关键词: 碳点, 聚己二酰己二胺, 阻燃, 改性, Fe³⁺检测, 防伪, 指纹检测

Abstract:

Objective Carbon dots (CDs) are a sort of zero-dimensional fluorescent nanomaterials that can be widely utilized across various fields due to their excellent biocompatibility and biosecurity. Research has demonstrated that carbon dots possess significant potential as flame retardants, but the current methods for preparing carbon dots are still limited to laboratory-scale production and have not yet achieved large-scale manufacturing. This limitation poses challenges for their application in flame retardant formulations that require substantial quantities. The objective of this study is to explore a method that not only enables the efficient recycling of waste but also facilitates the flame retardant modification of polyamide 66(PA66).

Method In this study, polyethylene terephthalate (PET) carbon dots (PET-CDs) were synthesized using a hydrothermal method with PET oligomers, urea, and phosphomolybdic acid (PMA) as precursors. The optimal synthesis conditions were determined through orthogonal experiments, which allowed for the optimization of reaction temperature, reaction time, and loading volume. A series of characterization tests were conducted on the prepared carbon dots, including optical and morphological assessments. Additionally, CDs-PA66 was created by blending PET-CDs with PA66, and the thermal stability, flame retardancy, and combustion properties of CDs-PA66 were evaluated. The influence of PET-CDs on fluorescence anti-counterfeiting and fingerprint recognition was also investigated.

Results Using PET oligomer, urea, and PMA as precursors, the optimal process conditions were determined to be 3 g of PET oligomer, 5 g of PMA, 4 g of urea, and 15 mL of H₂O. The reaction was conducted in a drying oven at 260 ℃ for 18 h. It is observed that the loading volume had minimal impact on the fluorescence intensity of PET carbon dots (PET-CDs), which was prepared in a 5 L kettle in equal proportions. PET-CDs were characterized using a fluorescence spectrometer, among other techniques, and the results indicate that PET-CDs exhibited no dependence on the excitation wavelength. The optimal excitation wavelength was found to be 410 nm, while the optimal emission wavelength was 485 nm, resulting in a fluorescence quantum yield of 70.78%. PET-CDs possess a spherical structure with an average particle size of 1.37 nm and a lattice spacing of 0.25 nm. The surface of the particles was rich in functional groups, including hydroxyl groups. When PET-CDs were utilized for the flame retardant modification of PA66, with an addition of 4% PET-CDs, the limiting oxygen index indicating a refractory level reached 28%. Additionally, the combustion time following the initial flame ignition decreased significantly from 188.7 s to 5.2 s. The fluorescence of PET-CDs can be specifically quenched by Fe³⁺, allowing for the quantitative detection of Fe³⁺ through the linear relationship between the degree of quenching of PET-CDs and the concentration of Fe³⁺ within the range of 0.00 to 10 μmol/L. Furthermore, fluorescent inks containing PET-CDs produced patterns that was invisible under natural light but become visible under ultraviolet light, demonstrating their anti-counterfeiting capabilities. Starch containing 1.5% PET-CDs can also be employed for fingerprint identification.

Conclusion PET oligomer, urea, and PMA serve as precursors with excellent fluorescence properties and a high fluorescence quantum yield. These materials can be utilized in PA66 flame retardants, fluorescent anti-counterfeiting applications, and fingerprint recognition technologies.

Key words: carbon dot, polyamide 66, flame retardant, modification, Fe³⁺ detection, anti-counterfeiting, fingerprint detection