Photo-assisted electrochemical degradation of sulfamethoxazole using a Ti/Ru0.3Ti0.7O2 anode: Mechanistic and kinetic features of the process

Abstract

This study examined the photo-assisted electrochemical degradation and mineralization of the antibiotic contaminant sulfamethoxazole (SMX). All the experiments were perform using a flow electrolytic cell, in which the influence of the current density (10–60 mA cm−2) and sodium chloride (0.02–0.10 mol L−1) in the supporting electrolyte composition was analyzed. The results showed that the total SMX and 50% TOC removal was achieved in the current density range used. As expected, the degradation kinetics presented a pseudo first order behavior and the rate constant increased from 0.05 min−1 to 0.50 min−1 as the current density raised from 10 to 60 mA cm−1. In addition, the values of the electrical energy per order (EEO) increased from 0.67 to 1.06 kW/hm−3 order−1 as the current density increased from 10 to 60 mAcm−2 and drop from 8.82 to 0.57 kW/hm−3 order−1 at supporting electrolyte concentration of 0.02–0.1 mol L−1. The reaction intermediates identified by liquid chromatography–mass spectrometry allowed proposing a mechanism for the degradation. The use of photo assistance in the electrochemical process involved simultaneous reactions, for example, aromatic ring substitutions and hydroxylation. These reactions led to aromatic rings opening that generated simpler organic molecules, making possible the mineralization of the SMX molecule. Probable degradation pathways were proposed and discussed. Comparison of the efficiencies of the photocatalytic, electrochemical (EC) and photo-assisted electrochemical (PAEC) techniques revealed that the combined process showed a synergism for TOC removal.