Carbon, surface labeled

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]. 

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

Figure 5 Molecular graphs for adamarrtane (LHS) and He C6H10. The He atom is shown encased by its four interatomic surfaces. In the text a methine carbon is labelled Cl and its bonded H atom HI a methylene carbon is labelled C2 and its two bonded H atoms H2. Critical points are denoted by dots red for bond, yellow for ring and green for cage. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this book.)...

Figure 7.40. Carbon-14-labeled ethylene (or other alkenes) was chemisorbed as a function of temperature on the flat Pt(l 11) crystal face. The (H/C) ratio of the adsorbed species was determined from hydrogen thermal desorption. The amount of preadsorbed alkene that could not be removed by subsequent treatment in 1 atm of hydrogen represents the irreversibly adsorbed fraction. The adsorption reversibility decreases markedly with increasing adsorption temperature as the surface species become more hydrogen-deficient. The irreversibly adsorbed species have long residence times, on the order of days [195].

A downward trend of specific catalytic activity when carbon surface area is increased is observed. This behaviour can be attributed to many factors, but the authors emphasized that the particle size (indicated in the labels of Fig. 7.7) and... 

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. 

It will be noted that the adhesion drops off with increasing conductivity of the oil. An increase in electrical conductivity favors charging of the particles and repulsion from the surface, thus reducing the quantity of adherent particles (see Section 33). Hence, in studying the operating mechanism of additives that reduce adhesion, a study was made of the behavior of a model disperse material (carbon black labeled with radioactive thallium) in an electric field [337]. The use of the additives gave a reduction in the quantity of adherent carbon particles in the electric field by a factor of approximately 20, in comparison with the quantity adhering to the surface when no additive was used. 

SSITKA. The idea behind this approach was to compare the time response of isotopically labelled surface and gas-phase species by DRIFT spectroscopy and MS analysis. This novel technique was applied for mechanistic analysis water-gas shift (WGS) and reversed WGS reactions over F t- and Au-based catalysts with the aim of identifying true surface intermediates. These authors found that both formate and carbonate species labelled with C were formed on the catalyst surface after switching from C0/H20/Ar = 2/7/91 to C0/H20/A = 2/7/91. In order to determine which surface species actively participated in CO2 formation, they compared temporal changes in the IR bands of these surface species with those of gas-phase C02. Since the rate of CO2 formation was ca. 60 times higher than the rate of the exchange of formate species it was concluded that the formates detected by DRIFT spectroscopy could not be the main surface intermediates of gas-phase CO2. However, the role of surface formates in CO2 production may change with rising temperature as demonstrated in Ref. 129 where the formate species were spectators at 160°C but became main reaction intermediates at 220 C. 

By exposing an alkali predosed surface to two carbon monoxide labeled isotopes and... 

The photodegradation of para-aramid in an 0 atmosphere allows the differentiation between the accelerated experimental photooxidative conditions from its usual daylight exposure effects. This study illustrated an estimation of the rates of photooxidation of a commercial para-aramid product (i.e., DuPont s Kevlar-29 woven fabric) based on the oxygen-18-labelled carbon dioxide ( CC and CC ) decarboxylated from the sample. The oxygen-18-labelled atoms, which are inserted in the macromolecules, were analyzed for the photodegradation processes. This technique also allows the radial l O-distribution measurement from the fiber surface toward the fiber center. 

Exchange reactions between bulk and adsorbed substances can be studied by on-line mass spectroscopy and isotope labeling. In this section the results on the interaction of methanol and carbon monoxide in solution with adsorbed methanol and carbon monoxide on platinum are reported [72], A flow cell for on-line MS measurements (Fig. 1.2) was used. 13C-labeled methanol was absorbed until the Pt surface became saturated. After solution exchange with base electrolyte a potential scan was applied. Parallel to the current-potential curve the mass intensity-potential for 13C02 was monitored. Both curves are given in Fig. 3.1a,b. A second scan was always taken to check the absence of bulk substances. 

FIGURE 1.10 Various possible surface species on a Pt or Pd (111) surface. A and B represent possible locations of 1,2-di-a-Cj 2-cyclohexane, and C, D, and E represent possible locations of Jt-complexed Jt-C -cyclohexene. Full complements of hydrogens are assumed at each angle and terminal that is not either a- or Jt-bonded to a surface site as indicated by a small circle. Half-hydrogenated states, which are mono-a-C -adsorbed species (where n is the number of the carbon attached to the surface), would be represented by one small circle at the carbon bonded to a surface site. F, G, and I represent possible locations of Jt-C -cyclohexene. F shows the three carbons of the Jt-allyl moiety adsorbed in three adjacent three-point hollow sites and G shows it over one three-point hollow site, whereas I shows adsorption over the approximate tops of three adjacent atoms. (Note Label H is not used to avoid confusion with hydrogen, which is not shown.)... 

The question 26-27> whether there is a preferred surface orientation for facile reduction of the carbon-halogen bond may also be answered by reference to the electrochemical behavior of 16-18. This question was investigated in two ways. The first method involved determination of the amount of iso-topically labelled chlorine remaining in 20 isolated from the electrochemical reduction of 16. This proportion was found to be 7 1 % under a variety of experimental conditions 25-29). This means that reduction of the exo chlorine... 

---