Optimization of the hydrothermal synthesis process and its formation mechanism and fluorescence mechanism of Lophatherum gracile-based CQDs

Abstract

Hydrothermal method became the main preparation method of the biomass carbon quantum dots (CQDs) by virtue of its strong operability and eco-friendliness. However, due to the differences of carbon precursors’ composition and the lack of statistical analysis of data in the synthesis process, hydrothermal synthesis process optimization was seriously insufficient, which had become the bottleneck of high − quality preparation and application of biomass CQDs. In this paper, the response surface methodology (RSM) was applied to optimize the hydrothermal synthesis process of Lophatherum gracile-based CQDs, so as to regulate the CQDs’ structure and properties by simply changing the synthesis parameters. In addition, the formation mechanism and fluorescence mechanism of the CQDs were interpreted by Materials Studio (MS) and density functional theory (DFT); and the morphology, FTIR spectrum, XPS spectrum, Zeta potential, fluorescence spectrum, UV–Vis absorption spectrum and fluorescence lifetime of the target CQDs were used to verify the interpretation. In coumarin parent nucleus, by introducing strong electron-donating groups such as amino and hydroxyl groups at C6&C7 and electron-withdrawing groups such as siloxy and aldehyde groups at C3&C4, the whole molecule formed a push–pull electron system, thus enhancing excitation-dependent fluorescence of CQDs. Finally, based on the good water solubility, fluorescence excitation dependence and fluorescence stability of the target CQDs, it was proved that the Lophatherum gracile-based CQDs had great application potential in fluorescence anti-counterfeiting. This study provided a new way for the high-value utilization of Lophatherum gracile.