Electrochemical degradation of an anthraquinonic dye on an expanded graphite-diamond composite electrode

Abstract In recent times, there has been increasing interest in the exploration of electrochemical approaches for the destruction of organic pollutants in wastewater owing to their ability to degrade recalcitrant pollutants in our water. This work demonstrated the use of expanded graphite-diamond anode for the degradation of acid blue 40 (AB 40) dye. Expanded graphite (EG) and expanded graphite-diamond (EG-diamond) electrodes were prepared and characterised using Raman spectrometry, x-ray diffraction, scanning electron microscopy and cyclic voltammetry. The electrolysis of the analyte in 0.1 M Na₂SO₄ electrolyte resulted in ca. 80 % dye removal at the EG-diamond electrode and 66 % removal at the pristine EG electrode at a current density of 20 mAcm⁻² after 4 h. However, in a chlorine-mediated electrolysis (NaCl as supporting electrolyte), the decolourisation of the dye was very rapid with over 98 % decolourisation in 25 min. The extent of mineralisation was measured by total organic carbon (TOC). EG-diamond and EG electrodes yielded TOC removal of 44 and 26 % respectively in the sodium sulphate supported cell. The degradation of AB 40 follows a pseudo first-order kinetic model with apparent rate constants of 2.34 × 10⁻³ min⁻¹ and 4.41 × 10⁻³ min⁻¹ obtained at EG and EGdiamond electrodes, respectively. The EG-diamond electrode was further applied in the degradation of orange II dye (OG II) and a mixture of OG II and AB 40 with a TOC removal of 49 % for the dye mixture.