Carbon-oxygen functional groups

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. 

Vibrational spectroscopy is a very versatile and, chemically, well-resolved technique for the characterization of carbon-oxygen functional groups. The immense absorption problems of earlier experiments seems to be overcome in present times with modem FT-IR, DRIFTS or photoacoustic detection instruments. 

The surface chemistry of carbon has been extensively studied and reviewed (14-18). It is generally believed that a variety of carbon-oxygen functional groups are present on carbon surfaces. Their nature and concentration are dependent on the sample history and depend, for example, on processing variables. 

Wide scans (0 to 600 eV) were performed for surface elemental analyses as well as detailed 20 eV scans of the C-ls (275 to 295 eV) region. Several standards were also analyzed under the same scan conditions in order to obtain accurate chemical shift data for various carbon-oxygen functional groups. These included polyCethylene terephthalate), poly(ethylene oxide), and anthra-quinone. The latter was run at -50 C in order to minimize volatility under our high vacuum conditions. Additional spectra were obtained on spectroscopic grade graphite for comparison purposes. All spectra were charge referenced to a C-ls line for an alkyl-like carbon at 284.0 eV. 

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. 

Organic Models for Determination of Carbon-Oxygen Functional Groups by XPS Oxygen-Containing Functional Group Data from the C-l-s Line of Poly(ethylene) terephthalate), Poly(ethylene oxide), and Anthraquinone... 

These peaks are shown to reasonably account for the asymmetry in the C-ls spectra of the carbon surfaces. These data lead us to believe that the assigned peaks are reasonable to a first approximation, and correspond to the carbon-oxygen functional groups indicated in Table III. Figure 8 also illustrates that the graphite spectrum shows similar carbon-oxygen functionality. 

Potentiodynamic and potentiostatic methods can also be used to activate nanotubes. Similar to chemical oxidation, electrochemical pretreatment can effectively remove impurities and cause the creation of carbon-oxygen functional groups at the exposed edge plane and defect sites. The same authors reported on an electrochemical pretreatment that involved potentiostating the electrode at +1.7 V vs. Ag/AgCl in pH 7 phosphate buffer for 3 min followed by 3 min at —1.5 V (84). Both the chemical and electrochemical oxidations improved the electrode response (smaller voltammetric A p and larger values) for Fe(CN)g " , serotonin, and caffeic acid. 

Retinoids have been defined as a class of compounds consisting of four isoprenoid units (H2C=C(CH3)-CH=CH2) joined in a head-to-tail manner. The retinoid molecule can be divided into three parts a trimethylated cyclohexene ring, a conjugated tetraene side chain, and a polar carbon-oxygen functional group. Retinol (I), retinaldehyde (II), and retinoic acid (III), as well as their derivatives whose structures are shown in Structure 1 (/), are included by this definition. 

Another reason for the low background current has been suggested to be the hydrogen termination of the diamond surface, which does not contain surface carbon-oxygen functional groups. For example, the etching of as-deposited diamond (hydrogen... 

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