Roles of water in the formation and preparation of graphene oxide

Abstract

The functional groups and physical properties of graphene oxide (GO) are found to be sensitive to and can be controlled by the water content in the reactions when GO samples are prepared at different concentrations of sulfuric acid using a modified Hummers method. GO prepared with 93% sulfuric acid (H₂SO₄) showed fewer structural defects, less π–π conjugation, and larger interlayer spacing than GO prepared with 99% H₂SO₄. The intensity ratio of the D-band to the G-band of the Raman spectrum is 0.89 ± 0.01 and 1.02 ± 0.01, corresponding to average interlayer spacing of 0.91 nm and 0.86 nm, respectively. The yield and carbon to oxygen ratio of the GO sheets prepared from different concentrations of H₂SO₄ are nearly identical. More importantly, compared with GO synthesized with 99% H₂SO₄, GO prepared with 93% H₂SO₄ contains more carbon–oxygen single bonds, such as epoxy groups and hydroxyl groups, but fewer carbonyl groups.