ELECTROCHEMICAL REDUCTION OF HYDROGEN PEROXIDE AT GLASSY CARBON ELECTRODES MODIFIED WITH METAL–HUMIC COMPLEXES (Mn, Mo)

Abstract

Hydrogen peroxide (H₂O₂) is an important analyte in medicine, food technology and environmental monitoring, and there is a continuing demand for inexpensive, enzyme-free electrochemical sensors for its determination. In this work, humic acid (HA) was isolated from sodium humate and used to prepare manganese– and molybdenum–humic complexes (Mn-HA and Mo-HA). The materials were characterized by Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) and immobilized on glassy carbon electrodes (GCE) using a Nafion film. The electrochemical behaviour of the modified electrodes was studied by cyclic voltammetry (CV) in acetate buffer. For both electrodes the highest currents were obtained at pH 5.6. Unmodified GCE and GCE/HA gave practically no response, whereas GCE/Mn-HA and GCE/Mo-HA showed pronounced redox activity and enhanced current in the presence of H₂O₂. The peak currents increased with scan rate and with H₂O₂ concentration in the range (1.3–20)×10⁻⁸ mol L⁻¹ for Mn-HA and (2.5–20)×10⁻⁸ mol L⁻¹ for Mo-HA. The lowest detectable concentrations were 1.3×10⁻⁸ and 2.5×10⁻⁸ mol L⁻¹, respectively. The results indicate that metal–humic complexes derived from inexpensive natural raw material are promising modifiers for enzyme-free H₂O₂ sensors.