Ion transfer processes across an interface between two immiscible electrolyte solutions (ITIES) can serve as the basis for amperometric sensors, electro-assisted ion extraction, pharmacokinetics, electrocatalysis, etc. [1]. One of the methods to drive ions to transfer is to utilize the electrode reactions of a suitable redox probe present in one phase. Since the electroneutrality must be maintained in each phase, the electrochemical transformations are often coupled to ion transfer processes which can be detected electrochemically [2].

Fullerene C₆₀ is a suitable redox probe for studying ion transfer processes across ITIES since it can be reversibly reduced and its neutral and reduced forms are known to be practically insoluble in water. In our previous paper [3] we examined ion transfer processes coupled to the first electroreduction of fullerene and we reported anion-sensitive voltammetric response. Herein, we have extended our studies to the remaining two electroreductions and, to our best knowledge, this is the first time that the ion transfer processes accompanied to the consecutive three reductions of fullerene C₆₀ have been reported.

We have found that in the studied biphasic system comprising of 1,2-dichlorobenzene and water, fullerene C₆₀ undergoes three chemically reversible electroreductions which are accompanied to the expulsion of the anions of the supporting electrolyte which seems to act as an ion-exchanger. The calculated association constants show that the ion pair formation is thermodynamically more favored for more hydrophilic anions and this may stand for the observed ion-sensitivity. Moreover, the evolution of voltammograms shows that during electrochemical oxidations of fulleride species, the organic phase is progressively enriched with the aqueous anions that are preferentially associated with the tetrahexylammonium cations. Such a behavior provides the basis for ion detection whose sensitivity might be tailored by the choice of an appropriate tetraalkylammonium salt. To provide further insight into the mechanism of the overall process, the association between consecutive fulleride anions and tetrahexylammonium cations has been also examined.

References:

[1] F. Reymond, D. Fermin, H. J. Lee, H. H. Girault, Electrochim. Acta 45 (2000) 2647.

[2] F. Scholz, U. Schröder, R. Gulaboski, Electrochemistry of Immobilized Particles and Droplets, Springer-Verlag Berlin Heidelberg 2005.

[3] W. Adamiak, G. Shul, M. Opallo, Electrochem. Commun. 11 (2008) 149.

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