On the intriguing emission characteristics of size tunable carbon dots derived from functionalized multi-walled carbon nanotubes

• Published in: Materials chemistry and physics Vol. 225; pp. 8 - 15
• Main Authors: Saheeda, P., Sabira, K., Joseph, Julin, Jayaleksmi, S.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.03.2019; Elsevier BV
• Subjects: Carbon; Carbon dots; Clusters; Crystal defects; De-protonation; Fluorescence; Fourier transforms; Functional groups; Functionalization; Image transmission; Multi wall carbon nanotubes; Multi-walled carbon nanotubes; Optical properties; Photoluminescence; Raman spectroscopy; Spectrum analysis; Synthesis; Transmission electron microscopy; X-ray diffraction; Fluorescence; De-protonation; Carbon dots; Functionalization; Multi-walled carbon nanotubes; Photoluminescence
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2018.11.062

Aqueous dispersions of carbon dots (C-dots) showing size tunable multi-colours in day light are obtained through surface functionalization of multi-walled carbon nanotubes (MWCNTs). The size of the C-dots varies with the functionalization temperature and smaller C-dots are found to be formed, at higher temperatures. The average size of the C-dots synthesized at temperatures of 100 °C, 80 °C and 60 °C lies in the range 6 nm–18 nm, based on transmission electron microscopy (TEM) images. The C-dots synthesized at these temperatures exhibit blue, green and golden yellow colours in day light without being excited by any external source. The structural characterizations using X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy confirm the presence of a high density of functional groups on the surfaces of the C-dots, giving rise to high aqueous solubility. Compared to the Raman spectrum of the MWCNTs, the spectrum of the C-dots shows a significant increase in the intensity of the defect related D band with respect to that of the crystalline G-band, which indicates the presence of a high concentration of defects and the formation of smaller sp2 carbon clusters. The synthesized C-dots exhibit size dependent optical absorption and emission characteristics. The intriguing optical properties of these C-dots, which include the multi-colour emission at day light and the excitation wavelength and the pH dependent photoluminescence emission, can be mainly attributed to the formation of sp2 clusters of different sizes embedded in the sp3 carbon matrix. Aqueous dispersions of the C-dots synthesized at (a) 100 °C, (b) 80 °C and (c) 60 °C. [Display omitted] •Carbon dots (C-dots) are synthesized by the acidic oxidation of carbon nanotubes.•Smaller C-dots are formed at higher reaction temperatures.•The C-dots show size dependent optical absorption and emission characteristics.•Aqueous dispersions of the C-dots exhibit multi-colour emission in day light.•The C-dots show pH and excitation wavelength dependent photoluminescence emission.