Electrochemical oxidation of diclofenac on CNT and M/CNT modified electrodes

The electrochemical oxidation of diclofenac (DCF), a non-steroidal anti-inflammatory drug considered as an emerging pollutant (frequently detected in wastewater), was investigated on CNT, Pt/CNT and Ru/CNT modified electrodes based on Carbon Toray in aqueous media. The electroreactivity of DCF on these modified electrodes was studied using cyclic voltammetry and the kinetic parameters were calculated from the scan rate study. Cyclic voltammograms show several oxidation processes, which confirm the interaction between DCF and the catalyst surface necessary for direct oxidation processes. Constant potential electrolysis of DCF was carried out on carbon nanotubes (CNT) and metal supported CNT (M/CNT) modified electrodes, in 0.1 M NaOH and 0.1 M Na2CO3/NaHCO3 buffer media. The highest DCF conversion (88% after 8 h of electrolysis) was found in carbonate buffer medium, for Ru/CNT, while the best carbon mineralization efficiency (corresponding to 48% of the oxidized DCF) was obtained on Pt/CNT modified electrode in 0.1 M NaOH medium. The products of the electrolyses were identified and quantified by HPLC-MS, GC-MS, HPLC-UV-RID and IC. The results show the presence of some low molecular weight carboxylic acids, confirming the cleavage of the aromatic rings during the oxidation process.he authors thank FCT (Fundação para a Cência e a Tecnologia, Portugal) for the PhD grant of Marta Ferreira, and the financing of projects: PTDC/AAGTEC/5269/2014, Centre of Chemistry (UID-QUI/00686/2013 and UID/QUI/0686/2016), and LSRE-LCM (Base Funding – UIDB/50020/2020 of the Associate Laboratory LSRE-LCM – funded by national funds through FCT/ MCTES (PIDDAC)). This work has been developed under the scope of the projects BioTecNorte (operation NORTE-01-0145- FEDER-000004), supported by the Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement through the European Regional Development Fund (ERDF). The authors also thank TUBITAK (Tu¨rkiye Bilimsel ve Teknolojik Aras-tirma Kurumu, operation TUBITAK-2219) for the post-doctoral grant to Dr Sevgi Gu¨ney.