Revealing hidden endotherm of Hummers' graphene oxide during low-temperature thermal reduction

Graphene oxide (GO) is a promising precursor material for fabricating graphene-like structures. However, the detailed kinetics and dynamics of GO thermal reduction still need to be revealed. Here, we present a new insight into low-temperature thermal reduction of Hummers' GO. During the low-temperature thermal treatment, the decomposition process of functional groups of Hummers' GO is found to consist of 4 steps (Step 1: below 160 degrees C, Step 2: between 160 and 210 degrees C, Step 3: between 210 and 300 degrees C, Step 4: above 300 degrees C). We discovered that Step 3 is an endothermic process. This finding differs from the common view that the thermal reduction of Hummers' GO is only an exothermic event. In addition, gaseous aromatic by-products form below 300 degrees C, implying that the basal carbon network could start to decompose at such low temperatures. This is in contrast to the former experimental finding that the GO carbon plane decomposes only at higher temperature (above 350 degrees C). Finally, based on the combined kinetic and compositional measurements, we observe the evolution of functional groups during heat-treatment, and thereby, reveal the mechanism of low temperature reduction of Hummers' GO. (C) 2018 Elsevier Ltd. All rights reserved.