Green and fast synthesis of amino-functionalized graphene quantum dots with deep blue photoluminescence

• Published in: Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology 2015-05, Vol.17 (5), p.1-13, Article 214
• Main Authors: Blanco, E., Blanco, G., Gonzalez-Leal, J. M., Barrera, M. C., Domínguez, M., Ramirez-del-Solar, M.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Emissions; Excitation; Graphene; Inorganic Chemistry; Lasers; Materials Science; Nanoparticles; Nanotechnology; Optical Devices; Optics; Photoluminescence; Photonics; Physical Chemistry; Quantum dots; Research Paper; Surface chemistry; Synthesis; Titanium dioxide; Wavelengths
• ISSN: 1388-0764; 1572-896X
• DOI: 10.1007/s11051-015-3024-3

Graphene quantum dots (GQDs) were prepared using a top-down approach with a green microwave-assisted hydrothermal synthesis from ultrathin graphite, previously ultrasound delaminated. Results obtained by transmission electron microscopy and atomic force microscopy indicate that the so-fabricated GQDs are plates with 6 nm of average diameter, mostly single- or bi-layered. Photoluminescence characterization shows that the strongest emission occurs at 410–415 nm wavelength when the samples are excited at 310–320 nm wavelength. In addition to these down-conversion features, GQDs also exhibit up-conversion photoluminescence when excited in the range 560–800 nm wavelength, with broad emission peaks at 410–450 nm wavelength. Analysis of X-ray photoelectron spectroscopy measurements indicates a higher proportion of C–C sp 2 than sp 3 bonds, with the sp 3 ones mainly located at the GQD surfaces. Also evidences of C–O and C–N bonds at the GQD surface have been observed. The combination of these results with Raman and ultraviolet–visible absorption experiments allows envisaging the GQDs to be composed of amino-functionalized sp 2 islands with a high degree of surface oxidation. This would explain the photoluminescent properties observed in the samples under study. The combined up- and down-conversion photoluminescence processes would made these GQDs a powerful energy-transfer component in GQDs–TiO 2 nanocomposite systems, which could be used in photocatalyst devices with superior performance compared to simple TiO 2 systems.