Carbon modification procedures

The various forms of adsorbed copper can alter the electrochemical behavior of modified carbon samples used as electrode materials (powdered working electrodes in cyclic voltammetry). Figures 45 and 46 show cyclic voltammograms (CVs) for powdered electrodes prepared from selected active carbon samples with and without preadsorbed copper recorded in solution, which do or do not contain Cu " ions. An aqueous solution of 0.5 M NaiS04 as background electrolyte was employed. The CV curves recorded in the solution containing copper ions exhibit a pair of cathodic and anodic peaks, the potentials of which are dependent on the carbon modification procedure and the electrolyte s pH. The estimated peak potentials and the midpoint potentials [formal potentials, Ef = ( p, — p,c)/2] are given in Table 13. 

Carbon Analytical Procedures. When total carbon in nitrogen contg compds or compds (such as expls or propints) is detd by combustion in a glass tube contg CuO (method of Dumas), there is always the possibility that oxidation of C to C02 will accelerate to such an extent that the sample will expl or defgr (thus destroying the combustion tube) even when the sample is previously mixed with materials retarding combustion such as benzophenone proposed by Jovinet et al, (Ref 8). Modifications of method of Dumas proposed by Boivin (Ref 6) or by Courtecuisse (Ref 9) are not always applicable to expls or proplnts... 

The dominant bands in the resolved spectra obey Beer s law in that the magnitude of the absorbance (defined in terms of the peak heights relative to a linear baseline drawn between 880 and 1880 cm1) is linear in both concentration and thickness (Figures 5 A B). Futhermore, when these spectra are divided by the magnitude of the intrinsic absorption at 2800 cm the resultant absorbances are independent of sample thickness and concentration as shown in Figure 6. This supports the previous conclusion that both the broad background absorption and the superimposed spectra are directly related to the chemical structure of the black. The data also demonstrate that the spectral features of carbon black can be routinely measured to within 0.005 absorbance units. This capabilitity for the quantitative measurement of the effects of various modification procedures... 

Developments in the synthesis of (nitroalkyl)phosphonic acids and their phosphinic acid analogues, as a group, have occurred extensively only during the last 10-15 years, and the potential of such compounds in further synthetic procedures is only now becoming apparent. The number of methods available for the synthesis of (nitroalkyl)phosphorus compounds is appreciable and, as for the functionalized phosphonic acids discussed in the previous chapter, can be subdivided into those which depend on the formation of the phosphorus-carbon bonds and those which are based on modification procedures. 

Modification procedures for carbon electrodes are quite diverse. For convenience, in this chapter, they are broadly divided into two parts covalent and non-covalent modifications. It is worth mentioning that this chapter is not intended to cover the entire hterature on carbon modification, instead the focus is given on basic features of each process of modification and how it changes the nature of carbon electrode surfaces. From the wide variety of applications of modified electrodes, a few selected articles are discussed in short at the end of each modification process to demonstrate its utility. 

Some studies have shown that certain modification procedures can be used to transform two-electron reduction metalloN4-macrocyclic complexes into hybrid materials with the capability to reduce oxygen to water, either via the direct four-electron transfer pathway or in the series two-electron transfer pathway. Carbon nanomaterials, carbon nanotubes in particular [58-65], have been reported to significantly increase the catalytic oxygen reduction current, with a substantial reduction of the overpotential for ORR reported in some cases, as shown by the examples in Table 7.4. 

Tab. 1 Tafel parameters of the H ER on variously modified glassy carbon electrodes. For modification procedures, see text. The test solution is 0.5 M H2SO4...

Using the same procedure as described above, carbon modification of Ti02 (All and P25) was carried out in ethanol vapor [167,171-173]. Carbon deposition reached 7 mass% and a marked decrease in both residual Ph fraction and turbidity... 

A more active product is obtained by the following slight modification of the above procedure. Dissolve the succinimide in a slight molar excess of sodium hydroxide solution and add the bromine dissolved in an equal volume of carbon tetrachloride rapidly and with vigorous stirring. A finely crystalline white product is obtained. Filter with suction and dry thoroughly the crude product can be used directly. It may be recrystallised from acetic acid. 

In one modification of this procedure, the starting material is pyroly2ed rice hulls in place of more conventional forms of sihcon dioxide (31). Another unique process involves chlorination of a combination of SiC and Si02 with carbon in a fluid-bed reactor (32). The advantages of this process are that it is less energy-intensive and substantially free of lower sihcon chlorides. 

The fuel properties of wood can be summarized by ultimate and proximate analyses and deterrnination of heating value. The analytical procedures are the same as those for coal, but with some modifications. Analytical results generally vary about as much within a species as they do between species, except that softwood species generally have a higher carbon content and higher heating values than hardwood species because of the presence of more lignin and resinous materials in softwood species (see Fuels from waste). 

The chlorohydrin process (24) has been used for the preparation of acetyl-P-alkylcholine chloride (25). The preparation of salts may be carried out mote economically by the neutralization of choline produced by the chlorohydrin synthesis. A modification produces choline carbonate as an intermediate that is converted to the desired salt (26). The most practical production procedure is that in which 300 parts of a 20% solution of trimethyl amine is neutralized with 100 parts of concentrated hydrochloric acid, and the solution is treated for 3 h with 50 parts of ethylene oxide under pressure at 60°C (27). 

This modification has become the standard procedure for the acyloin ester condensation. By doing so, the formation of products from the otherwise competitive Dieckmann condensation (Claisen ester condensation) can be avoided. A product formed by ring closure through a Dieckmann condensation consists of a ring that is smaller by one carbon atom than the corresponding cyclic acyloin. 

The two methods available for this determination are modifications of those described in Section 10.32 for hydroxide/carbonate mixtures. In the first procedure, which is particularly valuable when the sample contains relatively large amounts of carbonate and small amounts of hydrogencarbonate, the total alkali is first determined in one portion of the solution by titration with standard 0.1M hydrochloric acid using methyl orange, methyl orange-indigo carmine, or bromophenol blue as indicator ... 

The procedure described here is a modification of one involving the thermal fragmentation of 1-adamantyl hypoiodite and cycliza-tion of the resulting iodo ketone/ By means of this procedure, 4-protoadamantanone is obtained from 1-adamantanol with consistent yields in the range of 71 to 82% and a purity greater than 98%. This method is also applicable to the preparation of other polycyclic ketones from the related bridgehead alcohols with a-bridges of zero, one, or two carbon atoms (see Table I). 

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