Sub-micron alkylated graphene oxide from coal

•Coal-derived graphene oxide (C-GO) with a yield of 107% and a cost of 50-100 USD/kg.•Lower defect on the basal plane of C-GO compared with graphene oxide produced from graphite.•Alkyl functional groups inherited from coal structure render C-GO with anchoring effect for mechanical reinforcement in composite materials.•Sub-micron scale and low defect C-GO with higher surface area and electrical conductivity for potential energy storage applications. Sub-micron graphene oxide (GO) has emerged as a promising additive in the realms of composite films and fibers applications. Traditional GO preparation involves acid oxidation of high-purity graphite, yielding particles in micron scale. Achieving sub-micron dimensions typically demands rigorous conditions, leading to increased defects with low yield. In this study, the sp2 carbon domain from anthracite first undergoes graphitization, growing from nano to sub-micron scale, then sub-micron GO is extracted via oxidatively severing its bridging bonds. The resulting GO exhibits an average size of 800 nm, a thickness of 1-2 layers, and a yield of 107%. This methodology is applicable to bituminous and lignite as well. Furthermore, the broken bridging bonds act as alkyl danglings on sub-micron GO and serving as anchors in composites through hydrogen bonding. The reinforcing efficacy of sub-micron GO is demonstrated through the fabrication of composite films and fibers. This work pioneers cost-effective production of high-quality sub-micron GO, elevating coal’s value through advanced applications.