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 NaNO 3 , a source of toxic gases; and (2) use MnO 2 as the oxidizer. Other researchers fabricate GO by Marcano's method, where KMnO 4 substitutes for MnO 2 . Here, one uses a 9:1 volume ratio of H 2 SO 4 /H 3 PO 4 . The role of KMnO 4 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 KMnO 4 in H 2 SO 4 , and incomplete graphite oxidation. We overcame these challenges by growing GO sheets exhibiting an average size thickness of ∼3.1 ± 0.2 μ m by optimizing the quantity of KMnO 4 and H 2 SO 4 /H 3 PO 4 as oxidizer ion sources, in modifications of both the Hummers and Marcano methods, without using NaNO 3 . 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 sp 2 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 ( R C/O ), deduced from the C 1 s core level as per X-ray photoelectron spectroscopy, ranged from 0.43 to 6.84.