Electrolyte influence on light-assisted electrooxidation of an herbicide employing an Sb-SnO2 electrode coated with a Bi2WO6 photocatalyst

In this work, a series of photoelectrooxidation experiments of the herbicide bentazon (BTZ) under three different electrolytes (Na 2 SO 4 , NaCl, and a mixture of both) and using ceramic anodes of Sb-SnO 2 coated with a photocatalyst (Bi 2 WO 6 ) were carried out. Using Na 2 SO 4 as an electrolyte, 74.6 % of BTZ was degraded and 48.5 % was mineralized at 50 mA·cm −2 without light. Under light application, mineralization increased at this current density by a 31.6 %. This increase was partly due to the activation of persulfates towards the formation of high oxidative SO 4 − radicals. Using NaCl, up to 85.1 % of BTZ was degraded and 57.2 % was mineralized. Light noticeably fastened the degradation and increased its final value by 8.9 %, otherwise this effect was not as intense in the mineralization. Observed differences between degradation and mineralization under light application were attributed to the formation of photogenerated reactive chlorine species (RCS), which were proven to transform the BTZ faster into different chlorinated molecules, degrading but not mineralizing it. The mixed electrolyte achieved 85.1 % degradation and 54.5 % mineralization at 50 mA·cm −2 in absence of light. Under light application, degradation was enhanced by a final 6.8 % but the effect was lower than with pure NaCl, due to its lower concentration of the salt and therefore, lesser formation of derivative RCS. Mineralization was also enhanced by a 14.5 % under light application. The mixed electrolyte showed trends in between both pure electrolytes. Scavenging tests for OH free using tert -butanol, showed an inhibition of up to 11 % in the presence of light, meaning an important role of this species in the oxidation process. Detection of short-stringed carbon molecules such as formate and acetate confirmed proper oxidation of BTZ, and the detection of chlorate confirmed the formation of RCS. In general, Mineralization Current Efficiency (MCE), energy consumption, and extent of electrochemical combustion (Φ) showed improvements with light application, aligning with what was observed during the photoelectrooxidations. These results confirm that these photoanodes are quite sensitive to light, and are capable of oxidizing complex organic molecules, opening to future possibilities in the advanced environmental treatment.