Chemical Oxidation of Graphite: Evolution of the Structure and Properties

Abstract

Graphene oxide is a complex material whose synthesis is still incompletely understood. To study the time evolution of structural and chemical properties of oxidized graphite, samples at different temporal stages of oxidation were selected and characterized through a number of techniques: X-ray photoelectron spectroscopy for the content and bonding of oxygen, X-ray diffraction for the level of intercalation, Raman spectroscopy for detection of structural changes, electrical resistivity measurements for probing charge localization on the macroscopic scale, and scanning 2 transmission electron microscopy for the atomic structure of the graphene oxide flakes. We found a non-linear behavior of oxygen uptake with time where two concentration plateaus were identified: uptake reached 20 at.% in the first 15 minutes, and after one hour a second uptake started, reaching a highest oxygen concentration of more than 30 at.% after two hours of oxidation. At the same time, the interlayer distance expanded to more than twice the value of graphite and the electrical resistivity increased by 7 orders of magnitude. After four days of chemical processing, the expanded structure of graphite oxide became unstable and spontaneously exfoliated; more than two weeks resulted in a significant decrease of the oxygen content accompanied by re-aggregation of the GO sheets. These correlated measurements allow us to offer a comprehensive view into the complex oxidation process.

Graphene Nanomaterials: Synthesis, Biocompatibility, and Cytotoxicity

“…Because of the different surface oxidation states and features between GO, rGO, and TRG, such graphene materials have distinct chemical and physical properties. GO possesses many defects, such as vacancies due to synthesis, as revealed by high-resolution TEM images and Raman spectra [ 31 , 32 ]. TRG produced from rapid heating of GO at high temperatures exhibits a wrinkled feature [ 67 ].…”

“…Its application is limited to research only for studying electrical, mechanical, and optical properties of pure graphene. Therefore, numerous studies have been conducted by the researchers to synthesize graphene at a large scale, including its derivatives such as graphene oxide (GO), reduced graphene oxide (rGO), and thermally reduced graphene oxide (TRG) [ 14 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. The remarkable electrical, mechanical and optical properties of graphene sheets, and GQDs render them attractive materials for use in electronic, optoelectronic, and aerospace industries [ 35 , 36 , 37 ].…”

Synthetic Biodegradable Aliphatic Polyester Nanocomposites Reinforced with Nanohydroxyapatite and/or Graphene Oxide for Bone Tissue Engineering Applications

“…The synthesis of GO and rGO is well described in the literature, so it is discussed briefly herein [45,95,96]. Modified Hummers process is the most commonly adopted technique for synthesizing GO [97].…”

“…As a result, GOs possess different O contents or C/O ratios, especially those prepared from various oxidation times. Skakalova employed X-ray photoelectron spectroscopy (XPS) to evaluate oxygen content in the GOs prepared from modified Hummers method with different oxidation periods (Figure 4A,B) [95]. During chemical oxidation for the first 60 min, deconvoluted C-1s spectrum shows the main peak at about 284.7 eV and a small shoulder at 286.6 eV, corresponding to the sp 2 carbon and C–O–C bonded species, respectively.…”

Flow Field Patterns for Proton Exchange Membrane Fuel Cells

“…Metal plates can be machined very thin, but many metals are subject to corrosion when exposed to oxygen and water at high temperatures. Also, graphite is unstable and spontaneously exfoliated with respect to chemical oxidation (Skákalová et al, 2018).…”