Abstract
In this work we have comprehensively characterised 13 products from commercial suppliers that are claimed to be 2D materials: graphene, graphene oxide and reduced graphene oxide. The techniques used have investigated the materials from the macroscale to the atomic scale. The results are consistent across all length scales: none of the products meet the ISO definition of “a single layer of carbon atoms”. Rather, they are largely nanographite with a small percentage of single layer material present. One of the techniques used was inelastic neutron scattering (INS) spectroscopy. INS enables the materials to be examined in the C-H/O-H stretch region without the complications of electrical anharmonicity that bedevil infrared spectroscopy. The spectra clearly show that most of the hydrogen is present as sp2 C-H; sp3 C-H is either absent or present as a minority species. This provides strong support for the Lerf and Klinowski model of graphene oxide. The spectra also show that the number of hydroxyls present is small, indicating that most of the oxygen is present as epoxides or carbonyls.
| Original language | English |
|---|---|
| Pages (from-to) | 2810-2826 |
| Number of pages | 17 |
| Journal | Materials Advances |
| Volume | 3 |
| Issue number | 6 |
| DOIs | |
| State | Published - Feb 11 2022 |
Funding
The STFC Rutherford Appleton Laboratory is thanked for access to neutron beam facilities (RB1920447). AJRC and YC are supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC0500OR22725 with UT Battelle, LLC. Computing resources for DFT simulations were made available through the VirtuES and the ICE-MAN projects, funded by Laboratory Directed Research and Development program and Compute and Data Environment for Science (CADES) at ORNL. The trend induced by chemical changes (GO, rGO) to generate three-dimensional disorder, expansion and separation from two-dimensional ordered graphite and staples/packages of graphene sheets is also evident in the low energy region of the INS spectra recorded on TOSCA (). At the macroscopic scale the width and fine structure of the translational mode of the sheets in graphite (measured on TOSCA in a 100 g piece of commercial graphite) and the various graphenes in the c-direction is broadened and partly split to lower energy from a rather sharp band for pure bulky reference graphite, various GNP's with graphitic stacks of varying packing thickness, sizes and tilt/mismatch down to disordered bent sheets for GO and rGO with decreasing average number of layers (XRD). This interpretation is supported by TEM demonstrating differences down to the nanoscale in the electron micrographs .