Sustainable carbon quantum dots from forestry and agricultural biomass with amplified photoluminescence by simple NH4OH passivation

Abstract

High quality blue fluorescent carbon quantum dots (CDs) were fabricated from a dilute NH₄OH/water solution of waste biomass via one-step hydrothermal carbonization. Different from conventional synthesis methods, NH₄OH was used as the solvent as well as passivation agent rather than organic amine compounds. The best quantum yield (QY) of the nitrogen-doped biomass CDs was up to 16%, which was higher than the non-doped CDs (only 2%) and those passivated by organic molecules (7%). Further investigations revealed the unique emission behaviours of the NH₄OH-passivated CDs dependent on excitation, pH values and solvents and interesting up-conversion photoluminescence. In addition, an in vitro cytotoxicity test demonstrated the negligible toxicity of NH₄OH-passivated CDs, and they were successfully applied in bio-imaging of murine embryonic stem cells. This low-cost and green chemistry method provides a feasible route for value-added and sustainable utilization of waste biomass.