Micronized PET plastic waste-derived carbon dots with enhanced photoluminescence: A comparative analysis

Developing high-performance carbon dots (CDs) from PET waste offers a sustainable approach to reduce plastic pollution and generate value-added nanomaterials. However, use of bulk bottle scraps may cause inconsistent optical properties due to uncontrolled precursor size and uneven reaction conditions. This study introduces micronized PET (M-PET) as a size-controlled precursor for more uniform heat and oxidant diffusion during synthesis. A side-by-side comparison of surface oxidation (H 2 O 2 ) and N-doping (ethylene diamine, EDA) was conducted using both bulk PET cuttings (C-PET) and M-PET. M-PET-derived CDs exhibited smaller sizes, higher crystallinity, and enhanced surface functionalization, resulting in stronger blue photoluminescence under UV light. N-doped CDs also presented additional emission in the near-infrared region. The CDs showed a graphitic carbon framework with abundant oxygenated groups, however, O-content was significantly higher in M-PET-H 2 O 2 sample. Notably, M-PET-derived N-doped CDs contained higher graphitic N content, while bulk counterparts were richer in pyrrolic N. The quantum yield of M-PET-H 2 O 2 (∼52%) and M-PET-EDA (∼12%) was ∼2.4-fold higher than the bulk counterparts. While the highest luminescence output was observed for M-PET-H 2 O 2 CDs, they also exhibited excitation-independent emission, stable fluorescence across physiological pH, excellent biocompatibility in both RAW-Blue and epithelial cells. Meanwhile, N-doped CDs demonstrated pH- and excitation-dependent emission and notable cytotoxicity in epithelial cells but minimal immunogenicity in RAW-Blue cells. Both the CDs showed selective detection of Fe 3+ , Cu 2+ , and Ni 2+ through static quenching mechanism highlighting potential for environmental monitoring. Overall, this approach contributes to the development of a scalable and sustainable platform for high-performance nanomaterial synthesis from PET waste.