Sequential extraction, depolymerization and quantification of polyethylene terephthalate nanoplastics using magnetic ZIF-8 nanocomposites

• MOF-based extraction and depolymerization of PET nanoplastics. • Accurate detection of PET nanoplastics via depolymerization products. • Fast magnetic extraction in 60 sec. • Efficient PET nanoplastics depolymerization in 0.5 h. The detection and quantification of nanoplastics in aqueous medium is largely untapped because of an absence of appropriate sample processing methods. In this work, magnetic ZIF-8 nanoparticles (Nano-Fe@ZIF-8) have been applied for the magnetic extraction and depolymerization of polyethylene terephthalate (PET) nanoplastics. Nano-Fe@ZIF-8 enabled the fast aggregation and magnetic retrieval of PET nanoplastics from water. The Zn(II) present in Nano-Fe@ZIF-8 subsequently acted as a catalyst for the depolymerization of the extracted PET nanoplastics using ethylene glycol at 180 °C. PET nanoplastics were depolymerized in just 30 min, producing the depolymerization product bis(2-hydroxyethyl) terephthalate. The selective quantification of the depolymerization product using reversed-phase liquid chromatography enabled the measurement of the original PET nanoplastics present in water at parts-per-million level, and with a high reproducibility (RSD, 2.8–5.9 %). This is the first example of an integrated magnetic-catalytic nanomaterial enabling the isolation, depolymerization, and detection of nanoplastics from aqueous medium.