Electrochemical Reduction of Manganese Mediated by Carbon Nanotubes/Li+ Modified Glassy Carbon Electrodes

Abstract

Glassy carbon electrodes (GCE) were modified with carbon nanotubes (CNT) with and without Li⁺ dopant by a mechanical attachment method. These modified working electrodes, abbreviated as CNT/Li⁺/GCE and CNT/GCE, produced two reduction peaks of Mn(II) at +0.8 V and +0.1 V vs Ag/AgCl in 0.1 M KCl, which appeared irreversible during cyclic voltammetry. The sensing characteristics of the modified film electrodes demonstrated in this study were composed of: (i) a wide working potential window ranging from +1.8 V to -1.8 V (depending on different scan rates, pH, concentration and temperature); (ii) a wide applicable pH range (from at least 2-10); (iii) a wide applicable temperature range from 5-90 ºC; (iv) a current response that is stable and fast with a satisfactory and reproducible linear voltammetric and amperometric response to various analytes; (v) a good reproducibility and recovery rate in seawater and blood; (vi) interfering metal ions such as Hg²⁺, Cd²⁺ and Cu²⁺ appeared to pose positive interference on the reduction peaks of Mn²⁺. The reduction current of Mn2+ using CNT/Li⁺/GCE was largely influenced by concentration, pH, temperature and scan rate. Based on the calibration curve obtained, a linear graph of up to 1 mM Mn(II), with an impressive sensitivity response of 66.7 μA/mM, was obtained. Based on chronoamperometry, a diffusion coefficient for Mn²⁺ of 1.53 × 10^-7 cm²/s was determined.