Simultaneous degradation of hexazinone and diuron using ZrO2-nanostructured gas diffusion electrode

Abstract

Although several authors have reported the treatment of diuron in wastewater by advanced oxidative processes (AOPs), only a handful of investigations reported using commercial herbicides composed of a mixture of active organic molecules· H2O2 is a well-known oxidant that is widely employed in AOPs and which can be produced by oxygen reduction reaction (ORR) on gas diffusion electrode (GDE). However, the development of efficient non-noble electrocatalysts that consume less energy for ORR is still a matter of considerable interest. This study reports the electrogeneration of H2O2 on both unmodified and ZrO2-nanostructured GDE. The ZrO2-nanostructured GDE was applied toward the simultaneous degradation of hexazinone and diuron using the commercial formulation of these herbicides. The ZrO2-nanostructured and bare GDEs produced 435.6 mg L−1 and 225.8 mg L−1 of H2O2, respectively. Furthermore, an increase of 130.3% was observed in the current efficiency of oxygen reduction to H2O2 in the presence of ZrO2, indicating that less energy was consumed. Indeed, the production of 1 kg of H2O2 using ZrO2-nanostructured GDE consumes 10.2 kWh at 25 mA cm−2, while bare GDE consumes 32.8 kWh at the same current density. Hexazinone and diuron were found to have been completely removed, albeit 28% of the organic carbon remained in solution after 120 min of electrolysis by H2O2/Fe(II)/UV. A complete removal of organic load will require longer treatment time. The residual carbon may be associated with other species present in the formulation. The results show that ZrO2-nanostructured GDE is a promising material suitable for environmental applications.