Evolution of surface functional groups in a series of progressively oxidized graphite oxides

This study contributes to the sustained effort to unravel the chemical structure of graphite oxide (GO) by proposing a model based on elemental analysis, transmission electron microscopy, X-ray diffraction, C-13 magic-angle spinning NMR, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance investigations. The model exhibits a carbon network consisting of two kinds of regions (of trans linked cyclohexane chairs and ribbons of flat hexagons with C=C double bonds) and functional groups such as tertiary OH, 1,3-ether, ketone, quinone, and phenol (aromatic diol). The latter species give clear explanation for the observed planar acidity of GO, which could not be interpreted by the previous models. The above methods also confirmed the evolution of the surface functional groups upon successive oxidation steps.