Evolutionary characteristics of microstructure of coal-based graphene fromNingxia coals: Comprehensive characterized analysis

The preparation and characterization of coal-based carbon materials is a hot topic. The structural characteristics of coal-based graphene not only determine the performance of the products, but also provide reference for process control during product preparation. Therefore, it is necessary to have a clear understanding of the microstructure and morphology of coal-based graphene. This study collected 8 different coal ranks coals in Ningxia, and obtained coal-based graphite through high-temperature graphitization treatment after chemical demineralization. Graphene was prepared using an improved Hummer’s redox method, and the microstructure and structural parameters of coal-based graphene were comprehensively characterized by X-ray diffraction, Raman spectroscopy, atomic force microscopy, and high-resolution transmission electron microscopy. The results indicate that the coal–based graphene products prepared from coal samples of different coal ranks in Ningxia are all few-layer graphene. Graphitization can significantly improve the order and graphitization degree of coal structure, which is beneficial for the preparation of coal-based graphene, especially for low coals. In this study, the graphitization degree of coal-based graphites are more than 0.70, and the highest is 0.99. The higher the coal rank, the larger the diameter and stacking height of the graphene prepared, the fewer defects, and the better the peeling effect. and better the stripping effect of graphene prepared. The diameter of the coal-based graphene prepared in this study ranges from 3.78 to 13.04 nm, with interlayer spacing exceeding 0.355 0 nm and a maximum of 0.366 1 nm. As the coal rank increases, the diameter of coal-based graphene increases more significantly than the stacking height, the morphology of coal-based graphene tends to develop in a flattened form in general. The caking of coals can cause an increase in the surface roughness of graphene, but it does not affect the development of the crystal form and order of graphene microcrystalline domains. As the coal rank increases, the graphene structure undergoes an evolution path of vortex type -Y-type - semi-plane type -plane type. The plane type graphene structure is the final form of coal structure evolution during the preparation of coal-based graphene, characterized by obvious peeling, curling, and stretching, which also provides the possibility for the formation of step like of graphene structures.