The X-ray powder diffraction (XRD) patterns of graphite,graphene oxide, and sulfonated graphene ( Figure 2 A) indicate that the c -axis spacing increases from 0.34 nm (corresponding to the diffraction peak at 2 θ = 26.40 ° ) to 0.87 nm (corresponding to the diffraction peak at 2 θ = 10.03 ° ) during the oxidation process because of the creation of the oxygen-containing functional groups on the surface of graphene oxide. [ 7 ] The reappearance of the weak and broad diffraction peak at 2 θ = 26.16 ° is attributable to the rather limited ordering (only a few layers) in each sulfonated graphene sheet and the uneven interlayer spacing over the whole sulfonated graphene sample. [ 8 ] The same interlayer spacing of the sulfonic graphene as for the pure graphite is a result of the effective reduction of graphene oxide by sodium borohydride and hydrazine. It also implies that the
added sulfonic acid groups are on the edges of the graphene sheets, rather than in the fl at plane of the graphene sheets. The bands at ∼ 1580 and 1350 cm − 1 in the Raman spectra (Figure 2 B)
are assigned to the G band (associated with the vibration of sp 2 carbon atoms in a graphitic 2D hexagonal lattice) and D band (related to the vibrations of sp 3 carbon atoms of defects and
disorder). [ 9 ] The intensity ratio of the D band to the G band increases from 0.89 (for graphene oxide) to 1.00 (for sulfonated graphene) after the chemical reduction, suggesting a decrease
in the average size of the sp 2 carbon domains, which is caused by the increased number of smaller graphitic domains formed during the reduction process. [ 10 ] The weak and broad 2D peak
at 2700 cm − 1 is another indication of disorder as a result of an out of plane vibrational mode, and the cooperation between D and G peaks also gives rise to an S3 peak near 2950 cm − 1 . Both
DOI: 10.1002/adma.201101007 of the 2D and S3 peaks are similar to previous results.[ 11]