The Route to Functional Graphene Oxide

• Published in: Chemphyschem 2010-07, Vol.11 (10), p.2131-2139
• Main Authors: Haubner, Kinga, Murawski, Jan, Olk, Phillip, Eng, Lukas M., Ziegler, Christoph, Adolphi, Barbara, Jaehne, Evelin
• Format: Article
• Language: English
• Subjects: carbon; Chemistry; Colloidal state and disperse state; dyes/pigments; Exact sciences and technology; General and physical chemistry; graphene oxide; oxidation; Physical and chemical studies. Granulometry. Electrokinetic phenomena; reduction; Surface physical chemistry
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201000132

We report on an easy‐to‐use, successful, and reproducible route to synthesize functionalized graphite oxide (GO) and its conversion to graphene‐like materials through chemical or thermal reduction of GO. Graphite oxide containing hydroxyl, epoxy, carbonyl, and carboxyl groups loses mainly hydroxyl and epoxy groups during reduction, whereas carboxyl species remain untouched. The interaction of functionalized graphene with fluorescent methylene blue (MB) is investigated and compared to graphite, fully oxidized GO, as well as thermally and chemically reduced GO. Optical absorption and emission spectra of the composites indicate a clear preference for MB interaction with the GO derivatives containing a large number of functional groups (GO and chemically reduced GO), whereas graphite and thermally reduced GO only incorporate a few MB molecules. These findings are consistent with thermogravimetric, X‐ray photoelectron spectroscopic, and Raman data recorded at every stage of preparation. The optical data also indicate concentration‐dependent aggregation of MB on the GO surface leading to stable MB dimers and trimers. The MB dimers are responsible for fluorescence quenching, which can be controlled by varying the pH value. Dye/graphene oxide composites are obtained by interaction of methylene blue (MB) with functionalized graphene oxide (GO). Formation of MB dimers on the GO surface (see schematic) changes the optical properties of the composite: UV/Vis absorption bands shift to lower wavelength and fluorescence is quenched. By increasing the pH value, the strong electrostatic interaction can be weakened, and the fluorescence intensity increases at high pH.