Polyethylene terephthalate waste-derived carbon dots with enhanced photoluminescence

 

Carbon dots (CDs) are photoluminescent carbon nanoparticles, smaller than 10 nm, that have gained relevance in nanotechnology due to their chemical stability, low production cost, biocompatibility, and tunable optical properties. Thanks to these characteristics, CDs are used in fields such as bioimaging, sensors, optoelectronics, and catalysis. A particularly attractive aspect is that they can be obtained from waste, making them functional materials aligned with the principles of circular economy.

In a recent work, a group of researchers from UNAM’s Center for Nanosciences and Nanotechnology reported the transformation of polyethylene terephthalate (PET) waste into highly luminescent CDs. In previous studies, PET has been used in the form of large fragments from crushed bottles (C-PET), which leads to non-uniform heat transfer and chemical diffusion during synthesis. The central idea of the present work is that the size of the polymeric precursor plays a key role in the final quality of the nanomaterial.

In this study, the authors used micronized PET (M-PET), that is, PET ground into micrometric particles, and directly compared it with PET cut into fragments (C-PET). They analyzed two chemical routes: surface oxidation with hydrogen peroxide and nitrogen doping using ethylenediamine. This experimental design allowed to understand how precursor size and surface functionalization affect the structural and optical properties of the CDs.

Additionally, biocompatibility and cellular internalization of CDs were evaluated using macrophages and epithelial cells.

The results showed that CDs derived from M-PET are smaller, more crystalline, and considerably brighter. In particular, oxidized CDs produced from M-PET reached a quantum yield close to 52%, approximately 2.4 times higher than those obtained with C-PET. Moreover, they revealed photoluminescent emission at different excitation wavelengths between 260 and 380 nm, indicating a more homogeneous structure with fewer electronic defects. On the other hand, nitrogen-doped CDs showed an additional emission in the near-infrared and excitation-dependent fluorescence. However, they displayed higher cytotoxicity in epithelial cells. It is important to note that both types of particles were sensitive to pH changes, a crucial characteristic for applications in biological environments where pH may vary.

This study demonstrates that both precursor engineering and synthesis chemistry are important. Micronizing PET significantly enhances the optical performance of CDs without resorting to aggressive or unsustainable processes.

For further information go to:  Carbon