Solvent-free one-step covalent functionalization of graphene oxide and nanodiamond with amines

We attempted amide functionalization of the carboxylic groups present in graphene oxide (GO) and nanodiamond (ND) by means of a solvent-free gas-phase treatment with two aromatic amines 1aminopyrene (AP) and 2-aminofluorene (AF), and also with one aliphatic amine, 1-octadecylamine (ODA), for comparison. The procedure was carried out under moderate vacuum, at temperatures of 150-180 degrees C, using short reaction times of about 2 h. The amine treatment generally gave rise to changes in Fourier-transform infrared (FTIR), Raman, ultraviolet-visible, and X-ray photoelectron spectra (XPS), to a variable degree depending on the particular sample. Thermogravimetric analysis showed the highest amine content for GO and ND treated with ODA, which turned out to be roughly one order of magnitude higher than in the case of aromatic AF and AP. Considerable changes in sample morphology after functionalization were observed by transmission electron and atomic force microscopy. Based on the analysis of FTIR and XPS spectra, we concluded that amidation is the only possible route for ND functionalization with AF, AP and ODA, whereas we found spectroscopic evidence for an alternative reaction channel on GO sheets, which is amine addition onto epoxy bridges.