▎ 摘　　要

Renewable, cheap and green biomass resources could meet the urgent need for producing graphene quantum dots (GQDs) on a large scale if high quality can be obtained. Here we report the gram-scale synthesis of single-crystalline GQDs derived from lignin biomass via a two-step method. The synthetic processes involve the oxidized cleavage step followed by the aromatic refusion step of alkali lignin molecules. Notably, this approach successively converts the biomass commonly considered as waste into a high-valued nanoscale product. The as-prepared single-crystalline GQDs, presenting a hexagonal honeycomb graphene network, are 1-3 atomic layers thick. Due to the bright fluorescence, up-conversion properties, long-term photostability, water solubility and biocompatibility, these high quality GQDs have potential to be excellent nanoprobes for multicolour bioimaging. The utilization of renewable biomass resources paves the way for green, low-cost and large-scale production of high quality GQDs and allows for the development of sustainable applications.