New insights into the slow-drying modified hydrophilic graphite felt gas-diffusion cathode using acetylene black/PTFE for efficient electro-Fenton removal of norfloxacin

Abstract

In the electro-Fenton system, designing a low-cost and efficient 2e− oxygen-reducing cathode materials is critical for pollutants of degradation. In this work, we proposed a hydrophilic graphite felt gas diffusion cathode modified by acetylene black/PTFE under slow-drying mechanism to degrade norfloxacin (NOR). The results showed that the graphite felt gas diffusion cathode in slow drying mode had better curing effect due to weak capillarity and formed more 3-phase interfaces compared with the traditional quick-drying way, which was conducive to locally confined O2 storage and transfer. The slow-drying method had more H2O2 yield and efficient NOR removal rate. It was found that 30 mg/L NOR achieved 92.2 % degradation and almost 71.3 % of NOR was completely mineralized within 120 min under optimal reaction conditions. Interestingly, the H2O2 yield was only decreased by 5.2 % after 10 cycles, and the NOR removal rate decreased 3.8 % after pickling, which exerted an excellent reusability. The radicals quenching experiments revealed that ·OH and ·O2− were the main active species in NOR degradation process. Besides, it was found that PTFE coating was not beneficial for the activation of H2O2 by graphite structure. Finally, possible NOR degradation pathways were proposed by Ultra performance liquid chromatography-mass spectrometry (LC-MS).