Effective reduction of graphene oxide via a hybrid microwave heating method by using mildly reduced graphene oxide as a susceptor

Due to the poor microwave absorption ability of graphene oxide (GO), direct reduction of GO by solid-state microwave irradiation is inefficient. In this study, GO was reduced effectively by a hybrid microwave heating (HWH) method by using mildly reduced graphene oxide (MG) membrane as a external susceptor, in which MG was obtained by annealing of GO at 300 °C for 1 h under nitrogen by a conventional heating method. When the mass ratio of MG to GO is 0.045, the C/O atomic ratio of GO increases from 1.8 to 17.84 by microwave irradiation under argon at 2000 W for 30 s. However, when GO was irradiated solely under the same conditions, the ratio of C/O was unchanged (1.88). For comparison, the MG was further irradiated by microwave at 2000 W for 30 s, its C/O ratio is enhanced from 4.17 to 8.46, demonstrating the higher reduction efficiency due to a mixed heating mode in the HWH process. The conventional heating of GO occurs during the initial stage and a two-way heating mode during the later stage, in which MG heats the GO from the surface and the microwave heating from the GO itself. Therefore, more amount of carboxyls and epoxides can be removed in the HWH process to achieve higher C/O ratio compared with that of the product obtained by direct microwave irradiation of MG.