Using Au NPs anchored on ZrO2/carbon black toward more efficient H2O2 electrogeneration in flow-by reactor for carbaryl removal in real wastewater

Abstract

In the present study, we designed a highly efficient catalyst for H2O2 production using gold nanoparticles (Au NPs) anchored on hybrid substrate composed of ZrO2 and Printex L6 carbon (Au-ZrO2/PL6C). The higher selectivity of Au-ZrO2/PL6C (97%) toward H2O2 electrogeneration and its improved activity in terms of ORR onset potential (140 mV for more positive values) compared to Au/PL6C (80%) were attributed to the synergism between Au NPs anchored on ZrO2/PL6C hybrid support. The results obtained from the application of the catalysts for H2O2 generation on gas diffusion electrode (GDE) after 120 min of electrolysis reflected the following order of efficiency: PL6C (∼140 mg L−1) < ZrO2/PL6C (∼235 mg L−1) < Au/PL6C (∼374 mg L−1) < Au-ZrO2/PL6C (∼600 mg L−1). Given that Au-ZrO2/PL6C exhibited the highest catalytic efficiency, this catalyst was employed for the removal of carbaryl (CBR) using different electrochemical advanced oxidation processes. The CBR degradation tests exhibited pseudo first-order kinetics, with the electro-Fenton (EF) and photoelectro-Fenton (PEF) processes recording the fastest removal kinetics (3.5 × 10−2 s−1 and 4.1 × 10−2 s−1, respectively). The PEF process exhibited the highest efficiency in terms of organic by-products mineralization; this was attributed to the additional photodecarboxylation of the Fe(III)-RCOOH complexes by UVC light. The aromatic by-products, short chain carboxylic acids, and ionic nitrogen species produced during the mineralization process contributed to the successful degradation of CBR. Apart from the analysis with synthetic water, the study also analyzed the treatment of urban wastewater spiked with CBR using a pre-pilot flow plant.