Carbon materials modification

Modification of carbon materials by tri-nuclear complexes of 3d-metals with ethanolamine ligands increases the catalytic activity with regard to the electrochemical reaction of oxygen reduction. The Co-Ni complex is most active in this reaction if pyrolyzed at 600°C. 

Cycloalkenones are ubiquitous as reactive intermediates and bioactive materials. Modification of a simple cycloalkenone by addition of a carbon substituent at the o-position should be a useful transformation, but one that is not readily accomplished by conventional enone chemistry. a-Substituted cycloalkenones could of themselves be of interest, but perhaps, of more general importance would be their use as intermediates for the production of substituted cycloalkanones or a, 5-disubstituted cycloalkanones by a subsequent conjugate addition procedure.2 These strategies avoid many of the limitations attendant to the trapping of enolates with carbon electrophiles. The method of Kim involving treatment of enones with the combination of a dimethyl acetal, pyridine and trimethylsilyl triflates results in a-(1-methoxyalkyljenones.3 The metallation of a-bromoenones masked as ketals for [Pg.184]

In the previous edition of this book, Dryhurst and McAllister described carbon electrodes in common use at the time, with particular emphasis on fabrication and potential limits [1]. There have been two extensive reviews since the previous edition, one emphasizing electrode kinetics at carbon [2] and one on more general physical and electrochemical properties [3]. In addition to greater popularity of carbon as an electrode, the major developments since 1984 have been an improved understanding of surface properties and structure, and extensive efforts on chemical modification. In the context of electroanalytical applications, the current chapter stresses the relationship between surface structure and reproducibility, plus the variety of carbon materials and pretreatments. Since the intent of the chapter is to guide the reader in using commonly available materials and procedures, many interesting but less common approaches from the literature are not addressed. A particularly active area that is not discussed is the wide variety of carbon electrodes with chemically modified surfaces. 

The variety in properties of different produced carbon materials is conditioned by the electronic structure of a carbon atom. The redistribution of electron density, the formation of electronic clouds of different modifications around the atoms, the hybridization of orbitals (sp3-, sp2-, sp- hybridization) are responsible for the existence of different crystalline allotropic phases and their modifications. 

The zeolite-carbon adsorbents from mineral-carbon adsorbents group are novel and exhibit not quite well recognized properties with their unique, modified porous structure. The characteristic structures for zeolite, active carbon and intermediate structure exist in these materials. Such a structure results fi-om the modification of a surface of a mineral matrix by depositing carbon material. The efifectivity of enrichment of the structure of zeolite-carbon adsorbents (in relation to crystalline zeolite structure) in hydrophobic micropores (0.4 - 2 nm) and macropores (above 50 nm) is proportional to the fi action of carbon phase. Such combination of hydrophilic properties of mineral phase and hydrophobic properties of organic phase results in various sorptive properties of the material and the range of their application can be consequently extended. Additionally, the chemical resistance of these adsorbents for their exploitation in aggressive conditions takes place. 

Graphene is a new class of low dimensional carbon materials. It represents the two-dimensional form of carbon. We have elaborated several methods of graphene preparation with making use of mechanical and ultrasonic segregation. Now we are under investigation of graphene modification by FIB. 

The application of electrochemical investigations is an efficient method to characterize the microstructure of porous electrically conducting materials. Modifications in the chemical constitution of the skeleton which do not change the BET values can be identified by the electrochemically derived surface capacitance, as demonstrated in the case of anodically oxidized carbon aerogels. 

Bacic-Vukcevic, M. et al.. Surface characteristics and modification of different carbon materials. Mater. Sci. Eorutn. 518, 217, 2006. 

The use of critical fluids for the extraction and refining of components in natural products has now been facilitated for over 30 years. Early success in the decaffeination of coffee beans and isolation of specific fractions from hops for flavoring beer, using either supercritical carbon or liquid carbon dioxide, are but two examples of the commercial application of this versatile technology. Critical fluid technology, a term that will be used here to embrace an array of fluids under pressure, has seen new and varied applications which include the areas of engineering-scale processing, analytical, and materials modification. 

Nevertheless, it is hardly possible to assess the development within the last two decades and to perceive its impact on the multitalented carbon s perspectives in chemistry, material science, and physics, without an understanding of its long-known modifications, mainly graphite and diamond. Hence, the first chapter summarizes the essential facts on the classical modifications and their properties, for only a solid comprehension of basic concepts and principles enables us to understand the properties of new carbon materials and to develop new ideas. 

With this background, it should be clear that nanostructure is what defiues, in classical terminology, the three allotropic modifications of carbon materials ... 

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