Carbonaceous surfaces

At this point we should also recall another application of the already mentioned Bernal model of amorphous surface. Namely, Cascarini de Torre and Bottani [106] have used it to generate a mesoporous amorphous carbonaceous surface, with the help of computer simulation and for further application to the computer simulation study of adsorption. They have added a new component to the usual Bernal model by introducing the possibility of the deletion of atoms, or rather groups of atoms, from the surface according to some rules. Depending on the particular choice of those rules, surfaces of different porosity and structure can be obtained. In particular, they have shown examples of mono- as well as pohdispersed porous surfaces... 

Carbonaceous Surfaces Modification, Characterization, and Uses for Electrocatalysis... 

Traube s rule accommodates the balance between hydrophobicity and hydro-philicity. It has been extended somewhat and formalized with the development of quantitative methods to estimate the surface area of molecules based on their structures [19, 237]. The molecular surface area approach suggests that the number of water molecules that can be packed around the solute molecule plays an important role in the theoretical calculation of the thermodynamic properties of the solution. Hence, the molecular surface area of the solute is an important parameter in the theory. In compounds other than simple normal alkanes, the functional groups will tend to be more or less polar and thus relatively compatible with the polar water matrix [227,240]. Hence, the total surface area of the molecule can be subdivided into functional group surface area and hydro carbonaceous surface area . These quantities maybe determined for simple compounds as an additive function of constituent groups with subtractions made for the areas where intramolecular contact is made and thus no external surface is presented. 

In reality, it is believed that the oxidation of carbonaceous surfaces occurs through adsorption of oxygen, either immediately releasing a carbon monoxide or carbon dioxide molecule or forming a stable surface oxygen complex that may later desorb as CO or C02. Various multi-step reaction schemes have been formulated to describe this process, but the experimental and theoretical information available to-date has been insufficient to specify any surface oxidation mechanism and associated set of rate parameters with any degree of confidence. As an example, Mitchell [50] has proposed the following surface reaction mechanism ... 

Thus, at temperatures lower than the liquid us temperature (usually above —20 °C for most electrolyte compositions).EC precipitates and drastically reduces the conductivity of lithium ions both in the bulk electrolyte and through the interfacial films in the system. During discharge, this increase of cell impedance at low temperature leads to lower capacity utilization, which is normally recoverable when the temperature rises. However, permanent damage occurs if the cell is being charged at low temperatures because lithium deposition occurs, caused by the high interfacial impedance, and results in irreversible loss of lithium ions. An even worse possibility is the safety hazard if the lithium deposition continues to accumulate on the carbonaceous surface. 

Carbon surfaces of various types have been the subject of most studies. However, other types of surfaces, including alumina, fly ash, dust, MgO, V2Os, Fe203, and Mn02, have also been shown to oxidize S02 and/or remove it from the gas phase (Hulett et al., 1972 Judeikis et al., 1978 Liberti et al., 1978 Barbaray et al., 1977, 1978 Halstead et al., 1990). As expected, the rate of removal depends on the nature of the particular surface, the presence of copollutants such as N02, and, as in the case of carbonaceous surfaces, the relative humidity. The increase with increasing water vapor suggests that oxidation of the S02 may occur in a thin film of water on the surface of the solid. 

Wet adsorption relies on leaving DNA to interact with the carbonaceous surface through physical forces in the presence of water. During wet adsorption, the stabilization of B-DNA is expected to occur on the carbonaceous surface, by keeping the hydration water of the DNA molecule. In this case, the hydrated B-DNA form is stabilized over the GEC surface by weaker forces as the water is kept on the DNA adsorbed molecule, it can be easily desorbed from the GEC surface if soaked in aqueous solutions. 

A review is given on the physical and chemical reactions that occur if atomic hydrogen, hydrocarbon radicals, and low-energy ions interact with carbonaceous surfaces. In a first set of experiments the surface loss probabilities of different hydrocarbon radicals are determined in low-temperature plasmas using the cavity technique. The following values were determined / (C2H) = 0.90 0.05, / (C2H3) = 0.35 0.15, and / (CH3, C2H5) < KT2. 

A graphite plate (HOPG) and carbon particles, which were made from phenolic resin by pyrolyzmg above 2000TI.. were used to form a nanospace with carbonaceous surfaces The particles were evacuated at I lOTl for 24 h before use. The graphite plate was freshly cleaved before measurement. 

Three kinds of liquids of analytical grade (Wako Pure Chemicals) were used. All liquids were desiccated with zeolite 4A molecular sieve for one week before experimental use. Cyclohexane, and octamethylcyclotetrasiloxane (OMCTS), whose bulk freezing point were 6.4°C and ISTl respectively were used for the examination of freezing behavior. The reasons of the choice were i)affinity to carbonaceous surface, ii)freezmg point near ambient temperature, and iii)almost spherical molecular shape. Methanol, with bulk freezing point of -98 C was also used as a reference. All the force measurement were done after confirming the stability of the temperature under control for at least 10 minutes The temperature was set at various values above the bulk freezing point. 

The formation, nature, and reactions of surface complexes of carbon are obviously open to considerable question, largely because of the difficulty in determining accurately what is happening on a carbonaceous surface. The problem is that, at least in some cases, the nature of the surface complexes may well affect the reactions (catalytic or non-catalytic) of carbons. Keeping the difficulties of analysis of surface complexes in mind, it is convenient to discuss the catalytic activity and reactivity of carbons in the expectation that this can lead to a closer definition of the information that is needed in the context of the surface complexes. 

Chemisorption of gases on carbonaceous surfaces has been considered in... 

The macrocycles Co (111) (cyclam) and Fe( 111)TM PyP display high activity for dioxygen reduction and negligible affinity for carbonaceous surfaces providing close to ideal conditions to warrant analyses of electrochemical data within the strict homogeneous electrocatalysis framework. Their most salient features are summarized in the two sub-sections to follow. 

Based on the above information, the following sequence has been proposed (172,173, 181,182 for the formation of carbonaceous surface intermediates during alkane oxidation on platinum ... 

The models for gases interacting with carbonaceous surfaces can be broken into terms that depend on the coordinates of the interacting particles and the surface. First, one must describe the interaction of the adsorbate molecules with one another. For monatomic adsorbates, this can be done via an approximate (double) sum over distinct pairs of interacting molecules ... 

Scholl, A. et al., Energy calibration and intensity normalization in high-resolution NEXAFS spectroscopy, J. Electron Spectrosc. Relat. Phenom. 129, 1-8, 2003. Stbhr, J. et al., Liquid crystal alignment on carbonaceous surfaces with orientational order, Science 292, 2299-2302, 2001. 

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