Violet phosphorus-Fe3O4 as a novel photocatalysis-self-Fenton system coupled with underwater bubble plasma to efficiently remove norfloxacin in water

The contamination of water bodies has been caused by the overuse of antibiotics to an alarming extent. Green and enhanced treatment technologies for wastewater are necessary to limit the uncontrollable spread of antibiotic pollution. Herein, an efficient photocatalysis-self-Fenton system based on violet phosphorus (VP)-Fe3O4 is constructed to achieve significant degradation performance. The VP-Fe3O4 combined with underwater bubble plasma (UBP) has been demonstrated to obtain a norfloxacin (NOR) degradation rate as high as 91.8% with the VP content of 15 wt%, which is 77.3% and 22.2% higher than that in sole VP-Fe3O4 and UBP, respectively. The •OH radicals have been demonstrated by the radical trapping test to play a crucial role in NOR removal processes. The VP-Fe3O4 has also been found to have a higher synergistic degradation ability with UBP than the well-known reduced graphene oxide-Fe3O4, which is due to the excellent reducibility and electron donating ability of VP, boosting the cycle of Fe(II)/Fe(III) in Fenton reactions. The VP-Fe3O4 can also consume O3 generated by UBP, with the enhanced in-situ H2O2 production. Besides, the efficient utilization of H2O2 via the Fenton reaction improves the generation of •OH. A clear signal of DMPO-OH has been detected by electron spin resonance after 24 h post-discharge, further substantiating the sustainable regeneration of •OH by the synergetic system in the absence of additional reagents. Three possible degradation pathways are proposed based on the density functional theory (DFT) calculation and the degradation by-products of NOR determined during the synergetic treatment. Eventually, the synergetic degradation mechanism in the VP-Fe3O4/UBP system is elucidated. This research would provide a promising strategy for environmental remediation via the incorporation of photocatalysis-self-Fenton system and underwater bubble plasma.