Selective elimination of organic pollutants and analysis of effects and novel mechanisms of aged microplastics on wavelength-dependent UV-LED/H2O2 system

The selective removal of organic pollutants and potential impact of aged microplastics (MPs) as emerging pollutants in wavelength-dependent UV-LED/H2O2 system are not fully understood. This study found that cefalexin (CFX) degradation efficiency in UV-LED alone system was highly correlated with its UV molar absorbance (R-2=0.994), while in UV-LED/H2O2 system, it was correlated with <middle dot>OH yield (R-2=0.991) across various wavelengths. Quantitative structure-activity relationship (QSAR) analysis showed selective degradation of six pollutants based on their e(-)-donating capabilities (R-2=0.748-0.916). The coexistence of aged MPs, introducing C-O/C=O groups and rearranging their surface e(-), potentially affected the elimination efficiency of CFX. Aged polystyrene (PS) decreased the degradation efficiency of CFX by shorting the O-O bond length (l(O-O)) in H2O2 and capturing e(-) from H2O2, whereas aged polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) had negligible effects as the l(O-O) elongation balanced the e(-)-donating effect of H2O2. Additionally, phenol released from aged PS, with strong nucleophilicity, competing with CFX for <middle dot>OH, further decreasing CFX degradation efficiency. This study provides valuable insights into organic pollutant selective removal and reveals a novel inhibitory mechanism of aged PS on the performance of UV-LED/H2O2 technology.