Adhered microparticles

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). 

Chapter 14 presents the attributes of voltammetry of adhered microparticles in contact with ILs for determining the thermodynamics and kinetic properties of electroactive species. This technique provides an alternative and powerful electro-analytical tool, which has great versatility in ILs under conditions where conventional voltammetry with dissolved analyte is impractical. 

Voltammetry of Adhered Microparticles in Contact with Ionic Liquids Principles and Applications... 

The basic principles of the voltammetry of adhered microparticles in contact with ionic liquids in both bulk and thin-layer ionic liquid configurations are demonstrated in this section for the oxidation of Fc and trans-Mn (structure shown in Fig. 14.2). 

To characterize the conditions under which the shape and position of voltammograms of dissolved species and adhered microparticles are identical, as... 

Many other compounds also have similar solubility properties to Fc and exhibit a reaction scheme analogous to the Fc " case in ionic liquids (see schematic diagram in Fig. 14.5), which allows voltammograms from adhered microparticles to be essentially indistinguishable from that obtained with the dissolved material. Notable examples include Fc derivatives [12, 24, 25, 40], l,3,5-tris(3-((ferrocenylmethyl) amino)pyridiniumyl)-2,4,6-triethylbenzene hexafluorophosphate ([PD] [Pp6]3) [12, 41] and trans-Mn [23]. Thus, voltammetric studies using arrays of adhered solid microparticles are frequently able to provide an efficient method for obtaining the formal potentials of redox processes in ionic liquids. 

Analogous results were obtained with cis-W. A schematic diagram that illustrates the principal processes believed to be involved in the oxidation of microparticles of cw-Mn or cA-W adhered to an electrode surface in contact with an ionic liquid is provided in Fig. 14.13. The mechanism is now considerably more complicated than for the previously described systems, as dissolved electrogenerated species Oxl (ionic liquid), now undergoes a square reaction scheme. Nevertheless, despite the greater complexity in the ECE reaction mechanism, the voltammetry of adhered microparticles method can be used to determine the relevant thermodynamic and kinetic parameters when step C is a first-order homogeneous reaction, as applies in the case of an isomerization reaction. 

DIMCARB upon preparation of the polyoxometalate solutions to form an electroinactive species. Fortunately, the adhered microparticles technique avoids prolonged contact with DIMCARB, thereby allowing weU-defined voltammetry to be observed. The initial process involved in the reduction of adhered microparticles of [Bu4N]4[SiWi204o](s) (oc, p, and y isomers) in DIMCARB is summarized as follows for the first reduction process ... 

Fig. 14.17 Voltammograms of (a) 10 mM benzophenone and 10 mM 1,4-benzoquinone in wet (approx. 0.13 M water) [C4mpyr][N(Tf)2] recorded with a 1.0 mm diameter GC electrode at designated scan rates under a N2 atmosphere. The cyclic voltammogram obtained in the absence of benzophenone (dashed lines) is included for comparison. The inset figures show cyclic voltammograms for reduction of 100 mM benzophentme and 100 mM 1,4-benzoquinone in wet [C4mpyr][N(Tl)2] recorded with a 33 pm diameter carbon fiber microelectrode at a scan rate of 1,000 V s under a N2 atmosphere and (b) adhered microparticles of benzophenone and 1,4-benzoquinone on a 1.0 nun diameter GC electrode in contact with wet [C4mpyr][N(Tf)2] under a N2 atmosphtue, scan rate= 1.0 V s . Adapted with permission from Zhao et al., Electrochem Commun, 2012,16, 14-18 [52], Copyright (2013), Elsevier...

The reversible potentials for both compounds obtained under wet conditions ([C4mpyr][N(Tf)2], [H2O] 0.13 M) are very similar to those obtained in extensively dried ionic liquid. For these compounds, it may be concluded that the voltammetry of adhered microparticles provides an efficient and convenient method for obtaining water-free reversible potentials for water-sensitive reduction processes in ionic liquids under bench top conditions, without the need to use extensively dried ionic liquids or operate under more cumbersome dry box or vacuum line conditions. 

The history, theory, and application of the voltammetry of adhered microparticles in contact with both bulk and thin-layer forms of ionic liquids have been reviewed. In the short time since its introduction, the technique has enhanced the range of studies possible for a wide variety of compounds. For example, new insights have now become available when electroactive molecules undergo kinetically slow dissolution (e.g., for oxidation of Fc in an ionic liquid). Using this method, the... 

Zhang J, Bond AM (2004) Voltammetric studies with adhered microparticles and the detection of a dependence of organometallic cis — trans first-order isomerization rate constants on the identity of the ionic liquid. J Phys Chem B 108(22) 7363-7372. doi 10.1021/jp049294r... 

Zhao S-F, Lu J-X, Bond AM, Zhang J (2012) Voltammetric studies in wet 1-butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid using electrodes with adhered microparticles. Electrochem Commun 16(1) 14—18. doi 10.1016/j.elecom.2011.11.034... 

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