Tuning Poly(ionic liquid) as a Facile Anion (Hexacyanoferrate(III) ion) Exchanger after Being Adsorbed on Graphitic Nanomaterial and Its Versatile Electrocatalytic Oxidation of Ascorbic Acid

Abstract

Owing to their conductivity and high polarity, ionic liquids and poly(ionic liquids) (PILs) have been often used as an electrolyte for various applications in electrochemistry. Due to the unfavorable ion-exchange property and structural feature (hydrophobic environment and inaccessible ionic site), unmodified ILs and PILs are rarely worked out as an ion-exchanging system. Herein, we show elegant tuning of aromatic unit bearing PILs as an efficient anionic ion exchanger after being combined with graphite nanomaterials like graphite nanopowder (GNP) and carbon nanotube for novel electrocatalytic applications. A chemically modified electrode prepared out of GNP and random copolymer of 1-vinyl-3-pentylimidazolium chloride and styrene (coPIL₁Cl) composite ethanol suspension on a glassy carbon electrode (GCE) showed facile immobilization of hexacyanoferrate(III) ion (as a model anionic system), electrode designated as GCE/GNP-coPIL₁@Fe(CN)₆³–, in pH 7 phosphate buffer solution. The modified electrode yielded well-defined surface-confined redox peak at equilibrium potential, E₁/₂ = 100 ± 5 mV vs Ag/AgCl with a surface excess and relative standard deviation values of 3.0 nmol cm–² and 1.8%, respectively. From the experiments with different functional counterions (Cl–, SO₃CF₃–, BF₄–, and PF₆–), alkyl chains (butyl and pentyl groups), and N-terminal-substituted aromatic unit and from physicochemical characterizations of PIL-modified electrodes, how the π–π interaction, hydrophobic and hydrophilic sites, and steric factor of PIL influence the ion-exchanging behavior of the GNP-coPIL₁Cl composite with ferricyanide ion was demonstrated. Electrocatalytic oxidation of ascorbic acid (AA) was investigated as a model system for the ferricyanide-modified electrode performance using cyclic voltammetric and amperometric i–t techniques. Highly selective and superior electrocatalytic and sensing of AA over its unmodified electrodes were noted.