Carbon surface

In addition to the many applications of SERS, Raman spectroscopy is, in general, a usefiil analytical tool having many applications in surface science. One interesting example is that of carbon surfaces which do not support SERS. Raman spectroscopy of carbon surfaces provides insight into two important aspects. First, Raman spectral features correlate with the electrochemical reactivity of carbon surfaces this allows one to study surface oxidation [155]. Second, Raman spectroscopy can probe species at carbon surfaces which may account for the highly variable behaviour of carbon materials [155]. Another application to surfaces is the use... 

McCreery R L, Liu Y-C, Kagen M, Chen P and Fryling M 1996 Resonance and normal Raman spectroscopy of carbon surfaces relationships of surface structure and reactivity ICORS 96 XVth Int. Conf. on Raman Spectroscopy ed S A Asher and P B Stein (New York Wiley) pp 566-7... 

Catalysis. Catalytic properties of the activated carbon surface are useful in both inorganic and organic synthesis. For example, the fumigant sulfuryl fluoride is made by reaction of sulfur dioxide with hydrogen fluoride and fluorine over activated carbon (114). Activated carbon also catalyzes the addition of halogens across a carbon—carbon double bond in the production of a variety of organic haUdes (85) and is used in the production of phosgene... 

Utilization of resonance effects can facilitate unenhanced Raman measurement of surfaces and make the technique more versatile. For instance, a fluorescein derivative and another dye were used as resonantly Raman scattering labels for hydroxyl and carbonyl groups on glassy carbon surfaces. The labels were covalently bonded to the surface, their fluorescence was quenched by the carbon surface, and their resonance Raman spectra could be observed at surface coverages of approximately 1%. These labels enabled assess to changes in surface coverage by C-OH and C=0 with acidic or alkaline pretreatment [4.293]. 

Nitric acid treatment lowered the methane uptake by about ten percent. This could be due to oxygen occupying sites within pores, but may be the result of weaker interaction between methane and an oxide surface as is observed for silica. Reduction of these treated carbons with hydrogen restored their original methane uptake. Clearly for methane storage, there is no advantage in modifying the carbon surface by nitric acid treatment. 

From the above data, it would appear that methane densities in pores with carbon surfaces are higher than those of other materials. In the previous section it was pointed out that to maximize natural gas or methane storage, it is necessary to maximize micropore volume, not per unit mass of adsorbent, but per unit volume of storage vessel. Moreover, a porous carbon filled vessel will store and deliver more methane than a vessel filled wnth a siliea based or polymer adsorbent which has an equivalent micropore volume fraction of the storage vessel. 

Air pollution problems in which adsorption is considered a unit operation involve gaseous contaminants. The number of molecules present at the carbon surface is dependent on the number that reach the surface and on the residence time of these molecules on the carbon surface. If n molecules strike a unit area of a surface per unit time, and remain there for an average time, t, then a number of molecules are present per unit area of surface ... 

Where activated carbon is a potential treatment technology, the first evaluation step is generally to run simple isotherms to determine feasibility. Isotherms are based on batch treatment where impurities reach equilibrium on available carbon surface. While such tests provide an indication of the maximum amount of impurity a GAC can adsorb, it cannot give definite scale up data for a GAC operation due to several factors ... 

Tailoring Activated Carbon Surfaces for Water, Wastewater and... 

Hazardous Waste Treatment Operations - Tailoring Activated Carbon Surfaces for Water, Wastewater and Hazardous Waste Treatment... 

Although the detailed mechanism for the reduction of thionyl chloride at the carbon surface is rather complicated and has been the subject of much controversy, the battery reactions are described as follows ... 

A comprehensive review which discusses the surface properties and their role in the electrochemistry of carbon surfaces was written by Leon and Radovic [26]. This review provides a useful complement to the following discussion on the role of carbon in aqueous batteries. Four key parameters that are important for carbonaceous materials in batteries, which were identified by Fischer and Wissler [24], are ... 

In order to improve the electrochemical performance with respect to lower irreversible capacity losses, several attempts have been made to modify the carbon surface. Here the work of Peled s [38, 130-132] and Takamura s groups [133-138] deserves mention. A more detailed discussion can be found Chapter III, Sec. 6. 

Apart from reactions with the electrolyte at the carbon surface, the irreversible specific charge is furthermore strongly affected by the possible co-intercalation of polar solvent molecules between the graphene layers of highly graphitic matrices [139]. This so-called "solvated intercalation reaction" depends (i) on the crystallinity and the morphology of the parent carbonaceous material, which will be discussed in Sec. 

The physicochemical properties of carbon are highly dependent on its surface structure and chemical composition [66—68], The type and content of surface species, particle shape and size, pore-size distribution, BET surface area and pore-opening are of critical importance in the use of carbons as anode material. These properties have a major influence on (9IR, reversible capacity <2R, and the rate capability and safety of the battery. The surface chemical composition depends on the raw materials (carbon precursors), the production process, and the history of the carbon. Surface groups containing H, O, S, N, P, halogens, and other elements have been identified on carbon blacks [66, 67]. There is also ash on the surface of carbon and this typically contains Ca, Si, Fe, Al, and V. Ash and acidic oxides enhance the adsorption of the more polar compounds and electrolytes [66]. 

Figure 3. Schematic representation of the oxygen functional groups on the carbon surface (a) phenol (b) carbonyl (c) carboxyl (d) quinone (e) lactone 12].

At the electrode surface there is competition among many reduction reactions, the rates of which depend on iQ and overpotential q for each process. Both /0 and q depend on the concentration of the electroactive materials (and on the catalytic properties of the carbon surface). However, the chemical composition of the SEI is also influenced by the solubility of the reduction products. As a result, the voltage at... 

The chemical composition of the SEI formed on carbonaceous anodes is, in general, similar to that formed on metallic lithium or inert electrodes. However some differences are expected as a result of the variety of chemical compositions and morphologies of carbon surfaces, each of which can affect the i() value for the various reduction reactions differently. Another factor, when dealing with graphite, is solvent co-intercalation. Assuming Li2C03 to be a major SEI building material, the thickness of the SEI was estimated to be about 45 A [711. 

FIGURE 2-13 STM image of an electrochemically activated glassy-carbon surface. (Reproduced with permission from reference 46.)... 

S.2.2 Carbon Electrodes Solid electrodes based on carbon are currently in widespread use in electroanalysis, primarily because of their broad potential window, low background current, rich surface chemistry, low cost, chemical inertness, and suitability for various sensing and detection applications. In contrast, electron-transfer rates observed at carbon surfaces are often slower than those observed at metal electrodes. The electron-transfer reactivity is strongly affected by the origin... 

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