Synthesis of graphene mesosponge using CaO nanoparticles formed from CaCO3

Abstract

While graphene mesosponge (GMS) is a new type of mesoporous material with the potential for a variety of applications, its synthesis process requires costly templates such as Al2O3 and MgO nanoparticles. In this study, we present a new synthesis method for GMS, which achieves a high specific surface area of 1720 m2 g1 by employing calcium oxide (CaO) nanoparticles as templates. The CaO nanoparticles with an approximate diameter of 86 nm are formed through the thermal decomposition of calcium carbonate nanoparticles. However, the calcium carbonate nanoparticles contain a small amount of Mg (2 wt %), and the thermal decomposition process also yields impurities, including Mg. When the CaO nanoparticles, including the Mg-based impurities, are subjected to chemical vapor deposition, the CaO surface can be coated with a thin carbon layer, primarily consisting of single-layer graphene through the specific catalysis of the CaO surface in facilitating the CH4-to-C conversion reactions. However, at the same time, the presence of Mg-based impurities leads to the formation of low-crystalline carbons, which have a detrimental effect on the subsequent high-temperature annealing at 1800 °C, following the template removal process, resulting in an excessive number of edge sits in the GMS. We have found that the harmful low-crystalline carbons can be eliminated through heat treatment in air at 350 °C. By adopting such a removal process, high-quality GMS with a minimal number of edge sites can be produced.