Pairing CO2 electroreduction with the electrooxidation of pharmaceutical compounds in wastewater

The electroreduction of CO₂ has been abundantly studied, but little attention has been given to the reaction occurring at the anode of this electrolyzer. Herein, we report one of the rare attempts to investigate the anode and potential reactions that could occur on this electrode during CO₂ electrolysis. The electrooxidation of several aqueous pollutants, sulfamethazine (SMT), carbamazepine (CMP), ketamine and acetaminophen (ACE) was investigated at the anode of a CO₂ electrolysis cell. Pulsed laser ablation in liquid (PLAL) was used to prepare the catalysts. PLAL is a versatile, environmentally safe technique used to create nanoparticles for electrocatalysis. Herein, bismuth nanoparticles were prepared as the CO₂ reduction catalyst, as previously reported. Nickel nanoparticles were used for both the oxygen evolution reaction (OER) and the oxidation of the aqueous pollutants. Transmission electron microscopy (TEM) of the nickel nanoparticles indicates the production of monodisperse nanoparticles, with a 7.8 ± 2.8 nm average diameter. After evaluating the stability of the targeted pollutants, we focused on sulfamethazine, carbamazepine and acetaminophen due to their stability in aqueous environment. Among the various anode catalysts tested, nickel nanoparticles were the most versatile in degrading these pollutants; thus, further measurements were taken with this catalyst. A brief optimization of the degradation conditions (pH and potential) was also done, showing most efficient degradation at pH = 9 and 1.4 V vs Ag/AgCl. Once completed, CO₂ reduction was coupled with the oxidation of a matrix of all three pollutants. The results show that the efficiency of the CO₂ reduction was mostly unaffected by the combined presence of the pollutants at the anode. Oxidation of the target pharmaceuticals was also comparable to previous tests, reaching 62% for CMP, 53% for SMT and 33% for ACE within 20 min.

Graphical abstract