Physicochemical transformation of graphene oxide during heat treatment at 110–200 °C

Abstract

Graphene oxide (GO) was subjected to different heating pathways to investigate water removal at 110°C (GO-110), water removal followed by removal of surface groups at 140°C or 200°C (GO-110-140 or GO-110-200), and simultaneous removal of water and surface groups at 140°C or 200°C (GO-140 or GO-200). Physicochemical characteristics of GO samples at each stage were determined to quantify and understand the impact of each treatment pathway on porosity development, physical structure, or surface chemistry of GO. Surface elemental composition showed the following order for C/O ratio: GO-140-200 > GO-110-200 > GO-200, suggesting that a two-step heat treatment results in more oxygen removal from the surface, and FTIR profiles confirmed the lowest intensities of all functionalities for GO-140-200. Proton NMR spectra of as-received and heat-treated GO samples confirmed near complete removal of water and hydroxyl groups for samples treated at 200°C. XRD results showed that the interlayer spacing of GO reduced from 0.792 nm to the lowest values of 0.371 nm for GO-200 and 0.367 nm for GO-110-200. Porosity characterization revealed that only two pathways, GO-200 and GO-110-200, created a porous structure. Further analysis of data suggested that exfoliation is primarily triggered by decomposition of surface functionalities and release of a substantial volume of CO2/CO, but water vapor release helps to enhance the exfoliation. These results demonstrate that direct and rapid heat treatment of GO at 200°C (or higher temperatures) is the most effective option for developing a porous structure.