Graphite microparticles

Noble metals are eatalytieally very active, and many studies have been earried out on their surfaces, espeeially platinum, palladium, and rhodium. Noble metals have been used as polycrystalline metals or monocrystals, metal blacks, metals supported on graphite, microparticles ineorporated into redox active polymers, ete. The activity of these materials towards the electrocatalytieal hydrogenation depends mainly on the nature of the metal, pH, and supporting electrolyte, and the state of the surface. 

Fig. 4.25. Diagram respresenting a hypothetical carbon vapor nucleation scheme leading to concentric shells as those observed in graphite microparticles. Fullerene formation may occur by statistical closure at stage (c). Reproduced with permision from Kroto HW, McKay KG (1988) Nature 331 328...

Fig. 4.7 Cyclic voltammograms of 14 pg/mL TNT on single- (G-SL), few- (G-FL), and multilayer (G-ML) graphene nanoribbons and graphite microparticles. Conditions background electrolyte, 0.5 M NaCl scan rate, 100 mV s . Reproduced from Ref. [21] with permission from Springer Science and Business Media...

Goh, M. and Pumera, M. 2010. Single-, few-, and multilayer graphene not exhibiting significant advantages over graphite microparticles in electroanalysis. Anal. Chem. 82 8367-8370. 

These drawbacks can be avoided to a large extent, using the voltammetry of microparticles—a technique involving solid state electrochemistry where down to about 10 to 10 mol of sample [74-78] can be transferred by abrasion into the surface of an inert electrode, usually paraffin-impregnated graphite electrodes, and the electrode is later immersed in a suitable electrolyte for recording its voltam-metric response. The response of this sample-modified electrode, consisting of the reduction or oxidation of the solid materials, becomes phase-characteristic. 

Table 3.1 Diagnostic criteria for characterizing lead pigments via voltammetry of microparticles using deposits of the pristine pigments on parafiSn-impregnated graphite electrodes. Data from square-wave voltammograms at a potential step increment of 4 mV, square-wave amplitude of 25 mV, and frequency of 15 Hz. All potentials refer to AgQ (3M NaCl)/Ag. Electrolyte, 0.50 M acetate buffer, pH 4.85...

Domenech A, Domenech-Carbo MT, Sauri MC, Gimeno JV, Bosch F (2005) Identification of curcuma and safflower dyes by voltammetry of microparticles using paraffin-impregnated graphite electrodes. Microchim Acta 152 75-84. 

Paraffin impregnated graphite electrode (PIGE) - electrode prepared from graphite rods by impregnation with melted paraffin under vacuum. These electrodes are not permeated by aqueous solutions and can be used for solution studies, as well as for immobilizing microparticles and microdroplets to study their electrochemistry. See also - carbon, - voltammetry of immobilized microparticles. 

The employed technique for this purpose was the so-called colloidal-probe AFM (Atomic Force Microscopy). A carbon microparticle with high degree of carbonization was attached to the top of the cantilever tip, forming the colloidal probe, and its interaction force with cleaved graphite was measured within a liquid cell filled with organic liquid, controlled at a desired temperature above the bulk freezing point of the liquid. The two surfaces will form a slit-shaped nanospace because the radius of the particle is far larger than the separation distance concerned here. 

FIGURE 4.6 Variation of the peak current with the square-wave frequency for deposits on graphite of microparticles of zeolite Y having attached 2,4,6-triphenylthiopyrylium ion (TPYA upon immersion into 0.10 M 111 N( ()/Mei N. 

Solid electrodes, modified with microparticles attached onto the surface, can be assumed as the result of the usual abrasive transfer by rubbing, for example, a graphite rod over nanogram amounts of the respective sample. These adhered microparticles are randomly distributed over the surface, and the whole set-up can be understood and theoretically treated as random array of microdisk electrodes (unlike regular arrays, see Section 6.3.2.3) (Figure 6.12). 

The microparticles are assumed to cover a solid electrode surface, such as edge-plane graphite. A simple one-electron redox system ... 

In another report from the same group, different anthraquinone-based dyes were studied using square-wave voltammetry following the mechanical immobilization of microparticles on the surface of graphite/polyester composite electrodes [63]. 

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