Preparation and characteristic analysis of graphene based on coal macerals of different rank

Abstract

Graphene is prepared using the improved Hummers redox method to study the preparation and structural characteristics of coal-based graphene from coal macerals of rank between 0.52 % and 1.98 %. The macerals are separated and enriched by hand sorting, sieving, and isopyknic gradient centrifugation. The crystal characteristics of the macerals, coal-based graphite, and graphene are characterized by XRD, Raman, SEM and TEM. The flake graphene with stable structure, good extensibility, different cell parameters and defects can be prepared from macerals. All the preparation yields are less than 4.0 %. The XRD data shows that after high-temperature graphitization, the layer spacing d002 of each sample is less than 0.3400 nm, and the lamellar crystallite sizes La and Lc are 7.70–21.09 nm and 11.53–16.94 nm, respectively. After the redox reaction, inertinite MLI-GS, YCWI-GS, and vitrinite GMDV-GS have the layer spacing d002, lamellar extendability La, stacking thickness Lc, and average stacking layer Nave that tend to be graphite-like structure. The microcrystalline structure is well developed and stable. Raman also confirmes that inertinite and high-rank vitrinite-derived graphene have fewer structural defects, good ordering, and a high degree of graphitization. The average values of ID/IG and AD/AG of maceral → coal-based graphite → graphene are 0.73 → 0.29 → 1.06, 2.12 → 0.40 → 1.62, indicating a relationship between the structural order: coal-based graphite > maceral > graphene, and between the degree of graphitization: coal-based graphite > graphene > maceral. The SEM and TEM dates show that inertinite tends to form a flat graphene structure with four–six layers, and has good light transmission. The graphene has few folds and warps, good layer extensibility, and high lattice order. The layer spacing at the edge is consistent with the d002 of XRD analysis. Vitrinite, cutinite, and barkinite derived graphene are similar to a kneaded paper balls. The layers are mixed with each other, forming more folds and ripples, and the peeling effect is poor. Only the high-rank GMDV-GS is clean like gauzy graphene, indicating that the micromorphological characteristics of graphene are related to the coal rank and macerals.