Formation of environmentally persistent free radicals (EPFRs) and electron transfer in conjugated polymers and alkane polymers during aging

The electrons in environmental persistent free radicals (EPFRs) of aged microplastics (MPs) are highly mobile and reactive, readily interacting with oxygen and water to generate reactive oxygen species, possessing ecological hazards. However, it is still a big challenge to detect the formation of EPFRs and electrons in real-time by using the conventional technologies. Interestingly, the conductive atomic force microscopy (CAFM) can capture local electrical information on the sample surface with high resolution. Based on this, the present work provided an intuitive understanding of the dynamic evolution of surface currents in aged conjugated aromatic ring MPs and alkane chain MPs. The study found that photoexcitation induced electron transitions, promoting interactions between electrons and the chemical bonds of the polymers and ultimately generation of the persistent free radicals. Conjugated structures played a crucial role in the facilitating of electron transfer. And the aged PET MPs primarily generated carbon-centered and oxygen-centered free radicals, while the aged PS and PP MPs mainly produced oxygen-centered free radicals. Ultimately, the free electrons generated by the aged MPs enhanced their removal capacity for cationic dyes. This study provides a novel testing method and perspective to deeply investigate the formation of electrons on the surfaces of aged MPs.