Unique Tunability to Conducting Polymer Enabled by Ionic Liquid Doping and its Application in Nitrite Sensing

Abstract

Ionic liquids, owning multiple combinations of cations and anions, provide unique tunability for conducting polymer, which can provide distinctive properties tailored to different applications of these conducting polymer/ionic liquid composites. Herein, five different ionic liquids were utilized to dope poly (3, 4-ethylenedioxythiophene), PEDOT, affording five different PEDOT/ionic liquid composites, which were evaluated for their electrochemical sensing performance towards environmental pollutant nitrite. Among them, ionic liquid N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis(trifluoromethanesulfonyl)imide ([Deme][NTf2]) was unique in tuning PEDOT’s charge properties. No π-π intermolecular interactions were formed between bulky ammonium and PEDOT’s planar thiophene ring, thus cation [Deme] and anion [NTf2] tended to compete for doping into PEDOT matrix. The bulky cation N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium would remain more on PEDOT outside, affording more positive charge. The accumulated more positive charge on [Deme][NTf2]-doped PEDOT’s surface was beneficial to attract more adsorption of nitrite anion, contributing to its improved electrochemical sensing performance. [Deme][NTf2]-doped PEDOT was characterized by various techniques and served as excellent electrode modifier to enable nitrite determination, achieving a broad linear range of 0.05 to 10 mM and a high sensitivity of 642.38 μA mM−1 cm−2. Ionic liquid [Deme][NTf2] demonstrated its unique tuning capabilities to afford conducting polymer/ionic liquid composite, aiming for promising electrochemical sensing application.