Materialeigenschaften und Reinheit von C<sub>60</sub>

Werner, Harald; Bublak, Daniela; Göbel, U.; Henschke, B.; Bensch, Wolfgang; Schlögl, Robert

doi:10.1002/ange.19921040732

Cited by 18 publications

(9 citation statements)

References 25 publications

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“…The data can be quantified and provides the following information. The two adsorption sites differ in their acid strengths as can be concluded from the equilibrium constants (K = 14 (17) for the majority site and K = 64 (107) for the minority sites). The limiting values of coverage are 2.32 mmol/g (3.41 mmol/g) and 1.24 mmol/g (1.74 mmol/g) for the two species.…”

Section: Surface Oxygen Groupsmentioning

confidence: 98%

“…The respective molecular solid needs careful sublimation to remove solvent and gas adducts. Fullerenes are air-sensitive [17] and light-sensitive [11] and decompose slowly under polymerisation (becoming insoluble after storage of day in air). The large number of predicted larger molecular structures [18] have not been observed as pure compounds although evidence for the formation of larger cage molecules comes from TEM investigations of the residues of evaporated graphite after extraction of the small soluble fullerenes [19].…”

Section: The Less Well-defined Structuresmentioning

confidence: 99%

“…Activated carbons contain up to 800 µeq/g carbon of phenolate groups. The volumetric determinations are also sensitive to both carboxylic and phenolate groups (reactions (19) , (20)) so that specific derivatisation processes are needed (reactions (16) , (17)) to reliably discriminate the two types of groups.…”

Section: Surface Oxygen Groupsmentioning

confidence: 99%

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Carbons

Schlögl

2008

Handbook of Heterogeneous Catalysis

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The element carbon plays a multiple role in heterogeneous catalysis. In homogeneous catalysis it occurs of course as the most prominent constituent of ligand systems and will be treated as such there. Carbon-containing molecules are, in most catalytic applications, the substrates of the process under consideration. Deposits and polymers of carbon often occur as poisons on catalysts. Carbon deposition is the most severe problem in certain zeolite applications. In hydrogenation reactions carbon deposits are thought to act as modifiers for the activity of the catalyst and to provide selectivity by controlling the hydrogenationdehydrogenation activity of the metal part of the catalyst. Carbon deposits are even thought to constitute part of the active sites in some cases. Carbon is a prominent catalyst support material as it allows the anchoring of metal particles on a substrate which does not exhibit solid acid-base properties. Carbon is finally a catalyst in its own right allowing the activation of oxygen and chlorine for selective oxidation, chlorination and de-chlorination reactions. These multiple roles of the element carbon are in parallel with a complex structural chemistry giving rise to families of chemically vastly different modifications of the element. It is a special characteristic of carbon chemistry that many of these modifications cannot be obtained as phase-pure materials. This limits the exact knowledge of physical and chemical properties to a few archetype modifications, namely graphite and diamond. The reason for this poor definition of materials is found in the process of its formation. This is comprised of difficult to control polymerisation reactions. Such reactions will occur also in catalytic reactions with small organic molecules. The nature of carbon deposits will therefore reflect all the complexity of the bulk carbon materials. It is one aim of this article to describe the structural and chemical complexity of "carbon" or "soot" in order to provide an understanding of the frequently observed complexity of the chemical reactivity (e.g. in re-activation processes aiming at an oxidative removal of deposits). The surface chemistry of carbon which determines its interfacial properties is a rich field as a wide variety of surface functional groups are known to exist on carbon. The by far most important family of surface functional groups are those involving oxygen. Other prominent heteroatoms on the surface are hydrogen and nitrogen. This article focusses on the description and characterisation of oxygen surface functional groups. In the final section, selected case studies of carbon chemistry in catalysis will be discussed in order to illustrate characteristic properties of carbon materials as wanted or unwanted components in catalytic systems. Regarding the literature on basic properties of carbon materials, the reader is referred to the extensive collection of review papers published in the series Chemistry and Physics of Carbon. Editors P.L.

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Section: Surface Oxygen Groupsmentioning

confidence: 98%

Section: The Less Well-defined Structuresmentioning

confidence: 99%

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Carbons

Schlögl

2008

Handbook of Heterogeneous Catalysis

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“…In contrast to the common organic substances, fullerenes possess property to entrain solvent molecules during crystallization. Impurities are absorbed by the surface as well as by the substance bulk [5][6][7]. In the course of thermal treatment the solvent molecules can be fixed in the spaces of the crystals sintered what complicates purification of fullerenes by their holding under vacuum even with simultaneous heating.…”

Section: Introductionmentioning

confidence: 99%

Spectrophotometric Analysis of C60 and C70 Fullerences in the Toluene Solutions

Аникина¹,

Zaginaichenko²,

Maistrenko³

et al. 2004

Hydrogen Materials Science and Chemistry of Carbon Nanomaterials

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The method for determination of the molar absorption coefficient (MAC) of C 60 and C 70 fullerenes has been developed. The values of MAC obtained by the graphic method are refined there after by the mathematical method of successive approximation.The levels of analytical wavelengths, the ranges for concentrations of fullerene mixtures, solutions optimum for the qualitative analysis have been established.The spectra of C 60 solutions and solutions of its mixtures with C 70 containing C 60 0.5 10 -4 mol/l show the bathochromic shift of the absorption band with the maximum at =335 nm.

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“…Much research has been devoted to the studies of the interaction of oxygen with C60 fullerene [1][2][3][4][5][6][7][8][9][10][11]. Molecular oxygen is reported to be absorbed but not to react with the C60-molecules at room temperature (e.g.…”

Section: Introductionmentioning

confidence: 99%

Influence of Oxygen Impurities on Electrical Properties of Fullerene C₆₀

1995

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We present high temperature dc, ac and contactless microwave conductivity results on solid-state C60 (films and crystals) from room temperature up to 850 K. Heating pristine samples, which were exposed to the ambient atmosphere, under dynamic vacuum at first leads to a reduction of the electrical resistance and finally, above 700 K, to an increase in the resistance. The decrease is ascribed to oxygen desorption and the increase to the chemical reactivity of residual chemisorbed oxygen with the C60 host molecules, respectively. Samples, annealed above 800 K, display a reversible temperature dependence of the resistance. The high temperature regime of their resistance exhibits an activated behaviour with an universal activation energy of 2Ea = 1.85 ± 0.04 eV for crystals and films, which is identical to the HOMO-LUMO splitting of the C 60 -molecules.

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Materialeigenschaften und Reinheit von C₆₀

Cited by 18 publications

References 25 publications

Carbons

Carbons

Spectrophotometric Analysis of C60 and C70 Fullerences in the Toluene Solutions

Influence of Oxygen Impurities on Electrical Properties of Fullerene C₆₀

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Materialeigenschaften und Reinheit von C60

Cited by 18 publications

References 25 publications

Carbons

Carbons

Spectrophotometric Analysis of C60 and C70 Fullerences in the Toluene Solutions

Influence of Oxygen Impurities on Electrical Properties of Fullerene C60

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Materialeigenschaften und Reinheit von C₆₀

Influence of Oxygen Impurities on Electrical Properties of Fullerene C₆₀