Comparison of two different ceramic electrodes based on Sb-SnO2 coated with BiFeO3 and Bi2WO6 for the photoelectrooxidation of an emerging pollutant

Abstract

In this work, a comparison between novel photoanodes based on Sb-SnO2 (BCE) coated with BiFeO3 (BFO-BCE) and Bi2WO6 (BWO-BCE) was carried out. An improvement in the catalytic activity of the electrodes under light exposure was demonstrated by means of Linear Sweep Voltammetry, light pulsed chronoamperometry and Electrochemical Impedance Spectroscopy, being more notorious at current densities below 25 mA·cm−2 for the BFO-BCE and above 25 mA·cm−2 for the BWO-BCE. This improved performance was caused by an increase of the photogenerated oxidizing species. As compared with the uncoated BCE anode used without light, photoelectrooxidation tests led to improvements of around 40% in the degradation degree of norfloxacin (NOR) using both photoanodes at 8.33 mA·cm−2. This improvement was also observed in the mineralization degree of the model wastewaters, with an increase of 36% and 28% at 25 mA·cm−2 for the BWO-BCE and BFO-BCE, respectively. The degradation and formation of subproducts was followed by ion chromatography and HPLC analysis, where some of the main intermediates were detected, allowing us to elaborate a degradation route for NOR with these novel electrodes. The Mineralization Current Efficiency (MCE), energy consumption and extent of electrochemical combustion (Φ) showed improvements with light application for both electrodes at high current densities, being the BWO-BCE the one with the highest MCE and Φ at the cost of a slightly higher energy consumption. This showed the importance of light for these electrodes and its impact in the general process performance, which can be of great advantage in future applications.