Operando Nanocavity-Confined Raman Spectroscopy Uncovers a Drilling-Shearing Mechanism in Nanoplastic Photodegradation.

Deciphering how reactive oxygen species (ROS) govern nanoplastic photodegradation remains unresolved due to the lack of approaches capable of directly correlating chemical transformations with ROS activity at the single-particle level. Here, we report a nanocavity-confined Raman platform that enables operando molecular fingerprinting of individual nanoplastics with ultralow detection limits in both size and concentration. This approach allows real-time tracking of degradation intermediates within single photocatalytic nanoreactors. Time-resolved Raman analysis, combined with ROS-selective quenching experiments and electron paramagnetic resonance measurements, reveals distinct ROS-dependent pathways in which hydroxyl radicals (•OH) induce progressive surface oxidation, whereas superoxide radicals (•O2-) promote bond cleavage and bulk fragmentation. These assignments are further supported by electron microscopy, which shows morphology-dependent structural evolution under different ROS environments. Collectively, these converging lines of evidence support a cooperative degradation mechanism in which surface activation and subsurface fragmentation proceed concurrently. This coupled process gives rise to a drilling-shearing mechanism that accelerates nanoplastic breakdown. This work establishes a direct correlation between ROS activity and nanoscale chemical transformations at the single-particle level, providing a mechanistic framework for understanding and controlling nanoplastic photodegradation.