From Microplastics to Multifunctional Magnetic Nanomaterials: A Circular Strategy for Water Remediation

Microplastic remediation strategies often overlook the management and valorization of the recovered waste, limiting their overall sustainability. Herein, we propose a closed-loop water remediation strategy in which polyethylene terephthalate microplastics (MicroPET) are not only removed from water but also converted into new magnetic nanomaterials for subsequent remediation cycles. MicroPET was initially harvested using magnetic iron oxide nanoflowers (NFs) and subsequently depolymerized by neutral hydrolysis, achieving an unscaled gravimetric PET mass conversion of 97%. Upon process scale-up and downstream purification, an isolated monomer yield of 28.7% was obtained for both purified terephthalic acid (TPA) and ethylene glycol (EG), as confirmed by ¹H-NMR, FTIR, Raman, and osmometric analyses. The recovered supernatant from the unscaled hydrolysis was directly reused as the reaction medium for the microwave-assisted synthesis of maghemite magnetic iron oxide nanoparticles (MIONPs), producing bimodal single-core nanoparticles composed of 5 ± 1 and 29 ± 6 nm crystallites. Despite the absence of the multicore nanoflower architecture and the associated reduction in magnetic performance, the synthesized nanoparticles still demonstrated a remarkable MicroPET harvesting capacity of 1000 mg g^-1 under optimized conditions (compared with 10,000 mg g^-1 achieved by the original NFs). Furthermore, both the pristine nanoparticles and the MicroPET-loaded hybrid materials efficiently catalyzed methylene blue degradation through a heterogeneous Fenton-like process, with alternating magnetic field activation increasing the decolorization efficiency by ≈20% compared with room-temperature conditions. These results demonstrate that PET-derived EG can be directly reintegrated into the synthesis of functional magnetic nanomaterials, establishing a circular strategy that combines pollutant removal, plastic waste valorization, and catalytic water remediation.