Performance of Electrode Materials for the Anodic Oxidation of 2-Naphthol

Recent research has demonstrated that electrochemistry offers an attractive alternative to traditional methods for treating wastewaters containing biorefracto-organic compounds. In order to obtain a rapid and efficient oxidation of organics it is important to chose an appropriate electrode material that has a high electrochemical activity towards organic oxidation, low electrocatalytic activity towards secondary reactions and good electrochemical stability. The aim of this work was to study the influence of electrode materials during the electrochemical oxidation of 2-naphthol. In this frame three different types of electrodes were tested: Ti / TiO2 RuO2 SnO2 (DSA), Ti / PbO2 and boron-doped diamond (BDD). Bulk oxidation of 2-naphthol was carried out using an undivided electrochemical flow cell in galvanostatic mode. For each electrode the influence of the operating paramenters (e.g. pH, current density, temperature, chloride concentration) was studied in order to find the optimum conditions for the electrolysis. Experimental results showed that, in the appropriate conditions, each electrode allowed the complete oxidation of naphthol and the removal of the Chemical Oxigen Demand (COD) of the solution. In particular, using a DSA® electrode 2-naphthol combustion was obtained only in the presence of chlorides that acted as oxidation mediators, while using BDD and PbO2 electrodes it was obtained by means of the formation of hydroxyl radicals from water discharge. Furthermore, it was found that faster oxidation and consequently higher current efficiency was obtained with boron-doped diamond at low current density or high initial concentration of 2-naphthol.