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Exfoliation (chemistry)
In material science, layered materials are solids with highly anisotropic bonding, in which two-dimensional sheets are internally strongly bonded, but only weakly bonded to adjacent layers. Owing to their distinctive structures, layered materials are often suitable for intercalation reactions. One large family of layered materials are metal dichalcogenides. In such materials, the M-chalcogen bonding is strong and covalent. These materials exhibit anisotropic electronic properties such as thermal and electrical conductivity. Exfoliation Because the layers bond to each other by relatively weak van der Waals forces, some layered materials are amenable to exfoliation, the complete separation of the layers of the material. Exfoliation can be done using sonication, mechanical, hydrothermal, electrochemical, laser-assisted, and microwave-assisted methods. Typically aggressive conditions are required involving highly polar solvents and reagents. In the ideal case, exfoliation affords ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intercalation Reaction
In chemistry, intercalation is the reversible inclusion or insertion of a molecule (or ion) into layered materials with layered structures. Examples are found in graphite and transition metal dichalcogenides. : Examples Graphite One famous intercalation host is graphite, which intercalates potassium as a guest. Intercalation expands the van der Waals gap between sheets, which requires energy. Usually this energy is supplied by charge transfer between the guest and the host solid, i.e., redox. Two potassium graphite compounds are KC8 and KC24. Carbon fluorides (e.g., (CF)x and (C4F)) are prepared by reaction of fluorine with graphitic carbon. The color is greyish, white, or yellow. The bond between the carbon and fluorine atoms is covalent, thus fluorine is not intercalated. Such materials have been considered as a cathode in various lithium batteries. Treating graphite with strong acids in the presence of oxidizing agents causes the graphite to oxidise. Graphite bisulfate, 2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Conductivity
Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows electric current. Resistivity is commonly represented by the Greek letter (rho). The SI unit of electrical resistivity is the ohm-meter (Ω⋅m). For example, if a solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is , then the resistivity of the material is . Electrical conductivity or specific conductance is the reciprocal of electrical resistivity. It represents a material's ability to conduct electric current. It is commonly signified by the Greek letter ( sigma), but ( kappa) (especially in electrical engineering) and ( gamma) are sometimes used. The SI unit of electrical conductivity is siemens per metre (S/m). Resistivity and conductivity are inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Van Der Waals Force
In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and therefore more susceptible to disturbance. The van der Waals force quickly vanishes at longer distances between interacting molecules. Named after Dutch physicist Johannes Diderik van der Waals, the van der Waals force plays a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics. It also underlies many properties of organic compounds and molecular solids, including their solubility in polar and non-polar media. If no other force is present, the distance between atoms at which the force becomes repulsive rather than attractive as the atoms approach one another is called the van der Waals contact distance; this phenomenon resul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Single-layer Materials
In materials science, the term single-layer materials or 2D materials refers to crystalline solids consisting of a single layer of atoms. These materials are promising for some applications but remain the focus of research. Single-layer materials derived from single elements generally carry the -ene suffix in their names, e.g. graphene. Single-layer materials that are compounds of two or more elements have -ane or -ide suffixes. 2D materials can generally be categorized as either 2D allotropes of various elements or as compounds (consisting of two or more covalently bonding elements). It is predicted that there are hundreds of stable single-layer materials. The atomic structure and calculated basic properties of these and many other potentially synthesisable single-layer materials, can be found in computational databases. 2D materials can be produced using mainly two approaches: top-down exfoliation and bottom-up synthesis. The exfoliation methods include sonication, mechanical, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Graphene
Graphene () is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure. "Carbon nanostructures for electromagnetic shielding applications", Mohammed Arif Poothanari, Sabu Thomas, et al., ''Industrial Applications of Nanomaterials'', 2019. "Carbon nanostructures include various low-dimensional allotropes of carbon including carbon black (CB), carbon fiber, carbon nanotubes (CNTs), fullerene, and graphene." The name is derived from "graphite" and the suffix -ene, reflecting the fact that the allotrope of carbon contains numerous double bonds. Each atom in a graphene sheet is connecte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metal Dichalcogenide
: 220px, Cadmium sulfide, a prototypical metal chalcogenide, is used as a yellow pigment. A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for sulfides, selenides, tellurides, and polonides, rather than oxides. Many metal ores exist as chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS2 is a common solid lubricant. Alkali metal and alkaline earth chalcogenides Alkali metal and alkaline earth monochalcogenides are salt-like, being colourless and often water-soluble. The sulfides tend to undergo hydrolysis to form derivatives containing bisulfide (SH−) anions. The alkali metal chalcogenides often crystallize with the antifluorite structure and the alkaline earth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tantalum Disulfide
Tantalum(IV) sulfide is an inorganic compound with the formula Tantalum, TaSulfide, S2. It is a Layered material, layered compound with three-coordinate sulfide centres and trigonal prismatic or octahedral metal centres. It is structurally similar to molybdenum disulfide MoS2, and numerous other transition metal dichalcogenide materials. The 1T-TaS2 polytype exhibits some unusual properties. In common with many other transition metal dichalcogenide (TMD) compounds, which are metallic at high temperatures, it exhibits a series of charge-density-wave (CDW) phase transitions from 550 K to 50 K. It is unusual amongst them in showing a low-temperature insulating state below 200 K, which is believed to arise from electron correlations, similar to many oxides. The insulating state is commonly attributed to a Mott state. It is also superconducting under pressure or upon doping, with a familiar dome-like phase diagram as a function of dopant, or substituted isovalent element concentration. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Titanium Disulfide
Titanium disulfide is an inorganic compound with the formula Ti S2. A golden yellow solid with high electrical conductivity, it belongs to a group of compounds called transition metal dichalcogenides, which consist of the stoichiometry M E2. TiS2 has been employed as a cathode material in rechargeable batteries. Structure With a layered structure, TiS2 adopts a hexagonal close packed (hcp) structure, analogous to cadmium iodide (CdI2). In this motif, half of the octahedral holes are filled with a "cation", in this case Ti4+. Each Ti centre is surrounded by six sulfide ligands in an octahedral structure. Each sulfide is connected to three Ti centres, the geometry at S being pyramidal. Several metal dichalcogenides adopt similar structures, but some, notably MoS2, do not. The layers of TiS2 consist of covalent Ti-S bonds. The individual layers of TiS2 are bound together by van der Waals forces, which are relatively weak intermolecular forces. It crystallises in the space ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large scale (300 kton/year, in 1989) for uses in pencils, lubricants, and electrodes. Under high pressures and temperatures it converts to diamond. It is a weak conductor of heat and electricity. Types and varieties Natural graphite The principal types of natural graphite, each occurring in different types of ore deposits, are * Crystalline small flakes of graphite (or flake graphite) occurs as isolated, flat, plate-like particles with hexagonal edges if unbroken. When broken the edges can be irregular or angular; * Amorphous graphite: very fine flake graphite is sometimes called amorphous; * Lump graphite (or vein graphite) occurs in fissure veins or fractures and appears as massive platy intergrowths of fibrous or acicular crystalline ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Iron Oxychloride
Iron oxychloride is the inorganic compound with the formula FeOCl. This purple solid adopts a layered structure, akin to that of cadmium chloride. The material slowly hydrolyses in moist air. The solid intercalates electron donors such as tetrathiafulvalene and even pyridine to give mixed valence charge-transfer salts. Intercalation is accompanied by a marked increase in electrical conductivity and a color change to black. Production FeOCl is prepared by heating iron(III) oxide with ferric chloride at over the course of several days: :Fe2O3 + FeCl3 → 3 FeOCl Alternatively, FeOCl may be prepared by the thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is re ... of FeCl3⋅6H2O at over the course of one hour: :FeCl3 ⋅ 6H2O → FeOCl + 5 H2O + ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
