Abstract
Protonation of the molecularly rigid polymer of intrinsic microporosity PIM-EA-TB can be coupled to immobilisation of Fe(CN)63−/4− (as well as immobilisation of Prussian blue) into 1–2 nm diameter channels. The resulting films provide redox-active coatings on glassy carbon electrodes. Uptake, transport, and retention of Fe(CN)63−/4− in the microporous polymer are strongly pH dependent requiring protonation of the PIM-EA-TB (pKA ≈ 4). Both Fe(CN)64− and Fe(CN)63− can be immobilised, but Fe(CN)64− appears to bind tighter to the polymer backbone presumably via bridging protons. Loss of Fe(CN)63−/4− by leaching into the aqueous solution phase becomes significant only at pH > 9 and is likely to be associated with hydroxide anions directly entering the microporous structure to combine with protons. This and the interaction of Fe(CN)63−/4− and protons within the molecularly rigid PIM-EA-TB host are suggested to be responsible for retention and relatively slow leaching processes. Electrocatalysis with immobilised Fe(CN)63−/4− is demonstrated for the oxidation of ascorbic acid.Graphical abstract
Highlights
Ferrocyanide, Fe(CN)64−, is a well-studied redox mediator and homogeneous one-electron electrocatalyst
An aminecontaining polymer of intrinsic microporosity (PIM) with molecularly rigid nanochannels is investigated as a host for the Fe(CN)63−/4− redox mediator
It is shown that the presence of the Fe(CN)63−/4 − anions in PIM-EA-TB leads to an apparent shift in the polymer pKA by approximately 5 units, thereby providing a novel film electrode with embedded Fe(CN)63−/4− and with catalytic properties
Summary
Ferrocyanide, Fe(CN)64−, is a well-studied redox mediator and homogeneous one-electron electrocatalyst (see Eq 1). It is shown that the presence of the Fe(CN)63−/4 − anions in PIM-EA-TB leads to an apparent shift in the polymer pKA by approximately 5 units, thereby providing a novel film electrode with embedded Fe(CN)63−/4− and with catalytic properties. In part, this behaviour is linked to the first protonation equilibrium for Fe(CN)63−/4− with pKA,Fe(CN)64- = 4.2 and pKA,Fe(CN)63- < 1 at 25 °C [49, 50]. The crosssection morphology of the PIM-EA-TB film deposits was imaged by using a field emission scanning electron microscope (JEOL JSM-6301F FESEM)
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