Surface Functionalization of Graphene-based Materials
Ajayan, Pulickel M.
Doctor of Philosophy
Graphene-based materials have generated tremendous interest in the past decade. Manipulating their characteristics using wet-chemistry methods holds distinctive value, as it provides a means towards scaling up, while not being limited by yield. The majority of this thesis focuses on the surface functionalization of graphene oxide (GO), which has drawn tremendous attention as a tunable precursor due to its readily chemically manipulable surface and richly functionalized basal plane. Firstly, a room-temperature based method is presented to reduce GO stepwise, with each organic moiety being removed sequentially. Characterization confirms the carbonyl group to be reduced first, while the tertiary alcohol is reduced last, as the optical gap decrease from 3.5 eV down to 1 eV. This provides greater control over GO, which is an inhomogeneous system, and is the first study to elucidate the order of removal of each functional group. In addition to organically manipulating GO, this thesis also reports a chemical methodology to inorganically functionalize GO and tune its wetting characteristics. A chemical method to covalently attach fluorine atoms in the form of tertiary alkyl fluorides is reported, and confirmed by MAS 13C NMR, as two forms of fluorinated graphene oxide (FGO) with varying C/F and C/O ratios are synthesized. Introducing C-F bonds decreases the overall surface free energy, which drastically reduces GO’s wetting behavior, especially in its highly fluorinated form. Ease of solution processing leads to development of sprayable inks that are deposited on a range of porous and non-porous surfaces to impart amphiphobicity. This is the first report that tunes the wetting characteristics of GO. Lastly as a part of a collaboration with ConocoPhillips, another class of carbon nanomaterials - carbon nanotubes (CNTs), have been inorganically functionalized to repel 30 wt% MEA, a critical solvent in CO2 recovery. In addition to improving the solution processability of CNTs, composite, homogeneous solutions are created with polysulfones and polyimides to fabricate CNT-polymer nanocomposites that display contact angles greater than 150o with 30 wt% MEA. This yields materials that are inherently supersolvophobic, instead of simply surface treating polymeric films, while the low density of fluorinated CNTs makes them a better alternative to superhydrophobic polymer materials.
Graphene oxide; Wetting; Carbon nanotubes; Functionalization