▎ 摘　　要

Lignin is the most abundant renewable aromatic polymer in nature; however, its full potential for conversion to high-value materials for practical applications is yet to be explored. Herein, a flash Joule heating process that enables the efficient conversion of lignin into a graphene-based nanocomposite is demonstrated. This method leverages the mixing of lignin with a ferric trichloride (FeCl3) solution to allow the insulated lignin to be conductive, thus producing an instantaneous high-temperature and high-pressure environment through electrical flash Joule heating. This efficiently converts the cheap carbon source into graphene and in situ loads ferroferric oxide (Fe3O4) nanoparticles onto the graphene flakes. Importantly, the prepared graphene/Fe3O4 nanocomposites were naturally endowed with electromagnetic wave absorption properties. The developed method eliminates the need for multistep processes and expensive equipment and shows broad prospects for facile processing of functional materials from low-value carbon sources.