Waste-wood-derived biochar cathode and its application in electro-Fenton for sulfathiazole treatment at alkaline pH with pyrophosphate electrolyte

For the first time, a biomass-derived porous carbon cathode (WDC) was fabricated via a facile one-step pyrolysis of recovered wood-waste without any post-treatment. The WDC along with pyrophosphate (PP) as electrolyte were used in electro-Fenton (EF) at pH 8 for sulfathiazole (STZ) treatment. The H2O2 accumulation capacity of WDC was optimized via the following parameters: pyrolysis temperature, applied current and electrolyte. Results showed that the WDC cathode prepared at 900 degrees C achieved the highest H2O2 accumulation (13.80 mg L-1 in 3 h) due to its larger electroactive surface area (28.81 cm(2)). Interestingly, it was found that PP decreased the decomposition rate of H2O2 in solution as compared to conventional electrolyte, which resulted in higher H2O2 accumulation. PP allowed operating EF at pH of 8 due to the formation of Fe2+-PP complexes in solution. Moreover, Fe2+-PP was able to activate oxygen to produce (OH)-O-center dot. In this way, the degradation of STZ took place through four main pathways: 1) via (OH)-O-center dot from the Fe2+-PP complex, 2) via (OH)-O-center dot from EF reactions, 3) via surface (OH)-O-center dot at the boron doped diamond electrode (BDD) and 4) via SO4 center dot- from BDD activation. Finally, microtox tests revealed that some toxic intermediates were generated during WDC/BDD/PP EF treatment, but they were removed at the end of the process.