this material as the cathode. The preparation was accomplished by using the intercalation compound of FeOCl and aniline as an intermediate which has a high reactivity with water. The x-ray diffraction patterns of the reactant and product indicate that a structural change occurred, and the product structure became amorphous. The FT-IR spectrum of the reaction product indicates that an organic compound, which is similar to a secondary phenyl amine, remains in the interlayer space of this product. The discharge and charge characteristics of a lithium battery using this cathode were examined using a coin-type cell. The small cell showed excellent cycleability.
Article
The study investigates the intercalation of magnesium-aluminum layered double hydroxide with sodium dodecyl sulfate. Monolayer intercalation of the LDH-carbonate was achieved using an acetic acid-assisted ion exchange reaction. The carboxylic acid is believed to assist intercalation of dodecyl sulfate by facilitating the elimination of the carbonate ions present in the anionic clay. Bilayer intercalation was achieved by a coprecipitation method and this resulted in a highly crystalline product. However, in this case the interlayer contains a mixture of dodecyl sulfate anion, sodium dodecyl sulfate and the hydrolysis product dodecanol. The organic phase in the latter product shows an order-disorder transition between 100°C and 120°C, with thermal degradation and volatilization commencing above 170°C.
Article
The processing parameters, namely, clay loading, magnetic stirring time and sonication time, were optimized for the dispersion of two types of clay into an epoxy and into chopped strand mat (CSM) glass fiber-based epoxy nanocomposite laminates. A vacuum-assisted resin transfer molding setup was used to fabricate these laminates. Optimizations were performed based on improvements in Young's modulus. The intercalated and exfoliated distributions of clay in the composites were confirmed using X-ray diffraction and transmission electron microscopy. The transmission electron micrographs of optimized specimens showed a well-ordered intercalated structure within the epoxy. Using optimized processing conditions, three layered laminates of CSM, woven roving glass fibers or both were prepared with epoxy and clay for the preparation of new lightweight hybrid epoxy nanocomposites. The tensile, flexural and impact properties of these hybrid nanocomposites were investigated. A combination of the two types of glass fibers produced promising results.
Article
Chemical methods for the exfoliation of transition metal dichalcogenides in a liquid medium to give single-layer dispersions containing quasi-two-dimensional layers of these compounds are surveyed. Data on the structure of dispersions and their use in the synthesis of various types of heterolayered intercalation compounds are discussed and described systematically. Structural features, the electronic structure and the physicochemical properties of the resulting intercalation compounds are considered. The potential of this method of synthesis is compared with that of traditional solid-state methods for the intercalation of layered crystals.
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MnO2/graphene composite was synthesized by a facile and effective polymer-assisted chemical reduction method. The nanosized MnO2 particles were homogeneously distributed on graphene nanosheets, which have been confirmed by scanning electron microscopy and transmission electron microscopy analysis. The capacitive properties of the MnO2/graphene composite have been investigated by cyclic voltammetry(CV). MnO2/graphene composite exhibited a high specific capacitance of 324 F g−1 in 1 M Na2SO4 electrolyte. In addition, the MnO2/graphene composite electrode shows excellent long-term cycle stability (only 3.2% decrease of the specific capacitance is observed after 1,000 CV cycles).
Article
The layered compounds MnPS3 and CdPS3 were exfoliated to form single molecular layers of Mn0.8PS3 and Cd0.8PS3 in suspension in water by ion exchange. The x-ray diffraction patterns of the two single-layer suspensions showed profound differences in some of the Bragg peaks, and we demonstrated that the differences are not due to the quality or size of the single layers, but are caused by structure factor modulations of the Warren tail for two-dimensional systems. We also demonstrated that the Cd or Mn vacancies generated in the exfoliation process are not ordered at long range, in contrast to an earlier report of vacancy ordering on intercalated MnPS3.
Article
Solid acid catalysts offer the opportunity to reduce environmental impact owing to such advantages as ease of product separation and recyclability of the catalyst, which contribute considerably to green chemistry. Nanosheets, crystalline two-dimensional metal oxide sheets prepared from cation-exchangeable layered metal oxides through exfoliation and aggregation, are a novel class of potential solid acid catalysts for replacing liquid acids, such as sulfuric acid. This article reviews the acid strength and acid catalysis of several types of nanosheets, which are strongly dependent on novel strong Brønsted acid sites attributed to bridged OHgroups formed only on nanosheets. An efficient acid catalysis of layered protonated niobium molybdate in Friedel–Crafts alkylation, esterification and hydrolysis, owing to its unique intercalation availability, is also discussed.
Article
Layered materials with intracrystalline reactivity undergo intercalation and pillaring reactions to produce materials with useful properties for catalysis, electrodes for Li batteries and adsorbents. New possibilities for the use of layered inorganic solids came out from the layered structures capable of delamination. The exfoliated particles are considered a new class of nanomaterial based on single crystal nanosheets. Due to their unique morphological features and properties, these nanosheets can be used as building blocks for nanomaterials with innovative properties. In this feature article we describe the aspects related to layered niobate exfoliation and the new possibilities that arises from the use of niobatenanosheets in the manufacturing of thin films, layer-by-layer (LbL) assemblies, hybrid structures, sensors and other materials.
Article
Two-dimensional (2D) nanosheets obtained via exfoliation of layered compounds have attracted intense research in recent years. In particular, the development of exotic 2D systems such as stable graphene and transition-metal oxide nanosheets has sparked new discoveries in condensed matter physics and nanoelectronics. Here, we review the progress made in the synthesis, characterization and properties of oxide nanosheets, highlighting emerging functionalities in electronic and spin-electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanotechnology.
Article
A layered double hydroxide (LDH) with nitrate as the counter anion (LDH–NO3 with Mg/Al = 3) was, for the first time, successfully delaminated in formamide under ultrasonic treatment. Atomic force microscopy (AFM) images showed that a large part of the LDH was delaminated into single and double brucite layers (0.7–1.4 nm in thickness). The nano-sheets had disk-like shapes with a diameter of ca. 20–40 nm. Findings from AFM were in good agreement with the average hydrodynamic diameter determined using dynamic light scattering. Powder X-ray diffraction pattern of LDH dispersed in formamide also confirmed that LDH–NO3 was exfoliated. The dispersions of LDH in formamide were stable and transparent up to a concentration of 40 g L−1. However, formation of transparent gels was observed at concentrations higher than 5 g L−1. Delaminated LDH could be restacked by adding sodium carbonate or ethanol.
Article
A new method for delamination of layered double hydroxides (LDHs) is demonstrated: large quantities of LDHs containing lactate delaminated in water at room temperature to form stable translucent colloidal solutions.
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Exfoliation of layered double hydroxides (LDHs) into single layers provides a new type of nanosheet with ultimate two-dimensional anisotropy and positive charge. In this Highlight article, we briefly review the latest advances in this emerging field. In comparison with the previous studies, we show that micrometer-sized and well-defined LDH nanosheets can be readily attained by synthesizing large crystals of LDH-carbonate via so-called homogeneous precipitation and subsequent exfoliation of the nitrate form in formamide. Some general aspects including the exfoliating process and characterization, a plausible delaminating mechanism, and future challenges, are presented and discussed.
Article
For the first time procedures for the direct characterization of exfoliated nanosheets of LDH (Mg/Al = 3) in suspension are reported. The shape, size and layer thickness of the nanosheets were determined using small angle X-ray and neutron scattering (SAXS/SANS) in combination with dynamic light scattering (DLS) and atomic force microscopy (AFM). Furthermore, by using ultrasonic treatment we were able to delaminate a glycinate containing LDH up to a concentration of 42.5 g L−1, which is ten times higher than the value reported in the literature for the same system. The exfoliated LDH nanosheets were directly characterized in suspension by SAXS/SANS and gave an average layer thickness of 1.4 nm for both tested concentrations (10 and 42.5 g L−1). This result provides strong evidence that the LDH, even at concentrations as high as 42.5 g L−1, is totally delaminated into single or a few stacked brucite layers. AFM images of exfoliated LDH, after dilution and deposition on mica, confirm that exfoliated nanosheets mainly consist of single and double layers, corresponding to thicknesses of 0.6 ± 0.1 and 1.3 ± 0.1 nm, respectively. The diameters of the nanosheets in suspension determined using SAXS and SANS are very similar (between 30 and 40 nm), and are in good accordance with the value observed by AFM (between 10 and 40 nm). Hydrodynamic diameters determined by dynamic light scattering (DLS) were 35 and 60 nm at 10 and 42.5 g L−1, respectively.
Article
Organic compounds such as alkylpyridines, methyl viologen and azo compounds have been intercalated into MoO3layers by ion exchange in which MoO3x–(Na+)x reacted with the organic compounds. Indolinespirobenzopyran (SP) was intercalated by a multi-step method in which amine was intercalated in the first step, and by the co-intercalation of amine and SP the MoO3 layer expanded to 24–28 Å depending upon the kind of amine used in the first step. In the layers, SP existed as its isomerized coloured species, merocyanine (MC). Reduction of Mo by chemical reduction and intercalation of amines and SP was confirmed by X-ray photoelectron spectroscopy.
Article
The preparation and characterization of flexible, superconducting, nanophase materials consisting of organic polymers and NbSe2 layers is reported.
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Single-molecular-layer suspensions and various restacked forms of the metallic layered compounds TaS2 and NbS2 were prepared using the intercalation of hydrogen and water. It was found that the intercalation of water separates the layers by at least 10nm and single-layer X-ray diffraction patterns with only (hk.0) lines are observed for this system. Single layers in suspension are readily made from the water-intercalated material. Restacked films obtained from dried suspensions appear to have a random layer stacking sequence. Electron microscopy shows evidence of single layers up to 200 nm in lateral size in the suspension. The charge density wave superlattice diffraction pattern which is observed in bulk crystalline TaS2 below 75 K is not observed in thin platelets obtained from TaS2 suspensions.
Article
Three kinds of FeOOH derivatives were prepared from FeOCl using the ion exchange reaction of Cl− ion in FeOCl with OH− and CH3O−. The reaction products were identified as γ-FeOOH, the amorphous FeOOH including aniline, and FeOOCH3. The amorphous FeOOH including aniline showed a much better performance as cathode of the rechargeable lithium battery than that of γ-FeOOH and FeOOCH3. The discharge behavior of γ-FeOOH was similar to that of FeOOCH3. From these results, it was found that the aniline interacted with FeOOH matrix played an important role for the high discharge potential (more than 3.0 V versus Li/Li+) and the high discharge capacity (more than 200 mA h g−1) of the amorphous FeOOH including aniline.
Article
A derivative of was chemically prepared by ion exchanging Cl⁻ ions with OH⁻ ions. This modification was made in order to improve the discharge and charge characteristics of a secondary lithium battery made with this material as the cathode. The preparation was accomplished by using the intercalation compound of and aniline as an intermediate which has a high reactivity with water. The x‐ray diffraction patterns of the reactant and product indicate that a structural change occurred, and the product structure became amorphous. The FT‐IR spectrum of the reaction product indicates that an organic compound, which is similar to a secondary phenyl amine, remains in the interlayer space of this product. The discharge and charge characteristics of a lithium battery using this cathode were examined using a coin‐type cell. The small cell showed excellent cycleability.
Article
Delamination of the layered double hydroxide structure [Zn2Al(OH)6][C12H25SO4 ·nH2O] was realized by dispersion in butanol; translucent colloidal solutions are stable for at least 8 months with oriented LDH materials with extended crystallite size being obtained; the results presented here suggest that total delamination occurs in the colloidal solution.
Article
The exfoliation of zirconium phosphate with a layered structure of the γ-type is of interest from both a fundamental and a technological point of view. However, until now, the results reported in the literature have not been as good as those reported for α-zirconium phosphate. It has been found that a very good exfoliation of γ-zirconium phosphate with the formation of very stable colloidal dispersions can be obtained at temperatures higher than 55°C and for percentages of acetone in the range 35–80% in volume. The exfoliation was attributed to the formation of an expanded acetone intercalated phase in which the interlayer hydrogen bonds originally present in the γ-ZrPO4·O2P(OH)2·2H2O are broken. By filtration of the colloidal dispersions, very compact and flexible self-consistent films can be obtained.
Article
We investigate the blister features that appear in small-angle hollow-cone dark-field images of overlapping layers of delaminated calcium niobate. Modelling shows that the blister contrasts are caused by pockets of gas or liquid that have become trapped when calcium niobate layers are brought into contact and reseal. Hollow-cone dark-field contrast is primarily due to diffraction variations caused by sheet bending around the pressurized cracks.
Article
Thin films of Wo3 deposited on quartz substrates at room temperature have been shown to be amorphous in structure. The optical absorption spectra of the amorphous and crystalline films have been measured in the temperature range 110° to 500°K. The fundamental absorption edge of an amorphous film occurs at 3800 Å which on crystallization moves to 4500 Å. On the high-energy side of the absorption edge several absorption peaks are resolvable in both types of film. The frequency dependence of the absorption coefficient below 104 cm−1 is described by an expression of the form K (v, T) = K 0 exp[− (β/kT) (E 0 − hv)] and above 104 cm−1 it follows a square law dependency. The temperature coefficient of the band edges was found to be − 5.0 × 10−4 eV/°K and the estimated band gaps at 0°K were found to be 3.65 and 3.27 eV for the amorphous and crystalline films, respectively.The electrical conductivity of a thin film has been measured in the temperature range 298–573°K and the activation energy was found to be 1.04 eV. Irradiation within the fundamental absorption edge gives rise to photoconductivity. Threshold wavelengths for photoconductivity were observed at 3250 and 5500 Å for the amorphous and crystalline films, respectively.A broad colour-centre band having a maximum at 9100 Å and a shoulder at 1.6 μ has been observed on irradiating the amorphous film with wavelengths shorter than 3500 Å and also on applying an electric field of ∼ 104 V./cm. The colour centre, thus formed, shows a slight bleaching with light. However, it bleaches thermally and in presence of oxidizing atmosphere. The formation of colour-centres is associated with increased electrical conductivity of the film. No colouration is observed in fully oxidized samples of WO3. An energy level diagram has been proposed to account for the optical and electrical properties as well as the colour-centre formation in WO3 films.
Article
PbI2, BiI3, CdI2 and AgI crystalline samples intercalated with pyridine have been studied by Raman spectroscopy. Comparing the Raman spectra of pristine metal iodides with those of intercalated samples we have shown the coexistence, in the host crystalline lattice, of two adsorbed forms: a physisorbed one, featured by weak forces of van der Waals type and a chemisorbed one, involving stronger forces related to an electrostatic interaction. The physisorbed form is consistent with the molecules inserted into the interlayer spaces while the chemisorbed form is represented by the molecules forming coordination complexes with the crystalline lattice cations. The crucial role in the formation of such complexes is played by the lone pair of nitrogen atom belonging to the molecules.