Xem 1-20 trên 21 kết quả Transition metals
  • Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Solar light-driven photocatalytic hydrogen evolution over ZnIn2S4 loaded with transition-metal sulfides

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  • Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: First-Principles Study of Magnetic Properties of 3d Transition Metals Doped in ZnO Nanowires

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  • Cathodoluminescence (CL) is a non-destructive technique to characterize optical and electronic properties of nanostructures in many kinds of materials. Major subject is to investigate basic parameters in semiconductors, impurities in oxides and phase determination of minerals. CL is similar to photoluminescence (PL) technique, but the excitation by high energy electrons can produce all the transition to the higher energy excitation states and induce light emission in the wide energy range concerned with versatile types of electronic transitions in materials....

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  • Polyurethane [PU] is a class of polymers built up of carabamate linkages, which provide special characteristics to the material. It is the outcome of pioneering research work of Otto Bayer and his coworkers in 1937 at I.G. Farben laboratories, in Leverkusen, Germany. Initial PU consisted of foams and fibres, while today, innovations and researches in the past decades have brought colossal changes in the world of PU.

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  • The annual production of various polymers can be measured only in billion tons of which polyolefins alone figure around 100 million tons per year. In addition to radical and ionic polymerization, a large part of this huge amount is manufactured by coordination polymerization technology. The most important Ziegler-Natta, chromium- and metallocene-based catalysts, however, contain early transition metals which are too oxophilic to be used in aqueous media.

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  • Solubility of the catalysts in water is determined by their overall hydrophilic nature which may arise either as a consequence of the charge of the complex ion as a whole, or may be due to the good solubility of the ligands. Although transition metal complexes with small ionic ligands, such as halides, pseudohalides or simple carboxylates can be useful for specific reactions the possibility of the variation of such ligands is very limited. As in organometallic catalysis in general, phosphines play a leading role in aqueous organometallic catalysis (AOC), too.

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  • This volume, of a two volume set on ionic liquids, focuses on the applications of ionic liquids in a growing range of areas. Throughout the 1990s, it seemed that most of the attention in the area of ionic liquids applications was directed toward their use as solvents for organic and transition-metal-catalyzed reactions. Certainly, this interest continues on to the present date, but the most innovative uses of ionic liquids span a much more diverse field than just synthesis.

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  • Chemical precipitation and complexation are primarily important for the inorganic species. The formation of coordination complexes is typical behaviour of transition metals, which provide the cation or central atom. Ligands include common inorganic anions such as Cl - , F- , Br - , SO4 2- , PO4 3- and CO3 2- as well as organic molecules such as amino acids. Such complexation may facilitate the transport of metals. Biodegradation is a reaction process mediated by microbial activity (a biotic reaction).

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  • Depending on their structures, polyphenols (e.g. tea polyphenols) could also act by chelating prooxidant transition metal ions such as Fe2+, which are involved in reactions eliciting free radical production, including hydroxyl radicals (OH•) and alkoxyl radicals (RO•) (Dufresne & Farnworth, 2001).

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  • Single crystal X-ray crystallography is the most common and easily accessible way to determine the molecular structure of any crystalline material. This method provides two kinds of information which are needed for understanding both single molecule properties and bulk material properties: 1. Molecular Structure - Single Molecules: Unambiguous and three-dimensional information about the structure of the molecular entities.

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  • The first chapter (236) in this volume of the Handbook on the Physics and Chem- istry of Rare Earth is a recapitulation of the scientific achievements and contri- butions made by the late Professor LeRoy Eyring (1919–2005) to the science of the lanthanide oxides in which the lanthanide element has a valence equal to or greater than three. Although LeRoy had a broad range of interests in the chemistry of the rare earths and actinides the main focus of his outstanding scientific career was concerned with the lanthanide higher oxides. This chapter was written by Dr.

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  • But with other POPs the transition to safer alternatives will require more effort. Alternatives may be more expensive and their manufacture and use more complicated. That could put developing countries in an awkward spot – struggling from day to day, the world's poor tend to use what they can afford and what is available. So it is not enough for the Convention simply to say No to its target list of POPs: It must also help governments find a way to say Yes to replacement solutions. Take the case of DDT.

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  • In this paper, materials of ZnS:Cu, ZnS:Mn and ZnO:Co were prepared by ceramic method and co-precipitated method. The presence of transition metals such as Cu2+(3d9), Mn2+(3d5) in ZnS and Co2+(3d7) in ZnO make blue bands at around 476 nm, 486 nm and green band at around 514 nm disappeared. Simultaneously, there are luminescence bands at around 533 nm, 582 nm, 693 nm for bulk samples of ZnS:Cu, ZnS:Mn, ZnO:Co and 603 nm for nanocrystalline sample of ZnS:Mn.

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  • It is not yet clear how exposure to low ambient concentrations of particulates might produce the health effects observed in epidemiological studies and whether certain attributes of particles may be more closely associated to these health effects. The characteristics of particles that are being investigated for their roles in causing health effects include metal content, particle size, and particles as carriers of other toxic compounds (such as gases or biological toxins from bacteria and pollens etc.).

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  • 2D nanomaterials such as graphene and transition metal dichal  cogenides (TMDCS) have shown outstanding potential in many fields such as fl exible electronics, sensing and optics due to their desirable physical and structural properties. High quality black phosphorus atomic layers by liquid phase exfoliation include Experimental Section; Supporting Information and Acknowledgements.

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  • Since chemical vapor deposition of carbon-containing precursors onto transition metals tends to develop as the preferred growth process for the mass production of graphene films, the deep understanding of its mechanism becomes mandatory. In the case of nickel, which represents an economically viable catalytic substrate, the solubility of carbon is significant enough so that the growth mechanism proceeds in at least two steps: the dissolution of carbon in the metal followed by the precipitation of graphene at the surface.

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  • Polymers present a class of materials that play a role of importance growing in catalysis. Polymeric catalysts based on polypropylene-polyacrylic acid (PP-APA) were prepared by the two methods: co-polymerization in the presence of transition metal ions (Cu(II), Fe(III), Co(II), Mn(II)…) and soaking method. Their catalytic activity was determined by oxidation reactions of ions S2- and hydroquinone by molecular oxygen in normal condition.

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  • The formation of carbon–carbon single bonds is of fundamental importance in organic synthesis. As a result, there is an ever-growing number of methods available for carbon–carbon bond formation. Many of the most useful procedures involve the addition of organometallic species or enolates to electrophiles, as in the Grignard reaction, the aldol reaction, the Michael reaction, alkylation reactions and coupling reactions. Significant advances in both main-group and transition-metal-mediated carbon–carbon bond-forming reactions have been made over the past decade.

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  • Plastics have evolved to be a very useful material. Today, plastics are used in almost every area, from small bottle caps, disposable cutlery, and packages for dairy products, to large containers, such as laundry baskets and garbage pails. Plastics have transitioned from a “cheap” substitute for metal and glass to the material of choice providing almost unlimited design freedom, unique properties, and significant cost savings. Figure 2.1 shows various industrial containers and house wares that create durable products in cycles from 10–30 seconds....

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  • Vanadium. The transition element vanadium exists mostly in the 3, 4, and 5 oxidation states (Table 21.1), with the 4 and 5 states predominating under oxidizing conditions in the normal soil acidity of below pH 8 (1,2). Vanadium, with many other heavy metals, is released by anthropogenic activity.

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