Functional groups on carbon surface

Figure 13 3 Possible functional groups on carbon surfaces (a) carboxyl groups, (b) carboxylic anhydrides, (c) lactones, (d) lactols, (e) phenolic hydroxyl groups, (f) carbonyl groups, (g) e-quinone-hke structures, and (h) ether-type (or pyran- or xanthene-like) oxygen atoms. (Reprinted from Ref. [37] with permission from Elsevier.)...

Some of the functional groups expected on carbon surfaces are carboxylic adds, phenols, quinones, lactones, ethers, peroxides, and esters (Fig. 11). Functional groups on carbon surfaces have been detected by such methods as polarography [63], titration [63-68], X-ray photoelectron spectroscopy [34], radioisotope labeling [34], and infrared spectroscopy [63]. Some of these techniques are discussed below. 

Figure 11. Predicted oxygen functional groups on carbon surfaces (a) carboxyl, (b) phenolic hydroxyl, (c) quinone, (d) lactone, (e) fluoresceinlike lactone, (f) carboxylic add anhydride, and (g)

Proposed principal functional groups on carbon surfaces and their corresponding infrared assignments... 

Figure 4.26. Structures of oxygen functional groups on carbon surfaces (Rodriguez-Reinoso...

For the second method the threshold concentration of the filler in a composite material amounts to about 5 volume %, i.e. below the percolation threshold for statistical mixtures. It is bound up with the fact that carbon black particles are capable (in terms of energy) of being used to form conducting chain structures, because of the availability of functional groups on their surfaces. This relatively sparing method of composite material manufacture like film moulding by solvent evaporation facilitates the forming of chain structures. 

Several mechanisms have been proposed to explain the activation of carbon surfaces. These have Included the removal of surface contaminants that hinder electron transfer, an Increase In surface area due to ralcro-roughenlng or bulld-up of a thin porous layer, and an Increase In the concentrations of surface functional groups that mediate electron transfer. Electrode deactivation has been correlated with an unintentional Introduction of surface contaminants (15). Improved electrode responses have been observed to follow treatments which Increase the concentration of carbon-oxygen functional groups on the surface (7-8,16). In some cases, the latter were correlated with the presence of electrochemical surface waves (16-17). However, none of the above reports discuss other possible mechanisms of activation which could be responsible for the effects observed. 

Application of the Horner-Wadsworth-Emmons reaction to the functionalization of dendrimers allows one to prepare amino acid terminated macromolecules. Such a reaction conducted with dendrimers 10-[G ], 10-[G 3], lO-fG ] and phosphonates unsubstituted at the carbon a to the phosphoryl group affords in moderate yield dendrimers bearing various a, / unsaturated functional groups on the surface [18]. (Schemes 17 and 18). 

There are various possibilities for functional groups on the surface of carbonates, sulfides, phosphates etc. Using a very simple approach similar to the one in Fig. 2.1 for hydrous oxides one could postulate surface groups for carbonates (e.g., FeC03) and sulfides (e.g., ZnS), as follows ... 

For strong Pt fixation on CNM surface it is necessary to introduce functional groups, preferable from ones are -COOH, -OH and quinoid. The diversity of carbon allotropic forms and types of bonds between carbon atoms causes the different approaches to inculcation of a functional groups on CNM surface. 

The oldest method for the modification of carbon black surface chemistry is oxidation. Common oxidants include air, hydrogen peroxide, hypochlorites, nitric acid, nitrogen dioxide, ozone and persulfates. Each reagent produces a mixture of oxygen functional groups on the surface, with the distribution depending on the oxidant. Materials that disperse in water can be produced with sufficient oxidation, and hypochlorites and persulfates have been used to make water dispersible carbon blacks for inkjet inks. 

A careful examination of the C-ls and 0-1s regions of the oxygen-containing confounds listed in Table III allow us to deduce the nature of the carbon-oxygen functional groups on the surface of the polished lots LTI-C and LTI/SI-C. 

Free radicals have been used to introduce functional groups on the surface of carbon nanotubes (Figure 35) 233... 

Considerable attention has also been paid to the potentiometric response of powdered active carbon electrodes, which in considerable part depends on the type and concentration of functional groups on the surface [7,70,160,161]. The response of a carbon electrode to ionic species in aqueous solution arises from the adsorption behavior of surface functional groups. In addition, physically and/ or chemically adsorbed gases (mainly CO and oxygen) affect this process significantly. 

The comparison with amphoteric oxides [57-59] is also instructive. In an early review, Snoeyink and Weber [60] compared the surface functional groups on carbons and silicas but failed to point out the resulting differences in the symmetries" of their electrokinetic behavior. For amphoteric oxides, the symmetry (see Fig. 4a) is a consequence of the following equilibrium [57,61-66] ... 

There are various possibilities for functional groups on the surface of carbonates, sulfides, phosphates, and so on. Using a very simple approach similar... 

Spectroscopic Investigation of Functional Groups on the Surface of a Carbon-supported Catalyst FTIR and TPD... 

SPECTROSCOPIC INVESTIGATION OF FUNCTIONAL GROUPS ON THE SURFACE OF A CARBON-SUPPORTED CATALYST ... 

The most important inference is that Chemisorption is a direct response to carboxyl group concentration indicated by the XPS photopeak component at 288.7 eV. It seems likely that weak add functionality is of minor import to applications for surface treatments, while interfacial phenomena such as practical adhesion may be sensitive to small concentrations of very high site energies. Interphase modification in epoxy resins, for example, can occur by direct reaction of epoxide groups with surface carboxyls (17), or by accelerated cure chemistry near the surface (39). Carboxyl groups on carbon surfaces may interact with basic moieties in polymers such as polycarbonate or poly(ethylene)oxide (40=42), or promote interfacial crystallinity that improves impact strength and other aspects of composite performance (43, M)-... 

Figure 10.1 shows the effect of the addition of fillers to polypropylene on its crystallinity. This study was conducted under the same conditions for all specimens tested. There is a difference in the effect of CaCO-, and talc. Calcium carbonate lacks surface functional groups so it tends to have a very small influence on crystallinity and the crystallization behavior. Talc has interacting functional groups on its surface which cause the increase in crystallinity along with the concentration increase. 

Applications. XPS was used for the following purposes determination of elemental composition of nanocomposites, the effect of oxidation and reduction of carbon fibers by monitoring the 0/C ratio, 2- 35, 74 concentration of functional groups on the surface of carbon fibers, elemental composition of the surface of carbon fibers, the effect of surface coating on the surface composition of carbon fi-... 

Arico, A.S. et al.. The influence of functional groups on the surface acid-base characteristics of carbon-blacks. Carbon, 27, 337. 1989. 

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