Efficient degradation of polyethylene microplastics with VUV/UV/PMS: The critical role of VUV and mechanism

Microplastics (MPs) pose a severe threat to the environment and human health, and effective treatment techniques are urgently desired to prevent the global spread of MPs pollution. However, efficient degradation of MPs remains difficult. Herein, vacuum ultraviolet (VUV) activated peroxymonosulfate (PMS) was firstly proposed as a promising technique for the degradation of polyethylene MPs. The weight loss of MPs reaches as high as 51.5% under mild conditions ([PMS] = 32 mmol/L, initial pH = 7, [MPs] = 1 g/L, [Time] = 48 h), which is the record performance achieved at room temperature and ambient pressure for MPs degradation. The excellent degradation performance is uncovered to originate from the synergistic effect of VUV and activated PMS. Direct photolysis of VUV can rapidly oxidize the surface of MPs to reduce its hydrophobicity and thus enhance the adsorption of reactive oxidation species (i.e., SO4⋅− and HO⋅) rooted from the VUV activated PMS, which was further confirmed by DFT calculations. The degradation of MPs repeatedly undergoes the process of VUV photolysis oxidation of the surface, degradation via VUV/UV/PMS-derived reactive oxidation species, shedding, and re-exposure of the new surface via VUV photolysis oxidation. This study highlights the unique role of the VUV photolysis in MPs degradation, paving a new route for designing practical MPs pollution remediation techniques.