Ligand-promoted photoactivation aging of microplastics by composite clay minerals

• The ligand significantly improved the aging efficiency of the MPs, with a 61% increase in mass loss over 15 days compared to the system without the ligand. • Ligand-induced partial dissolution of Fe(II) into the liquid phase optimizes electron transfer and oxygen utilization and enhances the Fe(II)/Fe(III) cycle. • The ligand promoted the generation of •OH in the system, and the content of •OH increased to 64.83 μmol within 8 h, which was about three times that before the addition. Clay minerals in natural environments have the potential to produce reactive oxygen species (ROS) and thus age microplastics (MPs). The present study further demonstrates that the ligand can cause a change in the distribution of Fe morphology on the surface of clay minerals. Part of the Fe(II) was transferred to the liquid phase, which promoted the ability of clay minerals to generate ROS and improve the efficiency of photoaging MPs. After the addition of 1 mM Na 2 C 2 O 4 to the system suspension, the mass loss of MPs increased from 0.3% to 2.81% in one day, and finally reached 5.55% in 15 days. The electron paramagnetic resonance (EPR) results indicated that hydroxyl radicals (•OH) and superoxide radicals (•O 2 - ) play a key role in the photoaging process. The positive effect of ligands on photoaging MPs was quantified and the mechanism elucidated in detail by studying the water contact angle and carbonyl index. In conclusion, this study opens up a new research direction for the development of environmentally friendly microplastic pollution control technologies and elucidates the potential application value of ligand-mineral synergism in aging microplastics.