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Layered Double Hydroxides
Layered double hydroxides (LDH) are a class of ionic solids characterized by a layered structure with the generic layer sequence cB Z AcBsub>''n'', where c represents layers of metal cations, A and B are layers of hydroxide () anions, and Z are layers of other anions and neutral molecules (such as water). Lateral offsets between the layers may result in longer repeating periods. The intercalated anions (Z) are weakly bound, often exchangeable; their intercalation properties have scientific interest and industrial applications. LDHs occur in nature as minerals, as byproducts of metabolism of certain bacteria, and also unintentionally in man-made contexts, such as the products of corrosion of metal objects. Structure and formulas LDHs can be seen as derived from hydroxides of divalent cations (d) with the brucite (Mg(OH)2) layer structure dB AdBsub>''n'', by cation (c) replacement (Mg2+ → Al3+), or by cation oxidation (Fe2+ → Fe3+ in the case of green rust, Fe(OH)2), in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clay Mineral
Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals form in the presence of water and have been important to life, and many theories of abiogenesis involve them. They are important constituents of soils, and have been useful to humans since ancient times in agriculture and manufacturing. Properties Clay is a very fine-grained geologic material that develops plasticity when wet, but becomes hard, brittle and non–plastic upon drying or firing. It is a very common material, and is the oldest known ceramic. Prehistoric humans discovered the useful properties of clay and used it for making pottery. The chemistry of clay, including its capacity to retain nutrient cations such as potassium and ammonium, is important to soil fertility. Because the individual particles in clay are less ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Petroleum
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude oil and petroleum products that consist of refined crude oil. A fossil fuel, petroleum is formed when large quantities of dead organisms, mostly zooplankton and algae, are buried underneath sedimentary rock and subjected to both prolonged heat and pressure. Petroleum is primarily recovered by oil drilling. Drilling is carried out after studies of structural geology, sedimentary basin analysis, and reservoir characterisation. Recent developments in technologies have also led to exploitation of other unconventional reserves such as oil sands and oil shale. Once extracted, oil is refined and separated, most easily by distillation, into innumerable products for direct use or use in manufacturing. Products include fuels such as gasol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural or constitutional isomerism, in which ''bonds'' between the atoms differ; and stereoisomerism or spatial isomerism, in which the bonds are the same but the ''relative positions'' of the atoms differ. Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues. The depth of analysis depends on the field of study or the chemical and physical properties of interest. The English word "isomer" () is a back ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phthalate
Phthalates (, ), or phthalate esters, are esters of phthalic acid. They are mainly used as plasticizers, i.e., substances added to plastics to increase their flexibility, transparency, durability, and longevity. They are used primarily to soften polyvinyl chloride (PVC). Note that while phthalates are usually plasticizers, not all plasticizers are phthalates. The two terms are specific and unique and cannot be used interchangeably. Lower-molecular-weight phthalates, those derived from C3-C6 alcohols, are being gradually replaced in many products in the United States, Canada, and European Union over health concerns. They are being replaced by high-molecular-weight phthalates (those with more than six carbons in their backbone, which gives them increased permanency and durability), as well as alternative plasticizers not based on phthalic anhydride. In 2010, the market was still dominated by high-phthalate plasticizers; however, due to legal provisions and growing environmental aw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplankton productivity". Water bodies with very low nutrient levels are termed oligotrophic and those with moderate nutrient levels are termed mesotrophic. Advanced eutrophication may also be referred to as dystrophic and hypertrophic conditions. Eutrophication can affect freshwater or salt water systems. In freshwater ecosystems it is almost always caused by excess phosphorus. In coastal waters on the other hand, the main contributing nutrient is more likely to be nitrogen, or nitrogen and phosphorus together. This depends on the location and other factors. When occurring naturally, eutrophication is a very slow process in which nutrients, especially phosphorus compounds and organic matter, accumulate in water bodies. These nutrients ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitrophenol
Nitrophenols are compounds of the formula HOC6H5−x(NO2)x. The conjugate bases are called nitrophenolates. Nitrophenols are more acidic than phenol itself. Mono-nitrophenols with the formula HOC6H4NO2. Three isomeric nitrophenols exist: * ''o''-Nitrophenol (2-nitrophenol; OH and NO2 groups are neighboring; CAS number: 88-75-5), a yellow crystalline solid (m.p. 46 °C). * ''m''-Nitrophenol (3-nitrophenol, CAS number: 554-84-7), a yellow solid (m.p. 97 °C) and precursor to the drug mesalazine (5-aminosalicylic acid). * ''p''-Nitrophenol (4-nitrophenol, CAS number: 100-02-7), yellow crystals (m.p. 114 °C). It is a precursor to the rice herbicide fluorodifen, the pesticide parathion, and the human analgesic paracetamol (also known as acetaminophen). The mononitrated phenols are often hydrogenated to the corresponding aminophenols that are also useful industrially. Di- and trinitrophenols * 2,4-Dinitrophenol (m.p. 83 °C) is a moderately strong acid (pKa = 4.89). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Terephthalic Acid
Terephthalic acid is an organic compound with formula C6H4(CO2H)2. This white solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several million tonnes are produced annually. The common name is derived from the turpentine-producing tree '' Pistacia terebinthus'' and phthalic acid. History Terephthalic acid was first isolated (from turpentine) by the French chemist Amédée Cailliot (1805–1884) in 1846. Terephthalic acid became industrially important after World War II. Terephthalic acid was produced by oxidation of ''p''-xylene with dilute nitric acid. Air oxidation of ''p''-xylene gives ''p''-toluic acid, which resists further air-oxidation. Conversion of ''p''-toluic acid to methyl p-toluate (CH3C6H4CO2CH3) opens the way for further oxidation to monomethyl terephthalate, which is further esterified to dimethyl terephthalate. In 1955, Mid-Century Corporation and ICI announced the bromide-promoted ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synthon
In retrosynthetic analysis, a synthon is a hypothetical unit within a target molecule that represents a potential starting reagent in the retroactive synthesis of that target molecule. The term was coined in 1967 by E. J. Corey. He noted in 1988 that the "word ''synthon'' has now come to be used to mean synthetic ''building block'' rather than retrosynthetic fragmentation structures". It was noted in 1998 that the phrase did not feature very prominently in Corey's 1981 book ''The Logic of Chemical Synthesis'', as it was not included in the index. Because synthons are charged, when placed into a synthesis a neutral form is found commercially instead of forming and using the potentially very unstable charged synthons. Example : In planning the synthesis of phenylacetic acid, two synthons are identified: a nucleophilic "COOH−" group, and an electrophilic "PhCH2+" group. Of course, both synthons do not exist per se; synthetic equivalents corresponding to the synthons are reacte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agrochemical
An agrochemical or agrichemical, a contraction of ''agricultural chemical'', is a chemical product used in industrial agriculture. Agrichemical refers to biocides ( pesticides including insecticides, herbicides, fungicides and nematicides) and synthetic fertilizers. It may also include hormones and other chemical growth agents. Agrochemicals are counted among speciality chemicals. Categories Biological action In most of the cases, agrochemicals refer to pesticides. * Pesticides ** Insecticides ** Herbicides ** Fungicides **Algaecides ** Rodenticides ** Molluscicides ** Nematicides * Fertilisers *Soil conditioners * Liming and acidifying agents * Plant growth regulators Application method * Fumigants * Penetrant Ecology Many agrochemicals are toxic, and agrichemicals in bulk storage may pose significant environmental and/or health risks, particularly in the event of accidental spills. In many countries, use of agrichemicals is highly regulated. Government-issued permi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nanocomposite
Nanocomposite is a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm) or structures having nano-scale repeat distances between the different phases that make up the material. The idea behind Nanocomposite is to use building blocks with dimensions in nanometre range to design and create new materials with unprecedented flexibility and improvement in their physical properties. In the broadest sense this definition can include porous media, colloids, gels and copolymers, but is more usually taken to mean the solid combination of a bulk matrix and nano-dimensional phase(s) differing in properties due to dissimilarities in structure and chemistry. The mechanical, electrical, thermal, optical, electrochemical, catalytic properties of the nanocomposite will differ markedly from that of the component materials. Size limits for these effects have been proposed: in Kelly, A, ''Concise encyclopedia of composites materials'', El ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ibuprofen
Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that is used for treating pain, fever, and inflammation. This includes painful menstrual periods, migraines, and rheumatoid arthritis. It may also be used to close a patent ductus arteriosus in a premature baby. It can be used by mouth or intravenously. It typically begins working within an hour. Common side effects include heartburn and a rash. Compared to other NSAIDs, it may have other side effects such as gastrointestinal bleeding. It increases the risk of heart failure, kidney failure, and liver failure. At low doses, it does not appear to increase the risk of heart attack; however, at higher doses it may. Ibuprofen can also worsen asthma. While whether it is safe in early pregnancy is unclear, it appears to be harmful in later pregnancy, so is not recommended. Like other NSAIDs, it works by inhibiting the production of prostaglandins by decreasing the activity of the enzyme cyclooxygenase (COX). Ibuprofen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
