Online tracking of the thermal reduction of graphene oxide by two-dimensional correlation infrared spectroscopy

Abstract

Thermal reduction of graphene oxide (GO) via rapid heating is an environment-friendly and cost-effective method. However, the detailed reduction mechanism remains unclear because of lack of methods for online monitoring of GO thermal reduction. In this study, the thermal reduction of GO (from 20 °C up to 400 °C in argon atmosphere) was successfully monitored online and investigated through temperature-dependent FTIR spectroscopy combined with scaling-MW2D FTIR spectroscopy and generalized 2D correlation analyses. Raman spectroscopy, XPS, and XRD studies were also conducted to characterize the structural changes before and after reduction. SEM and AFM analyses were performed to directly observe the formation of defects in GO after thermal reduction. According to scaling-MW2D results, the thermal reduction of GO was divided into two processes, namely, 35 °C–182 °C (process I) and 182 °C–385 °C (process II). Process I rapidly eliminates oxygen functional groups, and process II gradual removes them. The 2D correlation analysis for each process indicated the sequential order of movements of the oxygen-containing functional groups during thermal reduction. Process I comprised six steps, and process II contained four sequential steps. This work elucidated the complex deoxygenation steps and the mechanism of GO thermal reduction.