Facile synthesis, high fluorescence and flame retardancy of carbon dots

doi:10.1016/j.jmst.2021.06.056

Abstract

Abstract:

Facile strategy enabling the fabrication of carbon dots (CDs) with favorable performance useful for various applications is highly desirable. Here, we report the fabrication of highly fluorescent carbon dots (CDs) towards sensitive metal ion detection, brightly fluorescent printing pattern, as well as green flame retardants for synthetic polymeric materials. CDs are synthesized by solvothermal treatment of polypropylene carbonate (PPC) with ethylenediamine, and the quantum yield of CDs could increase from 30 to 86% by further adding trace of citric acid. The abundant functional groups on the surface of CDs allow CDs well incorporated into polymers to form CD-loaded polystyrene (PS) microspheres, which are employed to construct fluorescent supraballs via triphase microfluidic technique and used as “inks” for uniform fluorescent patterns. Interestingly, the resultant CDs show good flame retardancy for highly flammable polymeric foams and fibers. The CDs surpass previously reported flame-retardant additives, to show excellent combustion resistance that the addition of 20 wt% CDs causes 75% decrease in the peak of heat release rate (P-HRR) for polyurethane (PU) foams. Significantly, a molecular dynamics simulation process for PU/CDs combustion is constructed. This work may spur the preparation and application of high-performance carbon-based nanomaterials.

Key words: Carbon dots, Fluorescence, Flame retardancy, Molecular dynamics simulation

Chang Liu, Hongying Li, Rui Cheng, Jiazhuang Guo, Guo-Xing Li, Qing Li, Cai-Feng Wang, Xiaoning Yang, Su Chen. Facile synthesis, high fluorescence and flame retardancy of carbon dots[J]. J. Mater. Sci. Technol., 2022, 104: 163-171.

Figures/Tables 5

Fig. 1. Synthesis and Characterizations of CDs. (a) Schematic solvothermal treatment of PPC with ethylenediamine yielding brown solution of CDs with bright blue fluorescence. (b) TEM image of CDs. Inset: particle size distribution of CDs. (c) HRTEM image of CDs. (d) XRD pattern of CDs. (e) XPS spectra of survey scan, and high-resolution N1s, O1s and C1s XPS spectra of CDs. (f) Raman spectrum of CDs. (g) UV-Vis absorption and PL emission spectra of CDs. (h) Fluorescence decay of CDs.

Fig. 2. Fluorescence applications of CDs. (a) Continuous production of CD-loaded PS supraballs via microfluidic technique. (b) TEM image of CD-loaded PS microspheres. (c) Confocal microscope images of fluorescent supraballs. (d) Scheme of inkjet printing and photographs of printed patterns obtained by using CD-loaded PS microspheres as fluorescent ink.

Fig. 3. Combustion resistance of CDs. (a-c) Photographs and combustion test of PU foams loaded with different concentrations of CDs. (d-g) Combustion process of PU/CDs-20 wt% foam. The PU/CDs-20 wt% foam did not ignite on the flame for 20 s but the stick got fire. (h) TGA curves of PU and PU/CDs-20 wt% foams measured in air with a heating rate of 40 ℃ min-1. (i) TG-MS curves of CDs. (j) HRR curves of PU, PU/CDs-10 wt% and PU/CDs-20 wt% foams. (k) Comparison of P-HRR reduction of different flame-retardant additives for PU foams, including Modified CNT [41], halogen and composite additives [42], polydopamine [43], Multi-layered MMT/CNT [44] and CDs in this case. (l) The mechanism of flame retardancy of CDs for polymeric foams and fibers.

Fig. 4. (a) SEM images of PU/CDs and (b) PAN/CDs nanofibers films. (c) HRR curves of PU/CDs nanofiber films with different concentrations of CDs. (d) HRR curves of PAN/CDs nanofiber films with different concentrations of CDs.

Fig. 5. Combustion process of CDs/PU from MD simulation. Unit structure of (a) CDs and (b) PU. The colors represent different atoms as follows; white: H, red: O, green: C, and blue: N. Combustion simulation process for (c) CDs combustion, (d) PU combustion and (e) PU/CDs combustion. The center panel (c-e): the weight proportion of the four types products after combustion.

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