Carbon surface basicity

More recently, Pereira and coworkers [44] found a close relationship between anionic dye adsorption and carbon surface basicity due to oxygen-free Lewis sites. Surface oxygen complexes of acid character inhibited anionic dye adsorption. However, the latter complexes had a positive effect on cationic dye adsorption. The removal of these groups by heat treatment in H2 at high temperature... 

Precipitated magnesium carbonate and basic magnesium carbonates are calciaed to produce magaesia having surface areas of ca 200 /g. These... 

Another important factor affecting carbon deposition is the catalyst surface basicity. In particular, it was demonstrated that carbon formation can be diminished or even suppressed when the metal is supported on a metal oxide carrier with a strong Lewis basicity [47]. This effect can be attributed to the fact that high Lewis basicity of the support enhances the C02 chemisorption on the catalyst surface resulting in the removal of carbon (by surface gasification reactions). According to Rostrup-Nielsen and Hansen [12], the amount of carbon deposited on the metal catalysts decreases in the following order ... 

The basicity of the carbon surface derives from the n electron decolization in graphite carbon layers and the antioxidant character of carbon forming oxygen-containing groups [180]. Delocalized n electrons are capable of nucleophilic attack giving Lewis basicity to the carbon [180,189]. 

Thus, two kinds of surface oxides became known. Basic surface oxides are formed always when a carbon surface is freed from all surface compounds by heating in a vacuum or in an inert atmosphere and comes into contact with oxygen only after cooling to low temperatures. As is now known 24), the irreversible uptake of oxygen starts at ca. —40° there is only reversible, physical adsorption at lower temperatures. Acidic surface oxides are formed when carbon is treated with oxygen at temperatures near its ignition point. King 21) found the maximum... 

R = H or Si are generated. An increase in the surface basicity (molar ratio Na2C03 or K2C03 0s = 10-20 1) leads to anionic [Os(CO)3(OR)2UOR) " (R = H or Si= m > 1) species up to [Os(CO)3(OH)3]". The low reactivity of this latter species explains why low yields of carbonyl clusters are obtained when adding to the siUca surface a stronger base such as an alkali hydroxide instead of an alkali carbonate [14, 60]. 

In addition to quinone groups, and to some extent to pyrones (which undoubtedly confer basicity to carbons), the possibility of existence of an oxygen-free, positively charged basic site on the carbon surface was acknowledged in the elegant early studies by Rivin [22] ... 

How much Conway appears to be out of touch with carbon (electrochemistry research is confirmed by his discussion of a 1972 paper by Thrower, presumably published in J Electroanal Chem anyone familiar with Peter Thrower s expertise—and that means any serious carbon researcher—knows that such a paper cannot (and does not ) exist. Finally, in the light of recent proposals regarding the edge chemistry of carbon surfaces [6], Conway s conclusion that [m]any porous or powder[ed] carbon materials have dangling surface bonds which are associated with free-radical behavior should also be viewed with caution (see Figure 5.4). Therefore, perhaps the most (and only ) reliable take-home message from this review is that much basic research of a substantive kind is required to relate the electrochemical behavior of various preparations more quantitatively to... (5) the surface chemistry of carbon preparations and their shelf-life stability, cycle life, and self-discharge characteristics. ... 

The basic problem with activated carbon is that, intrinsically, it is a poor electrical conductor. Moreover, the use of small particles instead of a bulk crystal adds a contribution to the contact resistance. A binder must be mixed with the powder to stick the carbon particles together. The choice of binder material type and amount is influenced by the carbon surface properties. 

Basically the available capacitance is maximum at low frequency. This may be explained with the longer time available for the ions in the electrolyte to reach the surfaces which are located deep in the carbon pores. At higher frequency, only the superficial carbon surface is accessible for the ions. The capacitance is consequently much smaller. 

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