Reduction of graphene oxide by in-situ heating experiments in the transmission electron microscope

Abstract

Reduced graphene oxide (rGO) can be obtained by thermal treatment of graphene oxide (GO), whereby most of the oxygen-containing groups are removed, partially re-generating the original structure of graphene. Experimental observation of in-situ reduction heating of GO was carried out using a Transmission Electron Microscope (TEM) equipped with a heating-chip. This investigation contributes to the understanding of the thermal behavior of GO as the reduction proceeds upon heating the material. By acquiring Selected Area Electron Diffraction patterns (SAED) at different temperatures, two diffuse rings (R2 and R3) were observed at 25 °C with an interplanar distance (d) of 2.0977 and 1.201, respectively. A third ring (R1), with a d = 3.8189 Å, appears at 120 °C reaching a d = 3.3939 Å at 1200 °C, indicating the crystalline reordering of the material. The SAED patterns were interpreted by calculating the linear profiles, revealing information about the reduction of GO that is difficult to observe through SAED. The method reliability was proved by comparing the results as a function of the reciprocal space (1/nm) and 2θ. High resolution images revealed the reordering of the graphitic hexagonal structure that took place upon in-situ heating of GO to 1200 °C, temperature at which the d = 3.3961 Å was achieved.