Effects of interactions with metal ions on the thermal reduction of graphene oxide

Abstract

The thermal reduction of graphene oxide (GO) is an efficient and green method for preparing graphene. Herein, the effect of metal ions interacting with oxygen functional groups on GO on its thermal reduction properties are reported for the first time. Graphene oxide aerogels (GOAs) modified with three different metal ions (Li+/Mg2+/Ce3+) have been prepared by a unidirectional freeze-drying method (UFDM). Scanning electron microscopy (SEM) images have revealed that metal ions obviously improve the 3D porous structure of GOA. Based on an analysis of Fourier-transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS), different interactions, such as coordination, chelation, and hydrogen bonding, as well as ring-opening reaction, between metal ions and functional groups on GO lead to dramatic decreases in the bond energies of functional groups, transforming high-energy chemical bonds into low-energy chemical bonds. Consequently, the thermal reaction temperature of the modified GOA drops by 10–50 °C compared with the pure GOA. Moreover, interactions with metal ions promote the thermal reduction of GOA. Indeed, the exothermic energy densities of the GOA in the three metal-ion-modified GOAs are 20–580 J/g larger than that of pure GOA. Hence, the reduction products of GOAs modified by metal ions are more stable.