Comparative characteristics of coal-based and graphite-based reduced graphene oxide materials

A pristine graphite-based graphene oxide (GO) sample and GO-like samples prepared from anthracite, bituminous, and subbituminous coals were subjected to thermal reduction in a wide temperature range of 170–2800 °C to perform a comparative investigation on the physicochemical characteristics of coal-based and graphite-based reduced graphene oxide (RGO) materials. X-ray photoelectron spectroscopy showed the surface composition of both graphite-based and coal-based RGO samples became more similar at 1000–2800 °C, in which the samples prepared at 1500 °C or above had >97 % carbon. Graphite-based and coal-based RGO samples exhibited increasing trends in the percentages of C[dbnd]C (for carbon-carbon groups) and C–O (for carbon-oxygen groups) when prepared at higher temperatures. The Fourier transform infrared profiles showed a declining trend in the surface oxygen functionalities for the samples prepared from 170 °C to 600 °C, and no oxygen groups at 1000 °C. Raman spectra showed similar D and G bands for all samples below 1000 °C, but more distinctive 2D bands were observed above 2000 °C, which were sharper for the graphite- and anthracite-based samples. Surface area of all RGO samples were maximized at 1000 °C, then the porosity collapsed by two orders of magnitude at higher temperatures. The X-ray diffraction profiles showed sharper graphitic peaks for the samples prepared at higher temperatures, in which anthracite- and graphite-based samples prepared at 2400–2800 °C had characteristics similar to those of the synthetic graphite. Scanning electron microscopy of different coal-based RGO samples showed similar structures for anthracite-based and graphite-based samples.