Investigation of acid red 88 oxidation in water by means of electro-Fenton method for water purification

• Oxidation of AR88 with hydroxyl radicals was investigated for water purification.
• Rate constant of oxidation of AR88 was calculated as (1.57 ± 0.06) × 1010 M−1 s−1.
• Intermediates of AR88 were determined by spectroscopic and chromatographic methods.
• Effects of current on the evolutions of formed carboxylic acids were examined.
• A general reaction route for AR88 oxidation was proposed for the first time.

In this study, electro-Fenton method was applied to acid red 88 (AR88) containing aqueous solutions for the removal of it from water. The mineralization of AR88 has been achieved by oxidation with hydroxyl radicals. These radicals were produced simultaneously by the electro-Fenton method using an electrochemical cell including a carbon felt cathode and a platinum anode. Applied current and concentrations of catalyst and supporting electrolyte were optimized to obtain the best effective parameters of 500 mA, 0.1 mM and 75 mM, respectively. The absolute rate constant for the oxidation reaction of AR88 with hydroxyl radical was determined as (1.57 ± 0.06) x 1010 M−1 s−1. Total organic carbon (TOC) analysis was performed to determine whether the organics were converted to carbon dioxide or not. A two-hour electrolysis at 500 mA is enough to remove 87% of initial TOC values of 0.25 mM AR88 solution. Electro-Fenton treatment of AR88 led to the formation of five aromatic intermediates, five short-chain carboxylic acids and three inorganic ions. Identified intermediates and complete mineralization of AR88 allowed us to propose a mineralization pathway for first time in the literature.