Tailoring the characteristics of graphite oxides by different oxidation times

Graphite oxide was synthesized using various oxidation times and characterized by its physical and chemical properties. The degree of oxidation of the graphite oxide was systematically controlled via oxidation time up to 24 h. Three phases of interlayer distances were identified by x-ray diffraction: pristine graphite (3.4 A), intermediate (4 A) and fully expanded graphite oxide (6 A) phases. These phases were distinguished by an atomic ratio of O/C, which occurred from the different compositions of epoxide, carboxyl and hydroxyl groups. The band gap of the graphite oxides was also tuned via the oxidation time, resulting in direct band gap engineering from 1.7 to 2.4 eV and strong correlation with the atomic ratio of O/C.