Multistep Fractionation of Coal and Application for Graphene Synthesis

Abstract

Despite its complex structure, coal has shown to be a promising precursor for graphene synthesis by chemical vapor deposition (CVD). However, the presence of heteroatoms and aliphatic chains in coal can lead to defects in the graphene lattice, preventing the formation of pristine graphene layers. Therefore, the goal of this study was to formulate a multistep coal fractionation scheme to extract and characterize the most aromatic fractions and explore their potential as graphene precursors. The scheme consisted of direct coal liquefaction under different conditions, Soxhlet extraction with heptane then toluene, and preparative liquid chromatography on silica gel using heptol solutions with different heptane/toluene ratios. The fractions obtained by this process were analyzed by proton nuclear magnetic resonance, thermogravimetric and elemental analyses, and automated SAR-AD (saturates, aromatics, resins-asphaltene determinator) separations. This characterization allowed the identification of two aromatic fractions with and without heteroatoms, which were subsequently used for graphene synthesis by CVD on nickel and copper foils. Raman spectrometry revealed that both fractions primarily formed defect-free multilayered graphene with approximately 11 layers on nickel due to the high solubility of carbon and the defect-healing effect of nickel. On the other hand, these fractions generated amorphous carbon on copper due to the high solubility of hydrogen in copper, which competed with carbon. Molecules in the more aromatic heteroatom-free fraction still contained alkyl pendant substituents and did not share the same planarity and symmetry to form defect-free graphene on copper. Thus, the quality of graphene was governed by the substrate on nickel and by the precursor quality on copper. When deposited directly on lacey carbon-coated copper grids of a transmission electron microscope, the heteroatom-free fraction gave rise to much larger graphene domains. The presence of heteroatoms promoted the formation of small self-assembled agglomerates of amorphous carbon.

High-performance cementitious composites containing nanostructured carbon additives made from charred coal fines

“…Coal is a carbon-rich feedstock and has been used to produce carbon nanomaterials with different techniques, such as chemical oxidation 21 , chemical vapor deposition (CVD) 22 , and flash Joule heating 23 . Low rank coals have poorly aligned aromatic carbon structures, while high rank coals have carbon lattices with more ordered and layered structures.…”

High-performance Cementitious Composites Containing Nanostructured Carbon Additives Made from Charred Coal Fines

“…Coal is a carbon-rich feedstock and has been used to produce carbon nanomaterials with different techniques, such as chemical oxidation [23], chemical vapor deposition (CVD) [24], and flash Joule heating [25]. Despite their abundance, coal materials have not been widely explored as feedstocks to produce carbon nanomaterial additives for cement applications.…”