Electrochemical preparation of bromo thymol blue-PEDOT composite electrode and characterization

Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with bromo thymol blue (BTB) composite electrode was prepared electrochemically by using cyclic voltammetric (CV) technique. Hereafter, the above-modified electrode is termed the BTB-PEDOT composite electrode. The BTB-PEDOT composite electrode showed a well-defined reversible symmetric redox peak at around 0.5 V (vs AgAgCl), with ΔE _p=75 mV, and the BTB modified electrode showed an ill-defined peak in 0.2 M H₂SO₄ solution. The symmetric peak in BTB-PEDOT composite electrode might be due to the small electronic bandgap and the high conductivity of PEDOT. The modified electrode was characterized using CV, electrochemical quartz crystal microbalance (EQCM), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy. FTIR spectroscopy helps to confirm presence of BTB on the composite electrode. The amount of composite deposited in the Au electrode was determined using the EQCM technique. The modified electrode displayed surface-confined and pH-dependent electrochemical properties. The BTB-PEDOT composite electrode was used for electrocatalytic reduction of Cr(VI). The composite electrode selectively detected Cr(VI) from its interference in the presence of a 10-fold excess of Cr(III) and humic acid. The sensitivity and detection limit of the electrode were 0.3 μAμM and 50 nM, respectively.