Incineration of acidic aqueous solutions of dopamine by electrochemical advanced oxidation processes with Pt and BDD anodes

Abstract

The degradation of 1.04mM of the drug dopamine hydrochloride (100mgL−1 of dissolved organic carbon (DOC)) solutions of pH3.0 has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation (AO) with a Pt anode and AO, electro-Fenton (EF) and photoelectro-Fenton (PEF) with a boron-doped diamond (BDD) anode. The AO processes were performed with a stainless steel cathode, whereas EF and PEF used an air-diffusion cathode that produced H2O2·AO with a Pt anode led to very poor mineralization because of the low oxidizing ability of OH formed at the Pt surface. The use of a BDD anode in AO yielded faster incineration due to the much greater oxidation of OH generated by BDD. The production of OH in the bulk from Fenton's reaction enhanced largely the mineralization process in EF, which was upgraded in PEF by the photodecomposition of some intermediates by UVA light. Almost total mineralization with 97% DOC removal was found after 360min of EF and 240min of the most powerful PEF at 100mAcm−2. The rise in current density from 16.7 to 100mAcm−2 caused increasing DOC reduction for all EAOPs. The change in mineralization current efficiency and specific energy consumption per unit DOC mass was also discussed. Generated short-linear carboxylic acids like maleic, tartronic, glycolic, acetic, oxalic, oxamic and formic were identified by ion-exclusion HPLC. These acids were quickly removed in EF and more rapidly in PEF due to the photolysis of their Fe(III) complexes. Ion chromatography revealed the pre-eminent generation of NH4+ ion along with a lower proportion of NO3− ion. This technique also confirmed the oxidation of the starting Cl− ion at both Pt and BDD anodes with high ClO4− production using BDD.