Graphene Oxide Synthesis: Optimizing the Hummers and Marcano Methods

Abstract

Fabricating graphene oxide (GO) in a cost-effective, efficient manner remains challenging. Some researchers manufacture GO that is comprised of a small number of layers by a modification of Hummers' method, as follows: (1) minimize use of NaNO3, a source of toxic gases; and (2) use MnO2 as the oxidizer. Other researchers fabricate GO by Marcano's method, where KMnO4 substitutes for MnO2. Here, one uses a 9:1 volume ratio of H2SO4/H3PO4. The role of KMnO4 is to diffuse slowly in the graphite interlayer and act as a peroxidation agent throughout the oxidation. For large-scale production, there is an explosion risk from using KMnO4 in H2SO4, and incomplete graphite oxidation. We overcame these challenges by growing GO sheets exhibiting an average size thickness of ∼3.1 ± 0.2 μm by optimizing the quantity of KMnO4 and H2SO4/H3PO4 as oxidizer ion sources, in modifications of both the Hummers and Marcano methods, without using NaNO3. Optimizing the reaction time and using small graphite flakes optimized oxidation to afford a high yield of GO sheets. X-ray diffraction showed an interlayer d-spacing of 5.7 Å for GO and 2.9 Å for the lesser quantity of remaining non-exfoliated graphite grains. Fourier-transform infrared spectroscopy showed no peaks for stretching vibrations within the graphitic domains, especially for GO grown via the modified Hummers method. Ultraviolet-visible and Raman spectroscopy showed that the number of layers with sp2 domains of interconnected carbon atoms, and disorder such as ripples and major defects at the edge planes, decreased compared to prior research. The Raman Id/Ig ratio of the GO sheets ranged from 1.21 to 1.75. The carbon/oxygen atomic ratio (RC/O), deduced from the C 1 s core level as per X-ray photoelectron spectroscopy, ranged from 0.43 to 6.84.