Abstract
Graphene oxide (GO), the oxidized form of graphene, shows unique properties including high mechanical strength, optical transparency, amphiphilicity and surface functionalization capability that make it attractive in fields ranging from medicine to optoelectronic devices and solar cells. However, its insolubility in non-polar and polar aprotic solvents hinders some applications. To solve this issue, novel functionalization strategies are pursued. In this regard, this study deals with the preparation and characterization of hexamethylene diisocyanate (HDI)-functionalized GO. Different reaction conditions were tested to optimize the functionalization degree (FD), and detailed characterizations were conducted via elemental analysis, Fourier-transformed infrared (FT-IR) and Raman spectroscopies to confirm the success of the functionalization reaction. The morphology of HDI-GO was investigated by transmission electron microscopy (TEM), which revealed an increase in the flake thickness with increasing FD. The HDI-GO showed a more hydrophobic nature than pristine GO and could be suspended in polar aprotic solvents such as N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO) as well as in low polar/non-polar solvents like tetrahydrofuran (THF), chloroform and toluene; further, the dispersibility improved upon increasing FD. Thermogravimetric analysis (TGA) confirmed that the covalent attachment of HDI greatly improves the thermal stability of GO, ascribed to the crosslinking between adjacent sheets, which is interesting for long-term electronics and electrothermal device applications. The HDI-GO samples can further react with organic molecules or polymers via the remaining oxygen groups, hence are ideal candidates as nanofillers for high-performance GO-based polymer nanocomposites.
Highlights
Graphene (G), an allotrope of carbon like diamond, graphite and fullerenes, has attracted a lot interest in recent years both for fundamental studies and potential applications [1]
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The HDI-graphene oxide (GO) displayed a more hydrophobic character than raw GO and could be dispersed in polar aprotic solvents such as DMF, NMP and dimethyl sulfoxide (DMSO) as well as in some low polar/non-polar solvents like THF, chloroform and toluene. The dispersibility in these solvents improved as the functionalization degree increased
Summary
Graphene (G), an allotrope of carbon like diamond, graphite and fullerenes, has attracted a lot interest in recent years both for fundamental studies and potential applications [1] It is a flat, atomically thick two-dimensional (2D) sheet composed of sp carbon atoms arranged in a honeycomb structure. Due to its hydrophobic nature and strong van der Waals forces between adjacent sheets, it is insoluble in water or common organic solvents and displays poor dispersion in most solvents, which hinders its applications In this context, graphene oxide (GO), originated from the exfoliation of graphite oxide or the chemical oxidation of G [8], has been studied in much research as an alternative to G. Such functionalization was first demonstrated by Lerf et al [12], who prepared a series of chemically modified graphite oxide derivatives
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