Highly Exfoliated Graphene Oxide with Enhanced Carbonyl Content and Facile Amine Functionalization for Biomedical Applications

A reroute process of Hummers’ method was carried out to reduce some steps in the synthesis of highly exfoliated graphene oxide (HEGO). Using pure KMnO4 and NaNO3 in concentrated H2SO4, HEGO was successfully prepared to contain extra carbonyl functional groups that helped stabilize the GO layer exfoliation. The oxidation reached its completion by one straight temperature level at 35 °C within a short reaction time (4 h). The obtained HEGO was observed to be highly dispersible through atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were also used to reveal the actual structure of HEGO and its analogues, which were formed from the reaction with aliphatic amines such as l-arginine (Arg) and β-alanine (Ala) as well as one aromatic amine, aniline (Ani). The results showed an interaction based on covalent bonding. The reduction reaction with l-ascorbic acid under basic conditions at 95 °C for 24 h was also performed. These facile functionalization and reduction process indicate the possible biomolecular adsorption.