Perforation of graphite is carried out by treating the graphite oxide with a boiling mineral acid H2SO4 or H3PO4. High-resolution transmission electron microscopy shows formation of a large number of vacancy defects (holes) in the graphene sheets, which are caused more likely by the CO2 liberation during the reduction process. The characteristic size of the holes is about 2 nm. The obtained materials are comparatively examined by X-ray diffraction, Raman and IR-absorption spectroscopy, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. It is found that the products obtained using a strong acid H2SO4 and a weak acid H3PO4 are different in the concentration and electronic state of oxygen and the mean distance between defects.
Left, schematic representation of the perforated graphite (PG); right, NEXAFS OK-edge spectra of the PG obtained using H3PO4 and H2SO4 acids demonstrate the different electronic state of oxygen in the samples.