Termination of Structural Deformation and Proton–Electron Conductive Inflection of Graphene Oxide in Six Years

Graphene oxide (GO) sustains with some natural decay of its epoxy sites. The time-duration needed for autotermination of this decay process is still unknown. We present the duration of ending GO’s structural deformation and proton–electron conductive inflection. The chemical structure (CS), proton conductivity (PC), and electron conductivity (EC) of GO synthesized from Hummers' method and preserved for six years at 1 atm pressure and 25 °C (ambient condition) have been studied at the 0th, 2nd, 4th, and 6th years of the synthesis. The physico-chemical changes were pronounced within 0–2 years. The changes continued but reduced in 2–4 years. Finally, the processes almost terminated within 4–6 years. The PC values significantly fall in the 2nd year, continued to some lower extent in the 4th year, and remained almost unchanged in the 6th year. The EC increased significantly in the 2nd year, moderately in the 4th year, and remained almost unchanged in the 6th year. The chemical structures analyzed by X-ray photoelectron spectroscopy (XPS) show that the amount of epoxy groups in freshly prepared GO gradually reduces with time up to the 4th year. Slight increases in the −OH and −COOH contents indicate the conversion of some epoxy groups into these functional sites. Raman spectra show that the C═C domain of freshly prepared GO increases gradually between 0 and 4 years and suffer insignificant changes in 4–6 years. Some shifting in the powder X-ray diffraction (PXRD) pattern indicates time-dependent changes of the interlayer distance (ID) of GO. GO’s chemical structure clearly suffers from some spontaneous and irreversible intraconversion of functional groups, which directly affects its conductive behavior.