Carbons glassy

It was also demonstrated that ssDNA is better adsorbed onto the GC electrode than dsDNA. The dsDNA molecule has some difficulty reaching the surface contours of the rough GC electrode surface, while ssDNA can approach closer to the electrode surface because of its greater flexibility. 

Although dsDNA can be adsorbed at the GC surface, it is not easily oxidized while ssDNA can be easily adsorbed and oxidized, giving higher oxidation signals, which is attributed to the oxidation of G ( 0.8 V) and A ( 1.1, vs SCE) respectively [38]. The dsDNA structure had greater difficulty transferring the electrons from the inside of the double-stranded structure to the electrode surface than the flexible ssDNA structure where the bases are in closer proximity to the GC surface. 

The electrochemical processes of adsorption and oxidation of ds- and ssDNA on the GC electrode were discussed and studied by in situ FTIR [42]. It was also demonstrated that the well-known oxidation product 8-oxoguanine adsorbs strongly on the GC surface [29]. Adsorbed ssDNA can form a DNA layer which impedes the oxidation product diffusing away, blocking the GC surface [43,44]. 

The surface of GC, like other sohd electrodes, is graduahy deactivated during exposure to the atmosphere or during electrochemical use (38, 39). Therefore, periodic pretrealment is 

HGC exhibits lower voltammetric background current, comparable electrochemical activity for several redox systems, enhanced S/B ratios, and improved response stability compared with freshly polished (i.e., oxygenated) GC. Cyclic voltammetric investigations revealed relatively rapid electrochemical reaction kinetics for Fe(CN) and RuCNHj) and slightly slower kinetics for dopamine and 4-methylcatechol. Very sluggish kinetics were found for Fe. For example, of 0.01-0.03 cm sec were determined for 

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The purity of a sample of K3Fe(CN)6 was determined using linear-potential scan hydrodynamic voltammetry at a glassy carbon electrode using the method of external standards. The following data were obtained for a set of calibration standards. 

Other Uses. Anisotropic and isotropic carbon are produced from furfural-modified systems glassy carbon is produced primarily from furfuryl alcohol or BHMF resins (78,79). 

Synthetic Resins. Various polymers and resins are utilized to produce some specialty carbon products such as glassy carbon or carbon foam and as treatments for carbon products. Typical resins include phenoHcs, furan-based polymers, and polyurethanes. These materials give good yields of carbon on pyrolysis and generally carbonize directly from the thermoset polymer state. Because they form Httle or no mesophase, the ultimate carbon end product is nongraphitizing. 

Glassy, or vitreous, carbon is a black, shiny, dense, brittle material with a vitreous or glasslike appearance (10,11). It is produced by the controUed pyrolysis of thermosetting resins phenol—formaldehyde and polyurethanes are among the most common precursors. Unlike conventional artificial graphites, glassy carbon has no filler material. The Hquid resin itself becomes the binder. 

There is Htfle crystal growth during carbonization, which always occurs in the soHd phase. The soHd cross-linking that occurs at this time does not lend itself to crystal growth. The glassy carbons are composed of random crystaUites of the order of 5.0 nm across and are not significantly altered by ordinary graphitization heat treatment to 2800°C. 

Eig. 7. CycHc voltammograms for the reduction of 1.0 mAf [2,2 -ethylene-bis(nitrilomethyHdyne)diphenolato]nickel(II) in dimethyl formamide at a glassy carbon electrode, in A, the absence, and B and C the presence of 2.0 and 5.0 mAf 6-iodo-l-phenyl-l-hexyne, respectively (14). 

Recent developments in Raman equipment has led to a considerable increase in sensitivity. This has enabled the monitoring of reactions of organic monolayers on glassy carbon [4.292] and diamond surfaces and analysis of the structure of Lang-muir-Blodgett monolayers without any enhancement effects. Although this unenhanced surface-Raman spectroscopy is expected to be applicable to a variety of technically or scientifically important surfaces and interfaces, it nevertheless requires careful optimization of the apparatus, data treatment, and sample preparation. 

Nitrophenyl groups covalently bonded to classy carbon and graphite surfaces have been detected and characterized by unenhanced Raman spectroscopy in combination with voltammetry and XPS [4.292]. Difference spectra from glassy carbon with and without nitrophenyl modification contained several Raman bands from the nitrophenyl group with a comparatively large signal-to-noise ratio (Fig. 4.58). Electrochemical modification of the adsorbed monolayer was observed spectrally, because this led to clear changes in the Raman spectrum. 

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]. 

Fig. 4.58. Raman spectra of nitrophenyl modi- 1336 and 1586 cm" might be affected by sub-fied (A) and untreated (B) glassy carbon, the dif- traction of closely neighboring, much stronger ference between spectra A and B (C), and the re- bands of the carbon bulk. Five further marked ference spectrum of solid 4-nitrobiphenyl (D). surface bands are clearly visible in the difference The strongest surface bands at approximately spectrum C [4.292],...

Biomass phenolic and furan resins polyimides glassy carbons, binder and matrix carbons" graphite films and monoliths activated carbons ... 

Fig. 2. Raman spectra (T = 300 K) from various sp carbons using Ar-ion laser excitation (a) highly ordered pyrolytic graphite (HOPG), (b) boron-doped pyrolytic graphite (BHOPG), (c) carbon nanoparticles (dia. 20 nm) derived from the pyrolysis of benzene and graphitized at 2820°C, (d) as-synthesized carbon nanoparticles ( 850°C), (e) glassy carbon (after ref. [24]).

Electrolysis on a glassy carbon electrode, DME. Bu4N BE4, 85% yield. ... 

Figure 3.6-1 The electrochemical window of 76-24 mol % [BMMIM][(CF3S02)2N]/Li [(Cp3S02)2N] binary melt at a) a platinum working electrode (solid line), and b) a glassy carbon working electrode (dashed line). Electrochemical window set at a threshold of 0.1 mA cm. The reference electrode was a silver wire immersed in 0.01 m AgBp4 in [EMIM][BF4] in a compartment separated by a Vicor frit, and the counter-electrode was a graphite rod.

Working electrode, Pt = platinum, GC = glassy carbon, W = tungsten. 

Indium and antimony The electrodeposition of In on glassy carbon, tungsten, and nickel has been reported [26]. In basic chloroaluminates, elemental indium is... 

Tellurium and cadmium Electrodeposition of Te has been reported [33] in basic chloroaluminates the element is formed from the [TeCl ] complex in one four-electron reduction step, furthermore, metallic Te can be reduced to Te species. Electrodeposition of the element on glassy carbon involves three-dimensional nucleation. A systematic study of the electrodeposition in different ionic liquids would be of interest because - as with InSb - a defined codeposition with cadmium could produce the direct semiconductor CdTe. Although this semiconductor can be deposited from aqueous solutions in a layer-by-layer process [34], variation of the temperature over a wide range would be interesting since the grain sizes and the kinetics of the reaction would be influenced. 

The electrodeposition of Ag has also been intensively investigated [41 3]. In the chloroaluminates - as in the case of Cu - it is only deposited from acidic solutions. The deposition occurs in one step from Ag(I). On glassy carbon and tungsten, three-dimensional nucleation was reported [41]. Quite recently it was reported that Ag can also be deposited in a one-electron step from tetrafluoroborate ionic liquids [43]. However, the charge-transfer reaction seems to play an important role in this medium and the deposition is not as reversible as in the chloroaluminate systems. 

Zinc and tin The electrodeposition of Zn [52] has been investigated in acidic chloroaluminate liquids on gold, platinum, tungsten, and glassy carbon. On glassy carbon only three-dimensional bulk deposition was observed, due to the metal s underpotential deposition behavior. At higher overvoltages, codeposition with A1... 

Impervious graphites, that is electro-graphites with appropriate resin impregnation are used in cascade-, shell- apd tube-type coolers, condensers, pre-heaters etc. in a wide variety of chemical plants. Similar resistance to corrosion applies to glassy carbon vessels and pyrolytic carbons and graphites. The corrosion resistance to principal chemical agents is given in Table 18.2. 

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